UBC Theses and Dissertations

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UBC Theses and Dissertations

Development and clinical evaluation of a frequency compressor for the hearing impaired Van Schyndel, André John 1984

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DEVELOPMENT AND C L I N I C A L EVALUATION OF A FREQUENCY COMPRESSOR FOR THE HEARING IMPAIRED By ANDRE JOHN VAN SCHYNDEL B . S c , McMas ter U n i v e r s i t y , 1978 M . S c , The U n i v e r s i t y of B r i t i s h C o l u m b i a , 1980 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF PHYSICS We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA September 1984 © A n d r e ' John Van S c h y n d e l , 1984 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements fo r an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y a v a i l a b l e for reference and study. I further agree that permission for extensive copying of t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the head of my department or by his or her representatives. I t i s understood that copying or p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of Physics  The University of B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 Date Aug. 28 1984 i i ABSTRACT The r e s i d u a l low-^f r e q u e n c y s e n s i t i v i t y d e m o n s t r a t e d by many s e v e r e l y h e a r i n g i m p a i r e d p e r s o n s has l e d t o t h e d e v e l o p m e n t of v a r i o u s methods o f p r e s e n t i n g s p e e c h i n f o r m a t i o n i n a l o w e r b a n d w i d t h . O n l y l i m i t e d s u c c e s s has t h u s f a r been r e p o r t e d . In t h i s t h e s i s a new f r e q u e n c y c o m p r e s s i o n a l g o r i t h m was d e v e l o p e d and r e a l i z e d a s a r e a l t i m e , p o r t a b l e , e l e c t r o n i c d e v i c e t o be worn as a h e a r i n g a i d . A c l i n i c a l s t u d y i n c o r p o r a t i n g o p t i m a l a m p l i f i c a t i o n and r e l a t i v e l y l o n g t r a i n i n g t i m e s w i t h t h e d e v i c e i n d i c a t e s t h a t a l t h o u g h s p e e c h c o m p r e h e n s i o n d r o p s i n i t i a l l y , i t ca n r i s e w e l l b eyond t h a t w h i c h i s d e m o n s t r a t e d w i t h c o n v e n t i o n a l h e a r i n g a i d s . A l e a r n i n g c u r v e i s p r e s e n t e d and i t s f e a t u r e s a r e j u s t i f i e d by t h e c l i n i c a l r e s u l t s . A f u l l a n a l y s i s o f t h e f r e q u e n c y c o m p r e s s i o n a l g o r i t h m i s p r e s e n t e d as w e l l a s r e s u l t s f r o m v a r i o u s s p e e c h c o m p r e h e n s i o n t e s t s a d m i n i s t e r e d i n t h e c l i n i c a l s t u d y . One s u b j e c t i s a l r e a d y a f u l l t i m e u s e r o f t h e d e v i c e , and more may f o l l o w . i i i TABLE OF CONTENTS page A b s t r a c t i i T a b l e o f C o n t e n t s i i i L i s t o f T a b l e s v i L i s t of F i g u r e s v i i Acknowledgements i x CHAPTER I - INTRODUCTION 1 1-1 - P r e l i m i n a r y Remarks 2 1-2 - P r e v i o u s R e s e a r c h on F r e q u e n c y L o w e r i n g 6 I - 3 - C l i n i c a l S t u d y p r o p o s a l 16 CHAPTER I I - ATTRIBUTES OF SPEECH AND HEARING 20 I I - 1 - The V o c a l O r g a n s 21 I I - 2 - V o i c e d S p e e c h 24 II -3 - U n v o i c e d S p e e c h 29 I I - 4 - The H e a r i n g Mechanism •••• 33 I I - 5 - The P r e d i c a m e n t of t h e H e a r i n g I m p a i r e d .... 38 CHAPTER I I I - FREQUENCY BAND COMPRESSION IN THE PRESENT STUDY 42 I I I -1 - The O b j e c t i v e . . . 43 I I I - 2 - D e f i n i t i o n o f F r e q u e n c y C o m p r e s s i o n 44 I I I - 3 - P i t c h S y n c h r o n o u s P r o c e s s i n g 46 I I I - 4 - P e r i o d i c P r o c e s s i n g 51 CHAPTER IV - TECHNICAL REALIZATION 72 CHAPTER V - THERAPY AND CLINICAL EVALUATION 82 V-1 - S u b j e c t s 83 V-2 - E t h i c a l C o n s i d e r a t i o n s 85 V-3 - E v a l u a t i o n M a t e r i a l s and P r o c e d u r e s 86 V- 4 - F a c i l i t i e s and Eq u i p m e n t 93 CHAPTER VI - CLINICAL STUDY OBSERVATIONS 95 V I - 1 - R e s p o n s e t o t h e S o l i c i t a t i o n of r e f e r r a l s .... 9.6 VI-2 - D a t a A n a l y s i s P r o c e d u r e s 97 VI - 3 - Case S t u d y S u b j e c t ! A1 105 VI-4 - Case S t u d y S u b j e c t * A2 108 V I - 5 - Case S t u d y S u b j e c t * B1 115 V I - 6 - Case S t u d y S u b j e c t * B2 1 1 8 VI-7 - Case S t u d y S u b j e c t * B3 121 VI-8 - Case S t u d y S u b j e c t * B4 124 V I - 9 - Case S t u d y S u b j e c t * B5 127 VI-10 - Case S t u d y S u b j e c t * B6 130 VI-11 - Case S t u d y S u b j e c t * B7 133 V I - 12 - Summary o f t e s t r e s u l t s 135 CHAPTER V I I - DISCUSSIONS AND RECOMMENDATIONS .... 144 V I I - 1 - D i s c u s s i o n 145 V I I - 2 - Recommendations 149 V APPENDIX I : Power S p e c t r u m o f t h e P e r i o d i c P r o c e s s i n g A l g o r i t h m f o r a S i n u s o i d a l I n p u t .... 152 APPENDIX I I : The MAC S u b t e s t s 155 APPENDIX I I I : Random Chance S c o r e C o r r e c t i o n 159 APPENDIX IV: The MAC T e s t Raw D a t a 161 BIBLIOGRAPHY 163 v i L I S T OF TABLES page 2.1 The dB S c a l e and some F a m i l i a r I n t e n s i t i e s .... 34 4.1 Model 3E S p e c i f i c a t i o n s 80 6.1 MAC S c o r e s f o r S u b j e c t # A2 110 6.2 H e a r i n g P e r f o r m a n c e I n v e n t o r y 139 A.1 The MAC T e s t Raw D a t a 162 v i i L I S T OF FIGURES FIGURE page 2.1 The V o c a l Organs 22 2 .2 A m p l i t u d e s p e c t r u m of t h e s t e a d y v o w e l i n "HEED" 26 2 . 3 A m p l i t u d e s p e c t r u m of t h e s t e a d y v o w e l i n "HOOD" 27 2 .4 A m p l i t u d e Spec t rum of t h e c o n s o n a n t / p / 30 2 .5 A m p l i t u d e Spec t rum of t h e c o n s o n a n t / t / 31 2 . 6 A m p l i t u d e Spec t rum of the c o n s o n a n t / k / 32 3.1 T r i g g e r c i r c u i t f o r p i t c h -s y n c h r o n o u s p r o c e s s i n g 49 3 .2 S c h e m a t i c d r a w i n g of c o m p r e s s i o n a l g o r i t h m . . . . 52 3 .3 C a l c u l a t e d o u t p u t s p e c t r u m 58 3 .4 Measured o u t p u t s p e c t r u m 59 3 .5 Spec t rum of t h e i d e a l t r a n s f e r c h a r a c t e r i s t i c . . . 61 3 .6 Spec t rum of the p e r i o d i c p r o c e s s i n g a l g o r i t h m f o r i n t e r m e d i a t e t o h i g h i n p u t f r e q u e n c i e s . . . . 62 3 .7 Spec t rum of t h e p e r i o d i c p r o c e s s i n g a l g o r i t h m f o r low i n p u t f r e q u e n c i e s 63 3 .8a A m p l i t u d e Spec t rum of the v o w e l [ i ] 67 3 .8b Same as a , a f t e r c o m p r e s s i o n by a p r o t o t y p e d e v i c e 67 3 .9a S p e c t r o g r a m of p h r a s e 69 3 .9b S p e c t r o g r a m of same p h r a s e t h r o u g h c o m p r e s s i o n d e v i c e 69 3 .10a S p e c t r o g r a m of p h r a s e 70 v i i i 3.10b S p e c t r o g r a m of same p h r a s e t h r o u g h c o m p r e s s i o n d e v i c e • • • • « • • • • • • • • • • • 70 4. 1a Power s u p p l y f o r M o d e l 3E • • • • • • • • • • • • • 74 4. 1b A n a l o g u e c i r c u i t s f o r Model 3E » • • • • • • • • • • • 75 4. 1c D i g i t a l c i r c u i t s f o r Model 3E » • • • • • • • • • • • 76 4. 2 P r i n t e d c i r c u i t a r t w o r k f o r Model 3E S c a l e i s 1: 1 • • • • • • • • • • • • • • • • • • • • 79 4. 3 P h o t o g r a p h of Model 3E • • • • » • • • • • • • • • • • 81 5. 1 C e r t i f i c a t e of E t h i c s A p p r o v a l • • • • • • • • • • • • 87 5. 2 L e a r n i n g C u r v e s • • • • • • • • • • • • • • • • 92 6. 1 A u d i o l o g i c a l I n f o r m a t i o n S u b j e c t * A1 104 6. 2 A u d i o l o g i c a l I n f o r m a t i o n S u b j e c t * A2 1 07 6. 3 A u d i o l o g i c a l I n f o r m a t i o n S u b j e c t * B1 1 1 4 6. 4 A u d i o l o g i c a l I n f o r m a t i o n S u b j e c t * B2 1 17 6. 5 A u d i o l o g i c a l I n f o r m a t i o n S u b j e c t * B3 120 6. 6 A u d i o l o g i c a l I n f o r m a t i o n S u b j e c t * B4 1 23 6. 7 A u d i o l o g i c a l I n f o r m a t i o n S u b j e c t * B5 126 6. 8 A u d i o l o g i c a l I n f o r m a t i o n S u b j e c t * B6 1 29 6. 9 A u d i o l o g i c a l I n f o r m a t i o n S u b j e c t * B7 1 32 6. 10 A v e r a g e l e a r n i n g c u r v e s b a s e d on t e s t s c o r e s 142 i x ACKNOWLEDGEMENTS S i n c e r e t h a n k s a r e e x t e n d e d t o D r . A-P. B e n g u e r e l , Dr. N. W e i s s , Dr . R.R. H a e r i n g , D r . A.V. G o l d and a l l members of t h e c o m m i t t e e whose many comments, i d e a s , l a b s p a c e , and g e n e r a l h e l p were i n v a l u a b l e t o t h e p r o j e c t . The e x p e r t i s e , i n t e l l e c t u a l i n p u t , and h a r d work o f a u d i o l o g i s t B e t h B r o o k s i s a l s o g r a t e f u l l y a c k n o w l e g e d . We o f f e r o u r g r a t i t u d e t o D r . N.S. L o n g r i d g e and t h e a d m i n i s t r a t i o n o f V a n c o u v e r G e n e r a l H o s p i t a l f o r t h e i r g e n e r o s i t y i n p r o v i d i n g t h e use o f t h e f a c i l i t i e s i n t h e Neuro-o t o l o g y U n i t , and t o t h e s t a f f o f t h e U n i t f o r t h e i r p a t i e n c e . S e v e r a l l o c a l c e n t r e s i n c l u d i n g S t . P a u l ' s H o s p i t a l , The W e s t e r n I n s t i t u t e f o r t h e D e a f , and V a n c o u v e r G e n e r a l H o s p i t a l h e l p e d p r o v i d e s u i t a b l e c a n d i d a t e s f o r t h e s t u d y . The c l i n i c a l t e s t i n g p r o g r a m was c a r r i e d o u t u nder c o n t r a c t w i t h t h e F e d e r a l Government o f C anada, and t h e b e n e v o l e n c e of Dr. R.K. Lomnes and Ambrex I n t e r n a t i o n a l I n c . The a u t h o r i s g r a t e f u l t o t h e N a t u r a l S c i e n c e s and E n g i n e e r i n g R e s e a r c h C o u n c i l o f Canada and t h e B o a r d o f T r u s t e e s o f t h e I z a a k W a l t o n K i l l a m T r u s t f o r deeming him w o r t h y o f t h e i r g e n e r o u s P r e - d o c t o r a l S c h o l a r s h i p s . S p e c i a l t h a n k s goes t o my w i f e P a u l a f o r h e r l o v i n g k i n d n e s s t h r o u g h o u t t h i s work and a l w a y s . 1 CHAPTER I INTRODUCTION 2 I-1 P r e l i m i n a r y Remarks A g e n e r a l f e a t u r e o f s e v e r e t o p r o f o u n d h e a r i n g i m p a i r m e n t s i s t h e l o s s o f s e n s i t i v i t y t o t h e h i g h e r f r e q u e n c i e s i n t h e a u d i o r a n g e w i t h t h e r e t e n t i o n of some r e s i d u a l h e a r i n g i n t h e l o w e r f r e q u e n c i e s . I t i s a p p a r e n t t h a t l i n e a r a m p l i f i c a t i o n a l o n e i s n o t an a d e q u a t e s o l u t i o n t o t h e p r e d i c a m e n t of t h e s e v e r e l y h e a r i n g i m p a i r e d i n d i v i d u a l . The most i m p o r t a n t i n f o r m a t i o n i n a s p e e c h s i g n a l i s c a r r i e d a t f r e q u e n c i e s w h i c h a r e m o s t l y i n a u d i b l e t o an i n d i v i d u a l w i t h a s e v e r e h e a r i n g l o s s . F r e q u e n c y l o w e r i n g t e c h n i q u e s a r e aimed a t p r e s e n t i n g t h e s p e e c h i n f o r m a t i o n i n t h e l o w e r ( a u d i b l e ) f r e q u e n c i e s . The t e r m " f r e q u e n c y c o m p r e s s i o n " has been u s e d t o mean many t h i n g s , most o f w h i c h would more p r o p e r l y be c a l l e d f r e q u e n c y l o w e r i n g . T h e s e terms r e f e r t o a wide v a r i e t y o f s i g n a l p r o c e s s i n g t e c h n i q u e s aimed a t r e p r e s e n t i n g an i n p u t s i g n a l by an o u t p u t s i g n a l w i t h l o w e r f r e q u e n c i e s . T h e r e i s no p r e s e t method f o r a c c o m p l i s h i n g t h i s t a s k s i m p l y b e c a u s e a l o w e r o u t p u t b a n d w i d t h c a n n o t c a r r y as much i n f o r m a t i o n as t h e i n p u t ( a t t h e same s i g n a l - t o - n o i s e r a t i o ) . The v a r i o u s schemes a d o p t e d t h e r e f o r e , a r e d e s i g n e d w i t h a s p e c i f i c end p u r p o s e i n mind. T h e r e a r e many h i g h l y s u c c e s s f u l b a n d w i d t h r e d u c t i o n t e c h n i q u e s u s e d i n d i g i t a l i n f o r m a t i o n t r a n s f e r and computer i n t e r f a c i n g . In t h i s work we d e a l w i t h one w h i c h i s f u n d a m e n t a l l y more d i f f i c u l t : t h e b a n d w i d t h r e d u c t i o n o f a human s p e e c h s i g n a l . The r e a s o n f o r t h e d i f f i c u l t y i s t h e f a c t t h a t t h e i d e a l a l g o r i t h m i s n o t known ( n o r c a n i t b e ) . In t h e computer i n t e r f a c e s i t u a t i o n , t h e b a n d w i d t h r e d u c t i o n may i n v o l v e 3 t e c h n i c a l l y s o p h i s t i c a t e d and complex c i r c u i t r y , b u t t h e a l g o r i t h m i s w e l l d e f i n e d b e f o r e one b e g i n s . T h e r e a r e many p o s s i b l e u s e s f o r a s p e e c h b a n d w i d t h r e d u c t i o n scheme, t h e most o b v i o u s b e i n g r a d i o t r a n s m i s s i o n . In 1901, when G u g l i e l m o M a r c o n i s u c c e e d e d i n t r a n s m i t t i n g a Morse c o d e "S" from E n g l a n d t o N e w f o u n d l a n d , he d i d not w o r r y a b o u t b a n d w i d t h . L a t e r , when h i s " w i r e l e s s " i n v e n t i o n was c a r r i e d by many s e a g o i n g v e s s e l s a t e c h n i q u e was d e v e l o p e d ( r e s o n a n t c i r c u i t s ) t o c a r r y d i f f e r e n t messages on d i f f e r e n t f r e q u e n c y b a n d s . S t i l l l a t e r , when a m p l i t u d e m o d u l a t i o n e n a b l e d a s p e e c h s i g n a l t o be b r o a d c a s t , t h e t o t a l u s e a b l e f r e q u e n c y band q u i c k l y became jammed w i t h c h a n n e l s . T h e s e p r o b l e m s b r o u g h t t h e a d v e n t o f s i n g l e s i d e b a n d t r a n s m i s s i o n and c a r r i e r s u p p r e s s i o n , h a l v i n g t h e b a n d w i d t h o f e a c h c h a n n e l . S t i l l more e l a b o r a t e and s o p h i s t i c a t e d t e c h n i q u e s came i n t o e x i s t e n c e , some o f w h i c h w i l l be d i s c u s s e d l a t e r . An example of s u c h a t e c h n i q u e c a l l s f o r an a s s u m p t i o n t h a t t h e t r a n s m i t t e d s i g n a l i s s p e e c h . R e s e a r c h e r s have f o u n d t h a t t h e r e i s a d e f i n i t e r a n g e o f f r e q u e n c i e s i n t h e t o t a l f r e q u e n c y band o f s p e e c h w h i c h a r e not e s s e n t i a l f o r i n t e l l i g i b i l i t y . I t was f o u n d t h a t v o w e l s and v o i c e d s p e e c h c a n be c a r r i e d by t h e low e r 2.5 kHz o f t h e s p e e c h band. The c o n s o n a n t s a r e c a r r i e d i n t h e h i g h e r r a n g e s . In t h i s example, t h e t e c h n i q u e o f band r e d u c t i o n c u t s o u t t h e i n t e r m e d i a t e band t h r o u g h t r a n s m i s s i o n and a d e c o d e r r e p l a c e s i t a t t h e r e c e i v i n g e n d . Two a t t r i b u t e s make t h i s example s i g n i f i c a n t . F i r s t l y , an a s s u m p t i o n was made a b o u t t h e i n p u t s i g n a l . T h i s r e d u c e s t h e p o s s i b i l i t i e s f o r t r a n s m i s s i o n . S e c o n d l y , t h e t e c h n i q u e r e q u i r e s an e n c o d e r a t t h e s e n d e r end and a d e c o d e r a t t h e 4 r e c e i v i n g e n d . A n o t h e r immediate a p p l i c a t i o n o f s p e e c h f r e q u e n c y c o m p r e s s i o n i s t h e c o d i n g o f s p e e c h i n f o r m a t i o n on m a g n e t i c t a p e . H e r e , I am not r e f e r r i n g t o p r o c e s s e s s u c h a s D o l b y , Of a m p l i t u d e c o m p r e s s i o n w h i c h a r e t e c h n i q u e s f o r o b t a i n i n g optimum use o f t h e dynamic r a n g e . T h e r e i s a l a r g e i n d u s t r y s e t up to r e c o r d books and o t h e r p r i n t e d m a t e r i a l f o r t h e v i s u a l l y i m p a i r e d and p h y s i c a l l y h a n d i c a p p e d , i . e . t h o s e who c a n n o t r e d d d i r e c t l y . S i n c e one c a n r e a d much f a s t e r t h a n one c a n speafc ; many b l i n d u s e r s o f s u c h r e c o r d e d m a t e r i a l ( e s p e c i a l l y s t u d e n t s ) l i k e t o l i s t e n t o t h e t a p e s a t an a c c e l e r a t e d r a t e . Some become v e r y good a t i n t e r p r e t i n g t h e " D o n a l d Duck" s p e e c h t h a t r e s u l t s , but few c a n i n t e r p r e t t h e t a p e s e f f e c t i v e l y a t t w i c e t h e o r i g i n a l s p e e d . T e c h n i q u e s of s p e e c h f r e q u e n c y c o m p r e s s i o n have made t h i s t a s k e a s i e r , and t h e r e a r e s e v e r a l c o m m e r c i a l d e v i c e s a v a i l a b l e ( c f . L e e , 1972) t o make t h e spe e d e d - u p s p e e c h sound more n a t u r a l . S p e e c h f r e q u e n c y c o m p r e s s i o n a l s o f i n d s a p p l i c a t i o n i n t h e u n d e r w a t e r w o r l d o f d e e p - s e a d i v i n g . A t s u f f i c i e n t l y h i g h p r e s s u r e s n i t r o g e n becomes n a r c o t i c ; t h i s i s why d e e p - s e a d i v e r s b r e a t h e a m i x t u r e o f h e l i u m and o x y g e n . The s p e e d o f sound i n h e l i u m i s r o u g h l y t w i c e t h a t i n a i r , so t h a t t h e r e s u l t i n g s p e e c h has most o f i t s f r e q u e n c y components r a i s e d . F r e q u e n c y l o w e r i n g d e v i c e s make t h i s s p e e c h more r e a d i l y u n d e r s t a n d a b l e . The d i r e c t a p p l i c a t i o n o f s p e e c h f r e q u e n c y band c o m p r e s s i o n t o t h e h e a r i n g i m p a i r e d i s t h e s u b j e c t o f t h i s work. A g e n e r a l f e a t u r e o f s e n s o r i n e u r a l h e a r i n g i m p a i r m e n t s i s a marked l o s s of s e n s i t i v i t y t o h i g h f r e q u e n c i e s i n t h e a u d i o r a n g e , w i t h t h e 5 r e t e n t i o n o f some r e s i d u a l h e a r i n g a t l o w e r f r e q u e n c i e s . When t h e r o l l o f f f r e q u e n c y i s low, a b o u t 1 t o 2 kHz, s p e e c h d i s c r i m i n a t i o n even i n an i d e a l p r e s e n t a t i o n s i t u a t i o n becomes q u i t e d i f f i c u l t . When r e v e r b e r a t i o n and n o i s e a r e i n t r o d u c e d , t h e p r o b l e m i s compounded. F o r r e a s o n s w h i c h w i l l be d i s c u s s e d l a t e r , a m p l i f i c a t i o n a t t h e h i g h e r f r e q u e n c i e s i s n o t an a d e q u a t e s o l u t i o n i n c a s e s w i t h s e v e r e h e a r i n g l o s s e s . A t t e m p t s t h e r e f o r e , have been made a t u s i n g f r e q u e n c y l o w e r i n g t e c h n i q u e s t o make optimum use of t h e r e s i d u a l h e a r i n g ( i . e . a t t h e l o w e r f r e q u e n c i e s ) . Many s e v e r e l y h e a r i n g i m p a i r e d i n d i v i d u a l s s u f f e r from i n t e r n a l l y g e n e r a t e d sounds ( t i n n i t u s ) w h i c h r a i s e t h e d e t e c t i o n t h r e s h o l d , and d i s t o r t s i g n a l s above t h e t h r e s h o l d . In c a s e s where t h i s t i n n i t u s t a k e s t h e f o r m o f h i g h f r e q u e n c y r i n g i n g , t h e a u d i o i n f o r m a t i o n p r e s e n t e d a t t h e h i g h f r e q u e n c i e s , w h i l e d e t e c t a b l e , has l o s t much of i t s m eaning. T h i s i s a n o t h e r c a s e where f r e q u e n c y l o w e r i n g t e c h n i q u e s may h e l p . We b e g i n o u r s t u d y o f t h e use o f f r e q u e n c y c o m p r e s s i o n f o r t h e h e a r i n g i m p a i r e d w i t h a r e v i e w o f t h e p a s t work t h a t has been done on h e a r i n g a i d s i n g e n e r a l , w i t h e m p h a s i s on t h e work i n f r e q u e n c y l o w e r i n g . We can t h e r e b y p l a c e t h e p r e s e n t work i n c o n t e x t , d e m o n s t r a t e t h e o r i g i n a l i t y o f s p e c i f i c i d e a s and j u s t i f y t h e a t t r i b u t e s o f t h e s t u d y . C h a p t e r I I d e a l s w i t h t h e s p e e c h s i g n a l and t h e h e a r i n g p r o c e s s . E m p h a s i s i s g i v e n t o t h e a t t r i b u t e s o f s p e e c h e s s e n t i a l f o r i n t e l l i g i b i l i t y and s i t u a t i o n s w h i c h make i t s i n t e r p r e t a t i o n d i f f i c u l t . What i s known ab o u t t h e a u d i t o r y p e r c e p t i o n o f t h e h e a r i n g i m p a i r e d w i l l a l s o be d i s c u s s e d . The 6 r e a d e r may w i s h t o p e r u s e s e c t i o n s of t h i s c h a p t e r f i r s t t o more a p p r e c i a t e t h e aim of t h e r e s e a r c h d e s c r i b e d i n C h a p t e r I . A d e f i n i t i o n of f r e q u e n c y c o m p r e s s i o n i s one o f t h e f i r s t c o n c e r n s o f C h a p t e r I I I . A d e t a i l e d a n a l y s i s o f our a l g o r i t h m f o l l o w s , a l o n g w i t h e x p e r i m e n t a l t e s t s o f t h e i n f o r m a t i o n t r a n s f e r t h r o u g h t h e c o m p r e s s i o n t r a n s f o r m a t i o n . The d e s i g n and hardware needed f o r t h e t e c h n i c a l r e a l i z a t i o n o f t h e a l g o r i t h m c o m p r i s e t h e c o n t e n t s o f C h a p t e r IV. The c l i n i c a l work p e r f o r m e d t o e v a l u a t e t h e u s e f u l n e s s o f s u c h a d e v i c e i s d e s c r i b e d i n C h a p t e r V, t h e r e s u l t s o f w h i c h a p p e a r i n C h a p t e r V I . We end i n C h a p t e r V I I w i t h a d i s c u s s i o n of t h e r e s u l t s and of t h e work i n g e n e r a l , i n t h e c o n t e x t o f f u t u r e e n d e a v o u r s t o b e t t e r a d d r e s s t h e p r e d i c a m e n t o f t h e h e a r i n g i m p a i r e d . The a p p e n d i c e s c o n t a i n d e t a i l e d i n f o r m a t i o n c o n c e r n i n g a n a l y s i s , c l i n i c a l e v a l u a t i o n and t e c h n i c a l d e s i g n . 1-2 P r e v i o u s R e s e a r c h on F r e q u e n c y L o w e r i n g I t i s a p p a r e n t t h a t a m p l i f i c a t i o n a l o n e i s i n s u f f i c i e n t t o r e s t o r e a d e q u a t e h e a r i n g t o many p e o p l e w i t h s e n s o r i n e u r a l h e a r i n g l o s s e s . As we s h a l l s ee i n C h a p t e r I I t h e h e a r i n g l o s s i s u s u a l l y a c c o m p a n i e d by d i s t o r t i o n n o t f o u n d i n n o r m a l s , a l o s s o f dynamic r a n g e and a l o s s o f r e s o l u t i o n i n t i m e , f r e q u e n c y , and a m p l i t u d e . B e c a u s e o f t h e g e n e r a l ( o f t e n s t e e p ) d e g r a d a t i o n of s e n s i t i v i t y w i t h f r e q u e n c y , v a r i o u s r e s e a r c h e r s have l o o k e d f o r ways o f p r e s e n t i n g h i g h f r e q u e n c y i n f o r m a t i o n ( p r i m a r i l y i n 7 speech) i n t h e l o w e r , u s e a b l e f r e q u e n c y b a n d . Some of t h e s e methods , w h i l e a d o p t i n g c h a r a c t e r i s t i c s of t h e b a n d w i d t h r e d u c t i o n schemes used i n b r o a d c a s t i n g and t e l e p h o n e s y s t e m s , a r e f u n d a m e n t a l l y d i f f e r e n t i n t h a t t h e r e i s no d e c o d e r a t the r e c e i v i n g e n d . The h e a r i n g i m p a i r e d u s e r i s p r e s e n t e d d i r e c t l y w i t h t h e f r e q u e n c y l o w e r e d s i g n a l . The e x c e l l e n t r e v i e w a r t i c l e of B r a i d a e t a l . (1979) has l e d t o many of t h e r e f e r e n c e s p r e s e n t e d h e r e , and t h e r e a d e r i s r e f e r r e d t o i t f o r more d e t a i l e d i n f o r m a t i o n . F r e q u e n c y l o w e r i n g i n p r e v i o u s r e s e a r c h has p r i m a r i l y been a c c o m p l i s h e d u s i n g one o f s i x m e t h o d s : S low P l a y b a c k , Time Compressed Slow P l a y b a c k , F r e q u e n c y S h i f t i n g , T r a n s p o s i t i o n , V o c o d i n g , and Zero C r o s s i n g Rate D i v i s i o n . These w i l l be d i s c u s s e d i n t u r n . S low P l a y b a c k . As i t s name s u g g e s t s , i t i n v o l v e s the p r e s e n t a t i o n of p r e r e c o r d e d sound a t a r a t e w h i c h i s s l o w e r t h a n t h a t a t w h i c h i t was r e c o r d e d . T h i s w o u l d r e s u l t i n a l o w e r i n g of a l l s p e c t r a l components by a f a c t o r e q u a l t o t h e r a t i o of the r e c o r d i n g speed t o t h e p l a y i n g s p e e d . Due t o t h e o v e r a l l l e n g t h e n i n g of t h e s i g n a l , the scheme as such c o u l d not be used i n r e a l t i m e . T h i s t e c h n i q u e i s one of the f i r s t e v e r u s e d , and r e s e a r c h i n t o i t s e f f e c t s has spanned t h e l a s t f i v e decades ( F l e t c h e r , 1929; O c h i a i and I z u m i t a c h i , 1955; O c h i a i , S a i t o and S a k a i , 1955; T i f f a n y and B e n n e t t , 1961; D a n i l o f f , S h r i n e r and Z e m l i n , 1 9 6 8 ) . The a u t h o r s r e p o r t t h a t b a n d w i d t h r e d u c t i o n s of 25% r e s u l t i n o n l y s l i g h t r e d u c t i o n s i n i n t e l l i g i b i l i t y . The l o s s o f i n t e l l i g i b i l i t y grows t o moderate and s e v e r e f o r b a n d w i d t h r e d u c t i o n s o f 50% and 66% r e s p e c t i v e l y . The 8 d e t e r i o r a t i o n was h i g h e s t f o r a d u l t male s p e a k e r s and l e s s f o r f e m a l e s and c h i l d r e n . They a l s o f o u n d t h a t vowel d i s c r i m i n a t i o n d e t e r i o r a t e d a t l e a s t as f a s t a s c o n s o n a n t d i s c r i m i n a t i o n . V o w e l s w i t h h i g h s e c o n d f o r m a n t , and low f i r s t f o r m a n t f r e q u e n c i e s p r e s e n t e d more d i f f i c u l t i e s t h a n v o w e l s w i t h h i g h f i r s t and low s e c o n d f o r m a n t f r e q u e n c i e s . T h i s may be due t o t h e f a c t t h a t t h e f o r m e r r e p r e s e n t s a l a r g e r o v e r a l l b a n d w i d t h . T i f f a n y and B e n n e t t (1961) f o u n d t h a t t r a i n i n g w i t h f e e d b a c k ( t h e s u b j e c t s a r e t o l d whether o r n o t t h e i r r e s p o n s e s were c o r r e c t ) i n c r e a s e d t h e d i s c r i m i n a t i o n a b i l i t y of t h e s u b j e c t s , w h i c h i s e v i d e n c e f o r t h e need f o r t r a i n i n g when u s i n g m a t e r i a l s where t h e s p e e c h c u e s have been a l t e r e d . None of t h e s t u d i e s done t h u s f a r has p r o v i d e d more t h a n f o u r h o u r s t r a i n i n g t i m e . The c o l l e c t i v e r e s u l t s p o i n t t o an o v e r a l l l o s s o f i n t e l l i g i b i l i t y i n a l l but t h e c a s e o f a f e m a l e s p e a k e r w i t h a b a n d w i d t h r e d u c t i o n of 20% i n w h i c h a s m a l l i n c r e a s e was o b s e r v e d i n h e a r i n g i m p a i r e d l i s t e n e r s ( B e n n e t t and B y e r s , 1967). The r e a s o n s p r e s e n t e d i n c l u d e t h e f o l l o w i n g . The r e d u c t i o n scheme employed moves t h e v o w e l f o r m a n t s , p r e s e n t i n g ambiguous o r u n f a m i l i a r sound t o t h e l i s t e n e r . The t i m e d i l a t i o n o b s c u r e s c u e s r e l a t e d t o d u r a t i o n and may a l s o c a u s e d i f f i c u l t i e s w i t h s h o r t - t e r m memory. The r e s e a r c h h a s n o t been e x t e n s i v e enough t o d e t e r m i n e t h e r e l a t i v e i m p o r t a n c e o f t h e s e r e a s o n s , o r t h e i m p o r t a n c e of t r a i n i n g t i m e and methods. Time C o m p r e s s e d Slow P l a y b a c k . T h e s e methods a r e a t t e m p t s t o a l l e v i a t e p r o b l e m s a s s o c i a t e d w i t h o v e r a l l t e m p o r a l d i l a t i o n , and t o p r o d u c e a r e a l t i m e a l g o r i t h m . A number o f schemes were d e s i g n e d t o b r i n g t h e s l o w p l a y b a c k s o u n d s back t o 9 t h e i r r e a l t i m e c o u r s e . These i n c l u d e p e r i o d i c p r o c e s s i n g w h i c h i n v o l v e s d e l e t i n g segments p e r i o d i c a l l y ( F a i r b a n k s , E v e r e t t . , and J a e g e r , 1954) and p i t c h s y n c h r o n o u s p r o c e s s i n g i n v o l v i n g t h e d e l e t i o n of segments i n c o n c o r d a n c e w i t h c e r t a i n r u l e s , such as s u c c e s s i v e v o i c e d p e r i o d s ( D a v i d and M c D o n a l d , 1956; S c o t t and G e r b e r , 1972; Reed e t a l . , 1 9 8 3 ) . The p r o c e s s i n g i n e v i t a b l y p r o d u c e s s a m p l i n g n o i s e and o t h e r d i s t o r t i o n s . The slowdown and c o m p r e s s i o n f a c t o r s a r e g e n e r a l l y chosen t o be e q u a l so t h a t t h e l o n g t e rm d u r a t i o n r e m a i n s u n a l t e r e d . W h i l e many' p i t c h s y n c h r o n o u s a l g o r i t h m s a r e s u g g e s t e d , o n l y one q u i t e r e c e n t s t u d y of t h e t e c h n i q u e a p p e a r s t o have been r e p o r t e d (Reed e t a l . , 1 9 8 3 ) . T h i s work used a f r e q u e n c y w a r p i n g a l g o r i t h m w h i c h compres sed the h i g h f r e q u e n c i e s more t h a n t h e l o w e r o n e s . The s t u d i e s were p e r f o r m e d w i t h norma l h e a r i n g a d u l t s w i t h l o w p a s s f i l t e r i n g . The b e s t r e s u l t s were c o m p a r a b l e t o t h o s e o b t a i n e d w i t h low pass f i l t e r i n g a l o n e . P i t c h s y n c h r o n o u s p r o c e s s i n g i s not r e a d i l y amenable t o a n y t h i n g e x c e p t s p e e c h . T h e r e i s l i t t l e p r o v i s i o n f o r t h e a c c o m o d a t i o n of n o i s e , r e v e r b e r a t i o n and o t h e r e v e r y d a y i n t e r f e r e n c e . T h i s i s a common p r o b l e m t o a l l p i t c h s y n c h r o n o u s p r o c e s s e s and i s d i s c u s s e d i n d e t a i l by Hess (1982) and S c h a f e r -V i n c e n t ( 1 9 8 2 ) . They r e p o r t t h a t even when t h e s p e e c h s i g n a l i s n o i s e f r e e , t h e d e t e r m i n a t i o n o f p i t c h p e r i o d i s a d i f f i c u l t t a s k . The p e r i o d i c p r o c e s s i n g a p p r o a c h i s not u n i q u e . There have been v a r i o u s a l g o r i t h m s used ( c f . F a i r b a n k s e t a l . , 1954; L e e , 1972; B e n n e t t and L i n v i l l , 1975; K n o r r , l 9 7 6 ) , but a l l employ t h e p r i n c i p l e o f c h o p p i n g and a b u t t i n g t h e i n p u t s i g n a l on a r e g u l a r 10 b a s i s and d i s c a r d i n g the r e m a i n i n g i n f o r m a t i o n . G a r v e y (1953) r e p o r t s t h e f i r s t e x p e r i m e n t s i n w h i c h he c u t r e c o r d e d speech t a p e s , removed i n t e r v a l s and s p l i c e d the r e m a i n i n g p i e c e s t o g e t h e r . He found t h a t t h e r e s u l t i n g speech r e t a i n e d much of i t s i n t e l l i g i b i l i t y . F a i r b a n k s e t a l . (1954) c o n s t r u c t e d a t ape p l a y e r upon w h i c h a c i r c u l a r d i s k w i t h f o u r p l a y b a c k heads r o t a t e d . As t h e tape p a s s e d b y , t h e t a p e -p l a y b a c k head speed c o u l d be v a r i e d , s i m u l a t i n g G a r v e y ' s t e c h n i q u e (I had o c c a s i o n t o l e a r n t h a t t h i s machine when used w i t h b l i n d r e a d e r s t o l i s t e n t o sped up t e x t , became a f f e c t i o n a t e l y known as t h e " W h i r l i n g D e r v i s h " ) . The p e r i o d i c p r o c e s s i n g t e c h n i q u e has been e v a l u a t e d u s i n g n o r m a l a d u l t l i s t e n e r s w i t h l e s s t h a n t h r e e h o u r s of t r a i n i n g ( F a i r b a n k s and Kodman, 1957; Klumpp and W e b s t e r , 1961; Z e m l i n , 1966; D a n i l o f f e t a l . , 1968; S h r i n e r e t a l . , 1969; and N a g a f u c h i , 1 9 7 6 ) . The t e s t i n g p r o c e d u r e s i n c l u d e d p h o n e t i c a l l y b a l a n c e d w o r d s , s i n g l e v o w e l s i n words b e g i n n i n g w i t h t h e c o n s o n a n t / h / and e n d i n g w i t h t h e c o n s o n a n t / d / and J apanese m o n o s y l l a b l e s . The s t u d i e s show t h a t t h e p r o c e s s i n g of the speech i m p r o v e s t h e i n t e l l i g i b i l i t y l i t t l e i f a t a l l . L a r g e r r e d u c t i o n s i n b a n d w i d t h can be accomodated f o r female t h a n f o r male s p e a k e r s . Vowel p e r c e p t i o n i s d e g r a d e d t o an e q u a l o r g r e a t e r e x t e n t t h a n t h a t o f c o n s o n a n t s . S t u d i e s by Osken (1963) used 40 s u b j e c t s w i t h s e n s o r i n e u r a l h e a r i n g l o s s ( a t l e a s t 40 dB l o s s between 1200 and 1500 H z . ) . There was no t r a i n i n g t i m e i n v o l v e d , and p e r c e p t i o n s c o r e s were l o w e r e d i n each ca se w i t h t h e p r o c e s s e d s p e e c h . U n s p e c i f i e d t r a i n i n g improved t h e r e s u l t s of 4 s u b j e c t s , but no t beyond what t h e y c o u l d a c c o m p l i s h w i t h 11 u n p r o c e s s e d s p e e c h . Z e m l i n (1966) r e p o r t e d u n s u c c e s s f u l improvement i n n o r m a l and h e a r i n g i m p a i r e d c h i l d r e n . There was no t r a i n i n g t i m e i n v o l v e d . The r e s u l t s were i n t e r p r e t e d as an i n d i c a t i o n t h a t p a s t a c e r t a i n f a c t o r , b a n d w i d t h r e d u c t i o n a l t e r s t h e s i g n a l beyond any p r e v i o u s l anguage e x p e r i e n c e and i n t e l l i g i b i l i t y i s r e d u c e d even i n t h e h e a r i n g i m p a i r e d f o r whom t h e t e c h n i q u e was e x p e c t e d t o p r o v i d e b e n e f i t . B e a s l e y , M o s h e r , and O r c h i k (1976) i n c l u d e d t r a i n i n g t i m e w i t h a s t u d y u s i n g a sy s tem based on work by Lee ( 1 9 7 2 ) . E i g h t e e n c h i l d r e n w i t h c o n g e n i t a l s e n s o r i n e u r a l h e a r i n g l o s s e s were t r a i n e d f o r 20 m i n u t e s per day on 15 c o n s e c u t i v e s c h o o l d a y s . The a u t h o r s r e p o r t t h a t the improvement o v e r a c o n t r o l g r o u p u s i n g l i n e a r a m p l i f i c a t i o n was m a r g i n a l a t b e s t . I t i s i n t e r e s t i n g t o no te t h a t i t was not s u b s t a n t i a l l y worse i n most c a s e s . Mazor e t a l . (1977) used t h e Lee (1972) sy s tem w i t h s e n s o r i n e u r a l a d u l t s . T r a i n i n g c o n s i s t e d o f 40 m i n u t e s of l i s t e n i n g . A l l r e s u l t s showed a d e c r e a s e i n i n t e l l i g i b i l i t y e x c e p t f o r a 20% b a n d w i d t h r e d u c t i o n w i t h a female s p e a k e r . T h i s e x c e p t i o n showed a s m a l l (3 p e r c e n t a g e p o i n t s ) i n c r e a s e . I n p a s t s t u d i e s , i t seems t h a t t r a i n i n g was n e v e r done w i t h an i n d i v i d u a l c o m p r e s s o r d e v i c e , o n l y w i t h a communal o n e . F r e q u e n c y S h i f t i n g . T h i s i s a t y p e o f f r e q u e n c y l o w e r i n g t h a t has been w i t h us f o r many y e a r s i n t h e form of AM m o d u l a t i o n ( a l t h o u g h i n t h i s c a se t h e f r e q u e n c y i s r a i s e d ) . H e t e r o d y n e t e c h n i q u e s ( c f . J o h n s o n , 1965) a l l o w t h e a d d i t i o n (or s u b t r a c t i o n ) of a f i x e d f r e q u e n c y ( t h e c a r r i e r ) t o an i n p u t s i g n a l i n r e a l t i m e . I f t h e i n p u t i s not f i l t e r e d , t h e n 12 f r e q u e n c y components l o w e r t h a n the c a r r i e r w i l l be r e v e r s e d i n o r d e r and any f r e q u e n c y component e q u a l t o t h e c a r r i e r w i l l appear a t the o u t p u t as a DC l e v e l . Any f i l t e r i n g w h i c h i s done may g r e a t l y reduce i n t e l l i g i b i l i t y on i t s own. N e v e r t h e l e s s , t e m p o r a l cues a r e u n a l t e r e d and the f r e q u e n c y ranges w h i c h c a r r y t h e s e t e m p o r a l cues may become a u d i b l e t o t h e l i s t e n e r . A n o t h e r form of f r e q u e n c y s h i f t i n g i s t h a t of u n f i l t e r e d s a m p l i n g . I f an i n p u t s i g n a l i s sampled a t a f r e q u e n c y F , then i n p u t f r e q u e n c i e s ( f ) l o w e r t h a n F / 2 r ema in u n a l t e r e d . F r e q u e n c i e s between F / 2 and F become F / 2 - f upon s a m p l i n g and t h e e f f e c t goes on f o r h i g h e r f r e q u e n c i e s s h i f t i n g a l l t o the range 0 t o F / 2 . T h i s phenomenon i s known as a l i a s i n g ( i n o p t i c s i t i s r e s p o n s i b l e f o r M o i r e p a t t e r n s ) . The t e c h n i q u e has been a p p l i e d w i t h v e r y l i m i t e d s u c c e s s ( B i o n d i and B i o n d i , 1968; L i n g , 1972) . F l e t c h e r (1953) found t h a t i n t e l l i g i b i l i t y f o r normal l i s t e n e r s d e c r e a s e d w i t h f r e q u e n c y s h i f t s b o t h upward and downward. O t h e r r e s e a r c h e r s ( C a m p b e l l e t a l . , 1976; Raymond and P r o u d , 1962; B i o n d i , and B i o n d i , 1968; L i n g , 1972) a l l r e p o r t t h a t a t b e s t o n l y v e r y l i m i t e d v o c a b u l a r i e s of sounds can be a c q u i r e d . F r e q u e n c y S h i f t i n g t e c h n i q u e s on t h e whole appear t o h o l d l i t t l e p r o m i s e of i m p r o v i n g speech p e r c e p t i o n f o r t h e h e a r i n g i m p a i r e d . The o n l y p o s i t i v e r e s u l t s come f rom a c o m b i n a t i o n of s a m p l i n g t e c h n i q u e s f o r f r e q u e n c y s h i f t i n g and e x t e n s i v e t r a i n i n g ( B i o n d i and B i o n d i , 1 9 7 3 ) . N o r m a l and m o d e r a t e l y i m p a i r e d l i s t e n e r s f i n d t h e sounds p r o d u c e d w i t h t h e s a m p l i n g method v e r y d i f f i c u l t t o i n t e r p r e t as s p e e c h . 13 T r a n s p o s i t i o n . T h i s f r e q u e n c y l o w e r i n g method i n v o l v e s t h e moving o f h i g h f r e q u e n c y p a r t s o f t h e i n p u t s p e c t r u m t o l o w e r f r e q u e n c i e s and a d d i n g them t o t h e e x i s t i n g l o w e r f r e q u e n c y i n p u t s p e c t r u m . T h i s i s t h e o n l y t e c h n i q u e p r e s e n t l y i n c o r p o r a t e d i n c o m m e r c i a l h e a r i n g a i d s . J o h a n s s o n (1961) d e s i g n e d a s y s t e m w h i c h t r a n s p o s e d sounds above 3 kHz by f i l t e r i n g and m i x i n g w i t h a 4.5 kHz ( t y p i c a l ) l o c a l o s c i l l a t o r . T h i s t e c h n i q u e combined w i t h a m p l i t u d e c o m p r e s s i o n ( s e e C h a p t e r 2) b r o u g h t v e r y e n c o u r a g i n g r e s u l t s ( J o h a n s s o n and S j o g r e n , 1965; J o h a n s s o n , 1966); however, L i n g (1968, 1969) r e p o r t s t h a t i n h i s e v a l u a t i o n o f t h e s y s t e m , no b e n e f i t s ( o r a d v e r s e e f f e c t s ) were p r o v i d e d . The r e s u l t s o f o t h e r r e s e a r c h e r s ( A h l s t r o m e t a l . , 1968; Spens and M a r t o n y , 1972; F o u s t and G e n g e l , 1973) show o n l y s l i g h t i n c r e a s e i n p e r c e p t i o n i f any when u s i n g t h i s t e c h n i q u e . O t h e r t r a n s p o s i t i o n d e v i c e s have been b u i l t ( c f . V e l m a n s , 1971, 1974) but t h e g e n e r a l p a t t e r n seems t h e same. Some s u c c e s s can be d e m o n s t r a t e d i n c l o s e d v o c a b u l a r i e s , but t h e d e v i c e s g e n e r a l l y do n o t enhance t h e i n t e l l i g i b i l i t y o f most s p e e c h m a t e r i a l s . V o c o d i n q . T h i s t e c h n i q u e i s u s e d w i t h g r e a t s u c c e s s i n s i g n a l t r a n s m i s s i o n ; however, i n t h a t c a s e t h e r e i s a d e c o d e r u s e d on t h e r e c e i v i n g end f u l l y r e s t o r i n g t h e s p e c t r a l w i d t h . The t e c h n i q u e u s e s a bank o f a n a l y s i n g b a n d p a s s f i l t e r s and t h e e n v e l o p e o f t h e o u t p u t i s u s e d f o r t r a n s m i s s i o n . A d e s c r i p t i o n o f t h e v o c a l sound ( h i s s o r b u z z ) i s a l s o s e n t , a l o n g w i t h t h e f u n d a m e n t a l f r e q u e n c y o f t h e v o i c e d s p e e c h . The r e c e i v i n g end employs a bank o f o s c i l l a t o r s ( o r narrow band n o i s e g e n e r a t o r s ) 14 t o r e c o n s t r u c t t h e spec t rum of the i n p u t . When used w i t h t h e h e a r i n g i m p a i r e d , the r e c o n s t r u c t i o n c h a n n e l s u s u a l l y g e n e r a t e f r e q u e n c i e s l o w e r than t h e i r a n a l y s i n g c o u n t e r p a r t s . The t e c h n i q u e a f f o r d s the o p p o r t u n i t y of v a r y i n g t h e c o m p r e s s i o n r a t i o w i t h f r e q u e n c y . L i n g and Druz (1967) used a s i x - c h a n n e l v o c o d e r w i t h h e a r i n g i m p a i r e d c h i l d r e n . T r a i n i n g t i m e c o n s i s t e d of 22 days w i t h 20 m i n u t e s p e r d a y . No improvement was shown over a c o n t r o l g roup u s i n g l i n e a r a m p l i f i c a t i o n . O t h e r t y p e s of v o c o d e r s t r a c k t h e fo rmant f r e q u e n c i e s and r e c o n s t r u c t t h e s i g n a l f rom t h e f r e q u e n c y i n f o r m a t i o n ( c f . F l a n a g a n and House , 1956; Reeder e t a l . , 1 9 7 5 ) . In t h i s c a se each r e c o n s t r u c t i o n c h a n n e l has a v a r i a b l e f r e q u e n c y o u t p u t . E v a l u a t i o n of t h i s a l g o r i t h m by S t e w a r t e t a l . (1976) shows t h a t the p e r c e p t i o n of v o i c e d speech i s u n a l t e r e d but t h e p e r c e p t i o n of n a s a l i t y and s i b i l a t i o n were a d v e r s e l y a f f e c t e d . Zero C r o s s i n g Rate D i v i s i o n . T h i s t e r m c o v e r s a c l a s s o f f r e q u e n c y l o w e r i n g t e c h n i q u e s a imed a t r e d u c i n g the z e r o c r o s s i n g r a t e of t h e speech wave form. S e v e r a l a u t h o r s ( c f . S c h r o e d e r e t a l . , 1967; Guttman and van B e r g e i j k , 1959; Guttman e t a l . , 1970; Thomas and F l a v i n , 1970; Morgan and S a v i d g e , 1975) have i n v e s t i g a t e d v a r i o u s a p p l i c a t i o n s of t h e method , but no p o s i t i v e r e s u l t s have been r e p o r t e d f o r any z e r o c r o s s i n g r a t e d i v i s i o n t e c h n i q u e when used t o improve i n t e l l i g i b i l i t y f o r t h e h e a r i n g i m p a i r e d . I n summary, t h e r e has been l i t t l e s u c c e s s w i t h f r e q u e n c y l o w e r i n g t e c h n i q u e s i n t h e p a s t . These n e g a t i v e r e s u l t s a r e not r e a d i l y e x p l a i n a b l e , but f rom t h e r e v i e w o f l i t e r a t u r e j u s t 15 p r e s e n t e d , we c a n s u g g e s t s i x p o s s i b l e r e a s o n s . Some of t h e s e a p p l y t o a l l t h e a p p l i c a t i o n s o f t h e t e c h n i q u e s p r e s e n t e d , but a l l a p p l y t o t h e a p p l i c a t i o n s of t h e Time Com p r e s s e d Slow P l a y b a c k method. P o s s i b l e e x p l a n a t i o n s a r e : (a) an i n s u f f i c i e n t amount o f i n f o r m a t i o n t r a n s m i t t e d t o t h e l i s t e n e r due t o t h e c o m p r e s s i o n a l g o r i t h m ; (b) an u n s u i t a b l e t r a n s f o r m a t i o n of t h e s p e e c h s i g n a l ; ( c ) an i n a d e q u a t e t i m e f o r t r a i n i n g o f t h e s u b j e c t s ; (d) i n e f f e c t i v e t r a i n i n g p r o c e d u r e s ; (e) t h e i m p o s s i b i l i t y f o r t h e s u b j e c t s t o h e a r d i r e c t l y t h e i r own s p e e c h sounds t r a n s f o r m e d ; ( f ) o p t i m a l l i n e a r a m p l i f i c a t i o n f i t t i n g was not i n c l u d e d a s p a r t of t h e t h e r a p y . In t h e Time Compressed Slow P l a y b a c k method, some of t h e s e l i m i t a t i o n s o f t h e p a s t work a r e s e v e r e i n d e e d . P e r i o d i c p r o c e s s i n g i s t h e o n l y method i n t h i s c l a s s w h i c h makes s e n s e i n r e a l t i m e w i t h t h e p r e s e n c e o f n o i s e . In t h i s method a c o n s i d e r a b l e amount o f i n f o r m a t i o n i s d i s c a r d e d . F o r a b a n d w i d t h r e d u c t i o n o f a f a c t o r o f 2, one h a l f of t h e i n p u t t e m p o r a l i n f o r m a t i o n i s l o s t . T h i s i n f o r m a t i o n may i n c l u d e t r a n s i e n t c o n s o n a n t s w h i c h a r e i m p o r t a n t c u e s f o r d i s c r i m i n a t i o n . In modern a u r a l r e h a b i l i t a t i o n , a t r i a l p e r i o d o f s i x t o t w e l v e weeks i s g e n e r a l l y a l l o w e d b e f o r e d e c i d i n g whether improvement i s s u f f i c i e n t t o w a r r a n t f u r t h e r t h e r a p y ( B a t e , 1980). V e r y few s t u d i e s even a p p r o a c h e d t h i s l e n g t h o f t i m e . In t h e n e x t s e c t i o n , we d i s c u s s p o s s i b l e methods f o r s o l v i n g , a t l e a s t i n p a r t , some o f t h e p r o b l e m s t o see w hether o r not t h e r e a s o n s g i v e n a r e v a l i d e x p l a n a t i o n s . 16 1-3 C l i n i c a l S t u d y P r o p o s a l Due t o t h e s h o r t c o m i n g s of v a r i o u s a s p e c t s of t h e p a s t r e s e a r c h i n f r e q u e n c y l o w e r i n g , i t seems unwise t o d i s m i s s t h e methods. The i n a d e q u a c y o f t h e p r e v i o u s s t u d i e s i s u n d e r s t a n d a b l e and i n no way d e t r a c t s from t h e e x c e l l e n c e of t h e r e s e a r c h a l r e a d y u n d e r t a k e n . The v e r y n a t u r e o f t h e t o p i c i s d i f f i c u l t a nd r e l i e s upon a s s u m p t i o n s a b o u t t h e human h e a r i n g s y s t e m . R e s e a r c h has p r o v i d e d no model on w h i c h t o base t h e s e a s s u m p t i o n s . S t u d i e s on t h e p e r c e p t i o n of f r e q u e n c y l o w e r e d s p e e c h may a c t u a l l y c o n t r i b u t e more t o s u c h an u n d e r s t a n d i n g , but f o r t h e p r e s e n t , c a r e f u l a s s u m p t i o n s a r e our o n l y c o u r s e . The r e s e a r c h i s a l s o n e c e s s a r i l y i n t e r d i s c i p l i n a r y . I n p u t t o t h e d e s i g n o f t h e a l g o r i t h m i s needed from s p e e c h and l i n g u i s t i c s s c i e n t i s t s , a s w e l l a s from e x p e r t s i n a c o u s t i c s . T h i s a l g o r i t h m must be put i n t h e form of a d e v i c e w i t h e x p e r t i s e f r o m t h e f i e l d o f e l e c t r i c a l e n g i n e e r i n g , and t h e a p p r o p r i a t e t e c h n i c a l p e o p l e a r e needed f o r i t s c o n s t r u c t i o n . O t o l a r y n g o l o g i s t s a r e needed t o p r o v i d e p r o p e r s u b j e c t s , and i n d e e d t h e c r i t e r i a f o r s u b j e c t s e l e c t i o n must be d e c i d e d upon. D u r i n g t h e s t u d y a s k i l l e d c l i n i c a l a u d i o l o g i s t i s needed t o p r o p e r l y a s s e s s h e a r i n g l o s s e s , f i t t h e s u b j e c t s w i t h p r o p e r e a r m o u l d s , and h e a r i n g a i d s . The a u d i o l o g i s t must a l s o a d m i n i s t e r t h e t e s t s f o r p e r c e p t i o n , and t h e r a p y f o r t r a i n i n g . D u r i n g t h i s t r a i n i n g t i m e , a t e c h n i c i a n must a l s o be p r e s e n t t o a s s u r e t h e p r o p e r w o r k i n g s o f t h e d e v i c e s and make a d j u s t m e n t s d i c t a t e d by t h e t h e r a p y and o n g o i n g t e s t r e s u l t s . Most of t h e p e o p l e d e s c r i b e d above a r e needed i n a l l s t a g e s of t h e s t u d y . S e v e r a l o f t h e d i s c i p l i n e s must meet t o d e s i g n t h e t e s t s f o r 17 s p e e c h d i s c r i m i n a t i o n , s i n c e v e r y l i t t l e has been p u b l i s h e d i n t h i s f i e l d . I t i s w i t h t h e s e b u r d e n s i n mind t h a t we embark on t h e p r e s e n t s t u d y . Not a l l o f t h e d i f f i c u l t i e s c a n be d i r e c t l y a d d r e s s e d , but we s t r i v e t o accomodate t h e f u n d a m e n t a l ones w i t h t h e end g o a l of a c h i e v i n g i m p r o v e d s p e e c h p e r c e p t i o n f o r t h e h e a r i n g i m p a i r e d . To d e a l w i t h t h e p r o b l e m of i n s u f f i c i e n t i n f o r m a t i o n t r a n s m i t t e d t o t h e l i s t e n e r , a new a l g o r i t h m was d e v i s e d w h i c h does n o t d i s c a r d any i n f o r m a t i o n . I n s t e a d , a l l t e m p o r a l i n f o r m a t i o n a t t h e i n p u t f i n d s i t s way t o t h e o u t p u t . T h i s i s a c c o m p l i s h e d by t h e o v e r l a y i n g o f t h e segmented t i m e i n t e r v a l s i n a s t a g g e r e d f a s h i o n a t t h e o u t p u t ( s e e C h a p t e r I I I ) . I t was b e l i e v e d , on t h e b a s i s o f t h e r e s u l t s o f T i f f a n y and B e n n e t t ( 1 9 6 1 ) , Osken (1963) and o t h e r s ( c f . B i o n d i and B i o n d i , 1968, 1973) t h a t i n s u f f i c i e n t t r a i n i n g o f t h e s u b j e c t s has been done i n p a s t r e s e a r c h . A p l a n o f t r a i n i n g was d e v i s e d f o r t h i s s t u d y t o encompass more t r a i n i n g t i m e t h a n had p r e v i o u s l y been r e p o r t e d . The t r a i n i n g p r o g r am c o n s i s t e d o f v a r i o u s f o r m s of t h e r a p y , i n c l u d i n g some i d e a s o f p a s t r e s e a r c h e r s and some o r i g i n a l t o t h i s work, made p o s s i b l e by t h e r e a l - t i m e n a t u r e o f t h e d e v i c e ( s e e b e l o w ) . In t h e r e a l i z a t i o n o f our new a l g o r i t h m i n t h e f o r m o f a d e v i c e , we made a t t e m p t s t o make i t s m a l l , p o r t a b l e and e a s y t o u s e . The d e v i c e would work i n r e a l t i m e , e n a b l i n g s u b j e c t s t o he a r t h e i r own s p e e c h sounds and h e a r a l l sounds i n t h e e n v i r o n m e n t i n w h i c h t h e y were p r o d u c e d . T h i s i s i n c o n t r a s t t o 18 most o f t h e work r e p o r t e d t h u s f a r ( c f . B r a i d a e t a l . , 1979; S a i t o e t a l . , 1981). T h e r e have been few t e s t s f o r a u d i t o r y p e r c e p t i o n w i t h p u b l i s h e d norms. Some of t h e s e have been u s e d , as w e l l as some of our own d e s i g n ( s e e C h a p t e r V ) . In t h e p a s t , l i t t l e i f any work seems t o have i n c l u d e d o p t i m a l f i t t i n g o f t h e s u b j e c t s w i t h l i n e a r a m p l i f i c a t i o n . T h i s s t u d y i n c o r p o r a t e s a p r o g r a m o f c u s t o m e a r m o u l d s u p p l y and o p t i m a l h e a r i n g a i d f i t t i n g a s p a r t of t h e o v e r a l l g o a l o f o p t i m a l l y m a t c h i n g th e s p e e c h s i g n a l t o t h e r e s i d u a l a u d i t o r y f u n c t i o n . As d i s c u s s e d i n t h e p r e v i o u s s e c t i o n , t h e i n t e r d i s c i p l i n a r y n a t u r e o f t h e work c a l l s f o r i n p u t from e x p e r t s i n v a r i o u s f i e l d s . To t h i s end, a team was formed c o n s i s t i n g m a i n l y of Dr. A-P. B e n g u e r e l of U.B.C.'s S c h o o l of A u d i o l o g y and S p e e c h S c i e n c e s , B e t h B r o o k s , a u d i o l o g i s t , Dr. N. W e i s s of U.B.C.'s d e p a r t m e n t o f p h y s i c s , and t h e a u t h o r . T h i s team, w i t h h e l p s o l i c i t e d ( a n d r e c e i v e d ) f r o m V a n c o u v e r a r e a o t o l a r y n g o l o g i s t s and a u d i o l o g i s t s , encompassed t h e r a n g e of d i s c i p l i n e s o u t l i n e d i n t h e p r e v i o u s s e c t i o n . T e c h n i c a l f a c i l i t i e s were f u r n i s h e d by D r . A.V. G o l d and D r . R.R. H a e r i n g o f U.B.C.'s p h y s i c s d e p a r t m e n t and a u d i o l o g i c a l f a c i l i t i e s were p r o v i d e d by Dr. N.S. L o n g r i d g e of V a n c o u v e r G e n e r a l H o s p i t a l ' s N e u r o - o t o l o g y U n i t . T h r o u g h o u t the p r o j e c t , i n t e l l e c t u a l i n p u t was t o be g i v e n by a l l o f t h e s e p e o p l e a n d o t h e r s f r o m v a r i o u s d i s c i p l i n e s and l o c a t i o n s . I t was f e l t by a l l t h a t t h e a l l - e n c o m p a s s i n g p r o g ram would p r o v i d e a v a l u a b l e a s s e t t o t h e c o l l e c t i o n o f r e s e a r c h on f r e q u e n c y l o w e r i n g as a means o f making s p e e c h more i n t e l l i g i b l e t h e s e v e r e l y h e a r i n g i m p a i r e d . CHAPTER I I ATTRIBUTES OF SPEECH AND HEARING 21 U - 1 The V o c a l O r g a n s F o r s p e e c h p r o d u c t i o n we use t h e l u n g s , t h e t r a c h e a ( o r w i n d p i p e ) , t h e l a r y n x ( i n c l u d i n g t h e v o c a l f o l d s ) , t h e p h a r y n x , t h e nose and t h e mouth ( i n c l u d i n g t h e l i p s , t h e t o n g u e , t h e velum, and t h e t e e t h ) . T o g e t h e r , t h e s e f o r m a t u b e from t h e l u n g s t o t h e l i p s . The s e c t i o n of t h i s t u b e above t h e l a r y n x i s c a l l e d t h e v o c a l t r a c t , and i t s shape (and t h e r e f o r e i t s a c o u s t i c p r o p e r t i e s ) c an be c h a n g e d i n a v a r i e t y o f ways. The e n e r g y s o u r c e f o r v o w e l s and most c o n s o n a n t s i s an o v e r p r e s s u r e o f a i r i n t h e l u n g s . In n o r m a l s p e e c h t h i s o v e r p r e s s u r e i s a b o u t 0.01 atm. o r ab o u t 10 cm H 2 0 ( i n n o r m a l E n g l i s h , s o unds a r e o n l y p r o d u c e d d u r i n g e x h a l a t i o n ) . The a v e r a g e volume o f a i r u s e d p e r i n h a l a t i o n i s 0.5 l i t e r . D u r i n g t h e c o u r s e of n o r m a l b r e a t h i n g , an i n h a l a t i o n / e x h a l a t i o n p e r i o d i s a b o u t 5 s e c . w i t h a d u t y c y c l e o f r o u g h l y 50%. D u r i n g s p e e c h , d u t y c y c l e s a s h i g h a s 85% a r e common, a s we i n f l u e n c e our b r e a t h i n g r a t e i n a c c o r d a n c e w i t h t h e needs o f p h r a s e l e n g t h . V o i c e d s o u n d s a r e g e n e r a t e d by t h e v i b r a t i o n o f t h e v o c a l f o l d s i n t h e l a r y n x ( s e e F i g . 2 . 1 ) . The l a r y n x c o n t a i n s a s t a c k of c a r t i l a g e s , and i s e a s i l y l o c a t e d by one o f them: t h e t h y r o i d c a r t i l a g e , o r "Adam's a p p l e " . The v o c a l f o l d s c h o p up t h e s t e a d y f l o w o f a i r from t h e l u n g s i n t o a s e r i e s o f p u f f s , p r o d u c i n g a b u z z i n g n o i s e . T h i s n o i s e i s p r o f o u n d l y m o d i f i e d by t h e v o c a l t r a c t t o form s p e e c h s o u n d s . The p h a r y n x i s t h e p a r t o f t h e v o c a l t r a c t c o n n e c t i n g t h e l a r y n x t o t h e o r a l c a v i t y and i t i s p r o l o n g e d i n t h e n a s a l c a v i t y . The p h a r y n x i s c r u c i a l i n p r o d u c i n g t h e " s i n g i n g 22 F i g 2 . 1 The V o i c e O r g a n F r o m " T h e A c o u s t i c s o f t h e S i n g i n g V o i c e " . C o p y r i g h t © M a r c h 1977 b y S c i e n t i f i c A m e r i c a n , I n c . A l l r i g h t s r e s e r v e d . 23 f o r m a n t " u s e d by o p e r a s i n g e r s ( S u n d b e r g , 1977). The n a s a l c a v i t y i s a b o u t f o u r i n c h e s l o n g e x t e n d i n g f r o m t h e p h a r y n g e a l w a l l t o t h e n o s t r i l s . R i d g e s and f o l d s i n t h e c a v i t y w a l l s b r e a k up some segments o f t h e n a s a l c a v i t y i n t o i n t r i c a t e l y s h a p e d c h a n n e l s . The n a s a l septum d i v i d e s t h e n a s a l c a v i t y i n h a l f a t t h e f r o n t . The most i m p o r t a n t p a r t o f t h e v o c a l t r a c t i s t h e o r a l c a v i t y . I t s shape c a n be v a r i e d e x t e n s i v e l y by a d j u s t i n g t h e r e l a t i v e p o s i t i o n s of t h e velum, t h e t o n g u e , t h e l i p s and t h e jaw. The most f l e x i b l e o f t h e s e t h r e e i s t h e t o n g u e . The e n t i r e t o n g u e can be moved up, down, f o r w a r d s , o r b a c k w a r d s . I t s e d g e s and c e n t e r c a n be moved t o a g r e a t e x t e n t , i n d e p e n d e n t l y . The l i p s change t h e shape o f t h e v o c a l t r a c t , but a l s o c o n s t i t u t e w i t h t h e t e e t h and t h e t i p o f t h e ton g u e t h e o n l y n o r m a l l y v i s i b l e p a r t s o f t h e s p e e c h p r o d u c t i o n s y s t e m . The v i s i b i l i t y of t h e s e o r g a n s , t o g e t h e r w i t h f a c i a l e x p r e s s i o n s c a n g i v e t h e l i s t e n e r i m p o r t a n t s p e e c h c u e s . F o r t h e s e v e r e l y h e a r i n g i m p a i r e d ( t h o s e who p r a c t i c e s p e e c h r e a d i n g ) , t h e s e c u e s a r e enough t o d e t e r m i n e up t o 80% o f t h e c o n t e n t o f n o r m a l s p e e c h . The t e e t h i n c o n j u n c t i o n w i t h t h e jaw, a s w e l l a s c h a n g i n g t h e shape o f t h e v o c a l t r a c t , c an be u s e d w i t h t h e l i p s o r t h e t o n g u e t o r e s t r i c t o r s t o p t h e a i r f l o w . R e s t r i c t i n g a i r f l o w t o t h e p o i n t o f t u r b u l e n c e p r o d u c e s a c l a s s o f sounds c a l l e d f r i c a t i v e s ( e . g . / s / , / s h / ) . S t o p p i n g t h e a i r f l o w and t h e n q u i c k l y r e l e a s i n g i t p r o d u c e s a c l a s s o f sounds c a l l e d p l o s i v e s ( e . g . /p/, / g / ) . F r i c a t i v e s and p l o s i v e s c a n be p r o d u c e d whether t h e v o c a l f o l d s a r e v i b r a t i n g o r n o t , i n a d d i t i o n , f r i c a t i v e s and p l o s i v e s a r e f u r t h e r 24 d i f f e r e n t i a t e d by m o d i f y i n g t h e v o c a l t r a c t . I t t u r n s o u t t h a t t h e d i s t i n g u i s h i n g c h a r a c t e r i s t i c s of t h e s e sounds a r e t h e i r h i g h f r e q u e n c y components, making them p a r t i c u l a r l y d i f f i c u l t t o d i s c r i m i n a t e w i t h a h i g h f r e q u e n c y h e a r i n g l o s s . Some A f r i c a n l a n g u a g e s use " c l i c k s " i n s p e e c h . T h e s e a r e p r o d u c e d by t r a p p i n g a i r i n t h e v o c a l t r a c t between two p o i n t s , c o m p r e s s i n g i t , and t h e n r e l e a s i n g i t . S p e a k e r s of some T u r k i s h and S p a n i s h d i a l e c t s c a n use w h i s t l e s a s an a u x i l i a r y mode of c o m m u n i c a t i o n . In t h e n e x t s e c t i o n s , we c o n s i d e r t h e v a r i o u s a t t r i b u t e s o f s p e e c h sounds p r o d u c e d by t h e v o c a l o r g a n s w h i c h make them d i s c e r n a b l e . I I - 2 V o i c e d S p e e c h The t e r m " v o i c e d s p e e c h " r e f e r s t o t h o s e p a r t s o f t h e s p e e c h wave w h i c h c o n s i s t o f sounds i n w h i c h t h e v o c a l f o l d s a r e v i b r a t i n g . The m o t i o n of t h e v o c a l f o l d s i s n e a r l y p e r i o d i c , and s i n c e t h e y p r o d u c e s h a r p p u f f s o f a i r , t h e r e s u l t i n g sound i s r i c h i n h i g h f r e q u e n c i e s . In g e n e r a l , t h e p e r i o d i c n a t u r e of t h e sound g i v e s r i s e t o h a r m o n i c s ( i n t e g e r m u l t i p l e s o f t h e f u n d a m e n t a l f r e q u e n c y ) . The s p e c t r u m of t h e v o c a l f o l d s ' b u z z i s a s e r i e s o f s p i k e s , o c c u r r i n g a t t h e h a r m o n i c f r e q u e n c i e s . The a m p l i t u d e o f t h e s e s p i k e s s l o p e s down g e n t l y (due t o t h e s h a r p n e s s of t h e p u f f ) and m o n o t o n i c a l l y w i t h i n c r e a s i n g f r e q u e n c y . The v o c a l t r a c t c a n be a d j u s t e d i n shape t o p r o d u c e r e s o n a n c e s a t c e r t a i n f r e q u e n c i e s . T h e s e r e s o n a n c e s a r e c a l l e d 25 f o r m a n t s and a r e c e n t r a l t o t h e d i s c r i m i n a b i l i t y of v o w e l s . I n d e e d , when s p e a k i n g , i t i s t h e shape of t h e v o c a l t r a c t t h a t one ends up t r a n s m i t t i n g t o the l i s t e n e r . A formant e s s e n t i a l l y a m p l i f i e s t h e p a r t of t h e s p e c t r u m a t w h i c h i t o c c u r s . I n g e n e r a l , t h e r e i s no harmonic c e n t e r e d a t t h e formant f r e q u e n c y s i n c e t h e f o r m a n t s and h a r m o n i c s a r e i n d e p e n d e n t l y c o n t r o l l e d . (An e x c e p t i o n i s t h e ca se of a t r a i n e d s i n g e r who can a c t u a l l y use feedback t o shape t h e v o c a l t r a c t so t h a t a formant i s c e n t e r e d on a h a r m o n i c . Sopranos f o r e x a m p l e , c l o s e l y match the f i r s t formant w i t h t h e f i r s t h a r m o n i c . ) One does not need the p e r i o d i c v o c a l c o r d buzz t o p r o d u c e i n t e l l i g i b l e s p e e c h . A w h i s p e r i s p r o d u c e d when a i r r u s h i n g t h r o u g h t h e g l o t t i s g e n e r a t e s w h i t e n o i s e and i n j e c t s i t i n t o t h e v o c a l t r a c t . The r e s o n a n c e s s e l e c t i v e l y a m p l i f y p a r t i c u l a r n o i s e f r e q u e n c i e s , and d i s t i n g u i s h a b l e v o w e l s a r e p r o d u c e d . A m p l i t u d e s p e c t r a ( the s q u a r e r o o t of t h e power s p e c t r a ) showing examples of t h e s e fo rmant s appear i n F i g s . 2 . 2 and 2 . 3 . The s p e c t r a show t h e harmonic c o n t e n t o f t h e s t e a d y p a r t of t h e v o w e l s i n t h e words "HEED" and "HOOD" r e s p e c t i v e l y . The s h a r p peaks o c c u r r i n g r o u g h l y e v e r y 200 Hz a r e t h e h a r m o n i c s o f t h e s t e a d y , p e r i o d i c f u n d a m e n t a l . The d e f i n i t e g r o u p s of h i g h h a r m o n i c s , o r t h e peaks i n the e n v e l o p e , a r e t h e f o r m a n t s . The f o r m a n t s a r e l a b e l l e d as f i r s t , s e c o n d , t h i r d a c c o r d i n g t o t h e i r o r d e r i n t h e s p e c t r u m . I n F i g . 2 . 2 , t h e f i r s t formant o c c u r s a t about 300 H z , t h e second a t about 1800 Hz and the t h i r d a t about 2770 H z . F o r t h e v o w e l i n "HOOD", t h e f i r s t f o u r f o r m a n t s o c c u r a t 450 H z , 1100 H z , 2080 Hz and 2940 H z . The maxima i n t h e 27 n o 28 r e s o n a n c e s i n g e n e r a l d o n o t l i n e u p w i t h a s p e c i f i c h a r m o n i c . I f t h e s p e a k e r w e r e t o p r o n o u n c e t h e same v o w e l a t a h i g h e r p i t c h , t h e r e s o n a n c e s ( t h e e n v e l o p e ) w o u l d r e m a i n e s s e n t i a l l y u n c h a n g e d , b u t t h e h a r m o n i c s w o u l d be s e p a r a t e d by a n i n c r e m e n t e q u a l t o t h e new f u n d a m e n t a l f r e q u e n c y . T h i s i s e a s i l y n o t i c e a b l e i n s p e c t r a o f women a n d c h i l d r e n whose a v e r a g e f u n d a m e n t a l f r e q u e n c y i s r o u g h l y t w i c e a s h i g h a s t h a t o f t h e a v e r a g e a d u l t m a l e . I n g e n e r a l , t h e f o r m a n t s o f women a n d c h i l d r e n a r e a l s o h i g h e r , b u t n o t by n e a r l y a s much a s a f a c t o r o f t w o , s i n c e t h e f o r m a n t f r e q u e n c i e s d e p e n d o n t h e l e n g t h o f t h e v o c a l t r a c t . I f a w h i s p e r i s a r t i c u l a t e d , t h e p e a k s due t o t h e h a r m o n i c s w o u l d be r e p l a c e d by a n i r r e g u l a r p a t t e r n o f n o i s e i n t h e s p e c t r u m , b u t t h e a m p l i t u d e w o u l d s t i l l be l a r g e a t t h e f o r m a n t f r e q u e n c i e s . ( I f o n e c o u l d a v e r a g e t h e s p e c t r u m o v e r a l o n g e n o u g h t i m e , the- s p e c t r u m o f t h e w h i s p e r w o u l d a p p r o a c h t h e e n v e l o p e o f t h e r e s o n a n c e s s i n c e t h e s p e c t r u m o f w h i t e n o i s e i s f l a t . ) The p r e s e n c e o f t h e f u n d a m e n t a l f r e q u e n c y c o m p o n e n t d o e s n o t g r e a t l y e n h a n c e s p e e c h p e r c e p t i o n . I t s v a l u e c a n be i n f e r r e d by t h e s p a c i n g o f t h e h a r m o n i c s , a n d i t s p o w e r i s u s u a l l y a s m a l l f r a c t i o n o f t h a t o f t h e f i r s t f o r m a n t . H i g h p a s s f i l t e r s t u d i e s show t h a t r o l l o f f f r e q u e n c i e s o f 1 kHz o n l y show a 10% l o s s o f s p e e c h p e r c e p t i o n ( D e n e s a n d P i n s o n , 1 9 6 3 ) . The h e a r i n g m e c h a n i s m i s e x t r e m e l y s e n s i t i v e t o t h e f r e q u e n c y p o s i t i o n s o f t h e f o r m a n t s i n s p e e c h . I t i s n o t n e a r l y s o s e n s i t i v e t o t h e i r a m p l i t u d e s , a n d e x t r e m e l y i n s e n s i t i v e t o p h a s e . We s h a l l u s e t h e s e f a c t s i n t h e d e s i g n o f o u r c o m p r e s s i o n a l g o r i t h m . The f r e q u e n c y p o s i t i o n o f e a c h f o r m a n t c h a n g e s f r o m s p e a k e r t o s p e a k e r , b u t i s q u i t e r e p r o d u c i b l e i n 29 t h e same i n d i v i d u a l . The l i s t e n e r r e a d i l y a d a p t s t o new s p e a k e r s , and t h i s t a s k i s made e a s i e r by t h e f a c t t h a t t h e r e i s v e r y l i t t l e o v e r l a p of v o w e l formant f r e q u e n c i e s f o r d i f f e r e n t p e r s o n s ( P e t e r s o n and B a r n e y , 1952) even w i t h men, women and c h i l d r e n i n c l u d e d as s p e a k e r s . Two t o t h r e e f o r m a n t s a r e needed t o d i s t i n g u i s h E n g l i s h v o w e l s . I t i s i m p o r t a n t t o r e a l i z e t h a t t h e f o r m a n t s occupy r e l a t i v e l y h i g h f r e q u e n c y p o s i t i o n s . To accomodate t h e f i r s t two f o r m a n t s of E n g l i s h v o w e l s f o r a l l s p e a k e r s (men, women and c h i l d r e n ) , one must have a b a n d w i d t h of about 3300 H z . T h i s c a u s e s p r o b l e m s of v o w e l d i s t i n c t i o n f o r c a s e s of s e v e r e h i g h f r e q u e n c y h e a r i n g l o s s . 11-3 U n v o i c e d Speech Sounds used i n speech w i t h o u t u s i n g t h e v o c a l f o l d s i n c l u d e v o i c e l e s s f r i c a t i v e s i . e . when a h i s s i n g sound i s used ( s u c h as / s / , / s h / and / f / ) and v o i c e l e s s p l o s i v e s i . e . when a p o p p i n g sounds i s u sed ( s u c h as / p / , / t / and / k / ) . These sounds s t i l l i n t r o d u c e a d i s t u r b a n c e i n t o t h e v o c a l t r a c t and a r e t h e r e f o r e m o d i f i e d by i t . T h i s i s e a s i l y d e m o n s t r a t e d by w h i s p e r i n g t h e words " k e y " and " caw" ( t h e same can be done f o r " p e a " and " p a w " ) . The main s o u r c e of d i s t i n c t i o n i s a g a i n i n t h e h i g h f r e q u e n c i e s . T h i s i s shown i n F i g s . 2 . 4 , 2 . 5 and 2 . 6 w h i c h a r e a m p l i t u d e s p e c t r a of t h e b u r s t of t h e c o n s o n a n t s / p / , / t / and / k / . The b a n d w i d t h needed f o r t h e d i s t i n c t i o n t o be p o s s i b l e i s even g r e a t e r t h a n f o r t h e v o w e l s : about 4 t o 5 k H z . The same h i g h b a n d w i d t h i s needed f o r f r i c a t i v e s . I n t h e i r c a s e , t h e s p e c t r u m shows r e s o n a n c e s i n t h e n o i s e w h i c h d e f i n e t h e f r i c a t i v e , but a g a i n , t h e needed r e s o n a n c e s o c c u r a t F r e q u e n c y (kHz) F i g . 2 . 4 A m p l i t u d e s p e c t r u m o f t h e c o n s o n a n t /p/ o F r e q u e n c y (kHz) F j g . 2 . 5 A m p l i t u d e s p e c t r u m o f t h e c o n s o n a n t / t / ZZ 33 f r e q u e n c i e s above 4 kHz. The l a c k o f s e n s i t i v i t y t o t h e s e u n v o i c e d sounds by s e v e r e l y h e a r i n g i m p a i r e d p e r s o n s i s u s u a l l y a p p a r e n t i n t h e i r s p e e c h . 11-4 The H e a r i n g Mechanism The r a n g e o f sounds w h i c h t h e h e a r i n g mechanism c a n d e a l w i t h i s a s t o u n d i n g ( c f . Mussen e t a l . , 1973). In t h e i n t e n s i t y domain, t h e r a n g e spans some 13 o r d e r s o f m a g n i t u d e . A t t h e low end, i t i s s e n s i t i v e t o a power of 1 0 " 1 6 W a t t s / c m 2 . In sound p r e s s u r e , t h i s c o r r e s p o n d s t o a b o u t 2 x 1 U ~ 5 P a s c a l o r , 1 0 " 1 ° a t m o s p h e r e s . At t h i s i n t e n s i t y l e v e l , t h e e a r d r u m i s moving o n l y 5x10" 9cm ( r o u g h l y t h e s i z e of a h y d r o g e n a t o m ) . B e c a u s e we a r e d e a l i n g w i t h a range as l a r g e as 13 o r d e r s of m a g n i t u d e , a n d b e c a u s e t h e e a r ' s r e l a t i v e a m p l i t u d e d i s c r i m i n a t i o n i s c o n s t a n t ( t o a f i r s t a p p r o x i m a t i o n ) , a l o g a r i t h m i c s c a l e i s u s e d f o r i n t e n s i t y . The l o g a r i t h m i c u n i t o f i n t e n s i t y i s t h e " d e c i - B e l l " ( d B ) , d e f i n e d as dB = 10 l o g 1 0 ( I / I o ) where I i s t h e i n t e n s i t y on a l i n e a r s c a l e , and I 0 i s a r e f e r e n c e i n t e n s i t y , a r b i t r a r i l y c h o s e n a s 1 0 " 1 6 W a t t s / c m 2 ( r o u g h l y t h e l o w e r l i m i t of d e t e c t i o n ) . T a b l e 2.1 shows t h e r e l a t i o n between t h e dB s c a l e and t h e i n t e n s i t i e s o f some f a m i l i a r s o u n d s . 34 T a b l e 2.1 The dB S c a l e and some F a m i l i a r I n t e n s i t i e s dB D e s c r i p t i o n 150 L e t h a l t o l a b a n i m a l s 140 Rock band a t c l o s e r a n g e , t h r e s h o l d of p a i n 120 T h r e s h o l d o f d i s c o m f o r t 110 J e t p l a n e 150 m e t e r s o v e r h e a d 100 Heavy t r u c k 90 P n e u m a t i c d r i l l a t 3 m e t e r s 80 L e v e l above w h i c h p r o l o n g e d e x p o s u r e may c a u s e damage 60 Low c o n v e r s a t i o n a l s p e e c h a t 1 meter 40 Q u i e t o f f i c e 20 W h i s p e r 0 T h r e s h o l d o f h e a r i n g 35 I n t h e f r e q u e n c y d o m a i n , young h e a l t h y e a r s can d e t e c t s i n u s o i d a l sounds from 20 Hz t o 20 k H z . The f r e q u e n c y r e s o l u t i o n i s about 1%. Complex sounds can be a n a l y s e d ; a c o n d u c t o r can f i n d w h i c h i n s t r u m e n t i n a g r o u p of some 60 o r c h e s t r a members i s p l a y i n g t o o l o u d l y o r o f f p i t c h . I n o r d e r t o do so w e l l a t a n a l y s i n g t h e s e s o u n d s , t h e h e a r i n g mechanism has a d a p t e d i t s e l f t o i g n o r e o t h e r i n f o r m a t i o n s u c h as the a b s o l u t e phase of t h e sound and t h e r e l a t i v e phases o f h a r m o n i c s . Some i n f o r m a t i o n can be d i s r e g a r d e d a t w i l l ; t h e speech d i s c r i m i n a t i o n mechanism l e a r n s t o p l a c e l i t t l e emphas i s on t h e a m p l i t u d e s of f o r m a n t s . The d e t e r m i n a t i o n of d i r e c t i o n i n t h e h o r i z o n t a l p l a n e i s a c h i e v e d by d e t e c t i n g a m p l i t u d e and phase d i f f e r e n c e s between t h e sounds a t each e a r . The d i r e c t i o n a l r e s o l u t i o n f o r low f r e q u e n c i e s i s about 1 0 ° . In the v e r t i c a l p l a n e , l o c a l i z a t i o n i s a c h i e v e d by v i r t u e of the a n i s o t r o p i c f r e q u e n c y dependence of t h e p i n n a ' s t r a n s m i s s i o n . (The p i n n a i s t h e v i s i b l e p o r t i o n of t h e o u t e r e a r ) . These mechanisms a r e sometimes augmented w i t h i n f o r m a t i o n f rom r e f l e c t i o n s . D i s t a n c e i s j u d g e d by i n t e n s i t y , t i m i n g i n f o r m a t i o n f rom r e f l e c t i o n s and r e l a t i v e i n t e n s i t y of t h e d i r e c t sound and r e s o n a n c e s i n t h e a c o u s t i c e n v i r o n m e n t . The d e t a i l s o f t h e anatomy of t h e ea r need not c o n c e r n us h e r e , but we s h a l l i n c l u d e a b r i e f d e s c r i p t i o n . F o r a more c o m p l e t e d i s c r i p t i o n , see Denes and P i n s o n ( 1 9 6 3 ) . I n c o m i n g sound s i g n a l s a r e f i r s t r e c e i v e d by t h e p i n n a ( t h e v i s i b l e p o r t i o n of t h e o u t e r e a r ) . The s i z e o f t h e human p i n n a 36 i s t o o s m a l l t o g r e a t l y a m p l i f y t h e sound by c o l l e c t i o n , but i t does have the d i r e c t i o n a l p r o p e r t i e s m e n t i o n e d a b o v e . The sound p r e s s u r e wave t r a v e l s down the ear c a n a l t o t h e e a r d r u m . The ea r c a n a l has r e s o n a n c e s i n t h e 3 - 4 kHz r a n g e , and s e l e c t i v e l y a m p l i f i e s components of t h e s i g n a l a t t h e s e f r e q u e n c i e s (by about 10 d B ) . The sound wave t h e n i m p i n g e s on t h e eardrum and s e t s i t i n t o v i b r a t i o n . The eardrum s e a l s t h e end of t h e e a r c a n a l and forms the boundary between t h e o u t e r e a r , and t h e m i d d l e e a r . The m i d d l e ea r c a v i t y c o n t a i n s t h e t h r e e s m a l l bones ( a u d i t o r y o s s i c l e s ) known as the hammer ( m a l l e u s ) , a n v i l ( i n c u s ) and t h e s t i r r u p ( s t a p e s ) . The end of t h e s t i r r u p i s a t t a c h e d t o t h e o v a l window w h i c h c o n s t i t u t e s the boundary between t h e m i d d l e ear and t h e i n n e r e a r . The i n n e r ear houses t h e c o c h l e a . T h i s i s a s m a l l , r o l l e d up bony tube i n w h i c h a f l u i d makes c o n t a c t w i t h m i n u t e h a i r c e l l s . When t h e f l u i d moves t h e b a s i l a r membrane w i t h r e s p e c t t o t h e h a i r c e l l s , t h e y r e s p o n d w i t h e l e c t r i c a l i m p u l s e s t o t h e b r a i n ( v i a t h e 8 t h n e r v e ) . There a r e some 15,000 h a i r c e l l s i n a h e a l t h y c o c h l e a . D i f f e r e n t f r e q u e n c i e s a t t h e o v a l window ( a t one end of t h e t u b e ) cause t h e f l u i d d i s p l a c e m e n t t o have a maximum a m p l i t u d e a t d i f f e r e n t p l a c e s . F r e q u e n c y r e s o l u t i o n i s sharpened by l a t e r a l i n h i b i t i o n w h i c h i s a h a i r c e l l ' s c a p a b i l i t y of i n h i b i t i n g n e i g h b o u r i n g c e l l s i f i t has been s t r o n g l y s t i m u l a t e d . These s i g n a l s f rom t h e c e l l s i n t h e c o c h l e a send i n f o r m a t i o n o f a s p e c t r a l n a t u r e ( i . e . i n t h e f r e q u e n c y domain) t o t h e b r a i n . Tempora l i n f o r m a t i o n (up t o a b o u t 1 kHz) i s a l s o t r a n s m i t t e d by i n d i v i d u a l n e r v e f i r i n g s . These d a t a a re the end p r o d u c t of t h e sound r e c e p t i o n p r o c e s s . They s e r v e as an i n p u t 37 t o t h e b r a i n w h i c h t h e n p e r f o r m s complex p r o c e s s e s w i t h the d a t a . The b r a i n has g a t h e r i n g , s o r t i n g and r e c o g n i t i o n p r o c e s s e s t o d e a l w i t h t h e immense amount of ( h i g h l y c o n v o l u t e d ) a u d i t o r y d a t a r e c e i v e d from the sound s e n s i n g o r g a n s . U n l i k e t h e a n a t o m i c a l and o b j e c t i v e a n a l y s i s of t h e sound r e c e p t i o n , sound p e r c e p t i o n i s e s s e n t i a l l y i n t h e r e a l m of e x p e r i m e n t a l p s y c h o l o g y . T h e r e a r e many i n - d e p t h w r i t i n g s on t h e s u b j e c t ( c f . G r e e n , 1976; M i n i f i e e t a l . , 1973) , and a d e t a i l e d t r e a t m e n t of p s y c h o a c o u s t i c s i s beyond t h e scope of t h i s w o r k . A summary of t h e a c c o m p l i s h m e n t s of t h e mechanism w i l l be g i v e n as i t r e l a t e s t o speech and p e r t i n e n t a s p e c t s w i l l be e x p l a i n e d l a t e r , as r e q u i r e d . As we have s e e n , speech sounds a r e c o m p l e x , but t h e y r a r e l y r e a c h t h e h e a r i n g mechanism w i t h o u t some k i n d of d i s t o r t i o n , n o i s e , and c o n v o l u t i o n . I t i s an i n t e r e s t i n g f a c t t h a t a t a c o c k t a i l p a r t y one can u n d e r s t a n d a s i d e c o n v e r s a t i o n i n t h e p r e s e n c e of n o i s e s u b s t a n t i a l l y l o u d e r t h a n t h e s p e a k e r ' s v o i c e . A s i d e f rom t h e v i s u a l c u e s m e n t i o n e d e a r l i e r , t h e h e a r i n g mechanism must s e l e c t i v e l y use or d i s r e g a r d i n f o r m a t i o n f rom b a c k g r o u n d n o i s e , r e v e r b e r a t i o n , d i r e c t i o n a l i t y and v a r y i n g formant p a t t e r n s f rom d i f f e r e n t s p e a k e r s . I n some s i t u a t i o n s , t h e b r a i n needs t h i s i n f o r m a t i o n t o c o r r e c t l y i n t e r p r e t t h e s o u n d . I n o t h e r s t h e s e e f f e c t s can t o t a l l y domina te t h e i n c o m i n g s i g n a l . I n t h e . i n t e r p r e t a t i o n of s p e e c h , t h e b r a i n uses t h e i n f o r m a t i o n from r h y t h m , a c c e n t s and i n t o n a t i o n . I t a l s o uses f a m i l i a r i t y , s h o r t t e r m memory and c o n t e x t t o nar row down t h e p o s s i b i l i t i e s f o r t h e i n c o m i n g u t t e r a n c e . 38 I t i s w i t h t h e s e complex p r o c e d u r e s i n mind t h a t we c a n more a p p r e c i a t e t h e p r e d i c a m e n t of t h e h e a r i n g i m p a i r e d . S i n c e t h e p r o c e s s e s d e s c r i b e d t h u s f a r a r e i n t r i c a t e l y i n t e r t w i n e d , t h e m a l f u n c t i o n o f any one o f t h e many p r o c e s s i n g s t a g e s has p r o f o u n d i m p l i c a t i o n s on t h e whole c h a i n . I I - 5 The P r e d i c a m e n t of t h e H e a r i n g I m p a i r e d From t h e l a s t s e c t i o n , i t i s r e a d i l y a p p a r e n t t h a t p r o c e s s i n g i n t h e h e a r i n g mechanism i s i n t r i n s i c a l l y n o n - l i n e a r . T h i s s h o u l d a l w a y s be kept i n mind t o p r e v e n t one f r o m j u m p i n g t o f a l s e c o n c l u s i o n s . The e a s i e s t example o f a f a l s e c o n c l u s i o n comes from t h e a r e a o f h e a r i n g a i d f i t t i n g . The l i n e a r s o l u t i o n t o t h e p r o b l e m i s t o measure t h e p a t i e n t s ' j u s t - a u d i b l e t h r e s h o l d s a s a f u n c t i o n of f r e q u e n c y , and f i t them w i t h a h e a r i n g a i d w i t h a f r e q u e n c y r e s p o n s e t h a t m i r r o r s t h e l o s s . In o t h e r words, i f t h e l o s s a t 1 kHz i s 30 dB, t h e n t h e h e a r i n g a i d s h o u l d have 30 dB g a i n a t 1 kHz and s i m i l a r l y f o r a l l f r e q u e n c i e s . T h i s i s v e r y f a r from an o p t i m a l f i t a s e v i d e n c e d by o b j e c t i v e p e r c e p t i o n t e s t s , and s u b j e c t i v e r e s p o n s e s from t h e u s e r s . As i n many c a s e s of n o n - l i n e a r p r o c e s s i n g , one i n v e n t s more and more methods w h i c h a r e l i n e a r t o d e a l w i t h i t , and i f enough o f t h e s e a r e i n c o r p o r a t e d a good a p p r o x i m a t i o n w i l l r e s u l t . W h i l e t h i s s o unds a s t h o u g h h e a r i n g a i d r e s e a r c h i s m e r e l y s t a b b i n g i n t h e d a r k , t h i s i s f a r f r o m t r u e . T h e r e a r e models w h i c h a c c o m o d a t e v a r i o u s a s p e c t s o f t h e h e a r i n g p r o c e s s , b u t l i k e s o many a r e a s o f s c i e n c e , t h e r e i s no u n d e r l y i n g b a s i s t o c o n n e c t a l l t h e m o d e l s . The most o b v i o u s f e a t u r e o f a h e a r i n g i m p a i r m e n t i s t h e 39 l o s s of a b s o l u t e s e n s i t i v i t y . The l o s s i s u s u a l l y f r e q u e n c y d e p e n d e n t , and t h e r e f o r e a c h a r t of h e a r i n g d e t e c t i o n t h r e s h o l d as a f u n c t i o n of f r e q u e n c y i s the f i r s t , and by f a r the most common measure of h e a r i n g i m p a i r m e n t . Such a c h a r t i s c a l l e d an a u d i o g r a m . F o r c o n v e n i e n c e , a d i f f e r e n t dB s c a l e i s used on s u c h a c h a r t . The dB HL ( " d e c i - B e l l " H e a r i n g L e v e l ) s c a l e i s d e f i n e d as dB HL = 10 log^0[l/IQ{t)] where I d e n o t e s i n t e n s i t y , and I 0 ( f ) i s t h e d e t e c t i o n t h r e s h o l d d e t e r m i n e d by t h e average f o r a p o p u l a t i o n of h e a l t h y young a d u l t s a t a f r e q u e n c y f . The f r e q u e n c y dependence i s e x p l i c i t l y w r i t t e n t o emphas ize t h e f a c t t h a t i n t h i s s c a l e , 0 dB HL does not d e f i n e an i n t e n s i t y u n l e s s t h e f r e q u e n c y i s a l s o g i v e n . A h e a l t h y young a d u l t s h o u l d have an a u d i o g r a m w h i c h i s c l o s e t o 0 dB HL a t a l l f r e q u e n c i e s t e s t e d . A l o s s i s i n d i c a t e d by a p o s i t i v e number . I f the p a t i e n t has a 30 dB HL t h r e s h o l d , h i s h e a r i n g l o s s i s 30 dB a t t h a t f r e q u e n c y . V a l u e s f o r t h e p a r a m e t e r s where a v o i c e i s r e q u i r e d ( e . g . Speech Awareness T h r e s h o l d ) t a k e t h e i r r e f e r e n c e t h r e s h o l d s f rom an i n t e n s i t y measured f o r a p o p u l a t i o n of young a d u l t s a t w h i c h t h e y w o u l d g i v e a p o s i t i v e r e s p o n s e 50 p e r c e n t o f t h e t i m e . The p r e s e n t e d speech i s not f i l t e r e d . As a l l u d e d t o p r e v i o u s l y , t h e a u d i o g r a m c o n s t i t u t e s o n l y a s m a l l p a r t of t h e c h a r a c t e r i s a t i o n of a h e a r i n g i m p a i r m e n t . U n d e r s t a n d a b l y , i t t e l l s most of t h e s t o r y i f t h e l o s s i s v e r y m i l d . I n more s e v e r e c a s e s , t h e a u d i o g r a m c o n v e y s f a r l e s s i n f o r m a t i o n . C e r t a i n n o n - l i n e a r a s p e c t s do not show up on an a u d i o g r a m . One of t h e s e n o n - l i n e a r a s p e c t s i s c a l l e d l o u d n e s s r e c r u i t m e n t . I t m a n i f e s t s i t s e l f as a r a p i d i n c r e a s e i n 40 p e r c e i v e d l o u d n e s s n e a r t h e t h r e s h o l d o f a h e a r i n g i m p a i r e d p e r s o n . T h i s ( p e r c e i v e d ) l o u d n e s s grows more q u i c k l y t h a n i n a p e r s o n w i t h n o r m a l h e a r i n g . The p l o t t i n g o f ( p e r c e i v e d ) l o u d n e s s ( i n s o n e s ) v s . l o u d n e s s l e v e l ( i n phons) r e s u l t s i n a g r e a t e r s l o p e f o r t h e h e a r i n g i m p a i r e d p e r s o n t h a n a n o r m a l . L e s t we jump t o .the c o n c l u s i o n t h a t t h i s i m p l i e s a b e t t e r a m p l i t u d e d i s c r i m i n a t i o n l e t us remember t h e i n t r i n s i c non-l i n e a r i t y o f t h e s y s t e m . In a c t u a l f a c t , t h e s l o p e of t h e c u r v e i s a p o o r measure o f a m p l i t u d e r e s o l u t i o n (even f o r n o r m a l s ) and o b j e c t i v e t e s t s show t h a t t h e r e s o l u t i o n of h e a r i n g i m p a i r e d l i s t e n e r s i s r a r e l y as good a s , and n e v e r b e t t e r t h a n t h a t of n o r m a l s ( S c h a r f , 1978). One of t h e c o n s e q u e n c e s o f l o u d n e s s r e c r u i t m e n t i s t h e e l e v a t i o n o f t h e d e t e c t i o n t h r e s h o l d , w i t h a r e t e n t i o n o f a n e a r n o r m a l p a i n t h r e s h o l d . T h i s e f f e c t s e r v e s t o r e d u c e t h e e f f e c t i v e dynamic r a n g e f o r t h e h e a r i n g i m p a i r e d l i s t e n e r . O t h e r n o n - l i n e a r a s p e c t s i n c l u d e l o u d n e s s summation ( a b n o r m a l g r o w t h of l o u d n e s s , o r a b s e n c e t h e r e o f , a s a f u n c t i o n of b a n d w i d t h ) , d e c r e a s e d f r e q u e n c y r e s o l u t i o n , l o u d n e s s a d a p t a t i o n ( d e c r e a s e i n t h e p e r c e i v e d l o u d n e s s as a f u n c t i o n o f how l o n g t h e t o n e i s p r e s e n t ) , d e t e r i o r a t i o n of l o c a l i z a t i o n ( l o s s o f d i r e c t i o n a l i t y ) , s p r e a d o f m a s k i n g ( i n c r e a s e d p r o b l e m s a s s o c i a t e d w i t h n o i s e i n t h e a u d i t o r y s i g n a l ) , s i g n a l d i s t o r t i o n , and t i n n i t u s ( i n t e r n a l l y g e n e r a t e d n o i s e , o r r i n g i n g ) . A l l o f t h e above a s p e c t s a r e p r o b l e m s t o some d e g r e e i n s e v e r e h e a r i n g i m p a i r m e n t s . The most o b v i o u s and c e r t a i n l y t h e f i r s t remedy t r i e d i s l i n e a r a m p l i f i c a t i o n , i n d e e d any a t t e m p t a t making a s i g n a l 41 a u d i b l e t o a p e r s o n w i t h e l e v a t e d t h r e s h o l d s must i n c l u d e i t . In many c a s e s , i t h e l p s a g r e a t d e a l , b u t t h e h e a r i n g n e v e r r e t u r n s t o n o r m a l , and i n most c a s e s does n o t come even c l o s e . As p r e v i o u s l y m e n t i o n e d , t h e i d e a l f r e q u e n c y d e pendence o f t h e a m p l i f i c a t i o n i s n o t one w h i c h would have a g a i n e q u a l t o t h e h e a r i n g l o s s . In some c a s e s i t i s j u s t t h e o p p o s i t e , t h e p a t i e n t s seem t o do b e s t when t h e most a m p l i f i c a t i o n i s p r o v i d e d a t f r e q u e n c i e s where t h e y c a n h e a r b e t t e r t o b e g i n w i t h . W i t h our c o l l e c t i o n o f n o n - l i n e a r a s p e c t s , t h i s i s p e r h a p s n o t s u r p r i s i n g . L a r g e amounts o f a m p l i f i c a t i o n o f t e n worsen t h e p r o b l e m s , making s i g n a l s a u d i b l e b u t m e a n i n g l e s s . In o r d e r t o a c c o m o d a t e l o u d n e s s r e c r u i t m e n t , a m p l i t u d e c o m p r e s s i o n o r a u t o m a t i c g a i n c o n t r o l has been u s e d i n h e a r i n g a i d s . Some d e v i c e s even have s e p a r a t e a m p l i t u d e c o m p r e s s i o n p a r a m e t e r s f o r d i f f e r e n t f r e q u e n c y b a n d s . I t a p p e a r s t h a t t h e p r o b l e m s a s s o c i a t e d w i t h t h e h e a r i n g l o s s a r e c o n f i n e d , f o r t h e most p a r t , t o t h e f r e q u e n c i e s where t h e t h r e s h o l d i s t h e h i g h e s t ( c f . S c h a r f , 1978). T h i s i s y e t a n o t h e r r e a s o n f o r l o o k i n g t o f r e q u e n c y l o w e r i n g t e c h n i q u e s f o r t h e p r e s e n t a t i o n o f s p e e c h i n f o r m a t i o n . I n any scheme w h i c h a t t e m p t s t o match t h e i n c o m i n g s i g n a l t o t h e h e a r i n g l o s s , t h e v a r i o u s a s p e c t s o f s p e e c h and t h e h e a r i n g p r o c e s s c o v e r e d i n t h i s c h a p t e r need t o be c o n s i d e r e d . In t h e f o l l o w i n g c h a p t e r , we make an a t t e m p t a t t h i s i n d e v i s i n g a f r e q u e n c y c o m p r e s s i o n a l g o r i t h m . CHAPTER I I I F r e q u e n c y Band C o m p r e s s i o n i n t h e P r e s e n t S t u d y 43 111-1 The O b j e c t i v e I n m e e t i n g t h e needs o f a s e v e r e l y h e a r i n g i m p a i r e d p e r s o n , a s i g n a l p r o c e s s i n g scheme w i t h f r e q u e n c y l o w e r i n g as one component seems t o be a l o g i c a l c h o i c e . In C h a p t e r II we saw t h a t t h e e l e v a t i o n o f d e t e c t i o n t h r e s h o l d s i s not t h e o n l y a t t r i b u t e o f a h e a r i n g i m p a i r m e n t . The o t h e r p r o b l e m s seem t o be w o r s t a t t h e f r e q u e n c i e s where t h e d e t e c t i o n t h r e s h o l d s a r e h i g h e s t . S i n c e , i n g e n e r a l , t h e h i g h e r f r e q u e n c i e s s u f f e r t h e most i n h e a r i n g d i s o r d e r s i t seems n a t u r a l t o t r y t o p r e s e n t t h e s p e e c h i n f o r m a t i o n a t l o w e r f r e q u e n c i e s . T i n n i t u s ( i n t e r n a l l y g e n e r a t e d n o i s e , o r r i n g i n g ) o f t e n m a n i f e s t s i t s e l f i n h i g h f r e q u e n c y r i n g i n g , and s i n c e s t u d i e s show ( c f . G r e e n , 1976) t h a t m a s k i n g i s l e s s o f a p r o b l e m when t h e n o i s e i s f a r removed i n f r e q u e n c y , s p e e c h r e c e p t i o n may be i m p r o v e d i f p r e s e n t e d a t t h e l o w e r f r e q u e n c i e s . I n c o m i n g sounds a t f r e q u e n c i e s a l r e a d y o c c u p i e d by t i n n i t u s a l s o seem t o become d i s t o r t e d . The o b j e c t i v e i s t o p r e s e n t t h e s p e c t r a l i n f o r m a t i o n i n t h e i n c o m i n g s i g n a l a t a l o w e r f r e q u e n c y band i n r e a l t i m e , w h i l e s t i l l r e t a i n i n g t h e , o t h e r l i n g u i s t i c and s p a t i a l c u e s t h a t accompany s p e e c h ( e . g . r hythm, i n t o n a t i o n , b a c k g r o u n d n o i s e , r e v e r b e r a t i o n , a c c e n t s and e m p h a s i s e t c . ) . From C h a p t e r I I we see t h a t we have some p a r a m e t e r s t o s a c r i f i c e b e c a u s e t h e r e i s much e v i d e n c e t h a t s p e e c h p e r c e p t i o n d o e s n o t r e l y s i g n i f i c a n t l y upon them. T h e s e i n c l u d e : t h e a b s o l u t e phase o f t h e s i g n a l , t h e r e l a t i v e p h a s e s o f t h e h a r m o n i c s , t h e a m p l i t u d e s o f t h e f o r m a n t s ( n o t t h e i r f r e q u e n c i e s ) and t h e p r e s e n c e o f t h e l o w e r f r e q u e n c i e s o f s p e e c h ( i . e . below 400 H z ) . To a c c o m p l i s h t h i s o b j e c t i v e , we must f i r s t t u r n t o a 44 d e f i n i t i o n of what we mean by r e a l t i m e f r e q u e n c y band c o m p r e s s i o n . 111-2 Def i n i t i o n of F r e q u e n c y C o m p r e s s i o n I t i s e a s y t o g e t an i n t u i t i v e f e e l f o r what a f r e q u e n c y a s i g n a l t o t h e i n p u t , t h e o u t p u t s h o u l d c o n s i s t of a s i g n a l whose f r e q u e n c y components o c c u r a t 1/R of t h e i r o r i g i n a l f r e q u e n c i e s where R i s t h e c o m p r e s s i o n f a c t o r . We m i g h t s t a r t our q u a n t i t a t i v e d e f i n i t i o n w i t h t h e F o u r i e r t r a n s f o r m i n e q u a t i o n [ 3 . 1 ] , t h e b a s i s of a l l s p e c t r a l a n a l y s e s . where x ( t ) i s t h e t i m e d e p e n d e n t s i g n a l , and , x ( f ) i s i t s s p e c t r u m . One d e f i n i t i o n of f r e q u e n c y c o m p r e s s i o n c o u l d be t h a t t h e s p e c t r u m of t h e o u t p u t s i g n a l i s e q u a l t o t h e s p e c t r u m of t h e i n p u t s i g n a l w i t h t h e o u t p u t f r e q u e n c y p a r a m e t e r d i v i d e d by R, i . e . i f x ( t ) i s t h e i n p u t t o t h e a l g o r i t h m , x 1 ( t ) i s t h e o u t p u t ; x ( f ) and x ' ( f ) a r e t h e i r r e s p e c t i v e t r a n s f o r m s , t h e n x ' ( f / R ) = x ( f ). I t t u r n s out t h a t t h i s i s n o t enough. I f we e s t a b l i s h x ' ( t ) a s a r e c o r d i n g o f x ( t ) p l a y e d back a t a s p e e d r e d u c e d by a f a c t o r R, we w o u l d meet t h e c o n d i t i o n x'(f/R) = x(f). T h i s i s e a s i l y s e e n by making a change o f v a r i a b l e s i n e q u a t i o n [ 3 . 1 ] . I t i s t h e i n f i n i t e l i m i t s i n t h e t r a n s f o r m w h i c h a l l o w t h i s . A r e a l t i m e d e v i c e must p r e s e n t i t s ( f r e q u e n c y c o m p r e s s e d ) o u t p u t c o m p r e s s i o n a l g o r i t h m s h o u l d do. I n r e a l t i m e , i f one p r e s e n t s oo 45 w i t h i n a n e g l i g i b l e d e l a y from the i n p u t , and t h e c o n v e n t i o n a l F o u r i e r t r a n s f o r m c a n n o t d i s t i n g u i s h t i m e t r a n s l a t i o n s . S h o r t t e r m a n a l y s i s i s needed , and we can i n v o k e t h e f i n i t e t ime window d i s c r e t e F o u r i e r t r a n s f o r m (DFT) d e f i n e d by e q u a t i o n [ 3 . 2 ] . N - l [ 3 . 2 ] A<k> " ]Txa)e- 2 7 r i j k / N k = 0,1 , 2 . . . N - l j-o where the x ( j ) a r e d i s c r e t e samples a t e q u a l i n c r e m e n t s i n t i m e . I f we c a l l A ( k ) the DFT of x ( j ) , we can d e f i n e t h e i d e a l f r e q u e n c y c o m p r e s s i o n a l g o r i t h m as one f o r w h i c h : t h e DFT of the o u t p u t i s i d e n t i c a l t o t h e DFT of t h e i n p u t i f t h e o u t p u t f r e q u e n c y p a r a m e t e r i s d i v i d e d by R; t h i s i s t r u e f o r a l l w i d t h s of t i m e w i n d o w s . I n o t h e r w o r d s , i f x ( j ) i s t h e i n p u t t o t h e a l g o r i t h m , and x ' ( j ) i s t h e o u t p u t ; A ( k ) and A ' ( k ) a r e t h e i r r e s p e c t i v e D F T ' s , t h e n A ' ( k / R ) = A ( k ) f o r a l l w i d t h s of t i m e w i n d o w s . H a v i n g d e f i n e d such a c h a r a c t e r i s t i c , one can i m m e d i a t e l y show t h e i m p o s s i b i l i t y of i t s r e a l i z a t i o n by e v o k i n g an e l e m e n t a r y theorem o f i n f o r m a t i o n t h e o r y : t h e amount o f i n f o r m a t i o n t r a n s m i t t e d by a c h a n n e l i s d i r e c t l y p r o p o r t i o n a l t o i t s b a n d w i d t h . C l e a r l y , our d e f i n i t i o n r e q u i r e s t h e o u t p u t t o c a r r y a s much i n f o r m a t i o n as t h e i n p u t u s i n g 1/R o f the f r e q u e n c y b a n d . The i d e a l t r a n s f e r c h a r a c t e r i s t i c a l s o c o n t r a d i c t s a s i m p l e theorem o f d i s c r e t e F o u r i e r a n a l y s i s , t h a t i s , one can o n l y know a f r e q u e n c y ( f ) p r e s e n t i n a s i g n a l t o w i t h i n a r e l a t i v e e r r o r o f 1 / ( T f ) where T i s t h e t o t a l t i m e l e n g t h of t h e s a m p l e . I n t h e i d e a l t r a n s f e r c h a r a c t e r i s t i c , the 46 output must appear immediately (which makes T = 0) at 1/R of the frequency of the in p u t . One p r a c t i c a l s o l u t i o n to t h i s problem i s to delay the output by a time which i s long compared to the lon g e s t p e r i o d of i n t e r e s t . These are fundamental l i m i t a t i o n s which r e q u i r e one to make some i n t e l l i g e n t approximations. These w i l l be d i s c u s s e d i n the next s e c t i o n . As d i s c u s s e d i n Chapter I, only the time-compressed slow-playback method was used i n t h i s work. In t h i s method the s i g n a l i s f i r s t u n iformly time d i l a t e d i n order to achieve the frequency lowering. The time d i l a t e d s i g n a l i s then brought back to i t s r e a l time course by chopping i t i n t o i n t e r v a l s ; some of which are o v e r l a i d with the others or d i s c a r d e d a l t o g e t h e r . The r a t e at which the chopping takes p l a c e may be determined by the s i g n a l i t s e l f ( p i t c h , synchronous p r o c e s s i n g ) or be independent of i t with a constant rate ( p e r i o d i c p r o c e s s i n g ) as d i s c u s s e d i n Chapter I. Both p o s s i b i l i t i e s were t r i e d , we begin with the former. 111 -3 P i t c h Synchronous P r o c e s s i n g In p i t c h synchronous p r o c e s s i n g we p l a c e some s p e c i a l r e s t r i c t i o n s on the nature of the input s i g n a l . I t i s w e l l known that among speech sounds, vowels and v o i c e d consonants are q u a s i - p e r i o d i c . The r a t e at which the frequency of the g l o t t a l source or the c o n f i g u r a t i o n of the v o c a l t r a c t change are t y p i c a l l y below 10 Hz i . e . w e l l below the g l o t t a l frequency. T h i s means that each p a r t i c u l a r (voiced) sound i s d e f i n e d by s e v e r a l g l o t t a l p e r i o d s ( t h i s i s of course, not true f o r v o i c e l e s s consonants). As we s h a l l see, the d e v i a t i o n s from the i d e a l t r a n s f e r c h a r a c t e r i s t i c of our p i t c h synchronous 47 p r o c e s s i n g a l g o r i t h m a r e v e r y s m a l l i f t h e f o l l o w i n g r e s t r i c t i o n s a p p l y . The i n c o m i n g s i g n a l i s q u a s i - p e r i o d i c ; the band o f t h e f u n d a m e n t a l f r e q u e n c y i s 70 t o 400 H z ; the t o t a l o u t p u t b a n d w i t h i s l e s s t h a n 3 .5 k H z . A g a i n , i f t h e s e r e s t r i c t i o n s a p p l y , the t r a n s f e r c h a r a c t e r i s t i c i s e s s e n t i a l l y i d e a l e x c e p t t h a t t h e o u t p u t i s d e l a y e d i n t i m e from the o r i g i n a l by a p p r o x i m a t e l y one f u n d a m e n t a l p e r i o d . The i n f o r m a t i o n t r a n s f e r theorem i s no t compromised because t h e assumed q u a s i - p e r i o d i c n a t u r e of t h e i n p u t r e s t r i c t s t h e amount o f i n f o r m a t i o n t r a n s f e r r e d by i t . In t h e d e s c r i p t i o n of t h e a l g o r i t h m t h a t f o l l o w s , one can e a s i l y see t h a t i f t h e r e s t r i c t i o n s a r e not met , t h e t r a n s f e r c h a r a c t e r i s t i c s of t h e d e v i c e can be e x t r e m e l y n o n - l i n e a r . The i d e a b e h i n d p i t c h s y n c h r o n o u s p r o c e s s i n g i s t o f i n d whole c y c l e s i n a q u a s i - p e r i o d i c s i g n a l and d i s c a r d them, t h u s b r i n g i n g the t i m e d i l a t e d s i g n a l back t o i t s r e a l t i m e c o u r s e . I n o r d e r t o f i n d r e p e t i t i v e c y c l e s , we need a c r i t e r i o n w h i c h t e l l s us where a c y c l e ends and a new one b e g i n s . The p o i n t so d e f i n e d i s c a l l e d t h e s t a r t i n g p h a s e , o r t r i g g e r p o i n t . S i g n e d z e r o c r o s s i n g s a r e e x c e l l e n t i n d i c a t o r s o f a s t a r t i n g phase f o r s i n u s o i d a l s i g n a l s , but f a i l m i s e r a b l y w i t h s p e e c h s i n c e t h e r e can be many z e r o c r o s s i n g s i n one f u n d a m e n t a l p e r i o d . A l t e r n a t i v e l y , one can use t h e a b s o l u t e maximum as t h e i n d i c a t o r t h a t a new c y c l e has s t a r t e d , s i n c e t h e r e c a n o n l y be one a b s o l u t e maximum i n each f u n d a m e n t a l c y c l e . The o v e r a l l a im i s t o chop up t h e s i g n a l and j o i n i t a g a i n a t d i f f e r e n t p o i n t s . A z e r o c r o s s i n g , w h i l e no t s a t i s f a c t o r y as a c r i t e r i o n t o d e t e r m i n e i f a new c y c l e has begun , i s t h e b e s t p l a c e f o r a 48 t r i g g e r p o i n t s i n c e t h e r e c o n s t r u c t e d s i g n a l would be c o n t i n u o u s ( a l t h o u g h i t s d e r i v a t i v e s may n o t b e ) . The s t a r t i n g phase was t h e r e f o r e c h o s e n t o be a t t h e f i r s t n e g a t i v e g o i n g z e r o c r o s s i n g a f t e r t h e a b s o l u t e maximum i n a f u n d a m e n t a l p e r i o d . A f u l l g l o t t a l p e r i o d i s c o n t a i n e d between any two t r i g g e r p o i n t s . The p i t c h s y n c h r o n o u s p r o c e s s i n g a l g o r i t h m r e c o r d s one f u l l p e r i o d , t h e n p l a y s i t back a t a s p e e d r e d u c e d by t h e f a c t o r R. D u r i n g t h i s p l a y b a c k , t h e n e x t i n p u t p e r i o d i s r e c o r d e d and s t o r e d f o r p l a y b a c k when t h e f i r s t i s c o m p l e t e d . The p r o c e s s t h e n r e p e a t s . On a v e r a g e , 1/R o f t h e i n p u t i s d i s c a r d e d . The a b s o l u t e maximum d e t e c t o r f o r t h e t r i g g e r c i r c u i t was b u i l t u s i n g a peak and h o l d c i r c u i t w i t h a b l e e d e r r e s i s t o r t o accomodate t h e q u a s i - p e r i o d i c i t y ( s e e F i g . 3 . 1 ) . A u t o m a t i c g a i n c o n t r o l was a c c o m p l i s h e d w i t h f e e d b a c k t o a f i e l d e f f e c t t r a n s i s t o r . W i t h r e f e r e n c e t o F i g . 3.1, when t h e i n p u t s i g n a l r e a c h e s a l e v e l c o m p a r a b l e t o t h e p r e v i o u s maximum, t h e v o l t a g e on t h e h o l d c a p a c i t o r jumps a b r u p t l y upward. The l a s t s t a g e i s a d i f f e r e n t i a t o r w h i c h t u r n s t h i s jump i n t o a p u l s e s h a p e d by a S c h m i d t t r i g g e r i n v e r t e r . The r e c o r d i n g and p l a y b a c k was a c c o m p l i s h e d u s i n g F IFO a n a l o g u e memories ( b u c k e t b r i g a d e s ) . T h e s e a r e n o t s t a t i c d e v i c e s so t h a t e x t e n s i v e l o g i c c i r c u i t r y was needed t o a s s u r e t h e p r o p e r t i m i n g . The f u l l c i r c u i t w i l l n o t be p r e s e n t e d h e r e . F o r q u a s i - p e r i o d i c s i g n a l s , t h e d e v i c e worked a d m i r a b l y . The c o m p r e s s i o n r a t i o was d e t e r m i n e d by t h e r a t i o o f two c l o c k r a t e s and was c o n t i n u o u s l y v a r i a b l e f r o m 2 t o 7. F o r v o i c e d s i g n a l s t h e optimum d e c a y r a t e o f t h e h o l d c a p a c i t o r i n t h e t r i g g e r c i r c u i t ( i . e . t h e b e s t b a l a n c e between F i g . 3.1 T r i g g e r c i r c u i t f o r p i t c h - s y n c h r o n o u s p r o c e s s i n g 50 d o u b l e t r i g g e r i n g and m i s s i n g a c y c l e a l t o g e t h e r ) c o r r e s p o n d s t o a d r o p from t h e peak o f 10-15% i n one g l o t t a l p e r i o d . The p r i c e one p a y s f o r a c c o m o d a t i n g q u a s i - p e r i o d i c s i g n a l s i s t h a t t h e d e v i c e sometimes t r i g g e r s t w i c e on t h e same c y c l e . In a c t u a l u s e , i t was d i f f i c u l t t o f i n d a good compromise between d o u b l e t r i g g e r i n g and m i s s i n g a c y c l e a l t o g e t h e r . I t seems t h a t s p e e c h , even when v o i c e d , i s n o t p e r i o d i c enough t o a l w a y s e n a b l e t h e s u c c e s s f u l d e f i n i t i o n o f a s t a r t i n g p h a s e . The o t h e r m a j o r p r o b l e m w i t h t h e a l g o r i t h m was t h e f a c t t h a t i t c a n e a s i l y m i s s a c o n s o n a n t , p a r t i c u l a r l y a v o i c e l e s s p l o s i v e , s i n c e s u c h a c o n s o n a n t i s n o t p e r i o d i c . Any n o i s e on t h e i n p u t s i g n a l would s e r v e t o f u r t h e r d e t e r i o r a t e i t s p e r i o d i c i t y . T h i s r e s u l t i s not s u r p r i s i n g i n t h e l i g h t of t h e work o f Hess (1982) and S c h a f e r - V i n c e n t (1982) who r e p o r t on t h e many d i f f i c u l t i e s i n d e t e r m i n i n g t h e l e n g t h of f u n d a m e n t a l p e r i o d s i n s p e e c h . T h e s e a r e n o t t e c h n i c a l p r o b l e m s , b ut f u n d a m e n t a l ones r e l a t e d t o t h e n a t u r e o f t h e p r o c e s s i n g . In t h e e v e r y d a y w o r l d , s p e e c h i s s e l d o m u n a c c o m p a n i e d by r e v e r b e r a t i o n , n o i s e , and many o t h e r f a c t o r s w h i c h make a t r i g g e r p o i n t v e r y d i f f i c u l t t o d e f i n e . I f one were t o b u i l d a r e a l t i m e d e v i c e t o cop e w i t h t h e s e p r o b l e m s , t h e p r o d u c t would be complex i n d e e d w i t h a t i m e d e l a y s u f f i c i e n t f o r i t t o p r e d i c t what p a r t o f t h e i n p u t i s s p e e c h , and s u i t a b l y t r i g g e r on i t . The d e v i c e would a l s o be u n a b l e t o c o p e w i t h i n p u t sounds w h i c h a r e n o t p e r i o d i c . F o r t h e s e r e a s o n s , i t i s not s u r p r i s i n g t o f i n d a l a c k o f any c l i n i c a l s t u d y u s i n g a c o m p r e s s o r w i t h p i t c h - s y n c h r o n o u s p r o c e s s i n g i n t h e l i t e r a t u r e . An i n t e r e s t i n g f a c t came t o l i g h t when u s i n g t h e t r i g g e r on 51 v o i c e d s i g n a l s . I t seems t h a t t h e v o i c e has an a b s o l u t e phase w h i c h i s i d e n t i f i a b l e . I n o t h e r words, one c a n w r i t e a c r i t e r i o n w h i c h e n a b l e s one t o d e t e r m i n e from t h e waveshape, w h i c h s i d e c o r r e s p o n d s t o c o m p r e s s i o n and w h i c h t o r a r e f r a c t i o n . The e a r i s h i g h l y i n s e n s i t i v e t o t h i s , f o r example, no one b o t h e r s t o w i r e h i s s p e a k e r s c o r r e c t l y f o r a b s o l u t e p h a s e , however, t h e asymmetry d o e s e x i s t . The p o i n t i s not w o r t h b e l a b o u r i n g ; however, i t i s an a m u sing f a c t w h i c h n e i t h e r my c o l l e a g u e s n o r I have seen i n t h e l i t e r a t u r e . I I I - 4 P e r i o d i c P r o c e s s i n g The a p p r o a c h t a k e n i n p e r i o d i c p r o c e s s i n g i s r a d i c a l l y d i f f e r e n t t o p i t c h s y n c h r o n o u s p r o c e s s i n g i n t h a t i n s t e a d o f p l a c i n g r e s t r i c t i o n s on t h e i n p u t s i g n a l i n o r d e r f o r t h e a l g o r i t h m t o o p e r a t e p r o p e r l y , i t a p p r o x i m a t e s t h e i d e a l t r a n s f e r c h a r a c t e r i s t i c f o r a l l i n p u t s i g n a l s . As we s h a l l s e e , t h e i n f o r m a t i o n t r a n s f e r t h e o r e m i s s a t i s f i e d b e c a u s e t h e a l g o r i t h m smears t h e o u t p u t s p e c t r u m r e s u l t i n g i n a r e d u c t i o n o f t h e t o t a l i n f o r m a t i o n t r a n s f e r r e d . The a l g o r i t h m w i l l be d e f i n e d , t h e n a n a l y s e d , and t h e n a p p l i e d t o s p e e c h . The p e r i o d i c p r o c e s s i n g a l g o r i t h m u s e s a f i x e d c h o p p i n g r a t e w i t h t r i g g e r p o i n t s s e p a r a t e d by a t i m e T. E a c h s u c c e s s i v e i n t e r v a l o f t i m e l e n g t h r i s i m m e d i a t e l y p l a y e d back a t one h a l f (R=2) o f t h e r e c o r d i n g s p e e d . O v e r l a p p i n g p l a y b a c k segments a r e a dded a t t h e o u t p u t . The a l g o r i t h m i s shown s c h e m a t i c a l l y i n F i g . 3.2. The v e r t i c a l l i n e s mark e q u a l i n c r e m e n t s ( r ) i n t i m e . The t o p s e t o f l i n e s r e p r e s e n t s t h e i n p u t , and t h e b o t t o m s e t r e p r e s e n t s t h e o u t p u t . The a r r o w s i n d i c a t e where t h e i n p u t ho 5 3 i n f o r m a t i o n i s p l a y e d back ( a t h a l f speed) a t t h e o u t p u t . The t e c h n i q u e o f o v e r l a y i n g segments a t t h e o u t p u t was a l s o used under somewhat d i f f e r e n t c i r c u m s t a n c e s by Inham (1967) t o compres s " s p e l l e d s p e e c h " f o r t h e b l i n d . H a v i n g d e f i n e d t h e a l g o r i t h m we can d e t e r m i n e t h e s p e c t r u m of i t s o u t p u t . C o n s i d e r an i n p u t s i g n a l V ( t ) . The o u t p u t of t h e d e v i c e i s T [ V . ( t ) ] , i . e . t h e t r a n s f o r m c h a r a c t e r i s t i c . 1 S i n c e t h e d e v i c e chops and a d d s , i t f o l l o w s t h a t T i s a l i n e a r f u n c t i o n a l i n a m p l i t u d e , i . e . T [ X V i ( t ) ] = X T [ V i ( t ) ] ( X = c o n s t a n t ) , and T t V ^ t ) + V ^ U ) ] = T f V ^ t ) ] + T [ v : ( t ) ] where V ^ ( t ) and V | ( t ) a r e ( t i m e dependent ) i n p u t s i g n a l s . T h i s l i n e a r i t y means i t i s u s e f u l t o d e t e r m i n e the s i n e w a v e r e s p o n s e s i n c e any i n p u t s i g n a l can be r e p r e s e n t e d by a sum of s i n u s o i d s . We w i l l i g n o r e the momentary s t a r t up t r a n s i e n t when the r e c o r d e r s s t a r t empty , and assume t h a t i n t h e a n a l y s e s , t h e a l g o r i t h m has a l r e a d y been w o r k i n g f o r a t i m e g r e a t e r t h a n 2 t r i g g e r p o i n t s . I f t h e i n c r e m e n t between t r i g g e r p o i n t s i s r , we can d e f i n e t i m e s t i » t 2 ' t 3 ' • • • e ach s e p a r a t e d by (t^ -tn_i = r) and tj, « + n r . I f we se t "V^U) = c o s ( w t ) , t h e n between t2 and t ^ , t h e o u t p u t V q w i l l become: V Q ( t ) = cos(a)t0 + (oj/2)(t-t 0)) +cos(wt 1 + (u/Dit-t^) Between any two a d j a c e n t t i m e s , V Q ( t ) •= cos(cotn + (u)/2)(t-tn)) + c o s O t n + 1 + (a)/2)(t-t n + 1)) and s i n c e t = t n + n r , 54 V Q ( t ) = cos{no)T + (u)/2)(t-nT)} + cos {(n+ss)u)T + (u>/2) (t-n-r) } T h i s c a n be p u t i n t h e f o r m : V Q ( t ) - A(n,u>,T) cos{((u/2) (t-nT)-a(n,a),T)} where A (n ,u ) , t ) = 2COS(UT/4) [3 . 3 ] = r , ^ r ^ r c o s C n m ) + cos((n4^)uiT)l and a (n ,u) ,T) = tan | —:—-t r — :—,< , u » | — T T/2 ' ' I sin(nu)T) + sin( (n+^)ioT) J F o r low f r e q u e n c i e s { O J T « 2n) , a = - nur and A = 2 so t h a t V Q ( t ) = 2 V ^ ( t ) , i . e . t h e waveform r e m a i n s e s s e n t i a l l y u n c h a n g e d . F o r h i g h f r e q u e n c i e s (CJT) >> 2-n, mod(na>T, 2%) ( i . e . t h e r e m a i n d e r o f t h e d i v i s i o n o f nur by 2ir) becomes a random v a r i a b l e u n i f o r m l y d i s t r i b u t e d on t h e i n t e r v a l ( 0 , 2 f f ) . I f we d e f i n e a q u a n t i t y . . -1 f 1 + CQS(COT/2) I , [ 3 . 4 ] * = t a n [ s i n( M T/2) j + 1 T / 2 w h i c h i s a c o n s t a n t f o r a g i v e n i n p u t f r e q u e n c y , one c a n show t h a t a = mod (na>r, 2ff) - <f> w h i c h means t h a t a i s a random v a r i a b l e u n i f o r m l y d i s t r i b u t e d on t h e i n t e r v a l ( 0 , 2 i r ) . F o r h i g h f r e q u e n c i e s t h e r e f o r e , t h e o u t p u t i s a s t r i n g of s i n u s o i d s o f ti m e l e n g t h r a n d f r e q u e n c y u>/2, w i t h a random p h a s e d i f f e r e n c e a t t h e i r j u n c t i o n . S p e c t r a l l y , t h i s means t h a t t h e a m p l i t u d e s p e c t r u m i s e s s e n t i a l l y p r e s e r v e d , b u t t h e p h a s e s p e c t r u m i s n o t . The e x a c t s o l u t i o n f o r t h e power s p e c t r u m o f t h e t r a n s f e r c h a r a c t e r i s t i c i s d e r i v e d i n A p p e n d i x I . The r e s u l t d e r i v e d t h e r e i s shown h e r e a s e q u a t i o n [ 3 . 5 ] . 55 [ 3 . 5 ] P(u') = COS' ; 2 ( ^ T ) Js(ijaj-w')T sln{%(^a)-to')T} JS(JSI)+U)')T where P(u)' ) i s the power spectrum of the ou t p u t f o r an i n p u t s i n u s o i d of a n g u l a r f r e q u e n c y u and T i s the increment between t r i g g e r p o i n t s , and the sum ranges over a l l i n t e g e r s . E q u a t i o n [ 3 . 5 ] h o l d s f o r a l l v a l u e s of u, and t o b e g i n w i t h our i n t e r p r e t a t i o n of i t , l e t us l o o k a t the l i m i t s of s m a l l and l a r g e i n p u t f r e q u e n c y . For UT « 27r, the l e a d i n g c o s i n e f a c t o r approaches 1 , and: T h i s l i m i t i n g v a l u e has nodes a t W ' T / 2 = nir f o r n * 0. These v a l u e s c o r r e s p o n d w i t h the maxima of the 6 f u n c t i o n s , so t h a t a l l t h e 6 f u n c t i o n s a r e b l a n k e d except and 6(a>+u'). I g n o r i n g m u l t i p l i c a t i v e c o n s t a n t s , the power spectrum becomes: P(w') = 6(w-w') i . e . a l l t h e power i s a t u. T h i s i s of c o u r s e c o n s i s t e n t w i t h our e a r l i e r r e s u l t t h a t f o r low u, t h e t r a n s f o r m c h a r a c t e r i s t i c i s t h e i d e n t i t y t r a n s f o r m . For UT » 2ir, the 6 f u n c t i o n s become v e r y c l o s e l y spaced, s in{^fea3±u) ' )T) Js(Jiu±u')T sinQsto'T) 56 and t h e p r e f a c t o r f o r t h e f i r s t s e r i e s : sin{*s(>sm-u)')T}| 2 becomes v e r y s h a r p l y p e a k e d a t u>/2. The w i d t h o f t h e main maximum i s ATI/T S O t h a t t h e o n l y 6 f u n c t i o n s r e m a i n i n g a r e t h e ones w i t h u>' - u/2 c l o s e s t t o z e r o . The b a n d w i d t h c o r r e s p o n d s t o a Q of UT/AH w h i c h i s l a r g e by d e f i n i t i o n . T h i s , a s b e f o r e , shows t h a t f o r W T > > 2-n, a l l t h e power i s a t O J / 2 , and t h e c o n t r i b u t i o n of t h e random p h a s e jumps goes t o z e r o . When w o r k i n g w i t h i n p u t f r e q u e n c y bands n o t c o v e r e d by t h e s e l i m i t s , t h e r e s u l t i s a l i t t l e more c o m p l i c a t e d . Of t h e two s e r i e s o f 6 f u n c t i o n s i n e q u a t i o n [ 3 . 5 ] , t h e f i r s t i s t h e most i m p o r t a n t s i n c e i t has a maximum ( e q u a t i o n [ 3 .5 ] i s an even f u n c t i o n o f u' and f o r t h e power s p e c t r u m we c o n s i d e r o n l y p o s i t i v e f r e q u e n c i e s ) . The m u l t i p l i e r f o r t h e f i r s t s e r i e s i s a s i n ( x ) / x f u n c t i o n where x = 0 when co' = D/2. The w i d t h o f t h i s maximum i s = 2v/r w h i c h i s a c o n s t a n t . The 6 f u n c t i o n s e r i e s a r e e q u a l l y s p a c e d s p i k e s , s e p a r a t e d by 2TT/T i . e . commensurate w i t h t h e r i n g i n g o f t h e s i n ( x ) / x m u l t i p l i e r , so we.do n o t e x p e c t t o s ee t h e f r i n g e s one u s u a l l y a s s o c i a t e s with t h i s f u n c t i o n . The 6 f u n c t i o n s a r e c e n t e r e d a t u w h i c h means t h a t i n g e n e r a l , there is no 6 f u n c t i o n at w/2, but n e i t h e r is there one f a r t h e r t h a n T T / T away from it. The s p e c t r u m from the first series is t h e n e x p e c t e d to c o n s i s t of a series of spikes with an e n v e l o p e h a v i n g a maximum at w/2 and f a l l i n g off s y m m e t r i c a l l y like on e i t h e r side. The s e c o n d 6 f u n c t i o n s e r i e s i s c e n t e r e d on u - 2V/T and 57 i t s p r e f a c t o r i s a l w a y s d e c r e a s i n g l i k e O A ; ' ) 2 . The s t r e n g t h of each s p i k e i s a l w a y s l e s s t h a n t h e c l o s e s t s p i k e t o i t f rom t h e f i r s t s e r i e s . The second s e r i e s can e a s i l y be v i e w e d as a c o n t i n u a t i o n of t h e f i r s t s e r i e s t o n e g a t i v e v a l u e s o f C J ' , and f o l d e d back a t t h e C J ' = 0 a x i s . F i g . 3 .3 shows t h e a m p l i t u d e s p e c t r u m c a l c u l a t e d from e q u a t i o n [ 3 . 5 ] f o r r = 0 . 0 3 3 s e c . and CJ/2TJ- = f = 200 Hz ( t h i s v a l u e f o r T i s c l o s e t o t h e one used f o r s p e e c h , and 200 Hz i s r o u g h l y t h e a v e r a g e f u n d a m e n t a l f r e q u e n c y f o r a d u l t s ) . F i g . 3 .4 i s a measured a m p l i t u d e s p e c t r u m from a p r o t o t y p e d e v i c e g i v e n r o u g h l y t h e same i n p u t p a r a m e t e r s . Note t h a t as e x p e c t e d , t h e l a r g e r s e r i e s has a s p i k e a t 200 H z , but o t h e r than t h a t , n o t h i n g s p e c i a l happens a t C J ' = C J . There i s no s p i k e a t 100 Hz w h i c h a c c o u n t s f o r t h e asymmetry of t h e h i g h and low s i d e s of t h e maximum. C o n s i d e r t h e ca se when t h e r e i s e x a c t l y one f u n d a m e n t a l p e r i o d i n an i n t e r v a l T . From t h e a l g o r i t h m d e f i n i t i o n we can see t h a t t h e two o v e r l a p p i n g p a r t s a r e e q u a l i n magn i tude but o p p o s i t e i n s i g n . T h i s i s r e p r e s e n t e d i n e q u a t i o n [ 3 . 5 ] as t h e f i r s t z e r o i n t r o d u c e d by t h e c o s i n e p r e f a c t o r . T h i s happens when t h e i n p u t f u n d a m e n t a l p e r i o d i s an odd m u l t i p l e of T , o r e q u i v a l e n t l y CJT = 2m7r, m = o d d . F o r an even number o f p e r i o d s i n a t i m e r not o n l y do t h e two s e r i e s o f 6 f u n c t i o n s l i n e u p , but t h e y l i e on t h e z e r o s o f t h e s i n ( x ) / x f u n c t i o n , and we end up w i t h an e x a c t h a l v i n g of t h e i n p u t f r e q u e n c y and a l l i t s h a r m o n i c s . The g e n e r a l a m p l i t u d e i s summarized by F i g s . 3 .6 and 3.7 w h i c h were g e n e r a t e d by e q u a t i o n [ 3 . 5 ] and a p l o t t i n g program w r i t t e n by t h e a u t h o r . F i g . 3 .4 shows what w o u l d be e x p e c t e d f rom t h e i d e a l ( i m p o s s i b l e ) t r a n s f e r c h a r a c t e r i s t i c , e x c e p t t h a t 0.9 0.8 -0.7 0.6 w •u •r-l % 0.5 ca u 0 .4 • H X> I-l 0.3 OJ •U • H 7! 0-2 0.1 -0.0 0 I 100 1 ll ll ll »1 »1 »» 200 300 r 400 i—ll 500 F r e q u e n c y F 1 K - 3 - 3 C a l c u l a t e d o u t p u t s p e c t r u m f o r T = . 0 3 3 s e c . a n d C O / 2 T T = 2 0 0 Hz F i g . 3.4 M e a s u r e d o u t p u t s p e c t r u m f r o m a p r o t o t y p e d e v i c e T = 33 msec. , C O / 2 T T = 200 Hz I 300 400 60 t h e p e a k s h a v e b e e n a r t i f i c i a l l y w i d e n e d . F i g . 3 . 3 w o u l d a p p e a r a s o n e s l i c e o f F i g . 3 . 7 . F i g . 3 . 6 s h o w s t h e o u t p u t s p e c t r u m f o r r e l a t i v e l y h i g h v a l u e s o f CJ . F i g . 3 . 7 s h o w s t h e o u t p u t s p e c t r u m f o r l o w e r f r e q u e n c i e s a n d r e m i n d s o n e o f a p e c u l i a r w a t e r wave m o t i o n ; a s o n e wave m o v e s , i t l o s e s i t s h e i g h t t o a wave b e h i n d i t t r a v e l l i n g a t t h e same v e l o c i t y . In t h i s w a y , t h e e n v e l o p e o f t h e c o l l e c t i v e wave m o t i o n moves s l o w e r t h a n t h e w a v e s t h e m s e l v e s . I n t h e same w a y , t h e 6 f u n c t i o n s p i k e s i n c r e a s e l i k e CJ b u t t h e a m p l i t u d e s h i f t i n g o f t h e s p i k e s m a k e s t h e e n v e l o p e i n c r e a s e l i k e CJ / 2 . I n s u m m a r y , t h e r e a r e no r e s t r i c t i o n s p l a c e d o n t h e i n p u t o f t h e p e r i o d i c p r o c e s s i n g a l g o r i t h m . T h e o u t p u t i s an a p p r o x i m a t i o n t o t h e i d e a l t r a n s f e r c h a r a c t e r i s t i c w h i c h b e c o m e s v e r y g o o d i f t h e f r e q u e n c y i s h i g h e n o u g h (CJT > 7 0 ) . The p a r a m e t e r T d e f i n e s t h e t i m e ( o r f r e q u e n c y ) s c a l e o v e r w h i c h t h e a p p r o x i m a t i o n h o l d s . When v o i c e d s i g n a l s a r e a p p l i e d t o t h e p e r i o d i c p r o c e s s i n g a l g o r i t h m , e a c h F o u r i e r c o m p o n e n t i s t r a n s f o r m e d a s a b o v e a n d a d d e d t o g e t h e r a t t h e o u t p u t . A s m e n t i o n e d i n C h a p t e r I I , o u r h e a r i n g m e c h a n i s m u s e s b o t h s p e c t r a l i n f o r m a t i o n f r o m t h e c o c h l e a , a n d r e a l t i m e i n f o r m a t i o n f r o m d i r e c t n e r v e f i r i n g s up t o a b o u t 1 k H z . T h i s f a c t c o u p l e d w i t h t h e i n h e r e n t d e l a y o f a t i m e T r e s t r i c t s t h e v a l u e o f T f o r s p e e c h . F r o m F i g s . 3 . 6 a n d 3 . 7 we s e e t h a t a s i d e f r o m a n a m p l i t u d e f a c t o r , t h e t r a n s f e r c h a r a c t e r i s t i c i s c l o s e t o i d e a l f o r CJT > 70 ( f = 340 H z , T = 0 . 0 3 3 s e c ) . S i n c e t h e f i r s t f o r m a n t u s u a l l y o c c u r s a b o v e 400 Hz ( e x c e p t f o r t h e v o w e l s [ i ] a n d [ u ] ) , . t h e l o w e r b o u n d o f T was s e t a t 3 0 m s e c . S t u d i e s on t h e e f f e c t s o f d e l a y on s p e e c h F i g . 3.5 S p e c t r u m o f t h e i d e a l t r a n s f e r c h a r a c t e r i s t i c F i g . 3.6 S p e c t r u m o f t h e p e r i o d i c p r o c e s s i n g a l g o r i t h m f o r i n t e r m e d i a t e t o h i g h i n p u t f r e q u e n c i e s F i g . 3.7 S p e c t r u m o f t h e p e r i o d i c p r o c e s s i n g a l g o r i t h m f o r l o w i n p u t f r e q u e n c i e s 64 d i s c r i m i n a t i o n f o r t h e dea f ( c f . M c G r a t h and S u m m e r f i e l d , 1984) show t h a t a t a d e l a y of 70 msec or more t h e p e r c e p t i o n b e g i n s t o s u f f e r . The r e a l t i m e i n f o r m a t i o n from t h e c h o p p i n g mechanism pushed T t o t h e l o w e s t end of t h i s r a n g e , and T = 30msec was used i n a l l c l i n i c a l work and most e x p e r i m e n t a l a n a l y s e s . W i t h t h i s a l g o r i t h m i t i s e x p e c t e d t h a t a l l t h e f o r m a n t s w i l l be p r e s e n t e d t o t h e l i s t e n e r a t h a l f t h e i r o r i g i n a l f r e q u e n c i e s . The a l g o r i t h m w i l l smear t h e s p e c t r a o v e r r o u g h l y 2IT/T - 200 r a d / s e c = 33 H z . Formant band w i d t h s a r e a l w a y s l a r g e r , so t h a t we e x p e c t the s p e c t r a l e n v e l o p e t o r e m a i n e s s e n t i a l l y unchanged . The c o s i n e a m p l i t u d e f a c t o r g i v e s a d i r e c t a m p l i t u d e dependence on i n p u t f r e q u e n c y , but i t t oo i s much s h a r p e r ( 8 . 2 Hz) t h a n any formant band w i d t h . The phase s p e c t r u m of t h e i n p u t i s e s s e n t i a l l y l o s t t h r o u g h the t r a n s f o r m , but as we have seen i n C h a p t e r I I , t h e speech p e r c e p t i o n mechanism i s e x t r e m e l y i n s e n s i t i v e t o even t h e r e l a t i v e phases of h a r m o n i c s . The r e l a t i v e a m p l i t u d e s of t h e f o r m a n t s may change f rom t h a t w h i c h i s p r e s e n t e d a t t h e i n p u t , but t h i s t o o i s one of t h e p a r a m e t e r s w h i c h we assumed t o be n o n - c r i t i c a l f o r speech p e r c e p t i o n . W i t h o u t s m o o t h i n g o f some s o r t , d i s c o n t i n u i t i e s a s s o c i a t e d w i t h t h e s p l i c i n g of n o n - c o n s e c u t i v e segments have o b j e c t i o n a b l e p e r c e p t u a l e f f e c t s and c o n s e q u e n t l y i n t e l l i g i b i l i t y may be d e c r e a s e d (Bennet and L i n v i l l , 1975 ) . Two methods were t r i e d i n an a t t e m p t t o reduce t h e s e e f f e c t s . The f i r s t method c o n s i s t e d o f p l a c i n g a v a r i a b l e t i m e c o n s t a n t ( low pas s RC) j u s t a f t e r t h e s p l i c e p o i n t . A t t h e s p l i c e p o i n t 2TTRC = 30msec g r a d u a l l y i n c r e a s i n g t o t h e f u l l 65 b a n d w i d t h w i t h i n 5-10msec . T h i s s e r v e d t o make the o u t p u t c o n t i n u o u s , but i f a n y t h i n g t h e r e was a d e c r e a s e i n s u b j e c t i v e i n t e l l i g i b i l i t y . The second method i n v o l v e d t h e w i n d o w i n g of t h e i n p u t t i m e s l i c e s . As one s l i c e b e g i n s a t t h e o u t p u t , i t s t a r t s w i t h z e r o a m p l i t u d e and r e a c h e s a maximum j u s t a t t h e p o i n t where t h e n e x t t i m e s l i c e i s a d d e d . I t t h e n d e c r e a s e s , r e a c h i n g z e r o when the t i m e s l i c e i s f i n i s h e d i t s p l a y b a c k . I n a l l our p r e v i o u s d i s c u s s i o n s t h i s window has been s q u a r e . V a r i o u s windows were t r i e d from t r i a n g u l a r t o s i n u s o i d a l . In e a c h c a s e , t h e o u t p u t waveform was c o n t i n u o u s , as were a l l i t s d e r i v a t i v e s ( p r o v i d e d t h e same was t r u e f o r t h e i n p u t ) . The r e s u l t was a r e m a r k a b l e absence of p e r c e i v e d d i f f e r e n c e . E a c h window i n c l u d i n g the square one , s t i l l p r o d u c e d a c l i c k i n g s e n s a t i o n a t 33 Hz ( = 1 / T ) . T h i s l e a d s one t o b e l i e v e t h a t t h e e a r i s o b j e c t i n g t o t h e phase jumps , not t h e d i s c o n t i n u i t i e s . T h i s i s c o n s i s t e n t w i t h t h e f a c t t h a t most l i s t e n e r s hear no d i f f e r e n c e between a square wave, and a c o n t i n u o u s s i g n a l w i t h i d e n t i c a l h a r m o n i c c o n t e n t . Due t o t h i s l a c k of n o t i c a b l e improvement i n i n t e l l i g i b i l i t y , t h e s e f e a t u r e s were not m a i n t a i n e d i n subsequent d e s i g n s . One of t h e most i m p o r t a n t r e s u l t s of t h e t r a n s f o r m i s t h a t t h e r e d u c t i o n of t h e f u n d a m e n t a l , i t s h a r m o n i c s and o f t h e formant f r e q u e n c i e s by a f a c t o r of two changes not o n l y the p i t c h o f t h e o u t p u t s o u n d s , but a l s o t h e i r p h o n e t i c q u a l i t y . I f one r e f e r s t o an a c o u s t i c v o w e l fo rmant d i a g r a m s u c h as t h a t p r e s e n t e d i n P e t e r s o n and Barney (1952) ( s econd formant f r e q u e n c y v s . f i r s t formant f r e q u e n c y ) , i t i s o b v i o u s t h a t an i n p u t v o w e l such as [a ] w i l l p r o d u c e an o u t p u t w h i c h i s more 66 l i k e l y t o be i d e n t i f i e d a s [o] on f i r s t l i s t e n i n g . S i m i l a r l y , an i n p u t s u c h as [ i ] w i l l p r o d u c e an o u t p u t o u t s i d e t h e t r a d i t i o n a l v o w e l l o o p and m ight a t f i r s t p r e s e n t d i f f i c u l t i e s f o r t h e l i s t e n e r . However, t h e mapping between i n p u t and o u t p u t i s b i u n i q u e , t h u s d i f f e r e n t i n p u t s ounds w i l l p r o d u c e d i f f e r e n t o u t p u t s . Whether t h e s e d i f f e r e n c e s ( i n t h e o u t p u t ) c a n be l e a r n e d and p e r c e i v e d c o n s i s t e n t l y by h e a r i n g i m p a i r e d l i s t e n e r s i s e xamined i n C h a p t e r V. A t y p i c a l a m p l i t u d e s p e c t r u m o f t h e v o w e l [ i ] i s shown i n F i g . 3.8a. F i g . 3.8b shows t h e s p e c t r u m o f t h e same vow e l t r a n s f o r m e d by t h e p e r i o d i c p r o c e s s i n g a l g o r i t h m u s i n g a p r o t o t y p e d e v i c e . Note t h e i n t e g r i t y n o t o n l y o f t h e f o r m a n t s , but a l s o o f t h e i n d i v i d u a l h a r m o n i c s . As we have seen i n C h a p t e r I I , t h e b r a i n does a s u b s t a n t i a l p a r t of o u r l i s t e n i n g . The a l g o r i t h m p r e s e n t s t h e l i s t e n e r w i t h a s u b s t a n t i a l p a r t o f t h e i n p u t i n f o r m a t i o n i n t h e same f o r m a t as i t was e n t e r e d . N o i s e , rhythm, i n t o n a t i o n , r e v e r b e r a t i o n e f f e c t s e t c . a r e a l l p r e s e r v e d t h r o u g h t h e t r a n s f o r m i n t h e f o r m a t w i t h w h i c h t h e a u d i t o r y f u n c t i o n s o f o u r b r a i n s a r e n a t u r a l l y f a m i l i a r . The c o n t i n u o u s t r i g g e r i n g o f t h e p e r i o d i c p r o c e s s i n g a l g o r i t h m and t h e o v e r l a p p i n g o f t h e o u t p u t segments a s s u r e s not o n l y t h e c a p t u r e o f a l l c o n s o n a n t s and t r a n s i e n t s , b u t a l s o t h a t a l l segments o f t h e i n p u t r e a c h t h e o u t p u t . The d o m i n a n t s p e c t r a l c o n t e n t o f t h e s e c o n s o n a n t s i s u s u a l l y a b o v e 1.5 kHz. The a l g o r i t h m c o m p r e s s e s t h e s p e c t r u m i n an a n a l o g o u s way t o t h e s t e a d y v o w e l s even t h o u g h t h e y a r e t r a n s i e n t s . A common t o o l i n t h e s t u d y o f s p e e c h i s t h e s p e c t r o g r a p h . 68 T h i s d e v i c e t a k e s a r e c o r d i n g of sound r o u g h l y 3 seconds l o n g and p r o d u c e s a s p e c t r o g r a m w i t h t h e f o l l o w i n g f e a t u r e s . L e f t t o r i g h t i s i n c r e a s i n g t i m e , upwards i s i n c r e a s i n g f r e q u e n c y , and d a r k n e s s i s i n t e n s i t y . I t s a im i s t o d i s p l a y t h e s p e c t r u m of t h e sound a t each t i m e . The d e v i c e c o n s i s t s of a bandpass f i l t e r w i t h a s w i t c h a b l e Q, and a h a r d d i s k c o a t e d w i t h m a g n e t i c m a t e r i a l v e r y much l i k e t h a t on m a g n e t i c r e c o r d i n g t a p e . A s t y l u s i s p l a c e d a t the bo t tom of a c y l i n d e r ( a t t a c h e d t o t h e d i s k ) upon w h i c h i s wrapped h e a t s e n s i t i v e p a p e r . The c y l i n d e r i s t h e n made t o s p i n , and a h e t r o d y n i n g sy s tem s e l e c t s d i f f e r e n t bands t o pa s s t h r o u g h t h e f i l t e r . A sample r e s u l t i s shown i n F i g s . 3 .9a and 3 . 9 b . F i g . 3 . 9 a i s a s p e c t r o g r a m of the o r i g i n a l s p e e c h , F i g 3 .9b i s a s p e c t r o g r a m of t h e i d e n t i c a l p h r a s e p r o c e s s e d by a p r o t o t y p e p e r i o d i c p r o c e s s i n g d e v i c e . R e s u l t s of i d e n t i c a l p r o c e d u r e s f o r a d i f f e r e n t p h r a s e appear i n F i g s . 3 .10a and 3 . 1 0 b . I n t h e s e s p e c t r o g r a m s we c l e a r l y see t h e i n t e g r i t y o f t h e f o r m a n t s t h r o u g h t h e t r a n s f e r c h a r a c t e r i s t i c , each a p p e a r i n g a t one h a l f of t h e i r o r i g i n a l f r e q u e n c i e s . The g l o t t a l f r e q u e n c y g i v e s r i s e t o t h e v e r t i c a l s t r i a t i o n seen f rom l e f t t o r i g h t a c r o s s the s p e c t r o g r a m . From t h i s we see t h a t t h e g l o t t a l f r e q u e n c y i s a l s o compres sed by a f a c t o r of 2 . Y e t a n o t h e r t e s t of t h e p r e s e r v a t i o n o f i n f o r m a t i o n i s d o u b l e speed l i s t e n i n g . I f one r e c o r d s s p e e c h p r o c e s s e d by our c o m p r e s s i o n a l g o r i t h m and p l a y s i t back a t d o u b l e s p e e d , a l l t h e l o w e r e d f r e q u e n c i e s r e t u r n t o t h e i r o r i g i n a l v a l u e s . The r e c o r d i n g of c o u r s e , t a k e s h a l f a s l o n g t o p l a y , so t h a t t h e s p e a k e r sounds q u i t e r u s h e d . Most n o r m a l - h e a r i n g p e o p l e t e s t e d c o u l d u n d e r s t a n d such a r e c o r d i n g upon f i r s t l i s t e n i n g . B l i n d F i g 3.9a ( a b o v e ) S p e c t r o g r a m o f p h r a s e b ( b e l o w ) S p e c t r o g r a m o f same p h r a s e t h r o u g h c o m p r e s s i o n d e v i c e THE QUICK SLY FOX JUMPED OVER THE LAZY BROWN DOG Time ( s e c o n d s ) F i g . 3.10a ( a b o v e ) S p e c t r o g r a m o f p h r a s e b ( b e l o w ) S p e c t r o g r a m o f same p h r a s e t h r o u g h c o m p r e s s i o n d e v i c e o 71 s t u d e n t s f a m i l i a r w i t h t i m e c o m p r e s s i o n d e v i c e s ( s e e s e c t i o n I -1) f o u n d our d e v i c e more e f f e c t i v e a t a c o m p r e s s i o n r a t i o of 2 t h a n t h e i r d e v i c e s ( t h e i r d e v i c e s o f c o u r s e , c o u l d v a r y t h e c o m p r e s s i o n r a t i o c o n t i n u o u s l y whereas o u r s i s f i x e d a t 2 ) . 72 CHAPTER IV TECHNICAL REALIZATION 73 The o b j e c t i v e was t o b u i l d a p o r t a b l e e l e c t r o n i c d e v i c e t h a t c o u l d be c a r r i e d and used e a s i l y by s u b j e c t s i n a c l i n i c a l t e s t . The d e v i c e s h o u l d c l o s e l y a p p r o x i m a t e t h e t r a n s f e r c h a r a c t e r i s t i c of t h e p e r i o d i c p r o c e s s i n g a l g o r i t h m d e f i n e d i n s e c t i o n 1 1 1 - 4 . I t s h o u l d a l s o be s m a l l , l i g h t w e i g h t , and easy t o u s e . S e v e r a l model s were c o n s t r u c t e d and t e s t e d w i t h a s p e c t r u m a n a l y s e r , a s p e c t r o g r a p h , and s u b j e c t i v e l i s t e n i n g t e s t s . The f i n a l model was d e s i g n a t e d Mode l 3 E . S i n c e t h i s model i n c o r p o r a t e s a l l t h e p o s i t i v e changes of e a r l i e r d e s i g n s , and because i t i s t h e one used i n a l l t h e c l i n i c a l s t u d i e s i n t h i s w o r k , i t w i l l be the o n l y one p r e s e n t e d h e r e . The s c h e m a t i c c i r c u i t d i a g r a m f o r M o d e l 3E a p p e a r s i n F i g . 4 . 1 . F i g . 4 . 1 a shows t h e power s u p p l y f o r t h e c i r c u i t . The " b u c k e t b r i g a d e s " u sed as a n a l o g u e r e c o r d e r s r e q u i r e a minimum of 10 V o l t s f o r o p e r a t i o n . The l a r g e s t v o l t a g e e a s i l y o b t a i n a b l e from a s m a l l b a t t e r y i s 9V. The power s u p p l y a c c e p t s a v o l t a g e f rom a b a t t e r y between v g A T T a n ^ 9 r o u n ^ and p r o v i d e s a r e g u l a t e d o u t p u t a t V+ and V - of ± 5 . 7 V r e s p e c t i v e l y . T h i s o u t p u t v o l t a g e w i l l r e m a i n c o n s t a n t f o r a b a t t e r y v o l t a g e range between 6 and 30V. The c i r c u i t uses a v o l t a g e d o u b l e r ( I C L 7 6 6 0 ) , and a n e g a t i v e f eedback r e g u l a t o r . The r e f e r e n c e v o l t a g e i s p r o v i d e d by an i n t e g r a t e d c i r c u i t Zener d i o d e L M 3 8 5 Z - 1 . 2 . F i g . 4 . 1 b shows t h e a n a l o g u e c i r c u i t r y . The i n p u t c i r c u i t ( a t t h e t o p o f t h e f i g u r e ) p r o v i d e s t h e p r o p e r g a i n , a n t i - a l i a s f i l t e r i n g , and D . C . b i a s f o r t h e " b u c k e t b r i g a d e s " . The o p e r a t i o n a l a m p l i f i e r s ICL7612 ( s i n g l e ) and ICL7642 (quad) a r e two i n a f a m i l y of v a r i a b l e q u i e s c e n t c u r r e n t , low power Fig. 4.1a Power Supply For Model 3E f X ("oOTTtff) F i g . 4 . l b A n a l o g u e c i r c u i t s f o r Model 3E F i g 4 . l c D i g i t a l c i r c u i t s f o r M o del 3E 77 d e v i c e s . The d e v i c e s have more s o u r c e c u r r e n t a v a i l a b l e t h a n s i n k c u r r e n t . Most of them i n M o d e l 3E a r e o p e r a t e d i n c l a s s A mode by means of r e s i s t i v e l o a d i n g t o t h e n e g a t i v e r a i l . The o u t p u t c i r c u i t r y i s e s s e n t i a l l y an i n t e r f a c e t o c o n v e n t i o n a l h e a r i n g a i d s w i t h a u d i o i n p u t c a p a b i l i t i e s . The h e a r i n g a i d s have r o u g h l y 5kfl i n p u t impedance , and t h e maximum i n p u t s i g n a l i s 3mV ( t h i s makes them d i r e c t l y c o m p a t i b l e w i t h e x t e r n a l m i c r o p h o n e s ) . The o u t p u t c i r c u i t c o n s i s t s o f two low pass f i l t e r s and an a t t e n u a t o r w i t h an o u t p u t impedance low enough t o d r i v e 2 h e a r i n g a i d s , s h o u l d b i n a u r a l f i t t i n g be d e s i r e d . Because of t h e h i g h a t t e n u a t i o n of t h e o u t p u t , c a r e was t a k e n t o p r o v i d e t h e o u t p u t j a c k w i t h c o n n e c t i o n s g e o m e t r i c a l l y a c r o s s t h e l o a d r e s i s t o r ( i . e . no t j u s t t o any c i r c u i t g r o u n d ) . The o u t p u t j a c k i s a female 3 - c o n d u c t o r m i n i -phone j a c k (3 .4mm). The mate i s a 2 - c o n d u c t o r j a c k . When i n s e r t e d , t h e l o w e r c o n d u c t o r i s s h o r t e d t o g r o u n d p r o v i d i n g an o n - o f f s w i t c h (see F i g . 4 . 1 b ) . F i g . 4 . 1 c shows t h e p e r i o d i c p r o c e s s i n g a l g o r i t h m i n d i g i t a l c i r c u i t r y . The p a r a m e t e r T i s d e f i n e d by an RC t i m e c o n s t a n t and a f r e e r u n n i n g low power phase l o c k l o o p ( 4 0 4 6 ) , p r o v i d i n g a c l o c k a t a f r e q u e n c y F . T h i s c l o c k f r e q u e n c y i s d i v i d e d down by a c o u n t e r (4040) t o p r o v i d e t h e r e c o r d i n g speed F / 2 and t h e p l a y b a c k speed F / 4 c l o c k i n p u t t o t h e b u c k e t b r i g a d e s . The same c l o c k f r e q u e n c y p r o v i d e s t h e t i m i n g o f t h e o v e r l a y i n g of r e c o r d e d segments a t F / 1 0 2 4 . The s a m p l i n g f r e q u e n c y i s 7 .76 k H z . The c l o c k i n p u t of t h e b u c k e t b r i g a d e s i s s w i t c h e d from r e c o r d i n g speed t o p l a y b a c k speed by t h e use of t h e 4053 ( t r i p l e ) SPDT s w i t c h ( a t any one t i m e , two b u c k e t b r i g a d e s a r e p l a y i n g and one i s r e c o r d i n g ) . 78 T h e o u t p u t i s s e l e c t e d f r o m t h e t w o p l a y i n g b u c k e t b r i g a d e s u s i n g a n o t h e r 4053 s w i t c h . T h e s e a r e a d d e d by v i r t u e o f t h e o u t p u t r e s i s t o r s a n d t h e o u t p u t a n a l o g u e c i r c u i t r y . T h e d e v i c e was c o n s t r u c t e d on t w o , d o u b l e s i d e d p r i n t e d c i r c u i t b o a r d s . E a c h b o a r d was " L " s h a p e d t o a c c o m o d a t e t h e 9V b a t t e r y . T h e e n c l o s u r e c o n s i s t e d o f a p l a s t i c box w i t h d i m e n s i o n s o f 1 0 x 5 x 2 c m ( 4 x 2 x 3 / 4 i n c h e s ) . T h e b o a r d s w e r e m o u n t e d o n e a b o v e t h e o t h e r a n d w e r e j o i n e d w i t h 15 c o n n e c t o r s f o r m i n g a " c o r p u s c a l l o s u m " on t h e i n s i d e o f t h e L . To c o n v e y a n o t i o n o f s i z e t h e a r t w o r k a p p e a r s a c t u a l s i z e i n F i g . 4 . 2 . Some c i r c u i t c h a n g e s w e r e made a f t e r p r i n t i n g t h e c i r c u i t . A t t h e t i m e o f p r i n t i n g t h e m o d e l n u m b e r was 3 D . E a c h d e v i c e was s h o c k t e s t e d b e f o r e u s e t o i n s u r e t h e r i g i d i t y o f t h e f i n i s h e d p r o d u c t . To p r e v e n t c l o t h e s n o i s e , a n d f o r m o s t c o n v e n i e n t p l a c e m e n t , t h e m i c r o p h o n e i s e x t e r n a l t o t h e d e v i c e a n d p l u g s i n w i t h a s t a n d a r d 3.4mm p h o n e j a c k . F i f t e e n s u c h d e v i c e s w e r e b u i l t f o r u s e i n t h e c l i n i c a l s t u d y . T h e s p e c i f i c a t i o n s f o r M o d e l 3E a p p e a r i n T a b l e 4 . 1 , a n d a p h o t o g r a p h o f t h e d e v i c e a p p e a r s i n F i g . 4 . 3 . F i g . 4 . 2 P r i n t e d c i r c u i t A r t w o r k f o r M o d e l 3 2 , S c a l e i s 1 : 1 80 T a b l e 4.1 Mode l 3E S p e c i f i c a t i o n s P a r a m e t e r V a l u e U n i t s E l e c t r i c a l I n p u t impedance Max. i n p u t l e v e l O u t p u t impedance Max. o u t p u t l e v e l Power s u p p l y B a t t e r y d r a i n 1 3 1 3 9V B a t t e r y 4.1 kOhm mV kOhm mV mA G e o m e t r i c a l D i m e n s i o n s W e i g h t ( b a t t e r y i n c l . ) C a s e M i c . c o n n e c t o r O u t p u t c o n n e c t o r S i g n a l t o n o i s e r a t i o 10x5x2 120 b l u e p l a s t i c 3.4mm phone j a c k 3.4mm phone j a c k 500 ( t y p ) cm CHAPTER V THERAPY AND CLINICAL EVALUATION 83 V-1 Su b j e c t s R e f e r r a l s of p o t e n t i a l s u b j e c t s were s o l i c i t e d from a u d i o l o g i s t s and o t o l a r y n g o l o g i s t s i n the gr e a t e r Vancouver ar e a . Meetings were arranged at audiology c l i n i c s s e r v i n g the a d u l t p o p u l a t i o n : S t . Paul's H o s p i t a l , Vancouver General H o s p i t a l , Worker's Compensation Board, Shaughnessy H o s p i t a l , and the Western I n s t i t u t e f o r the Deaf, to demonstrate the compressor and to request a s s i s t a n c e i n f i n d i n g a p p r o p r i a t e s u b j e c t s . S e v e r a l l o c a l o t o l a r y n g o l o g i s t s were c o n t a c t e d p e r s o n a l l y and an i n f o r m a t i o n l e t t e r was sent to a l l members of the B.C. Otolaryngology A s s o c i a t i o n . R e f e r r a l agencies were s u p p l i e d with i n f o r m a t i o n sheets f o r p o t e n t i a l s u b j e c t s and consent f o r r e l e a s e of i n f o r m a t i o n forms to d i s t r i b u t e to c l i e n t s whom they f e l t c o u l d q u a l i f y f o r p a r t i c i p a t i o n . When a consent f o r r e l e a s e of i n f o r m a t i o n form was r e c e i v e d , background i n f o r m a t i o n was obtained from the r e f e r r a l agency. The p r o j e c t a u d i o l o g i s t reviewed t h i s i n f o r m a t i o n to see i f the c l i e n t might meet the p r o j e c t c r i t e r i a . I f so, an i n i t i a l appointment was arranged; i f not, a l e t t e r was sent to the c l i e n t thanking him f o r the i n t e r e s t shown and e x p l a i n i n g why they d i d not meet the p r o j e c t c r i t e r i a . There were s i x c r i t e r i a used to ev a l u a t e whether or not the c l i e n t was s u i t a b l e f o r p a r t i c i p a t i o n i n the study: 1. Only a d u l t s over 18 years of age were c o n s i d e r e d . T h i s s t i p u l a t i o n was made so that the s u b j e c t s c o u l d make t h e i r own independent d e c i s i o n s ; i t a l s o ensures that the p r o j e c t would not i n t e r f e r e with any on-going education of deaf c h i l d r e n . 84 2 . Severe t o p r o f o u n d h e a r i n g l o s s was r e q u i r e d ; b i l a t e r a l l y w i t h t h e average pure tone t h r e s h o l d s a t f r e q u e n c i e s of 500 , 1000 and 2000 Hz of 85 dB HL o r p o o r e r i n t h e b e t t e r e a r . T h i s c r i t e r i o n was c h o s e n as i n d i v i d u a l s w i t h b e t t e r h e a r i n g a r e u s u a l l y a b l e t o wear c o n v e n t i o n a l a m p l i f i c a t i o n w i t h g r e a t e r b e n e f i t t h a n was a n t i c i p a t e d from the speech f r e q u e n c y band c o m p r e s s o r . 3 . The h e a r i n g l o s s must have been a c q u i r e d p o s t - l i n g u a l l y . T h i s c r i t e r i o n was chosen as i n d i v i d u a l s w i t h a c q u i r e d h e a r i n g l o s s a f t e r d e v e l o p i n g n o r m a l speech and l anguage s k i l l s may be assumed t o have d e v e l o p e d t h e i r a u d i t o r y n e u r a l pathways and t h e a u d i t o r y c o r t e x of t h e i r b r a i n s . T h i s c r i t e r i o n a l s o a s s u r e d t h a t c o m m u n i c a t i o n t h r o u g h spoken l anguage c o u l d be used and e n c o u r a g e d t h r o u g h o u t the p r o j e c t . 4 . The s u b j e c t s were r e q u i r e d t o l i v e i n the g r e a t e r V a n c o u v e r a r e a . As t h e p r o j e c t i n v o l v e d r e g u l a r t h e r a p y s e s s i o n s , s u b j e c t s needed t o l i v e w i t h i n a g e o g r a p h i c a l l y c o n v e n i e n t r a n g e . 5 . C u r r e n t h e a r i n g a i d u s e r . T h i s was an o p t i o n a l c r i t e r i o n i n c l u d e d t o e n s u r e h e a r i n g a i d f a m i l i a r i t y and a c c e p t a n c e . 6 . Good s p e e c h r e a d i n g s k i l l s . T h i s was an o p t i o n a l c r i t e r i o n i n c l u d e d t o f a c i l i t a t e c o m m u n i c a t i o n w i t h t h e s u b j e c t s and t o a l l o w t h e emphas i s t o be p l a c e d on a u d i t o r y t r a i n i n g and c o m b i n i n g a u d i t o r y i n p u t w i t h s p e e c h r e a d i n g s k i l l s i n t h e r a p y s e s s i o n s . Two s u b j e c t s who v o l u n t e e r e d t r i a l s b e f o r e t h e f o r m a l s e s s i o n s had begun w i l l a l s o be i n c l u d e d i n t h e r e s u l t s . These 85 s u b j e c t s d i d not p a r t i c i p a t e i n t h e u s u a l t h e r a p y s e s s i o n s d e s i g n e d f o r t h e s t u d y . V - 2 E t h i c a l C o n s i d e r a t i o n s S i n c e t h e p r o j e c t i n v o l v e d human s u b j e c t s , c a r e was t a k e n t o e n s u r e t h a t the p r o c e d u r e s were e t h i c a l , and would not cause t h e s u b j e c t s undue d i s c o m f o r t . To t h i s e n d , t h e p r o j e c t p r o t o c o l was r e v i e w e d by t h e " C l i n i c a l S c r e e n i n g Committee f o r R e s e a r c h and O t h e r S t u d i e s I n v o l v i n g Human S u b j e c t s " . Not o n l y does the p r o c e d u r e of the e x p e r i m e n t i t s e l f need t o be a p p r o v e d , but a l s o t h e s u b j e c t s ' knowledge o f t h e s t u d y as i t i n v o l v e s them. S u b j e c t s a r e r e q u i r e d t o have w r i t t e n i n f o r m a t i o n about t h e f o l l o w i n g : 1. T i t l e of t h e p r o j e c t . 2 . I d e n t i f i c a t i o n of t h e i n v e s t i g a t o r s . 3 . B r i e f but c o m p l e t e d e s c r i p t i o n i n l a y l anguage of t h e purpose of t h e e x p e r i m e n t and of a l l e x p e r i m e n t a l p r o c e d u r e s . 4 . S t a t ement of a l l known s i d e e f f e c t s w i t h an e s t i m a t e of the p r o b a b i l i t y of t h e i r o c c u r r e n c e . 5 . A s s u r a n c e t h a t t h e i d e n t i t y o f t h e s u b j e c t w i l l be kept c o n f i d e n t i a l and a d e s c r i p t i o n of how t h i s w i l l be a c c o m p l i s h e d . 6 . A s t a t e m e n t of t h e t o t a l amount of t i m e t h a t w i l l be r e q u i r e d of t h e s u b j e c t s beyond t h a t needed f o r t r e a t m e n t . 7 . D e t a i l s of monetary c o m p e n s a t i o n t o be o f f e r e d t o t h e s u b j e c t s . 8 . An o f f e r t o answer any i n q u i r i e s c o n c e r n i n g t h e p r o c e d u r e s 86 t o e n s u r e t h a t t h e y a r e f u l l y u n d e r s t o o d by t h e s u b j e c t . 9. An unambiguous s t a t e m e n t t h a t t h e s u b j e c t may d e c l i n e t o e n t e r o r t o w i t h d r a w from t h e s t u d y a t any t i m e w i t h o u t any c o n s e q u e n c e s t o c o n t i n u i n g m e d i c a l c a r e . 10. S i g n a t u r e o f s u b j e c t c o n s e n t i n g t o p a r t i c i p a t e i n t h e r e s e a r c h p r o j e c t and a c k n o w l e d g i n g r e c e i p t of a c o p y o f t h e c o n s e n t form i n c l u d i n g a l l a t t a c h m e n t s . 11. S i g n a t u r e o f a w i t n e s s . In t h i s s t u d y a l l r e f e r r a l s were o b t a i n e d by a t h i r d p a r t y and t h e s u b j e c t s were r e q u i r e d t o s i g n a C o n s e n t f o r R e l e a s e o f I n f o r m a t i o n f o r m b e f o r e we c o u l d r e v i e w t h e i r f i l e s . When w r i t i n g t h e i n f o r m a t i o n s h e e t s f o r p o t e n t i a l s u b j e c t s , and when we s u b s e q u e n t l y t a l k e d w i t h them, c a r e was t a k e n so as no t t o g e n e r a t e a n o t i o n t h a t t h i s d e v i c e w o u l d end a l l t h e i r h e a r i n g p r o b l e m s . The l i m i t a t i o n s o f t h e d e v i c e (and t h e c o n c e p t b e h i n d i t ) were c a r e f u l l y d i s c u s s e d . A l l l e t t e r s w r i t t e n t o t h e p r o j e c t were a n s w e r e d p r o m p t l y . The c o m p l e t e d e t a i l s of t h e e t h i c a l r e v i e w need n o t be i n c l u d e d h e r e ; however, t h e C e r t i f i c a t e o f A p p r o v a l a p p e a r s i n F i g . 5.1. V-3 E v a l u a t i o n M a t e r i a l s and P r o c e d u r e s S e v e r a l t e s t s , d e s c r i b e d below a s t e s t s i - x i i i , were p e r f o r m e d t o a s s e s s h e a r i n g , a i d e d f u n c t i o n , s p e e c h r e a d i n g , c o m m u n i c a t i o n and t h e s u b j e c t s ' p e r s o n a l r e s p o n s e t o h e a r i n g i m p a i r m e n t . T h i s s e l e c t i o n o f t e s t s was a r r a n g e d f o r f i v e p u r p o s e s : 88 1. To a s s e s s t h e s u b j e c t s ' h e a r i n g , e n s u r i n g the m e e t i n g of t h e c r i t e r i a f o r t h e s t u d y (see s e c t i o n V - 4 ) ( t e s t s i - v i ) . 2 . To e n s u r e o p t i m a l a m p l i f i c a t i o n w i t h c o n v e n t i o n a l a i d s ( t e s t s v i i - v i i i ) . 3 . To e v a l u a t e c o m m u n i c a t i o n s k i l l s and s t r a t e g i e s ( t e s t s x -x i i ) . 4 . To no te any change i n a b i l i t y t o d e t e c t sounds and u n d e r s t a n d speech w i t h t h e c o m p r e s s o r compared t o c o n v e n t i o n a l a m p l i f i c a t i o n by a u d i t o r y means o n l y ( t e s t s v i i and i x ) 5 . To a s s e s s p e r s o n a l a d j u s t m e n t s t o c o m m u n i c a t i o n as a r e s u l t of p a r t i c i p a t i o n i n t h e s t u d y ( t e s t s x i - x i i ) . The a c t u a l t e s t s used i n the s t u d y w e r e : i ) M o n a u r a l h e a r i n g t h r e s h o l d s a t 250 t o 8 ,000 H z . i i ) M o n a u r a l speech awarenes s t h r e s h o l d , s p e e c h r e c e p t i o n t h r e s h o l d , most c o m f o r t a b l e l e v e l and t h r e s h o l d of d i s c o m f o r t t o s p e e c h , i i i ) Unmasked bone c o n d u c t i o n t h r e s h o l d s a t 250 t o 4 ,000 H z . i v ) Impedance t e s t i n g t o e v a l u a t e m i d d l e ear f u n c t i o n , v ) U n a i d e d sound f i e l d t h r e s h o l d s t o w a r b l e d t o n e s a t 250 t o 4 ,000 H z . v i ) U n a i d e d s o u n d f i e l d s p e e c h awareness t h r e s h o l d , speech r e c e p t i o n t h r e s h o l d and most c o m f o r t a b l e l e v e l , v i i ) A i d e d s o u n d f i e l d t h r e s h o l d s t o w a r b l e d t o n e s a t 250 t o 4 ,000 H z , speech r e c e p t i o n t h r e s h o l d , speech awarenes s t h r e s h o l d , most c o m f o r t a b l e l e v e l and t h r e s h o l d of d i s c o m f o r t t o s p e e c h . These t e s t s were p e r f o r m e d w i t h 89 t h e s u b j e c t s ' own a i d , a s w e l l a s two o r t h r e e o t h e r a i d s h a v i n g d i r e c t a u d i o i n p u t c a p a b i l i t y . The t e s t s were a l s o p e r f o r m e d w i t h t h e a i d o f c h o i c e i n c o n j u n c t i o n w i t h t h e c o m p r e s s o r , v i i i ) I n f o r m a l t e s t i n g o f v a r i o u s a i d s f o r s u b j e c t i v e r e s p o n s e . i x ) The M i n i m a l A u d i t o r y C a p a b i l i t i e s (MAC) t e s t b a t t e r y ( s e e A p p e n d i x I I ) : a t a p e d s e t o f 14 s u b t e s t s e v a l u a t i n g v a r i o u s a s p e c t s o f t h e i n d i v i d u a l s ' a b i l i t y t o u n d e r s t a n d s p e e c h and e n v i r o n m e n t a l sound s t i m u l i . The MAC t e s t was a d m i n i s t e r e d w i t h c o n v e n t i o n a l a m p l i f i c a t i o n a l o n e and w i t h t h e c o m p r e s s o r , x) S p e e c h r e a d i n g t e s t s w i t h o u t a m p l i f i c a t i o n , w i t h c o n v e n t i o n a l a m p l i f i c a t i o n and w i t h t h e h e a r i n g a i d i n c o n j u n c t i o n w i t h t h e c o m p r e s s o r ; u s i n g CID E v e r y d a y S e n t e n c e s (MAC s u b t e s t #14), t h e U t l e y T e s t ( U t l e y , 1946) and t h e B a r l e y S p e e c h r e a d i n g T e s t - C I D E v e r y d a y S e n t e n c e s ( J e f f e r s and B a r l e y , 1971). x i ) H e a r i n g P e r f o r m a n c e I n v e n t o r y (Henoch, 1982), a 90 i t e m q u e s t i o n a i r e a s k i n g how t h e i n d i v i d u a l s ' h e a r i n g p r o b l e m a f f e c t s t h e i r e v e r y d a y l i v e s . S e c t i o n s i n c l u d e : u n d e r s t a n d i n g s p e e c h w i t h v i s u a l c u e s , u n d e r s t a n d i n g s p e e c h w i t h o u t v i s u a l c u e s , l o u d n e s s , r e s p o n s e t o a u d i t o r y / c o m m u n i c a t i o n f a i l u r e , p e r s o n a l e m o t i o n a l r e s p o n s e s , c o m m u n i c a t i o n f u n c t i o n i n g r o u p s i t u a t i o n s and c o m m u n i c a t i o n when a t work, x i i ) V o i c e r e c o r d i n g of c o n v e r s a t i o n a l s p e e c h t o a s s e s s any change i n v o i c e o r s p e e c h a s a r e s u l t of p a r t i c i p a t i o n 90 i n t h e p r o j e c t , x i i i ) S u b j e c t s were a sked t o keep a d i a r y . The main t e s t f o r m e a s u r i n g improvement i n s p e e c h d i s c r i m i n a t i o n was the M i n i m a l A u d i t o r y C a p a b i l i t i e s (MAC) t e s t w h i c h c o n s i s t s of 13 s u b t e s t s . The MAC t e s t was t o be a d m i n i s t e r e d b o t h w i t h a c o n v e n t i o n a l h e a r i n g a i d and t h e c o m p r e s s o r , b e f o r e and a f t e r t h e t r a i n i n g t i m e . In o r d e r t o have two d i f f e r e n t t e s t v e r s i o n s , and because t h e MAC t e s t i s q u i t e l o n g , i t was s p l i t i n t o two t e s t s ( m i n i m a c s ) . More s p e c i f i c a l l y , each s u b t e s t of t h e o r i g i n a l MAC t e s t was s p l i t i n t o two minimac s u b t e s t s of e q u a l l e n g t h . Care was t a k e n t o e n s u r e t h a t each minimac s u b t e s t was p h o n e t i c a l l y b a l a n c e d ; f o r example t h e s p l i t vowe l t e s t s i n c l u d e d r o u g h l y t h e same number of each t y p e o f v o w e l . A l t h o u g h t h e pa s t r e s e a r c h has shown i t s o n l y s u c c e s s when u s i n g female s p e a k e r s , t h e MAC t e s t i s g i v e n e x c l u s i v e l y by a male v o i c e . The MAC t e s t has been used f o r a s i m i l a r t y p e of a s se s sment w i t h c o c h l e a r i m p l a n t s u b j e c t s ( E d g e r t o n , e t a l . , 1 9 8 3 ) . I t was found t h a t t h e t e s t was too d i f f i c u l t f o r t h e s e c o c h l e a r i m p l a n t s u b j e c t s and t h e y s c o r e d r o u g h l y a t chance l e v e l . The MAC t e s t was c h o s e n f o r t h i s s t u d y s i n c e we e x p e c t e d our s u b j e c t s t o have more r e s i d u a l h e a r i n g t h a n t h e c o c h l e a r i m p l a n t s u b j e c t s , and because i t i s one of a v e r y few t e s t s of i t s t y p e a p p e a r i n g a t l e a s t i n name, i n t h e l i t e r a t u r e . I n o r d e r t o f a c i l i t a t e t h e s u b j e c t s ' a d j u s t m e n t t o t h e c o m p r e s s o r , i n d i v i d u a l r e v i e w and t h e r a p y s e s s i o n s were a r r a n g e d 91 f o r one t o two h o u r s p e r week p e r s u b j e c t . D u r i n g t h i s t i m e , t h e p h y s i c a l o p e r a t i o n o f t h e c o m p r e s s o r and h e a r i n g a i d s y s t e m was i n s p e c t e d and any p r o b l e m s were a d d r e s s e d . The s u b j e c t s ' d i a r i e s were r e v i e w e d w i t h a d i s c u s s i o n of c o m p r e s s o r use i n c l u d i n g b e n e f i t s n o t e d and d i f f i c u l t i e s e x p e r i e n c e d . In o r d e r t o d e t e r m i n e a u d i t o r y s k i l l s i n a l i v e - v o i c e s i t u a t i o n , t h e GASP t e s t ( E r b e r , 1982) was a d m i n i s t e r e d . T h i s i n c l u d e d s c r e e n i n g of E n g l i s h phoneme d e t e c t i o n and d i s c r i m i n a t i o n , r e c o g n i t i o n o f a c l o s e d s e t o f 14 words o f v a r y i n g l e n g t h and s t r e s s , and r e s p o n s e t o f a m i l i a r q u e s t i o n s . T h e r a p y i n v o l v e d a u d i t o r y t r a i n i n g t a s k s f o r e n v i r o n m e n t a l sounds and s p e e c h , c o m b i n i n g a u d i t o r y and v i s u a l c u e s and s t r a t e g i e s f o r e a s i n g communicat i o n . The e x p e c t a t i o n was t h a t t h e s u b j e c t s would i m m e d i a t e l y do b e t t e r w i t h t h e new h e a r i n g a i d s we p r o v i d e d f o r them. T h i s improvement was e x p e c t e d t o p l a t e a u a t a l e v e l c l o s e t o where i t was b e f o r e . The s p e e c h d i s c r i m i n a t i o n w i t h t h e c o m p r e s s o r was e x p e c t e d t o plummet upon f i r s t l i s t e n i n g . The d i s c r i m i n a t i o n was t h e n e x p e c t e d t o r i s e t o t h e p o i n t where i t would be t h e same a s w i t h t h e c o n v e n t i o n a l a m p l i f i c a t i o n , and t h e n r i s e a b o v e . T h i s t y p e o f " l e a r n i n g c u r v e " i s shown s c h e m a t i c a l l y i n F i g . 5.2. The c u r v e i s e x p e c t e d t o have d i f f e r e n t p a r a m e t e r s f o r d i f f e r e n t p e o p l e , a n d d i f f e r e n t a s p e c t s o f d i s c r i m i n a t i o n . The d e t a i l e d shape o f t h e l i n e s a r e g u e s s e s , but p r e s u m a b l y t h e y s h o u l d be m o n o t o n i c a l l y i n c r e a s i n g . I f i t c a n be shown t h a t t h i s i s i n d e e d t h e c a s e , i t must be d e c i d e d i f t h e i n c r e a s e i n c o m p r e h e n s i o n ( c ) i s w o r t h t h e t r a i n i n g t i m e ( t ) . F i g . 5 .2 L e a r n i n g c u r v e s 93 V-1 F a c i l i t i e s and Equipment The c l i n i c a l p a r t o f t h i s work was c a r r i e d o u t under c o n t r a c t w i t h t h e F e d e r a l Government o f Canada. We a r e g r a t e f u l t o D r . N.S. L o n g r i d g e , D i r e c t o r o f t h e N e u r o - o t o l o g y U n i t a t V a n c o u v e r G e n e r a l H o s p i t a l f o r making h i s f a c i l i t i e s a v a i l a b l e t o u s . The s o u n d s u i t e u s e d t o c o n d u c t t h e t e s t s c o n s i s t s o f two a c o u s t i c a l l y s e a l e d rooms w i t h an a d j o i n i n g window. The s u b j e c t s ' room c o n t a i n s s p e a k e r s and e a r p h o n e s c o n t r o l l e d by t h e o p e r a t o r . The o p e r a t o r s ' room c o n t a i n s t h e t o n e g e n e r a t o r s f o r t h e h e a r i n g t e s t s , a m p l i f i e r s and f a c i l i t i e s f o r p l a y i n g t a p e d m a t e r i a l . The e n t i r e s y s t e m was c a l i b r a t e d b e f o r e commencement of t h e s t u d y . We were a l s o g i v e n a c c e s s t o a s m a l l o f f i c e i n w h i c h t o t a k e e a r m o u l d i m p r e s s i o n s , do t h e t h e r a p y and c o n s u l t a t i o n a s w e l l as s t o r e our e q u i p m e n t . S i n c e t h e h e a r i n g i m p a i r m e n t o f t h e a n t i c i p a t e d s u b j e c t s w ould be i n t h e s e v e r e t o p r o f o u n d r a n g e , h i g h g a i n h e a r i n g a i d s were o r d e r e d . T h e s e h e a r i n g a i d s a r e of t h e b e h i n d - t h e - e a r t y p e , w i t h t h e c a p a b i l i t y o f a c c e p t i n g an e x t e r n a l i n p u t i n s t e a d of t h e i n d i g e n o u s s o u r c e m i c r o p h o n e . T h r e e d i f f e r e n t m o d e ls from two m a n u f a c t u r e r s were o b t a i n e d . T h i s would e n a b l e t h e s u b j e c t s i n t h e s t u d y t o c h o o s e a h e a r i n g a i d more s u i t a b l e t o t h e i r p a r t i c u l a r n e e d s . S t a n d a r d e q uipment and s u p p l i e s f o r making e a r m o u l d s were p r o c u r e d . E a r m o u l d s a r e c u s t o m made t o an i n d i v i d u a l ' s e a r c a n a l s h a p e , and must f i t w e l l t o p r e v e n t sound f r o m l e a k i n g o u t . I f a l e a k o c c u r s , f e e d b a c k c a n r e s u l t , a s w e l l a s a l o s s of a m p l i t u d e f o r t h e l i s t e n e r . The e a r m o u l d must a l s o be 94 c o m f o r t a b l e . In t h i s s t u d y a m p l i f i c a t i o n w h i c h makes t h e S e v e r a l i m p r e s s i o n s needed t o r e s u l t e d . t h e s u b j e c t s a l l r e q u i r e h i g h g a i n e a r m o u l d p r o b l e m much more a c u t e , be made b e f o r e a s u i t a b l e e a r m o u l d 95 CHAPTER VI CLINICAL STUDY OBSERVATIONS 96 VI-1 Response t o t h e S o l i c i t a t i o n o f R e f e r r a l s A l l a u d i o l o g i s t s and o t o l a r y n g o l o g i s t s w i t h whom t h e p r o j e c t was d i s c u s s e d were v e r y e n c o u r a g i n g and s u p p o r t i v e . They v o i c e d a p p r e c i a t i o n of t h e a t t e m p t t o a d d r e s s t h e a u r a l r e h a b i l i t a t i o n n e e d s o f t h e d e a f a d u l t . A t o t a l o f 20 r e f e r r a l s were r e c e i v e d . Of t h e s e , t e n were u n s u i t a b l e on r e v i e w o f r e f e r r a l i n f o r m a t i o n : t o o much h e a r i n g i n f o u r c l i e n t s , p r e l i n g u a l d e a f n e s s i n two and p r e s e n t l y l i v i n g o u t s i d e o f commuting d i s t a n c e i n t h r e e c a s e s . The r e m a i n i n g p o t e n t i a l s u b j e c t i n d i c a t e d no f u r t h e r r e s p o n s e t o our f o l l o w up l e t t e r . I n i t i a l a p p o i n t m e n t s were made f o r t h e t e n c l i e n t s who p a s s e d t h e i n i t i a l r e f e r r a l - r e v i e w . Of t h e s e , t h r e e met a l l t h e c r i t e r i a o u t l i n e d i n t h e p r e v i o u s s e c t i o n ; one met a l l t h e c r i t e r i a e x c e p t f o r c u r r e n t h e a r i n g a i d u s e ; two met a l l t h e c r i t e r i a e x c e p t f o r p o o r f l e x i b i l i t y i n s p e e c h r e a d i n g s k i l l s ; one met a l l t h e c r i t e r i a e x c e p t he i s p r e l i n g u a l l y d e a f ; and t h r e e had t o o much r e s i d u a l h e a r i n g . The c l i e n t s w i t h t o o much h e a r i n g were e l i m i n a t e d f r o m t h e s t u d y , and t h e o t h e r s e v e n were i n c l u d e d . A l t h o u g h a major p a r a m e t e r o f t h i s p r o j e c t was t o e v a l u a t e t h e c o m p r e s s o r w i t h i n d i v i d u a l s w i t h p o s t - 1 i n g u a l l y a c q u i r e d h e a r i n g l o s s , one p r e - 1 i n g u a l l y d e a f a d u l t was i n c l u d e d a s i t seemed u n l i k e l y t h a t we would o b t a i n r e f e r r a l s f o r any o t h e r c l i e n t s who would meet a l l t h e c r i t e r i a i n t h e t i m e a v a i l a b l e ( t h i s p a r t i c u l a r i n d i v i d u a l was e x c e p t i o n a l l y m o t i v a t e d w i t h e x c e l l e n t o r a l s k i l l s ) . 97 V I - 2 Da ta A n a l y s i s P r o c e d u r e s There was a l a r g e amount of raw d a t a c o l l e c t e d d u r i n g t h i s s t u d y . The major t r e n d s and a v e r a g e d r e s u l t s w i l l be p r e s e n t e d h e r e . The raw d a t a c o n s i s t of some 364 i n d i v i d u a l MAC s u b t e s t s , 42 s p e e c h r e a d i n g t e s t s , 18 H P I s , 36 a u d i o l o g i c a l r e p o r t s , a c a s s e t t e t ape w i t h t h e s u b j e c t s ' speech and a f i l e f o r each s u b j e c t i n c l u d i n g a u d i o l o g i c a l h i s t o r y , a r e c o r d of the t h e r a p y g i v e n , s u b j e c t i v e i m p r e s s i o n s of t h e a u d i o l o g i s t and t h e s u b j e c t , i n d i v i d u a l GASP t e s t s , and the s u b j e c t ' s d i a r y . The ma jor t e s t of speech d i s c r i m i n a t i o n was t h e MAC t e s t (see A p p e n d i x I I ) . E d g e r t o n e t a l . (1983) found t h e t e s t t o o d i f f i c u l t f o r c o c h l e a r i m p l a n t p a t i e n t s , and t h i s was l a r g e l y t r u e f o r our s u b j e c t s as w e l l . There was a l a r g e f r a c t i o n of s u b t e s t s i n w h i c h t h e s u b j e c t s s c o r e d b e t t e r t h a n chance h o w e v e r , and i n a n a l y s i n g t h e r e s u l t s , o n l y t h e s e t e s t s were c o n s i d e r e d . These were e s s e n t i a l l y o n l y t h e c l o s e d s e t t e s t s i . e . t h e ones where the s u b j e c t was a s k e d t o choose from a s e t of r e s p o n s e s w h i c h one was c o r r e c t . One must be c a r e f u l i n d e c i d i n g how t o d e a l w i t h t h e r e m a i n i n g random component i n t h e t e s t s c o r e s , o t h e r w i s e t h e d a t a may become b i a s e d . On a p a r t i c u l a r s u b t e s t , i f a s u b j e c t s c o r e s a t chance l e v e l a t t h e b e g i n n i n g of t h e s t u d y and above chance l e v e l a t t h e e n d , we know he has i m p r o v e d . The magni tude of t h e improvement h o w e v e r , i s u n d e r e s t i m a t e d by the t e s t s c o r e s , s i n c e we do not know how much improvement t h e s u b j e c t had undergone i n o r d e r t o s c o r e j u s t above c h a n c e . A p p r o p r i a t e s c o r e s t h e n , s h o u l d o n l y be o b t a i n e d from s u b t e s t s upon w h i c h t h e s u b j e c t a l w a y s s c o r e d above c h a n c e . The c o m p r e s s o r s c o r e s 98 a r e most p r o n e t o low p r e t e s t s c o r e s s i n c e we e x p e c t a s u b j e c t ' s c o m p r e h e n s i o n t o s t a r t o u t l o w e r w i t h t h e c o m p r e s s o r t h a n w i t h t h e a i d ( s e e F i g . 5 . 2 ) . On t h e o t h e r hand, i f we e l i m i n a t e a s u b t e s t f o r w h i c h a s u b j e c t ' s c o m p r e s s o r s c o r e s a r e r o u g h l y a t c h a n c e , and t h e h e a r i n g a i d s c o r e s a r e above c h a n c e , we would be n e g l e c t i n g t h e f a c t t h a t t h e s u b j e c t i n d e e d d i d b e t t e r w i t h t h e a i d . To d e a l w i t h t h e s i t u a t i o n s d e s c r i b e d a bove, t h e f o l l o w i n g p r o c e d u r e s were f o l l o w e d . The t e s t s were a l l o f t h e c l o s e d s e t t y p e . F o r c o m p l e t e l y random a n s w e r s , t h e mean (P) and s t a n d a r d d e v i a t i o n (a) a r e as f o l l o w s : P = 1u0/(number o f c h o i c e s ) and o 2 = (P(100-P)/N) where N i s t h e number o f q u e s t i o n s on t h e t e s t ( f o r a r e v i e w o f s t a t i s t i c a l methods see B e v i n g t o n ( 1 9 6 9 ) ) . F o r random a n s w e r s i n a G a u s s i a n d i s t r i b u t i o n we e x p e c t 90% o f t h e s c o r e s t o l i e w i t h i n 1.65 s t a n d a r d d e v i a t i o n s f r o m t h e mean. O n l y 5% o f t h e t o t a l l y random a n s w e r s would l i e 1.65a above t h e mean (and 5% b e l o w ) . As m e n t i o n e d i n C h a p t e r V, e a c h MAC s u b t e s t was a d m i n i s t e r e d f o u r t i m e s t o e a c h s u b j e c t ( t h e c o n s t r u c t i o n o f t h e m i n i m a c s p r e v e n t e d r e p e t i t i o n ) , e a c h i n a d i f f e r e n t s i t u a t i o n . The f o u r s i t u a t i o n s a r e : p r e - t r a i n i n g w i t h t h e a i d a l o n e , p r e -t r a i n i n g w i t h t h e c o m p r e s s o r , p o s t - t r a i n i n g w i t h t h e a i d a l o n e and p o s t - t r a i n i n g w i t h t h e c o m p r e s s o r . F o r e a c h s u b j e c t , and f o r e a c h s u b t e s t , l e t us r e f e r t o t h e a v e r a g e o f t h e p r e - and p o s t - h e a r i n g a i d s c o r e s a s t h e " a i d e d p r e - p o s t mean". S i m i l a r l y , l e t us r e f e r t o t h e a v e r a g e o f t h e p r e - and p o s t -t r a i n i n g c o m p r e s s o r s c o r e s a s t h e " c o m p r e s s o r p r e - p o s t mean". The d a t a a n a l y s i s from h e r e on was done c o m p l e t e l y i n e a c h of two methods: 99 1. The t e s t s u s e d i n t h e a n a l y s i s were o n l y t h e ones where t h e " a i d e d p r e - p o s t mean" AND t h e " c o m p r e s s o r p r e - p o s t mean" were g r e a t e r t h a n 1.65a above t h e mean. 2. The t e s t s u s e d i n t h e a n a l y s i s were o n l y t h e ones where e i t h e r t h e " a i d e d p r e - p o s t mean" OR t h e " c o m p r e s s o r p r e - p o s t mean" ( o r b o t h ) was g r e a t e r t h a n 1.65a above t h e mean. In b o t h c a s e s , i f a t e s t was a c c e p t e d , a l l f o u r s c o r e s f o r t h e t e s t were u s e d i n t h e a n a l y s i s . The r e s u l t s o f method 1 w i l l be p r e s e n t e d i n S e c t i o n V I - 1 2 . E a c h o f t h e t r e n d s p r e s e n t e d i n t h a t s e c t i o n a r e shown by b o t h method 1 and method 2. F o r example, i t i s r e p o r t e d i n S e c t i o n VI-12 t h a t t h e c o m p r e s s o r s c o r e s i n c r e a s e d more d u r i n g t h e t r a i n i n g t h a n t h e h e a r i n g a i d s c o r e s d i d ; t h i s c a n be a r r i v e d a t by e i t h e r method 1 o r method 2. The same i n d e p e n d e n c e o f method i s d e m o n s t r a t e d by a l l of t h e t r e n d s p r e s e n t e d . A p r o p o r t i o n a l ( l i n e a r w i t h z e r o i n t e r c e p t ) measure o f s p e e c h d i s c r i m i n a t i o n was d e s i r e d , so t h e e f f e c t s of c h a n c e were c o r r e c t e d f o r . The p e r c e n t a g e s c o r e c o r r e c t e d f o r c h a n c e (S) i s o b t a i n e d f r o m t h e raw p e r c e n t a g e s c o r e (R) and t h e p e r c e n t a g e c h a n c e l e v e l s c o r e (P) by an e q u a t i o n d e v e l o p e d i n A p p e n d i x I I I : S = R - (1 0 0 - R ) P / ( 1 0 0 - P ) ( i n p e r c e n t ) U s i n g t h e s e s c o r e s , t h e d i f f e r e n c e i n p o s t - and p r e -t r a i n i n g r e s u l t s a v e r a g e d o v e r s u b j e c t s and s u b t e s t s were o b t a i n e d t o a s s e s s t h e d i f f e r e n c e i n t h e r a t e o f l e a r n i n g w i t h t h e c o m p r e s s o r and w i t h t h e h e a r i n g a i d a l o n e i . e . t h e d i f f e r e n c e i n t h e s l o p e s o f t h e c u r v e s i n F i g . 5.2 j u s t a f t e r t h e i n t r o d u c t i o n o f a i d s . The a v e r a g e p r e - t r a i n i n g s c o r e was c a l c u l a t e d f o r t h e h e a r i n g a i d a l o n e and t h e c o m p r e s s o r . From 100 t h i s we can d e t e r m i n e t h e d i f f e r e n c e i n c o m p r e h e n s i o n a t t h e t i m e of t h e i n t r o d u c t i o n o f t h e a i d s ( see F i g . 5 . 2 ) . The a v e r a g e p o s t - t r a i n i n g s c o r e was e v a l u a t e d f o r t h e compres sor and t h e h e a r i n g a i d a l o n e . T h i s e n a b l e s us t o judge r o u g h l y where t h e t r a i n i n g t i m e appear s on t h e a b s c i s s a of F i g . 5 . 2 . I t i s not a s t r a i g h t f o r w a r d t a s k t o e v a l u a t e t h e e r r o r on t h e r e s u l t s . The s t a n d a r d d e v i a t i o n means l i t t l e because each i n d i v i d u a l i s e x p e c t e d t o have d i f f e r e n t l e a r n i n g c u r v e s . The s t a n d a r d d e v i a t i o n c a l c u l a t e d w i t h i n t h e s u b t e s t s of each i n d i v i d u a l i s a l s o a poor measure s i n c e each s u b t e s t measures d i f f e r e n t a s p e c t s of s p e e c h d i s c r i m i n a t i o n and some may grow much f a s t e r t h a n o t h e r s ; t h i s w o u l d show up as e r r o r and i s c e r t a i n l y no i n d i c a t i o n of i t . The s t a n d a r d d e v i a t i o n of t h e s c o r e s of s e v e r a l MAC t e s t s g i v e n a t or near t h e same t ime w o u l d , be a much b e t t e r measure of e r r o r , but t h i s i s q u i t e i m p r a c t i c a l . I t was t h u s d e c i d e d t o use as a measure of e r r o r , t h e t r e n d s o b s e r v e d f o r e a c h i n d i v i d u a l . F o r e x a m p l e , i f t h e a v e r a g e p o s t - t r a i n i n g c o m p r e s s o r s c o r e i s h i g h e r t h a n t h e p r e -t r a i n i n g c o m p r e s s o r s c o r e by x p e r c e n t , we w i l l say t h a t t h e t r e n d has " e x c e l l e n t " r e l i a b i l i t y i f e ach s u b j e c t showed an i n c r e a s e . S i m i l a r l y we w i l l say t h a t t h e r e l i a b i l i t y i s " g o o d " i f a l l but one show an i n c r e a s e , " f a i r " i f a l l but two show an i n c r e a s e , and " p o o r " o t h e r w i s e . The r e l i a b i l i t y was d e t e r m i n e d i n b o t h d a t a a n a l y s i s methods and were found t o d i f f e r by a t most one l e v e l ( e . g . method 1 d e t e r m i n e s good r e l i a b i l i t y , method 2 d e t e r m i n e s e x c e l l e n t r e l i a b i l i t y ) f o r any t r e n d p r e s e n t e d . The s p e e c h r e a d i n g t e s t s c o r e s were a l r e a d y r o u g h l y 101 p r o p o r t i o n a l t o c o m p r e h e n s i o n , and t h e f o l l o w i n g p a r a m e t e r s were e v a l u a t e d : t h e p o s t - t r a i n i n g minus p r e - t r a i n i n g s c o r e s a v e r a g e d o v e r s u b j e c t s and s u b t e s t s f o r t h e c o m p r e s s o r and t h e a i d a l o n e , a g a i n t o show t h e d i f f e r e n t i a l improvement. The a v e r a g e p r e -t r a i n i n g s c o r e s were c a l c u l a t e d f o r t h e h e a r i n g a i d and t h e c o m p r e s s o r , a g a i n t o show t h e d i f f e r e n c e i n t h e a b s o l u t e c o m p r e h e n s i o n a t t h e i n t r o d u c t i o n o f t h e a i d s . F i n a l l y , t h e a v e r a g e p o s t - t r a i n i n g s c o r e s f o r t h e h e a r i n g a i d and t h e c o m p r e s s o r were c a l c u l a t e d t o show t h e t r a i n i n g t i m e p o s i t i o n on t h e a b s c i s s a o f F i g . 5.2. The r e l i a b i l i t y c r i t e r i o n u s e d f o r t h e MAC t e s t was a p p l i e d h e r e as w e l l . The t e s t s d e s c r i b e d so f a r c a n be g r o u p e d i n t o p r e - t r a i n i n g t e s t s and p o s t - t r a i n i n g t e s t s . In a l l c a s e s , t h e p r e - t r a i n i n g t e s t s were g i v e n w i t h i n a t most one a d j a c e n t t h e r a p y s e s s i o n o f e a c h o t h e r . The same i s t r u e f o r t h e p o s t - t r a i n i n g t e s t s a l t h o u g h t h e s e were u s u a l l y g i v e n on t h e same d a y . T h i s was done t o t r y t o m i n i m i z e t h e e f f e c t s of t h e t i m e d e p e n d e n t e m o t i o n a l o u t l o o k o f t h e s u b j e c t s . S i n c e we a r e p r i m a r i l y i n t e r e s t e d i n d i f f e r e n c e s between t h e h e a r i n g a i d s c o r e s and t h e c o m p r e s s o r s c o r e s , t h e e m o t i o n a l d i f f e r e n c e i n t h e s u b j e c t s ' o u t l o o k between t h e p r e - t r a i n i n g and p o s t - t r a i n i n g w i l l c a n c e l o u t . The s c o r e s on t h e HPI a r e somewhat more s u b j e c t i v e . In t h i s c a s e , i f a s u b j e c t had had a bad day when f i l l i n g o ut one o f t h e t e s t s , i t would most d e f i n i t e l y show up. N e v e r t h e l e s s , t h e s c o r e s w i l l be p r e s e n t e d a s p o s t - t r a i n i n g minus p r e - t r a i n i n g and v a r i o u s c r o s s a v e r a g e s w i l l be c a l c u l a t e d t o - show r e l i a b i l i t y . 1 02 In t h e d a t a a n a l y s e s , we w i l l use t h e f o l l o w i n g a b b r e v i a t i o n s : p r e p r e - t r a i n i n g p o s t p o s t - t r a i n i n g a i d h e a r i n g a i d a l o n e comp f r e q u e n c y c o m p r e s s i o n s y s t e m ave a v e r a g e o v e r p a r a m e t e r s not s p e c i f i c a l l y m e n t i o n e d i n t h e a b b r e v i a t i o n . MAC M i n i m a l A u d i t o r y C a p a b i l i t i e s t e s t b a t t e r y SR s p e e c h r e a d i n g t e s t HPI H e a r i n g P e r f o r m a n c e I n v e n t o r y R raw s c o r e (%) S p r o c e s s e d s c o r e p r o p o r t i o n a l t o s p e e c h c o m p r e h e n s i o n (%) P c h a n c e l e v e l s c o r e (%) a s t a n d a r d d e v i a t i o n (%) F o r example, ave SR p o s t comp - ave SR p r e comp i s t h e a v e r a g e o f t h e p o s t - t r a i n i n g c o m p r e s s o r s c o r e s on t h e s p e e c h r e a d i n g t e s t minus t h e a v e r a g e o f t h e p r e - t r a i n i n g c o m p r e s s o r s c o r e s on t h e s p e e c h r e a d i n g t e s t , g i v e n a s a p e r c e n t a g e i n c r e a s e ; t h e a v e r a g e s a r e o v e r s u b j e c t s and s u b t e s t s . In a d d i t i o n t o t h e t e s t s a d m i n i s t e r e d a t t h e b e g i n n i n g and t h e end o f t h e s t u d y , t e s t s were a d m i n i s t e r e d d u r i n g t h e i n d i v i d u a l t h e r a p y s e s s i o n s a s d i s c u s s e d i n C h a p t e r V. In o r d e r t o d e t e r m i n e a u d i t o r y s k i l l s i n a l i v e - v o i c e s i t u a t i o n , t h e GASP t e s t s ( E r b e r , 1982) were u s e d . T h e s e i n c l u d e d t h e s c r e e n i n g o f 103 E n g l i s h phoneme d e t e c t i o n and d i s c r i m i n a t i o n , t h e r e c o g n i t i o n of a c l o s e d s e t o f 14 words o f v a r y i n g l e n g t h and s t r e s s , and t h e r e s p o n s e t o f a m i l i a r q u e s t i o n s . T h e r a p y i n v o l v e d a u d i t o r y t r a i n i n g t a s k s f o r e n v i r o n m e n t a l sounds and s p e e c h , c o m b i n i n g a u d i t o r y and v i s u a l c u e s and s t r a t e g i e s f o r e a s i n g c o m m u n i c a t i o n . The s u b j e c t s were not d i r e c t l y t a s k t r a i n e d , t h a t i s , t r a i n i n g f o r s p e c i f i c t a s k s ( s u c h as a MAC s u b t e s t ) was n o t done. As t h e r e were marked d i f f e r e n c e s i n t h e a b i l i t i e s o f e a c h s u b j e c t , t h e i n d i v i d u a l c a s e s w i l l be d i s c u s s e d , f o l l o w e d by a summary of g e n e r a l t r e n d s . The f i r s t two s u b j e c t s (#A1 and #A2) were t h e f i r s t t o use t h e c o m p r e s s o r , but d i d n o t t a k e p a r t i n t h e f o r m a l s t u d y , hence t h e i r r e s u l t s do not a p p e a r i n t h e d a t a a n a l y s e s . 1 0 4 S u b j e c t / / A l AUDIOGRAM S to Z < CD UJ > UJ O X V) u cc X r -o z £ 2 X -10 0 10 20 30 40 SO 60 70 eo 90 too 110 120 12J 2S0 FREQUENCY IN Hx 500 1000 2000 4000 •000 i » \ < ) \ \ \ < > \ A \ C V / A ^ \ \ \ A C } \ \ t ) i ( \ \ \ O t A <> > u c ... >10 0 10 30 30 40 SO M TO •0 •0 100 110 120 K e y : X l e f t e a r 0 r i g h t e a r A a i d e d w i t h c o n v e n t i o n a l a i d C a i d e d w i t h c o n v e n t i o n a l a i d p l u s c o m p r e s s o r U n a i d e d dBHL A i d e d dBHL Speech Awarenes s T h r e s h o l d Most C o m f o r t a b l e L e v e l T h r e s h o l d o f D i s c o m f o r t r i g h t 45 90 105 l e f t 40 80 105 c o n v e n t i o n a l 10 50 80 c o m p r e s s o r 55 SO F i g . 6.1 A u d i o l o g i c a l i n f o r m a t i o n s u b j e c t ^ A l 105 V I - 3 Case S tudy Sub jec t# AJ_ T h i s s u b j e c t i s a f emale aged 29 y e a r s , employed as an o c c u p a t i o n a l t h e r a p i s t . Her a u d i o l o g i c a l d a t a appear i n F i g . 6 . 1 . She has a moderate s e n s o r i n e u r a l h e a r i n g l o s s a t low f r e q u e n c i e s , s h a r p l y s l o p i n g t o p r o f o u n d a t h i g h e r f r e q u e n c i e s . The l o s s i s b i l a t e r a l and l i k e l y c o n g e n i t a l , but was d i a g n o s e d a t age s i x . She r e c e i v e d speech t h e r a p y i n e l e m e n t a r y and h i g h s c h o o l and has been a h e a r i n g a i d u s e r s i n c e age s i x . T h i s s u b j e c t s t a r t e d her i n v o l v e m e n t w i t h t h i s s t u d y i n J u l y 1983, a t w h i c h t i m e she was f i t t e d b i n a u r a l l y w i t h U n i t r o n E1 PL h e a r i n g a i d s . She was p r o v i d e d w i t h a c o m p r e s s o r i n September 1983 and has been seen f o r 12 t h e r a p y s e s s i o n s . D u r i n g t h i s t i m e , her a u d i t o r y s k i l l s and c o n f i d e n c e improved r a p i d l y t o the p o i n t where she was a b l e t o r a p i d l y i d e n t i f y s h o r t f a m i l i a r p h r a s e s i n an open s e t w i t h c o n v e n t i o n a l a i d s and w i t h t h e c o m p r e s s o r . The GASP s u b t e s t I I (word i d e n t i f i c a t i o n ) was p e r f o r m e d w i t h a p e r f e c t s c o r e r e s u l t i n b o t h s i t u a t i o n s . She had no d i f f i c u l t y i m i t a t i n g r h y t h m and i n t o n a t i o n . Work was s t a r t e d on s i n g l e phoneme d i s c r i m i n a t i o n , but was hampered by n o i s e i n t h e compres sor sy s tem (a t t h a t t i m e M o d e l 3 C ) . T h e r a p y was d i s c o n t i n u e d i n e a r l y November 1983, due t o p e r s o n a l p r o b l e m s . When ready t o resume, t h e f o r m a l t e s t i n g p rogram was w e l l u n d e r w a y , and a new c o m p r e s s o r sys tem (Mode l 3E) was made f o r h e r . She used i t a t home, u s u a l l y when w a t c h i n g t e l e v i s i o n . D u r i n g t h i s l a t e r t r a i n i n g p e r i o d she was t i r e d and i l l . The ( s i n g l e ' s e t o f ) t e s t s were a l l a d m i n i s t e r e d f o u r weeks l a t e r on June 10 1984. Her s u b j e c t i v e i m p r e s s i o n s of t h e c o m p r e s s o r a r e as 106 f o l l o w s : - The v o i c e q u a l i t y i s h a r s h , deeper and "a l o w e r r e g i s t e r " . - Some b a c k g r o u n d n o i s e i s p r e s e n t . - I t i s d i f f i c u l t t o t e l l male and female s p e a k e r s a p a r t . - The t i m e d e l a y i s not n o t i c e a b l e . - The f o l l o w i n g sounds can be d e t e c t e d w i t h t h e compres sor sy s tem but n o t w i t h t h e h e a r i n g a i d a l o n e : f r o n t door k n o c k e r , dog b a r k i n g from a n o t h e r room and t h e phone r i n g i n g . - For s p e e c h , t h e r e i s no t much advantage o v e r t h e r e g u l a r a i d s a t p r e s e n t T h i s s u b j e c t i s a v e r y s o p h i s t i c a t e d h e a r i n g a i d u s e r and knows many s t r a t e g i e s f o r u n d e r s t a n d i n g c o n v e r s a t i o n s . A t t h e t i m e of t e s t i n g , her MAC s c o r e s were c o n s i s t e n t l y h i g h e r w i t h the h e a r i n g a i d s a l o n e ( e x c e p t MAC S u b t e s t X I I I ) . T h i s i s p e r h a p s not s u r p r i s i n g c o n s i d e r i n g her h i s t o r y , and our a s s u m p t i o n s i n F i g . 5 . 2 . I n t h e s p e e c h r e a d i n g t e s t s , she s c o r e d 100% on a l l t e s t s w i t h t h e c o m p r e s s o r s y s t e m , w i t h c o n v e n t i o n a l a i d s , and w i t h no a i d w h a t s o e v e r . The HPI s c o r e s a r e as f o l l o w s : (see s e c t i o n V I - 1 2 f o r a f u l l d e s c r i p t i o n of t h e HPI p a r a m e t e r s ) U n d e r s t a n d i n g speech w i t h v i s u a l c u e s : 80% U n d e r s t a n d i n g speech w i t h o u t v i s u a l c u e s : 40% I n t e n s i t y l e v e l h i g h e n o u g h : 42% Response t o a u d i t o r y f a i l u r e : 54% P e r s o n a l e f f e c t s : 76% S o c i a l e f f e c t s : 63% O c c u p a t i o n a l e f f e c t s : 80% 107 S u b j e c t / / A2 155 -10 ca s 0 • 10 AN 20 CD 30 Z -1 40 UJ > SO UJ -1 o 60 _J OH 70 u 80 oc z t- 90 o z 100 oc 2 110 X 120 350 AUDIOGRAM F R E Q U E N C Y IN H i 500 1000 2000 4000 •000 ( i \ k y c u > c ( -10 0 10 20 30 40 SO to TO •0 •0 100 110 120 K e y : S s o u n d f i e l d A a i d e d w i t h c o n v e n t i o n a l a i d C a i d e d w i t h c o n v e n t i o n a l a i d p l u s c o m p r e s s o r S p e e c h A w a r e n e s s T h r e s h o l d M o s t C o m f o r t a b l e L e v e l T h r e s h o l d o f D i s c o m f o r t U n a i d e d dBHL A i d e d dBHL s o u n d f i e l d c o n v e n t i o n a l c o m p r e s s o r 35 25 30 85 80 DNT 90+ 90+ DNT F i g . 6 .2 A u d i o l o g i c a l i n f o r m a t i o n s u b j e c t # A2 108 V I - 4 Case S tudy S u b j e c t * A2 T h i s s u b j e c t i s male aged 25 y e a r s and i s employed as a p o l i c y a n a l y s t . He has a s e n s o r i n e u r a l h e a r i n g i m p a i r m e n t due t o M e n i e r e ' s d i s e a s e . The h e a r i n g l o s s onse t o c c u r r e d a t age 2 0 . The s e v e r i t y of t h e l o s s d i s p l a y s t h e l a r g e f l u c t u a t i o n s c h a r a c t e r i s t i c of t h i s a f f l i c t i o n and F i g . 6 .2 shows h i s a u d i o l o g i c a l d a t a f o r May 1984. A month or so p r e v i o u s t o t e s t i n g , he had a M e n i e r e ' s a t t a c k , p r o v o k e d by t h e a n e s t h e t i c u sed d u r i n g a knee o p e r a t i o n . The more u s u a l a u d i o g r a m f o r him i s f a r worse t h a n t h a t shown i n F i g . 6 .2 (some 30-40 dB a c r o s s t h e board ) and we i n d e e d o b t a i n e d such an a u d i o g r a m i n J u l y 1983. T h i s s u b j e c t i s p e r h a p s our p r i z e p e r f o r m e r i n t h e sense t h a t he has o b t a i n e d by f a r t h e most b e n e f i t from t h e compres sor s y s t e m . S i n c e the t i m e he f i r s t u sed i t ( a t t h e t i m e : Mode l 3C i n c o n j u n c t i o n w i t h U n i t r o n E I P L ' s b i n a u r a l l y ) he has worn the sy s tem e s s e n t i a l l y a l l h i s w a k i n g h o u r s . The sy s tem has made t h e d i f f e r e n c e between u s i n g t h e t e l e p h o n e and a " V i s u a l E a r " ( t e l e t y p e - t e l e p h o n e d e v i c e f o r the d e a f ) . In f a c t , he does v e r y w e l l on the phone because he can a d j u s t t h e volume t o h i s l i k i n g and h i s HPI i n t e n s i t y s c o r e shows poor a c c o m o d a t i o n of i n t e n s i t y . The b a c k g r o u n d n o i s e i s a l s o l e s s on t h e p h o n e . F o r d e t e c t i o n he uses a m a g n e t i c s e n s o r w i t h a s u c t i o n cup ( t h e t y p e used t o r e c o r d phone c a l l s ) . He wears t h e m i c r o p h o n e b e h i n d h i s t i e so " p e o p l e d o n ' t l e a n i n t o t h e m i c r o p h o n e . . . I c a n ' t see t h e i r f a c e s " . He i s p r e s e n t l y u s i n g M o d e l 3E ( s e r i a l * 12) and f i n d s i t b e t t e r t h a n h i s p r e v i o u s v e r s i o n (Model 3 C ) . 109 H i s most c o m f o r t a b l e h e a r i n g a i d a m p l i f i c a t i o n l e v e l i s a good 20 dB l o w e r w i t h t h e c o m p r e s s o r , more t h a n d o u b l i n g h i s h e a r i n g a i d b a t t e r y l i f e and a v o i d i n g t h e p o s s i b i l i t y of a c o u s t i c . t rauma a s s o c i a t e d w i t h h i g h i n t e n s i t y s o u n d . H i s s u b j e c t i v e r e a s o n i s t h a t h i s t i n n i t u s m a n i f e s t s i t s e l f as a h i g h f r e q u e n c y r i n g i n g , and c o n v e n t i o n a l a m p l i f i c a t i o n competes w i t h i t . The compres sor sound i s removed i n f r e q u e n c y from t h e t i n n i t u s and he can hear i t more e a s i l y . He can u n d e r s t a n d 40-50% of a r a d i o news c a s t and 95% of a t e l e v i s i o n news c a s t . I n f o r m a l t e s t s ( w i t h an a c c o r d i o n ) show t h a t he can b a r e l y d i s c r i m i n a t e a ma jor 3 rd i n t e r v a l ( f r e q u e n c y change of 25%) w i t h h e a r i n g a i d s a l o n e . He has many d e v i c e s t o h e l p h i m ge t a b e t t e r s i g n a l t o n o i s e r a t i o i n c l u d i n g the phone a d a p t e r j u s t m e n t i o n e d and an i n f r a r e d t e l e c o i l f o r m e e t i n g s where a s p e a k e r ' s words a r e t r a n s l a t e d and t r a n s m i t t e d . We o n l y have p o s t - t r a i n i n g s c o r e s f o r t h i s s u b j e c t s i n c e he s t a r t e d b e f o r e we had even c o l l e c t e d the t e s t s ; the r e s u l t s appear i n T a b l e 6 . 1 . T a b l e 6.1 MAC S c o r e s f o r S u b j e c t * A2 MAC S u b t e s t I I I I I I IV V VI V I I V I I I IX X XI X I I X I I I a v e r a g e (#IX not i n c l . ) - a l o n e s c o r e 40% 20 4 45 30 0 60 60 0 47 12 40 36 31% compres sor 60% 40 38 75 80 36 80 80 0 73 0 55 60 54% d i f f e r e n c e 20% 20 34 30 50 36 20 20 0 26 -12 1 5 24 23% 111 The a v e r a g e i n c r e a s e w i t h t h e c o m p r e s s o r i s 23%, a d d i t i o n a l l y improvement was shown i n each i n d i v i d u a l s u b t e s t ( e x c e p t X I ) . I t seems c l e a r t h a t t h e t r a i n i n g t i m e f o r t h i s s u b j e c t i s w e l l beyond t h e c r o s s o v e r p o i n t i n F i g . 5 . 2 and i n h i s c a s e t h e s p e e c h c o m p r e h e n s i o n i n c r e a s e was w e l l w o r t h the t r a i n i n g t i m e . The HPI t e s t r e s u l t s f o l l o w : (20% i s the minimum p o s s i b l e s c o r e , 100% i s t h e maximum) U n d e r s t a n d i n g speech w i t h v i s u a l c u e s : 59% U n d e r s t a n d i n g speech w i t h o u t v i s u a l c u e s : 45% I n t e n s i t y l e v e l h i g h enough : 33% Response t o a u d i t o r y f a i l u r e : 62% P e r s o n a l e f f e c t s : 84% S o c i a l e f f e c t s : 72% O c c u p a t i o n a l e f f e c t s : 72% T h i s s u b j e c t i s i n d e e d a v e r y s u c c e s s f u l c o m p r e s s o r u s e r . S i n c e h i s r e s u l t s a r e so p o s i t i v e , and f o r r e a s o n s of u n u s u a l a u d i o l o g y t e s t r e s u l t s , v a r i o u s f a c t o r s were e x p l o r e d t o see i f t h i s s u b j e c t was e x h i b i t i n g f u n c t i o n a l h e a r i n g l o s s . F u n c t i o n a l h e a r i n g l o s s i s a t e r m meaning p s y c h o l o g i c a l e f f e c t s on the r e s u l t s e i t h e r c o n s c i o u s l y o r u n c o n s c i o u s l y a p p l i e d . F o r some r e a s o n t h e s u b j e c t may want you t o o b t a i n c e r t a i n r e s u l t s and c o n s c i o u s l y o r u n c o n s c i o u s l y a l t e r s h i s r e s p o n s e s t o t e s t s . For an i n - d e p t h d i s c u s s i o n o f f u n c t i o n a l h e a r i n g l o s s , see E n g e l b e r g (1970) and K a t z ( 1 9 7 8 ) . I f f u n c t i o n a l h e a r i n g l o s s i s i n d e e d a f a c t o r , l e t us 1 12 assume t h a t i t wo u l d t e n d t o r a i s e t h e c o m p r e s s o r r e s u l t s a n d / o r l o w e r t h e u n a i d e d r e s u l t s and r e s u l t s w i t h r e g u l a r a i d s . The u n u s u a l a u d i o l o g i c a l r e s u l t s a p p e a r i n F i g . 6.2. H i s a i d e d r e s u l t s a r e r o u g h l y 20 dB above t h e u n a i d e d sound f i e l d r e s u l t s . The a i d s s h o u l d have p r o v i d e d a b o u t 35 dB g a i n . O t h e r e v i d e n c e o f f u n c t i o n a l h e a r i n g l o s s i s c o n t a i n e d i n t h e s u b j e c t i v e i m p r e s s i o n s o f t h e a d m i n i s t e r i n g a u d i o l o g i s t who r e p o r t s f a l s e n e g a t i v e b u t no f a l s e p o s i t i v e r e s p o n s e s t o t o n e s , d e l a y e d r e s p o n s e s , " w a v e r i n g f i n g e r " , f i d g e t i n g d u r i n g t h e t e s t s e t c . Of c o u r s e t h e s e b e h a v i o u r s do n o t mean f u n c t i o n a l h e a r i n g l o s s , but t h e y a r e e v i d e n c e . The d a t a were a l s o i n t e r p r e t e d a s p o s s i b l y t y p i c a l o f a f u n c t i o n a l h e a r i n g l o s s by a n o t h e r a u d i o l o g i s t . T h e r e i s a l s o a p s y c h o l o g i c a l m o t i v e p r e s e n t w h i c h c a n n o t be d i s c l o s e d h e r e f o r e t h i c a l r e a s o n s . E v i d e n c e a g a i n s t f u n c t i o n a l h e a r i n g l o s s i s t h e f o l l o w i n g . The s u b j e c t r e p o r t s a h i s t o r y o f u n e x p e c t e d a u d i o l o g i c a l r e s u l t s and t h a t a b r a i n s t e m t e s t was p e r f o r m e d when f a c e d w i t h t h i s p r o b l e m p r e v i o u s l y . A b r a i n stem t e s t d o e s not r e q u i r e c o n s c i o u s r e s p o n s e s s i n c e t h e d e t e c t i o n o f sound i s measured by e l e c t r o d e s . The s u b j e c t r e p o r t s a g r e e m e n t between t h e b r a i n s t e m t e s t a n d a u d i o l o g i c a l t e s t s . The o n l y u n e x p l a i n e d r e s u l t i s t h e a i d e d and s o u n d f i e l d d i s p a r i t y . The a u t h o r was r e f e r r e d t o an e x p e r t i n f u n c t i o n a l h e a r i n g l o s s t o whom a l l i n f o r m a t i o n was d i s c l o s e d . The c o n c l u s i o n r e a c h e d was t h a t t h e r e was p r o b a b l y no f u n c t i o n a l h e a r i n g l o s s f o r t h e f o l l o w i n g r e a s o n s . F i r s t l y t h e e x p e r t p l a c e s l i t t l e i m p o r t a n c e on t h e b e h a v i o u r a l e v i d e n c e r e p o r t e d by t h e a d m i n i s t e r i n g a u d i o l o g i s t . S e c o n d l y , i n t e r n a l c o n s i s t e n c y i n a u d i o l o g i c a l t e s t s i s an i m p o r t a n t t e s t f o r 1 13 f u n c t i o n a l l o s s and t h e r e a r e s e v e r a l i n t e r n a l c h e c k s w h i c h t h e d a t a p a s s e s . T h e r e i s no i n c o n s i s t e n c y i n SAT ( s p e e c h a w a r e n e s s t h r e s h o l d ) and a u d i o g r a m f o r e i t h e r of t h e a u d i o g r a m s t a k e n . The c o m p r e s s o r s c o r e s a r e c o n s i s t e n t w i t h t h e a u d i o g r a m f r e q u e n c y r e s p o n s e f o r b o t h a u d i o g r a m s t a k e n . T h i r d l y , r e f l e x a c t i o n i n impedance t e s t s and t h e f l u c t u a t i o n l o s s a r e c o n s i s t e n t w i t h t h e symptoms o f M e n i e r e ' s d i s e a s e . F o u r t h l y , t h e d i s c r e p a n c y i s n o t c o n s i s t e n t w i t h t h e m o t i v a t i o n , i . e . t h e c o m p r e s s o r s c o r e s a r e n o t h i g h e r t h a n t h e a i d e d s c o r e s . The h e a r i n g a i d g a i n i s l o w e r f o r t h e c o m p r e s s o r , b ut t h e s u b j e c t s e t h i s a i d s a t t h e most c o m f o r t a b l e l e v e l , and knew t h a t we n o t e d t h e g a i n . The e x p e r t c o u l d n o t d e f i n i t e l y e x p l a i n t h e s o u n d f i e l d / a i d e d a u d i o g r a m r e s u l t s , but c o n s i d e r e d t h e non-f u n c t i o n a l l o s s e v i d e n c e a s much s t r o n g e r . A n o t h e r i n d e p e n d e n t r e s u l t c o n f i r m i n g t r o u b l e w i t h i n t e n s i t y i s t h e s u b j e c t ' s a b n o r m a l l y low HPI " I n t e n s i t y " s c o r e . The s u b j e c t r e p o r t s much t r o u b l e w i t h t h e a c c o m o d a t i o n o f i n t e n s i t y . T h i s i s c o n s i s t e n t w i t h h i s t e l e p h o n e r e s u l t s , and h i s t i n n i t u s ; t h e s o u n d f i e l d / a i d e d a u d i o g r a m d i s p a r i t y i s i n t e n s i t y r e l a t e d . I t s h o u l d a l s o be n o t e d t h a t b i l a t e r a l M e n i e r e ' s d i s e a s e i s q u i t e uncommon, and some symptoms a r e u n i q u e . S i n c e t h e a u t h o r has a s t r o n g m o t i v e t o d i s c l a i m f u n c t i o n a l l o s s i n t h i s c a s e , i t i s f e l t t h a t a c o n c l u s i o n s h o u l d n o t be p r e s e n t e d h e r e . 114 S u b j e c t / / B l 123 -10 s 0 » 10 AN 20 CD T> 30 Z -J 40 UJ > 30 UJ o 60 -1 HO 70 V) VJ 80 cc z 90 O z 100 £ 2 110 z 120 250 A U D I O G R A M FREQUENCY IN Hz 500 1000 2000 4000 1000 -s. t K ( A • / \ ( t C 7 ( f n -10 0 10 20 30 40 30 M 70 •0 90 100 110 120 No m e a s u r a b l e r e s p o n s e a t a n y f r e q u e n c y f o r t h e r i g h t e a r K e y : X l e f t e a r 0 r i g h t e a r A a i d e d w i t h c o n v e n t i o n a l a i d C a i d e d w i t h c o n v e n t i o n a l a i d p l u s c o m p r e s s o r U n a i d e d dBHL S p e e c h A w a r e n e s s T h r e s h o l d M o s t C o m f o r t a b l e L e v e l T h r e s h o l d o f D i s c o m f o r t r i g h t C N T 0 5 CNT l e f t 95 105 105+ A i d e d dBHL l e f t e a r o n l y c o n v e n t i o n a l c o m p r e s s o r 35 65 105+ F i g 6 . 3 A u d i o l o g i c a l i n f o r m a t i o n s u b j e c t / / B l 1 1 5 V I - 5 Case S t u d y S u b j e c t * B 1 T h i s s u b j e c t i s a male, aged 44 y e a r s , h a v i n g had a s e v e r e h e a r i n g l o s s f o r t h e p a s t 20 y e a r s due t o f a m i l i a l o t o s c l e r o s i s . He has worn a h e a r i n g a i d f o r t h e p a s t 20 y e a r s and a t p r e s e n t u s e s a c o n v e n t i o n a l b e h i n d - t h e - e a r a i d f o r h i s r i g h t e a r o n l y . He i s employed as an e l e c t r i c i a n and has v e r y good s p e e c h r e a d i n g s k i l l s . He has had no p r i o r a u r a l r e h a b i l i t a t i o n e x c e p t f o r h e a r i n g a i d r e c o m m e n d a t i o n s . In t h e s t u d y , he has been s e e n f o r n i n e s e s s i o n s : t h r e e f o r i n i t i a l e v a l u a t i o n , f o u r f o r h e a r i n g a i d , e a r m o l d and c o m p r e s s o r m o d i f i c a t i o n s , and two where h i s e n t i r e s y s t e m was w o r k i n g w e l l enough t o a l l o w f o r t h e r a p y . D e s p i t e h i s p r o f o u n d h e a r i n g l o s s , t h i s man has s u r p r i s i n g l y good a i d e d f u n c t i o n i n t h e m i d d l e t o h i g h f r e q u e n c y r a n g e ( 1 0 0 0 - 3 0 0 0 Hz) w i t h c o n v e n t i o n a l a m p l i f i c a t i o n ( s e e F i g . 6 . 3 ) . He d i d s i g n i f i c a n t l y b e t t e r w i t h one o f t h e p r o j e c t a i d s t h a n w i t h h i s own a i d on s o u n d f i e l d t e s t i n g , i n f o r m a l c o n v e r s a t i o n , and s u b j e c t i v e r e a c t i o n . He and h i s w i f e a l s o r e p o r t e d t h a t he c o u l d m o n i t o r t h e l o u d n e s s o f h i s own v o i c e and speak more c l e a r l y w i t h t h i s new a i d . G i v e n h i s a i d e d f u n c t i o n w i t h c o n v e n t i o n a l a m p l i f i c a t i o n , i t i s n o t s u r p r i s i n g t h a t t h e r e i s l i t t l e d i f f e r e n c e i n sound f i e l d t e s t i n g between t h e c o n v e n t i o n a l a i d and t h e a i d p l u s c o m p r e s s o r ( s e e F i g . 6 . 3 ) . I n i t i a l a b i l i t y t o u n d e r s t a n d s p e e c h d e t e r i o r a t e d m a r k e d l y when he j u s t p u t on t h e c o m p r e s s o r . As soon as he was f i t t e d w i t h t h e c o m p r e s s o r , he wore i t a t home and a t work f o r a b o u t one week and f o u n d c o m m u n i c a t i o n v e r y f r u s t r a t i n g w i t h m i n i m a l improvement a t t h e end o f t h e week 116 compared t o t h e b e g i n n i n g . In t h e r a p y he was a b l e t o d e t e c t a l l s p e e c h sounds and i d e n t i f y a p p r o x i m a t e l y 60% o f them i n i s o l a t i o n u s i n g t h e GASP I t e s t and i d e n t i f y 5 o u t o f 14 words i n a c l o s e d s e t (GASP I I ) u s i n g t h e c o m p r e s s o r w i t h o u t v i s u a l c u e s . He was u n a b l e t o i d e n t i f y any f a m i l i a r q u e s t i o n s (GASP I I I ) w i t h o u t v i s u a l c u e s . T e s t i n g w i t h c o n v e n t i o n a l a i d s a l o n e was n o t done. G i v e n t h e a b s e n c e o f any improvement i n a b i l i t y t o d e t e c t m i d - h i g h f r e q u e n c i e s of s o u n d s , we i n i t i a l l y q u e s t i o n e d t h e l i k e l i h o o d o f any improvement f o r u n d e r s t a n d i n g s p e e c h w i t h t h e c o m p r e s s o r f o r t h i s man. However he w i s h e d t o c o n t i n u e i n t h e p r o j e c t and t o keep t r y i n g any m o d i f i c a t i o n s we m i g h t make. As of March 1984, he was u s i n g t h e c o m p r e s s o r i n home and s o c i a l s i t u a t i o n s , b u t n o t a t work. 117 S u b j e c t / / B2 o X z < CO XJ U i > U) o z v» cc X o z e 2 X -10 0 10 20 30 40 50 60 70 80 90 100 110 120 125 250 AUDIOGRAM FREQUENCY IN Hi 500 1000 2000 4000 9000 ( •A \ \ / X \ c \ \ \ f ^ X K X ; > V K A — ' -10 0 10 20 30 40 SO •0 70 •0 90 100 110 120 No m e a s u r a b l e r e s p o n s e a t any f r e q u e n c y f o r r i g h t e a r K e y : X l e f t e a r 0 r i g h t e a r A a i d e d w i t h c o n v e n t i o n a l a i d C a i d e d w i t h c o n v e n t i o n a l a i d p l u s c o m p r e s s o r U n a i d e d dBHL S p e e c h A w a r e n e s s T h r e s h o l d M o s t C o m f o r t a b l e L e v e l T h r e s h o l d o f D i s c o m f o r t r i g h t N R 1 0 5 CNT l e f t 95 105 105+ A i d e d dBHL l e f t e a r o n l y c o n v e n t i o n a l c o m p r e s s o r 35 65 105+ F i g . 6 . 4 A u d i o l o g i c a l i n f o r m a t i o n s u b j e c t / * B2 118 V I - 6 Case S tudy Sub jec t# B2 T h i s s u b j e c t i s a f e m a l e , aged 64 y e a r s , h a v i n g had a p r o g r e s s i v e h e a r i n g l o s s of unknown e t i o l o g y o v e r t h e p a s t 30 y e a r s . She has been a h e a r i n g a i d u s e r f o r 24 y e a r s ; a t p r e s e n t , she wears a c o n v e n t i o n a l b e h i n d - t h e - e a r a i d f o r her l e f t ear o n l y . She i s a homemaker and has v e r y good s p e e c h r e a d i n g s k i l l s w h i c h her f a m i l y s u p p l e m e n t s w i t h some f i n g e r s p e l l i n g . She has p a r t i c i p a t e d i n a w e e k l y s p e e c h r e a d i n g / a u r a l r e h a b i l i t a t i o n c l a s s f o r a p p r o x i m a t e l y one y e a r . In t h e s t u d y , she has been seen f o r n i n e s e s s i o n s , t h r e e f o r i n i t i a l e v a l u a t i o n and s i x f o r t h e r a p y . She s u b j e c t i v e l y p r e f e r r e d , and had a b e t t e r s c o r e i n sound f i e l d t e s t i n g w i t h one o f t h e new p r o j e c t a i d s t h a n w i t h her own a i d . W i t h the c o m p r e s s o r , t h e r e was an improvement i n a b i l i t y t o d e t e c t 2000 Hz w a r b l e d t o n e s (see F i g . 6 . 4 ) . Her use w i t h t h e c o m p r e s s o r has been i n t e r m i t t e n t w i t h i n i t i a l e n t h u s i a s m f o l l o w e d by f r u s t r a t i o n and t h e n a g a i n renewed m o t i v a t i o n . Her s u b j e c t i v e r e a c t i o n was t h a t t h e c o m p r e s s o r i s v e r y n o i s y and t h a t v o i c e s sounded u n p l e a s a n t l y h o a r s e , e s p e c i a l l y her own. She and h e r f a m i l y f i n d t h a t she i s a b l e t o m o n i t o r her own v o i c e l e v e l b e t t e r w i t h t h e c o m p r e s s o r t h a n w i t h a c o n v e n t i o n a l a i d . On t h e GASP I , she was a b l e t o d e t e c t a p p r o x i m a t e l y 80% of speech sounds i n i s o l a t i o n but u n a b l e t o i d e n t i f y any w i t h the a i d p l u s t h e c o m p r e s s o r s i m i l a r t o her p e r f o r m a n c e w i t h the c o n v e n t i o n a l a i d . She c o u l d not answer any f a m i l i a r q u e s t i o n s (GASP I I I ) i n e i t h e r c o n d i t i o n . These t e s t s were a l l 119 a d m i n i s t e r e d w i t h o u t v i s u a l c u e s . Over t h e c o u r s e o f t h e r a p y , she has i m p r o v e d g r e a t l y i n her a u d i t o r y a w a r e n e s s and c o n f i d e n c e , now b e i n g a b l e t o d i s t i n g u i s h i n a c l o s e d s e t up t o n i n e p h r a s e s o f s i m i l a r l e n g t h d e s p i t e t h e v a r i a t i o n o f rhythm and i n t o n a t i o n i n t h e p r e s e n t a t i o n . She f i n d s h e r g r e a t e s t d i f f i c u l t y i s t h a t she i s v e r y e a g e r t o u n d e r s t a n d when p e o p l e t a l k w i t h h e r and she f i n d s t h e c o m p r e s s o r n o i s y and c o n f u s i n g . However, she g o t t o t h e p o i n t where she was u s i n g t h e c o m p r e s s o r s e v e r a l h o u r s p e r day p r a c t i s i n g t a l k i n g and r e a d i n g a l o u d t o h e r s e l f and w a t c h i n g t h e t e l e v i s i o n w i t h h e r c a p t i o n d e c o d e r and t h e sound t u r n e d on ( p r e v i o u s l y she would t u r n o f f t h e s o u n d ) . She a l s o e n j o y s l i s t e n i n g t o t h e t a p e r e c o r d e d s t o r i e s we have made f o r h e r t o l i s t e n t o and f o l l o w s t h e s c r i p t . H o p e f u l l y , a s h e r a u d i t o r y s k i l l s and c o n f i d e n c e i n c r e a s e she w i l l c o n t i n u e t o i m p r o v e . 120 S u b j e c t / / B3 125 -10 s 0 Ql V -• 10 55 AN 20 CO •© 30 z - J 40 Ui > SO UJ _ J o 60 HO 70 UJ to a X »- 90 o z too cc 2 110 X 120 250 AUDIOGRAM FREQUENCY IN Hi 500 1000 2000 4000 9000 < X;< --^ - f \- c *\ 1 > \ ; ) V o < > I > * •10 0 10 20 30 40 SO M 70 •0 90 100 110 120 K e y : X l e f t e a r O r i g h t e a r A a i d e d w i t h c o n v e n t i o n a l a i d C a i d e d w i t h c o n v e n t i o n a l a i d p l u s c o m p r e s s o r S p e e c h A w a r e n e s s T h r e s h o l d M o s t C o m f o r t a b l e L e v e l T h r e s h o l d o f D i s c o m f o r t U n a i d e d dBHL A i d e d dBHL r i g h t l e f t c o n v e n t i o n a l 95 90 45 105+ CNT 65 105+ 105 90+ c o m p r e s s o r 45 65 90+ • F i g 6 .5 A u d i o l o g i c a l i n f o r m a t i o n s u b j e c t / / B3 121 VI-7 C ase S t u d y S u b j e c t # B3 T h i s s u b j e c t i s a male, a g e d 46 y e a r s , who a c q u i r e d a s e v e r e - p r o f o u n d h e a r i n g l o s s f o l l o w i n g t u b e r c u l a r m e n i n g i t i s a t age 12 y e a r s . He had u s e d a body s t y l e h e a r i n g a i d a s a t e e n a g e r and has had i n t e r m i t t e n t h e a r i n g a i d use i n a d u l t h o o d . He l i k e s t o have a h e a r i n g a i d f o r h i s r i g h t e a r but a t t h e t i m e of e n t e r i n g t h e p r o j e c t h i s own a i d had been l o s t f o r s e v e r a l months and he had been u n a b l e t o o b t a i n f u n d i n g t o r e p l a c e i t . H i s s p e e c h r e a d i n g s k i l l s a r e f a i r w i t h s p e a k e r s he knows and he u s e s some s i g n l a n g u a g e . He i s v o c a t i o n a l l y u n s k i l l e d and l i v e s on a d i s a b i l i t y p e n s i o n f o r h i s m u l t i p l e p h y s i c a l h a n d i c a p s . He has r e c e i v e d no p r i o r a u r a l r e h a b i l i t a t i o n t r a i n i n g e x c e p t f o r h e a r i n g a i d r e c o m m e n d a t i o n s . He has been s e e n f o r e i g h t s e s s i o n s , f i v e f o r i n i t i a l e v a l u a t i o n s and t h r e e f o r t h e r a p y . He i n i t i a l l y t r i e d two h e a r i n g a i d s ( b i n a u r a l f i t t i n g ) b ut f o u n d t h a t t h e l e f t e a r a i d e d r e s p o n s e was " j u s t a r a c k e t " , so s w i t c h e d t o an a i d f o r t h e r i g h t e a r o n l y . Sound f i e l d t e s t i n g r e v e a l e d a s l i g h t improvement i n a b i l i t y t o d e t e c t w a r b l e d t o n e s a t 2000 and 3000 Hz w i t h t h e c o m p r e s s o r , as compared t o t h e c o n v e n t i o n a l a i d . T h i s s u b j e c t f i n d s t h e s o u n d q u a l i t y o f t h e c o m p r e s s o r " h o a r s e " , " r e m o t e " and "mumbling". He i s b o t h e r e d by t h e e n v i r o n m e n t a l b a c k g r o u n d n o i s e p r o c e s s e d by t h e c o m p r e s s o r w h i c h he d e s c r i b e s a s a " d e l i r i u m " ; t h i s may be a g g r a v a t i n g h i s t i n n i t u s . The s i n g l e s p e e c h sound d e t e c t i o n t e s t (GASP I) was n o t a t t e m p t e d a s t h i s s u b j e c t f i n d s i t v e r y f r u s t r a t i n g t o do a u d i t o r y work w i t h o u t v i s u a l c u e s e s p e c i a l l y f o r n o n s e n s e 122 s o u n d s . On t h e GASP I I , he i d e n t i f i e d 2 o u t o f 14 s i n g l e words i n a c l o s e d s e t w i t h t h e a i d p l u s c o m p r e s s o r and 14 o u t of 14 w i t h v i s u a l c u e s . T e s t i n g was n o t done w i t h t h e c o n v e n t i o n a l a i d a l o n e . D u r i n g t h e c o u r s e o f t h e r a p y he has g r e a t l y i m p r o v e d h i s a t t e n t i o n t o s p e e c h and use o f s p e e c h r e a d i n g . He has l e a r n e d t o i d e n t i f y f a m i l i a r e n v i r o n m e n t a l sounds w h i c h he d o e s n o t d e t e c t w i t h o u t a m p l i f i c a t i o n . He c a n a u d i t o r i l y d i s c r i m i n a t e between t h r e e f a m i l i a r s e n t e n c e s a t a t i m e , a l t h o u g h he much p r e f e r s t o do t h e t a s k s w i t h s p e e c h r e a d i n g . He p r a c t i c e s h i s a u d i t o r y t r a i n i n g homework w i t h h i s s o c i a l w o rker w i t h i n t e r e s t . H o p e f u l l y , w i t h t h e d e v e l o p m e n t o f h i s a u d i t o r y and c o m m u n i c a t i v e c o n f i d e n c e , t h i s s u b j e c t w i l l c o n t i n u e t o p r o g r e s s . 123 S u b j e c t * B4 12$ -10 s 0 « 10 AN 20 CO 30 z - J 40 UJ > SO u • J o 60 HO 70 V) Ul to cc z t- 90 o z IOO cr 2 110 z 120 250 AUDIOGRAM FREQUENCY IN Hz 500 1000 2000 4000 1000 c fv \ N , fc-c \ \ V r\ \ V >-/ X 0 o c I > k — * s J > o -10 0 10 20 30 40 SO •0 70 •0 90 100 110 120 K e y : X l e f t e a r 0 r i g h t e a r A a i d e d w i t h c o n v e n t i o n a l a i d C a i d e d w i t h c o n v e n t i o n a l a i d p l u s c o m p r e s s o r S p e e c h A w a r e n e s s T h r e s h o l d M o s t C o m f o r t a b l e L e v e l T h r e s h o l d o f D i s c o m f o r t U n a i d e d dBHL A i d e d dBHL r i g h t l e f t c o n v e n t i o n a l 105 95 40 105+ 105+ 65 105+ 105+ • 90 c o m p r e s s o r 30 55 85 • F i g 6 .6 A u d i o l o g i c a l i n f o r m a t i o n s u b j e c t * B4 124 V I - 8 Case S t u d y S u b j e c t * B4 T h i s s u b j e c t i s f emale aged 55 y e a r s . She began t o l o s e her h e a r i n g a t age 16 due t o o t o s c l e r o s i s . She has had u n s u c c e s s f u l s u r g e r y on b o t h e a r s ; she has been a h e a r i n g a i d u s e r f o r 30 y e a r s . At p r e s e n t she wears a b e h i n d - t h e - e a r a i d f o r her l e f t e a r o n l y . She i s employed as an o f f i c e c a r e t a k e r and has v e r y good s p e e c h r e a d i n g s k i l l s . She has had no p r i o r a u r a l r e h a b i l i t a t i o n e x c e p t f o r h e a r i n g a i d c o u n s e l l i n g . She has been seen f o r n i n e s e s s i o n s , t h r e e f o r i n i t i a l e v a l u a t i o n and s i x f o r t h e r a p y . From t h e h e a r i n g a i d e v a l u a t i o n she was found t o be a p p r o p r i a t e l y f i t t e d and she p r e f e r r e d her own h e a r i n g a i d model t o o t h e r model s of a i d s a v a i l a b l e i n t h e p r o j e c t . S i n c e her own model was one of t h e model s used i n t h e p r o j e c t , she was s i m p l y g i v e n t h e same model w i t h the d i r e c t a u d i o i n p u t o p t i o n . W i t h t h e a i d p l u s c o m p r e s s o r she was a b l e t o d e t e c t w a r b l e d t o n e s a t 1000 t o 3000 Hz s i g n i f i c a n t l y b e t t e r t h a n w i t h her c o n v e n t i o n a l a i d (see F i g . 6 . 6 ) . On the GASP I she c o u l d d e t e c t a l l speech sounds e x c e p t f o r / s / , / f / , / t h / and / s h / but was u n a b l e t o d i s c r i m i n a t e between them. She i d e n t i f i e d 9 out of 14 words on t h e GASP I I but was u n a b l e t o answer any o f t h e f a m i l i a r s e n t e n c e s on the GASP I I I t e s t . A l l t h i s t e s t i n g was done w i t h t h e c o m p r e s s o r and t h e a i d but was not done w i t h t h e c o n v e n t i o n a l a i d a l o n e . When she was g i v e n t h e c o m p r e s s o r , she wore i t about 4 h o u r s p e r d a y , a t home and a t w o r k , f o r about a week. She found i t v e r y f r u s t r a t i n g and n o i s y . F o l l o w i n g t h i s , she d e v e l o p e d ea r d r a i n a g e p r o b l e m s f o r w h i c h she had m e d i c a l a t t e n t i o n . D u r i n g t h i s t i m e her h e a r i n g was f l u c t u a t i n g , l i m i t i n g her 1 25 a b i l i t y t o use a m p l i f i c a t i o n . I n i t i a l l y , she d e s c r i b e d t h e s o u n d q u a l i t y a s " h o a r s e " and "not c l e a r " b u t f o l l o w i n g a m o d i f i c a t i o n t o t h e c o m p r e s s o r t o i n c r e a s e t h e s i g n a l t o n o i s e r a t i o (Model 3D t o Model 3 E ) , she d e s c r i b e d i t a s "much c l e a r e r " . In t h e r a p y she i s a b l e t o d i s c r i m i n a t e up t o n i n e f a m i l i a r p h r a s e s a t a t i m e and i s a b l e t o f o l l o w t h e p r i n t e d t e x t o f a t a p e r e c o r d i n g w i t h o u t a s s i s t a n c e . She i s a l s o a b l e t o d e t e c t e n v i r o n m e n t a l s ounds, e . g . phone r i n g i n g a t 2 m e t e r s , k e y s j a n g l i n g a t 1 meter, w h i c h she i s u n a b l e t o h e a r w i t h t h e c o n v e n t i o n a l a i d a l o n e . When h e r e a r d r a i n a g e had c l e a r e d up, she u s e d t h e c o m p r e s s o r more f r e q u e n t l y and p r a c t i s e d a u d i t o r y t r a i n i n g e x e r c i s e s w i t h h e r son, who a t t e n d e d one of t h e March t h e r a p y s e s s i o n s w i t h h e r . She f o u n d t h e c o m p r e s s e d s p e e c h sound more c o m f o r t a b l e t o l i s t e n t o w h i l e s p e e c h r e a d i n g . As t r a i n i n g t i m e w i t h t h e c o m p r e s s o r i n c r e a s e s and she d e v e l o p s more c o n f i d e n c e i n h e r a u d i t o r y s k i l l s , t h i s s u b j e c t w i l l c o n t i n u e t o p r o g r e s s . 126 S u b j e c t / / B5 -10 s 0 HI t 10 AN 20 CO n 90 Z - i 40 u > SO Ui « i O eo _ i OH 70 1 0 Ui 80 oc X » 0 o z 100 2 110 X 120 250 AUDIOGRAM FREQUENCY IN Hx 500 1000 2000 4000 •000 t \ / \ > \ \ \ \ > t \ \ r Q 1 I O •V 5 o 1—*-< ) O -10 0 10 20 30 40 SO •0 70 •0 •0 100 110 120 K e y : X l e f t e a r 0 r i g h t e a r A a i d e d w i t h c o n v e n t i o n a l a i d C a i d e d w i t h c o n v e n t i o n a l a i d p l u s c o m p r e s s o r U n a i d e d dBHL S p e e c h A w a r e n e s s T h r e s h o l d M o s t C o m f o r t a b l e L e v e l T h r e s h o l d o f D i s c o m f o r t r i g h t 85 95 105 l e f t 100 105+ 105+ A i d e d dBHL l e f t e a r o n l y c o n v e n t i o n a l c o m p r e s s o r 40 25 65 55 90+ 90+. F i g 6 . 7 A u d i o l o g i c a l i n f o r m a t i o n s u b j e c t / / B5 127 V I - 9 Case S tudy Sub jec t# B5 T h i s s u b j e c t i s a m a l e , aged 42 y e a r s . He l o s t h e a r i n g i n h i s r i g h t ea r a t age 6 from mumps and i n h i s l e f t ear a t age 18 f rom a m a s t o i d i n f e c t i o n and from s u r g e r y f o l l o w i n g c h r o n i c m i d d l e ear i n f e c t i o n s . He used a "body s t y l e " h e a r i n g a i d w h i l e he was i n s c h o o l but he s t o p p e d a l l h e a r i n g a i d use when he became p r o f o u n d l y deaf i n b o t h e a r s . He i s employed as a m a c h i n i s t . He i s a v e r y good s p e e c h r e a d e r and knows f i n g e r s p e l l i n g , w h i c h he has t r i e d t o encourage h i s f a m i l y t o u s e . He has been seen f o r n i n e s e s s i o n s , t h r e e f o r i n i t i a l e v a l u a t i o n and s i x f o r t h e r a p y . D e s p i t e a g r e a t e r amount of m e a s u r a b l e r e s i d u a l h e a r i n g i n h i s r i g h t e a r , he had much b e t t e r t o l e r a n c e f o r sound i n h i s l e f t e a r . H i s a b i l i t y t o d e t e c t a w a r b l e d tone a t 2000 Hz i s m a r k e d l y improved w i t h t h e c o m p r e s s o r sy s tem o v e r c o n v e n t i o n a l a m p l i f i c a t i o n (see F i g . 6 . 7 ) . One t h e r a p y s e s s i o n began w i t h h i s r e p o r t of h e a r i n g a s i r e n t h r o u g h t h e compres sor s y s t e m . H a v i n g not h e a r d one f o r many y e a r s , he was o n l y f a m i l i a r w i t h t h e s l o w l y w a i l i n g t y p e , and e x p r e s s e d s u r p r i s e a t t h e h i g h e r m o d u l a t i o n r a t e of modern e l e c t r o n i c s i r e n s . W i t h t h e c o m p r e s s o r , he c o u l d d e t e c t many sounds t h a t he had not h e a r d f o r a l o n g t i m e e . g . k n o c k i n g , keys r a t t l i n g , t e l e p h o n e r i n g i n g , but remarked t h a t speech sounded l i k e "quack quack q u a c k " . However , he c o u l d i m i t a t e a r h y t h m p a t t e r n and f e l t t h a t t h e sound enhanced h i s speech r e a d i n g . I t i s s i g n i f i c a n t t h a t t h i s s u b j e c t was not used t o h e a r i n g any s o u n d , so he c o u l d not s u b j e c t i v e l y d i s t i n g u i s h t h e changes i n h i s a u d i t o r y r e s p o n s e due t o t h e compres sor v e r s u s t h o s e due t o a m p l i f i c a t i o n a l o n e . He i s no t b o t h e r e d by b a c k g r o u n d n o i s e , as 1 28 r e p o r t e d by some o t h e r s u b j e c t s . On t h e GASP II he was a b l e t o i d e n t i f y 7 o u t o f 14 words w i t h t h e a i d p l u s t h e c o m p r e s s o r . GASP I and I I I were not a t t e m p t e d . F o r t h e f i r s t t h r e e weeks he wore t h e c o m p r e s s o r t o work. U n f o r t u n a t e l y , t h e f a c t o r y where he works i s q u i t e n o i s y ; a l t h o u g h he became u s e d t o l i s t e n i n g t o n o i s e i t was of l i t t l e b e n e f i t i n u n d e r s t a n d i n g . A l t h o u g h he a t t e m p t e d t o p r a c t i s e h i s a u d i t o r y t r a i n i n g homework w i t h h i s w i f e , i t was o n l y a f t e r she was a b l e t o a t t e n d a t h e r a p y s e s s i o n (#5) t h a t t h e y began h a v i n g s u c c e s s w i t h t h e e x e r c i s e s . He i s now w e a r i n g t h e c o m p r e s s o r a t home a f t e r work and on weekends, he d o e s f i n d t h a t t h e sounds a s s i s t him i n s p e e c h r e a d i n g . He was a b l e t o d i s c r i m i n a t e t h r e e f a m i l i a r p h r a s e s o f s i m i l a r l e n g t h u s i n g a u d i t o r y c u e s o n l y . He was a l s o a b l e t o f o l l o w t h e w r i t t e n t r a n s c r i p t o f a s h o r t t a p e r e c o r d e d s t o r y w i t h p r a c t i c e . T h i s s u b j e c t i s c l e a r l y d e v e l o p i n g h i s a u d i t o r y s k i l l s but r e q u i r e s c o n t i n u e d s u p p o r t and e n c o u r a g e m e n t . I t i s l i k e l y t h a t , as h i s a u d i t o r y c o n f i d e n c e i n c r e a s e s , he w i l l become a f u l l t i m e u s e r of t h e c o m p r e s s o r s y s t e m . 129 S u b j e c t / / B6 8 to 2 < CD XJ z _ J U l > UJ O z in u cc X *-o z E 2 X -10 0 10 20 30 40 SO 60 70 80 90 100 110 120 12S 250 AUDIOGRAM FREQUENCY IN Hi 500 1 000 2000 4000 9000 t K : - - - - ( s /• \ f V -> A \ L > r > \ I x n } < X u c •> / o -10 0 10 20 30 40 90 •0 70 •0 90 100 110 120 K e y : X l e f t e a r 0 r i g h t e a r A a i d e d w i t h c o n v e n t i o n a l a i d C a i d e d w i t h c o n v e n t i o n a l a i d p l u s c o m p r e s s o r S p e e c h A w a r e n e s s T h r e s h o l d M o s t C o m f o r t a b l e L e v e l T h r e s h o l d o f D i s c o m f o r t U n a i d e d dBHL r i g h t "DNT DNT l e f t 90 DNT DNT A i d e d dBHL r i g h t e a r o n l y c o n v e n t i o n a l c o m p r e s s o r 50 35 65 60 90+ 90+. F i g . 6 . 8 A u d i o l o g i c a l i n f o r m a t i o n s u b j e c t / ^ B6 130 V I - 1 0 Case S tudy S u b j e c t # B6 T h i s s u b j e c t i s a female age 59 y e a r s . She has had a p r o g r e s s i v e h e a r i n g l o s s of unknown e t i o l o g y o v e r t h e p a s t 35 y e a r s . She has been a h e a r i n g a i d u s e r f o r 30 y e a r s and a t p r e s e n t wears a b e h i n d - t h e - e a r a i d f o r her r i g h t ear o n l y . She t r a i n e d as a n u r s e and i s p r e s e n t l y a homemaker. She moved t o Canada f rom Kenya a p p r o x i m a t e l y one y e a r a g o . A l t h o u g h her s p e e c h r e a d i n g s k i l l s a r e v e r y good w i t h h e r f a m i l y members i n b o t h E n g l i s h and G u j a r a t i , she f i n d s i t v e r y d i f f i c u l t t o u n d e r s t a n d t h e C a n a d i a n a c c e n t . She f r e q u e n t l y needed t o have t h i n g s w r i t t e n by t h e t h e r a p i s t b u t , as she became more f a m i l i a r w i t h t h e a u d i o l o g i s t , her s p e e c h r e a d i n g i m p r o v e d . She has had no p r i o r a u r a l r e h a b i l i t a t i o n e x c e p t f o r h e a r i n g a i d c o u n s e l l i n g . She has been seen f o r s i x s e s s i o n s , t h r e e f o r i n i t i a l e v a l u a t i o n and t h r e e f o r t h e r a p y . D u r i n g t h e h e a r i n g a i d e v a l u a t i o n , a new a i d was found w i t h w h i c h she r e sponded b e t t e r on sound f i e l d t e s t i n g ; she a l s o s u b j e c t i v e l y p r e f e r r e d t h i s a i d . Use o f t h e a i d p l u s compres sor e n a b l e d her t o d e t e c t a 2000 Hz w a r b l e d tone a t 10 dB b e t t e r and a 3000 Hz tone a t 25 dB b e t t e r t h a n w i t h t h e c o n v e n t i o n a l a i d (see F i g . 6.8). I n i t i a l l y , she was q u i t e h o p e f u l t h a t t h e c o m p r e s s o r would e n a b l e h e r t o " s o l v e " a l l her c o m m u n i c a t i o n d i f f i c u l t i e s (an i m p r e s s i o n w h i c h we were v e r y c a r e f u l no t t o g e n e r a t e i n any p o t e n t i a l s u b j e c t ) and she wore the c o m p r e s s o r s e v e r a l h o u r s per day f o r t h e f i r s t week. She found t h e sound bothersome and r e p o r t e d t h a t i t gave her a headache and a g g r a v a t e d her t i n n i t u s . She t h e n f e l t u n w e l l f o r about a week and d i d not use 131 t h e c o m p r e s s o r v e r y much. The n e x t week, she t r i e d f o l l o w i n g t e l e v i s i o n shows; she was e n c o u r a g e d t o o b t a i n a c a p t i o n d e c o d e r i n o r d e r t o f a c i l i t a t e u n d e r s t a n d i n g . The GASP t e s t was n o t a d m i n i s t e r e d and t h e r a p y f o c u s s e d on f a c i l i t a t i n g b o t h s p e e c h r e a d i n g and a u d i t o r y t r a i n i n g . At t h e end of t h e s t u d y , t h i s s u b j e c t i s f e e l i n g e n c o u r a g e d but she r e q u i r e s a g r e a t d e a l of s u p p o r t and a s s u r a n c e . Her c o m m u n i c a t i o n s k i l l s a r e i m p r o v i n g and she s h o u l d f i n d t h e c o m p r e s s o r more c o m f o r t a b l e t o wear and c o n t i n u e t o p r o g r e s s . 132 S u b j e c t * B7 '125 -10 s 0 • 10 55 AN 20 CD T3 30 z _ i 40 w > 50 _l D eo _J HO 70 M UJ to CC z »- 90 o z too 2 110 z 120 250 AUDIOGRAM FREQUENCY IN Hz 500 1000 2000 4000 9000 \ I V • \ / • • 1 ( \ < •> \ ? < > i \ V / c > ( 5 •10 0 10 20 30 40 50 •0 70 •0 90 100 110 120 K e y : X l e f t e a r 0 r i g h t e a r A a i d e d w i t h c o n v e n t i o n a l a i d C a i d e d w i t h c o n v e n t i o n a l a i d p l u s c o m p r e s s o r S p e e c h A w a r e n e s s T h r e s h o l d M o s t C o m f o r t a b l e L e v e l T h r e s h o l d o f D i s c o m f o r t U n a i d e d dBHL r i g h t 80 95 105+ l e f t 75 100 105+ A i d e d dBHL r i g h t e a r o n l y c o n v e n t i o n a l c o m p r e s s o r 25 30 50 50 85 85 . F i g . 6 . 9 A u d i o l o g i c a l i n f o r m a t i o n s u b j e c t * B7 133 VI-11 Case S t u d y S u b j e c t # B7 T h i s s u b j e c t i s a male aged 40 y e a r s . He i s p r e l i n g u a l l y d e a f , e i t h e r s i n c e b i r t h or s i n c e an i l l n e s s a t age 18 months. He was f i r s t f i t t e d w i t h a i d s a t age 4 and was e d u c a t e d i n r e g u l a r p u b l i c s c h o o l s and r e c e i v e d t u t o r i n g and s p e e c h t h e r a p y f r o m t e a c h e r s f o r t h e h e a r i n g i m p a i r e d . He p r e s e n t l y wears a b e h i n d - t h e - e a r a i d f o r h i s r i g h t e a r o n l y . He i s a c u r r e n t l y unemployed p r i n t e r . He i s a v e r y good s p e e c h r e a d e r . He d o e s no t know s i g n l a n g u a g e . He has been seen f o r f i v e s e s s i o n s , t h r e e f o r i n i t i a l t e s t i n g , and two f o r t h e r a p y . On h e a r i n g a i d e v a l u a t i o n , he was found, t o o b t a i n b e t t e r a i d e d f u n c t i o n w i t h one o f t h e p r o j e c t a i d s t h a n w i t h h i s own, b o t h i n sound f i e l d t e s t i n g and i n s u b j e c t i v e r e a c t i o n . W i t h t h e c o m p r e s s o r , t h e r e was a s l i g h t improvement i n t h e d e t e c t i o n o f 2000 Hz w a r b l e d t o n e ( s e e F i g . 6 . 9 ) . He d e s c r i b e d t h e c o m p r e s s o r as g i v i n g t o s p e e c h a " d u l l r a s p y " s o u n d, w i t h h i s own v o i c e h a v i n g an u n p l e a s a n t " r a s p y " q u a l i t y . He i s a l s o b o t h e r e d by b a c k g r o u n d e n v i r o n m e n t a l sounds which., when p r o c e s s e d by t h e c o m p r e s s o r , sound l i k e " h i s s i n g " and " c l i c k i n g " . He r e p o r t s t h a t he c o u l d h e a r t h e t e l e p h o n e r i n g w i t h t h e c o m p r e s s o r , and not w i t h c o n v e n t i o n a l a i d s . On t h e GASP t e s t s , he c o u l d d e t e c t a l l t h e s p e e c h sounds e x c e p t /if a n d / t h / b u t was u n a b l e t o i d e n t i f y any o f them. He i d e n t i f i e d 4 o u t o f 14 s i n g l e words and c o u l d n o t answer any f a m i l i a r q u e s t i o n s . T h e s e t e s t s were a d m i n i s t e r e d w i t h t h e c o m p r e s s o r s y s t e m o n l y . He was a b l e t o d i s c r i m i n a t e up t o 4 f a m i l i a r s e n t e n c e s of s i m i l a r l e n g t h , u s i n g a u d i t o r y c u e s o n l y , 134 and he was a b l e t o f o l l o w t h e p r i n t e d t r a n s c r i p t o f a t a p e r e c o r d e d s h o r t s t o r y . T h i s s u b j e c t i s d e f i n i t e l y i m p r o v i n g i n h i s a b i l i t y t o use t h e c o m p r e s s o r . W i t h f u r t h e r t h e r a p y and e n c o u r a g e m e n t he w i l l c o n t i n u e t o p r o g r e s s i n d e v e l o p i n g h i s a u d i t o r y a b i l i t i e s and h i s c o n f i d e n c e i n l i s t e n i n g . 1 35 VI-12 Summary of T e s t R e s u l t s The d a t a a n a l y s i s p r o c e d u r e s g i v e n i n s e c t i o n VI-2 were f o l l o w e d . Seven of t h e 13 MAC s u b t e s t s were j u d g e d o b v i o u s l y t o o d i f f i c u l t . F o r t h e 6 s u b t e s t s r e m a i n i n g , p and a were c a l c u l a t e d and 68 s c o r e s f u l f i l l e d t h e c r i t e r i o n : R > p + 1.65a. I f t h e t e s t r e s u l t s were t o t a l l y random w i t h a G a u s s i a n d i s t r i b u t i o n , we would e x p e c t o n l y 8 t o f u l f i l t h i s c r i t e r i o n . At t h i s p o i n t , two s u b j e c t s (#B3 and #B6) had no s u b t e s t s l e f t and one s u b j e c t (#B5) had o n l y one s u b t e s t l e f t . In r e t r o s p e c t , s i m p l e r s u b t e s t s would have been more a p p r o p r i a t e f o r t h e s e s u b j e c t s . A l l r e m a i n i n g t e s t s c o r e s were c o n v e r t e d t o p r o p o r t i o n a l s c o r e s by a p p l i c a t i o n o f : S = R - ( 1 0 0 - R ) p / ( 1 0 0 - p ) . The f o l l o w i n g q u a n t i t i e s : ave MAC p o s t a i d - ave MAC p r e a i d = 7% and ave MAC p o s t comp - ave MAC p r e comp = 12% show f i r s t l y t h a t c o m p r e h e n s i o n i n c r e a s e d o v e r t h e t r a i n i n g t i m e f o r b o t h t h e c o m p r e s s o r and w i t h t h e a i d a l o n e . The r e l i a b i l i t y of t h e c o m p r e s s o r i n c r e a s e i s " e x c e l l e n t " ( a l l s u b j e c t s showed an i n c r e a s e ) and t h e r e l i a b i l i t y o f t h e a i d i n c r e a s e i s "good" ( a l l s u b j e c t s e x c e p t #B4 showed an i n c r e a s e ) . S e c o n d l y , t h e q u a n t i t i e s show a l a r g e r i n c r e a s e i n c o m p r e s s o r s c o r e s t h a n a i d s c o r e s o v e r t i m e . The r e l i a b i l i t y o f t h i s t r e n d i s "good" ( a l l but #B5); p e r h a p s a l i t t l e b e t t e r t h a n "good" s i n c e #B5 had o n l y one s u b t e s t i n c l u d e d i n t h e s e r e s u l t s . T h e s e r e s u l t s c o n f i r m t h a t t h e s l o p e s o f t h e l e a r n i n g c u r v e s i n F i g . 5.2 a f t e r t h e i n t r o d u c t i o n o f a i d s a r e p o s i t i v e and t h a t t h e s l o p e o f t h e c o m p r e s s o r l e a r n i n g c u r v e i s g r e a t e r . 136 The q u a n t i t i e s : ave MAC p r e a i d = 47% and ave MAC p r e comp = 40% show t h a t a t t h e i n t r o d u c t i o n of t h e a i d s , t h e c o m p r e s s o r c o m p r e h e n s i o n i s l o w e r t h a n t h a t w i t h t h e c o n v e n t i o n a l a i d , as shown i n F i g . 5 . 2 . The r e l i a b i l i t y of t h e t r e n d i s " g o o d " . The q u a n t i t i e s : ave MAC p o s t a i d = 54% and ave MAC p o s t comp = 52% show t h a t t h e end of t h e t r a i n i n g t i m e i s v e r y near t o t h e c r o s s o v e r p o i n t i n F i g . 5 . 2 . The f a c t t h a t e x a c t l y h a l f of t h e s u b j e c t s s c o r e d h i g h e r w i t h t h e c o m p r e s s o r and h a l f l o w e r (one s t a y e d t h e same) c o n f i r m s t h a t we a r e c l o s e t o t h e c r o s s o v e r p o i n t . The a v e r a g e a i d s c o r e i s h i g h e r , so t h a t on a v e r a g e , t h e end of t h e s t u d y f a l l s a l i t t l e s h o r t of t h e c r o s s o v e r p o i n t . Two s u b j e c t s were e l i m i n a t e d f rom t h e s p e e c h r e a d i n g s c o r e s as t h e i r t e s t s were e i t h e r i n c o m p l e t e or low and u n r e l i a b l e . These s u b j e c t s (#B3 and #B6) a r e t h e same ones who had no MAC s u b t e s t s h i g h enough t o pa s s t h e random r e s p o n s e c r i t e r i o n . The q u a n t i t i e s : ave SR p o s t a i d - ave SR p r e a i d = 5% and ave SR p o s t comp - ave SR p r e comp = 9% show a g a i n w i t h " e x c e l l e n t " r e l i a b i l i t y t h a t t h e c o m p r e s s o r l e a r n i n g c u r v e i s p o s i t i v e a f t e r t h e i n t r o d u c t i o n of a i d s , and w i t h " f a i r " r e l i a b i l i t y t h a t t h e h e a r i n g a i d c u r v e i s p o s i t i v e . M o r e o v e r , t h e c o m p r e h e n s i o n i n c r e a s e was g r e a t e r w i t h t h e c o m p r e s s o r w i t h " g o o d " r e l i a b i l i t y . The q u a n t i t i e s : ave SR p r e a i d = 86% and 137 ave SR p r e comp = 75% show w i t h " e x c e l l e n t " r e l i a b i l i t y t h a t t h e c o m p r e s s o r s c o r e s a r e l o w e r when t h e sys tem i s f i r s t i n t r o d u c e d . F i n a l l y t h e q u a n t i t i e s : ave SR p o s t a i d = 91% and ave SR p o s t comp = 84% a l o n g w i t h t h e f a c t t h a t one s u b j e c t showed a h i g h e r c o m p r e s s o r s c o r e t h a n h e a r i n g a i d s c o r e , two showed t h e same s c o r e and two showed a h i g h e r a i d s c o r e i m p l y a n e a r n e s s t o t h e c r o s s o v e r p o i n t i n F i g . 5 . 2 . The H e a r i n g P e r f o r m a n c e I n v e n t o r y (HPI) i s a q u e s t i o n n a i r e of 90 i t e m s d e s i g n e d t o i n v e s t i g a t e t h e s u b j e c t s ' s u b j e c t i v e i m p r e s s i o n of how t h e i r h e a r i n g l o s s a f f e c t s t h e i r d a i l y l i v i n g . V a r i o u s e v e n t s , s i t u a t i o n s and r e a c t i o n s a r e e x p l o r e d u s i n g a s c a l e r a t i n g r a n g i n g from " p r a c t i c a l l y a l w a y s " t o " a l m o s t n e v e r " . The q u e s t i o n s come f rom t h e c a t e g o r i e s l i s t e d b e l o w . They a r e p r e c e d e d by t h e i r c o r r e s p o n d i n g a b b r e v i a t i o n s , w h i c h a r e used t h r o u g h o u t t h e d a t a p r e s e n t a t i o n . US /V U n d e r s t a n d i n g speech w i t h v i s u a l c u e s . US/NV U n d e r s t a n d i n g speech w i t h o u t v i s u a l cues I I n t e n s i t y . ( i s t h e sound l o u d enough f o r y o u t o h e a r ? ) RAF Response t o a u d i t o r y f a i l u r e (what do y o u do when you d o n ' t u n d e r s t a n d ? ) P P e r s o n a l ( e f f e c t of h e a r i n g l o s s on p e r s o n a l a c t i v i t i e s , and a t t i t u d e s ) S S o c i a l ( e f f e c t of h e a r i n g l o s s on s o c i a l a c t i v i t i e s , 138 u n d e r s t a n d i n g s p e e c h i n g r o u p s i t u a t i o n s ) 0 O c c u p a t i o n a l ( e f f e c t of h e a r i n g l o s s on work r e l a t e d a c t i v i t i e s ) The p o s t - t r a i n i n g minus p r e - t r a i n i n g s u b s c o r e s a p p e a r i n T a b l e 6.1. They a g a i n show a c o n s i s t e n t i n c r e a s e i n s u b j e c t i v e l i s t e n i n g a b i l i t y , as j u d g e d by t h e s u b j e c t s . T a b l e 6.2 H e a r i n g P e r f o r m a n c e I n v e n t o r y The numbers p r e s e n t e d h e r e a r e t h e d i f f e r e n c e s between t h e p o s t - and p r e - t r a i n i n g s c o r e s . I n c r e a s e s a p p e a r as p o s i t i v e numbers ( s e e t e x t ) . S u b j e c t # US/V US/NV I. RAF P S 0 1 1 3 15 9 20 1 6 19 12 2 -4 6 5 -7 1 1 -5 N/A 3 1 3 2 9 46 -8 22 N/A 4 3 7 1 1 -1 -12 4 -15 5 ' -8 0 2 -10 -27 -6 -14 6 19 0 4 13 8 1 1 N/A 1 40 A l l s u b j e c t s were a b l e t o r e s p o n d t o t h i s q u e s t i o n n a i r e e a s i l y . They f o u n d t h e q u e s t i o n n a i r e r e l e v a n t t o t h e i r e x p e r i e n c e s and e n j o y e d t h e o p p o r t u n i t y t o i n d i c a t e t h e i r p a r t i c u l a r d i f f i c u l t i e s . In g e n e r a l , p r e - t e s t s c o r e s were p o o r , l i k e l y due t o t h e s u b j e c t s ' p r o f o u n d d e g r e e o f h e a r i n g l o s s and l a c k of p r i o r a d u l t a u r a l r e h a b i l i t a t i o n e x p e r i e n c e ( e x c e p t s u b j e c t #B2), a s i d e from h e a r i n g a i d c o u n s e l l i n g . The two s u b j e c t s who a p p e a r e d t o be b e s t a d j u s t e d t o t h e i r h e a r i n g l o s s (#B2 and B 4 ) , a c c o r d i n g t o t h e i r d i s c u s s i o n s and manner w i t h t h e a u d i o l o g i s t , showed m i n i m a l change i n t h e i r p r e -t o p o s t - HPI s c o r e s . I t i s i n t e r e s t i n g t h a t b o t h t h e s e s u b j e c t s (#B2 and B4) had g r a d u a l l y p r o g r e s s i v e h e a r i n g l o s s e s o v e r 20 t o 30 y e a r s . A l l o f t h e o t h e r s u b j e c t s had e i t h e r sudden o r r a p i d l y p r o g r e s s i v e l o s s e s . Of t h e o t h e r s u b j e c t s , #B1, B3 and B6 showed marked improvement i n a b i l i t y t o u n d e r s t a n d s p e e c h w i t h v i s u a l c u e s , r e s p o n s e t o a u d i t o r y f a i l u r e , and a b i l i t y t o u n d e r s t a n d i n g r o u p s i t u a t i o n s . A d d i t i o n a l l y , #B1 showed improvement i n a l l c a t e g o r i e s . The a v e r a g e o f t h e p o s t - t r a i n i n g minus p r e - t r a i n i n g s c o r e s o v e r s u b j e c t s f o r e a c h c a t e g o r y ; and t h e a v e r a g e p o s t minus p r e s c o r e s o v e r c a t e g o r i e s f o r e a c h s u b j e c t a p p e a r b e l o w : U S / V U S / N V I RAF P S O 4 4 6 8 -1 6 13 141 #B1 #B2 #B3 #B4 #B5 #B6 #B7 1 5 1 14 0 -9 9 -4 The a v e r a g e o v e r s u b j e c t s and c a t e g o r i e s i s +4% As m e n t i o n e d i n C h a p t e r V, a t a p e r e c o r d i n g was made of e a c h s u b j e c t ' s s p e e c h b e f o r e a n d a f t e r t r a i n i n g . A new r e c o r d i n g was made from t h i s t a p e . In t h e new r e c o r d i n g , t h e p r e - t r a i n i n g c o n v e r s a t i o n was r e c o r d e d on one c h a n n e l , t h e p o s t -t r a i n i n g c o n v e r s a t i o n was r e c o r d e d on a n o t h e r , so t h a t one c o u l d s w i t c h back and f o r t h t o compare. No d i s c e r n a b l e change i n s p e e c h was n o t i c e d f o r any s u b j e c t . O p t i m a l f i t t i n g o f e a r m o u l d s , h e a r i n g a i d s and c o m p r e s s o r s t o o k more t i m e t h a n e x p e c t e d . W i t h o u t i n c l u d i n g t h e s e s s i o n s u s e d t o p r o p e r l y f i t t h e s u b j e c t s w i t h t h e e q u i p m e n t , t h e a v e r a g e number o f t h e r a p y s e s s i o n s was f o u r . P e r u s a l o f t h e s u b j e c t s ' d i a r i e s showed t h a t n ot much p r a c t i c e o c c u r r e d o u t s i d e o f t h e s e s s i o n s , p r o b a b l y b e c a u s e o f t h e i n i t i a l d i f f i c u l t y i n u n d e r s t a n d i n g a n d o f t h e e x t r a h a r d w a r e needed. The t r a i n i n g t i m e was p e r h a p s t r i p l e t h e t h e r a p y t i m e on a v e r a g e . T h i s g i v e s an a v e r a g e t r a i n i n g t i m e o f 12 h o u r s f o r t h e c o m p r e s s o r . I f we view t h e s p e e c h r e a d i n g t e s t a s a MAC s u b t e s t , we c a n make an a t t e m p t t o q u a n t i f y t h e l e a r n i n g c u r v e s f o r t h i s s t u d y , a v e r a g e d o v e r s u b j e c t s and s u b t e s t s . T h i s a p p e a r s i n F i g . 6.10. The d e t a i l e d s h a p e s a r e somewhat s c h e m a t i c , b u t t h e a v e r a g e s l o p e s o f t h e c u r v e s i n t h e a r e a between t h e d a s h e d l i n e s and t h e i r v a l u e s a t t h e end p o i n t s have been made t o match our n u m e r i c a l r e s u l t s . Some e v i d e n c e t h a t t h e c o m p r e s s o r c u r v e has Fig. 6.10 Average l e a r n i n g curves based on t e s t s c o r e s ; t r a i n i n g time with compressor i s approximately 12 Hrs 143 n o t y e t r e a c h e d a p l a t e a u i s a f f o r d e d by t h e r e s u l t s o f s u b j e c t #A2 whose a v e r a g e p o s t - t r a i n i n g MAC s c o r e s a r e 23% h i g h e r f o r t h e c o m p r e s s o r s y s t e m t h a n f o r t h e h e a r i n g a i d , and he r e p o r t s he i s s t i l l g e t t i n g b e t t e r . More e v i d e n c e t h a t t h e c o m p r e s s o r c u r v e i s s t i l l i n c r e a s i n g i s g i v e n by t h e s u b j e c t i v e i m p r e s s i o n s of t h e a u d i o l o g i s t and t h e s u b j e c t s . A l t h o u g h t h e c u r v a t u r e s of t h e l e a r n i n g c u r v e s i s t h e o r e t i c a l , we do e x p e c t t h e h e a r i n g a i d c u r v e t o p l a t e a u much s o o n e r t h a n t h e c o m p r e s s o r c u r v e , s i n c e t h e s u b j e c t s have l o n g been f a m i l i a r w i t h t h e c u e s f r o m t h e r e g u l a r a i d , w h i l e t h e c o m p r e s s o r sound i s q u i t e a new e x p e r i e n c e . I t s h o u l d a l s o be n o t e d t h a t t h r o u g h t h e s t u d y , t h e s u b j e c t s p r e f e r r e d t h e h e a r i n g a i d a l o n e , and when t h e y were n o t u s i n g t h e c o m p r e s s o r , t h e y were u s i n g t h e r e g u l a r a i d . T h i s means t h a t t h e t r a i n i n g t i m e f o r t h e a i d a l o n e i s a c t u a l l y v e r y much l o n g e r t h a n t h a t shown i n F i g . 6.10. The v a r i o u s r e s u l t s c o n f i r m i n g t h e g e n e r a l f e a t u r e s o f t h e l e a r n i n g c u r v e s a r e v e r y s t r o n g e v i d e n c e f o r t h e i m p o r t a n c e o f t r a i n i n g t i m e f o r t h i s s y s t e m and p r o b a b l y f o r any s y s t e m i n w h i c h s p e e c h c u e s a r e a l t e r e d . CHAPTER V I I DISCUSSIONS AND RECOMMENDATIONS 145 V I I - 1 D i s c u s s i o n T h i s work i n c l u d e s t h e f i r s t r e p o r t o f a s u b s t a n t i a l i n c r e a s e i n s p e e c h c o m p r e h e n s i o n f o r any f r e q u e n c y l o w e r i n g t e c h n i q u e o t h e r t h a n t r a n s p o s i t i o n , and c e r t a i n l y one o f t h e v e r y few f o r any t e c h n i q u e o t h e r t h a n a m p l i f i c a t i o n . A s i g n i f i c a n t r e s u l t i s s u b j e c t #A2 who i s p r e s e n t l y u s i n g t h e c o m p r e s s o r s y s t e m f u l l - t i m e . A new f r e q u e n c y c o m p r e s s i o n a l g o r i t h m was d e v i s e d r e t a i n i n g a l l t e m p o r a l i n f o r m a t i o n . T h i s a l g o r i t h m was r e a l i z e d a s a r e a l - t i m e , p o r t a b l e e l e c t r o n i c d e v i c e and u s e d i n a c l i n i c a l s t u d y . A l e a r n i n g c u r v e was p r e s e n t e d a s a h y p o t h e s i s . R e s u l t s o f t h e c l i n i c a l s t u d y c o n f i r m v a r i o u s a s p e c t s of t h e l e a r n i n g c u r v e , and t h e r e b y g i v e s t r o n g e v i d e n c e f o r t h e i m p o r t a n c e o f t r a i n i n g t i m e . T h i s c o n s t i t u t e s a p r o b a b l e e x p l a n a t i o n o f many n e g a t i v e r e s u l t s r e p o r t e d t o d a t e w i t h l i t t l e o r no t r a i n i n g t i m e i n c l u d e d . The c l i n i c a l s t u d y i n c o r p o r a t e d n o v e l f e a t u r e s , i n c l u d i n g : (a) an o p t i m a l c o n v e n t i o n a l a m p l i f i c a t i o n f i t t i n g ( w i t h new e a r m o u l d s f o r e v e r y s u b j e c t ) , (b) r e l a t i v e l y l o n g ( b ut p e r h a p s n o t q u i t e l o n g enough) t r a i n i n g t i m e s w i t h a p r o f e s s i o n a l c l i n i c a l a u d i o l o g i s t c o n d u c t i n g t h e r a p y and t e s t i n g and ( c ) a r e a l t i m e c o m p r e s s i o n d e v i c e w h i c h c a n be worn a s a h e a r i n g a i d . T h e r e a r e many f a c t o r s w h i c h c a n i n f l u e n c e t h e r e s u l t s o f t e s t s s u c h a s t h e ones u s e d h e r e . The d i f f i c u l t y o f t h e MAC t e s t f o r our s u b j e c t s was u n f o r t u n a t e b u t n o t u n e x p e c t e d , g i v e n t h e i r v e r y p r o f o u n d d e g r e e o f h e a r i n g l o s s . Not a s i n g l e s u b j e c t h a v i n g r e s i d u a l h e a r i n g i n t h e upper r a n g e o f o u r 146 c r i t e r i a was r e f e r r e d . T r a i n i n g t i m e i n t h i s s t u d y i s below t h a t recommended f o r t h e r a p y ( c f . B a t e , 1980) . There i s l i t t l e doubt however , t h a t t h e s p e e c h r e a d i n g s k i l l s ^of s u b j e c t #B5 have i n c r e a s e d u s i n g t h e c o m p r e s s o r s y s t e m . The a u d i o l o g i s t , t h e s u b j e c t ' s w i f e , and the s u b j e c t h i m s e l f a l l f e e l t h a t the e x t r a a u d i t o r y cues a r e a h e l p t o h i s s p e e c h r e a d i n g a b i l i t y . D e s p i t e t h e i n e v i t a b l e d i f f i c u l t i e s o f o b t a i n i n g adequate e a r m o u l d s , t h e t e c h n i c a l p r o b l e m s w i t h a i d s and c o m p r e s s o r s , and t h e i n i t i a l d i s c o u r a g e m e n t a f t e r t h e f i r s t week o r two of compres sor use t h a t a l l s u b j e c t s e x p e r i e n c e d due t o d i f f i c u l t y i n u n d e r s t a n d i n g compres sed s p e e c h , e v e r y o n e p e r s e r v e r e d . Most of the s u b j e c t s got t o t h e s t a g e of b e i n g more s u i t a b l y f i t t e d w i t h t h e i r s y s t e m s , and p e r s o n a l l y e x p e r i e n c e d renewed e n t h u s i a s m . They, g a i n e d a new awareness of t h e i r a u d i t o r y s k i l l s , a p p r e c i a t i n g t h a t t h e y c o u l d l e a r n t o r e c o g n i z e and u n d e r s t a n d f a m i l i a r sounds and speech by h e a r i n g o n l y . A l l s u b j e c t s a p p e a r e d t o be g a i n i n g c o n f i d e n c e i n t h e i r l i s t e n i n g , speech r e a d i n g and c o m m u n i c a t i o n s k i l l s . As of A p r i l 20 1984, o n l y s u b j e c t #A2 was u s i n g t h e compres sor f u l l t i m e . S u b j e c t s #B3 and B5 b o t h l i k e t o have p e r i o d s of no h e a r i n g a i d use d u r i n g t h e d a y . The o t h e r s u b j e c t s r e p o r t e d t h a t u n d e r s t a n d i n g speech i s s t i l l e a s i e r w i t h t h e c o n v e n t i o n a l h e a r i n g a i d . However , e v e r y o n e a p p e a r e d t o be i m p r o v i n g i n t h e i r a u d i t o r y s k i l l s w i t h t h e c o m p r e s s o r , p a r t i c u l a r l y i n t h e d i s c r i m i n a t i o n of rhythm and i n t o n a t i o n and the d i s c r i m i n a t i o n of f a m i l i a r s e n t e n c e s of s i m i l a r l e n g t h . E n v i r o n m e n t a l sounds were becoming more f a m i l i a r and i d e n t i f i a b l e . 147 I t i s i n t e r e s t i n g t o n o t e t h a t a l l s u b j e c t s p r e f e r t h e c o n v e n t i o n a l h e a r i n g a i d s t h e y were f i t t e d w i t h f o r t h e p r o j e c t t o t h e i r own a i d s . They a l s o s u b j e c t i v e l y p r e f e r t h e c o m p r e s s o r t o be f i t t e d t o t h e o p t i m a l c o n v e n t i o n a l a i d t h a n t o any o f t h e o t h e r p r o j e c t a i d s . S u b j e c t s were shown how t o o p e r a t e t h e h e a r i n g a i d t o n e c o n t r o l (low c u t f i l t e r ) t o a d j u s t t h e a i d t o t h e most c o m f o r t a b l e sound q u a l i t y when u s e d as a c o n v e n t i o n a l a i d , or when u s e d w i t h t h e c o m p r e s s o r . D e s p i t e i n f o r m a l t r i a l s w i t h b i n a u r a l f i t t i n g s , s u b j e c t s #B1 t o B7 p r e f e r r e d h a v i n g a m p l i f i c a t i o n t o one e a r o n l y . T h e r e a p p e a r t o be two s e r i o u s l i m i t i n g f a c t o r s i n t h i s s t u d y : t h e n a t u r e o f t h e p o p u l a t i o n u s e d and t h e t r a i n i n g / t h e r a p y t i m e a l l o w e d . R e g a r d i n g t h e f i r s t l i m i t i n g f a c t o r , a l l of t h e s u b j e c t s have v e r y l i m i t e d r e s i d u a l h e a r i n g . A l t h o u g h t h e r e f e r r a l c r i t e r i a c a l l e d f o r s u b j e c t s w i t h a g r e a t e r amount o f r e s i d u a l h e a r i n g i n t h e low f r e q u e n c i e s , g i v i n g more o f a " s l o p i n g " e f f e c t t o t h e a u d i o g r a m , no one w i t h t h a t t y p e of l o s s p a t t e r n was r e f e r r e d . A g r e a t e r d e g r e e o f l e a r n i n g c o u l d have been e x p e c t e d i f t h e s u b j e c t s had had more h e a r i n g w i t h w h i c h t o work. D e s p i t e a c c e p t i n g a l l r e f e r r a l s w h i c h met t h e c r i t e r i a , o n l y s i x s u b j e c t s were o b t a i n e d . A f t e r i n i t i a l t e s t i n g s e s s i o n s w i t h s e v e r a l p o t e n t i a l s u b j e c t s who were f o u n d t o have t o o much h i g h f r e q u e n c y h e a r i n g , a s e v e n t h s u b j e c t who was p r e l i n g u a l l y d e a f was a c c e p t e d i n o r d e r t o i n c r e a s e t h e number o f s u b j e c t s . Most o f t h e s u b j e c t s l a c k e d p r e v i o u s a u r a l r e h a b i l i t a t i o n e x p e r i e n c e . S u b j e c t s #B2 and B7, who had had p r e v i o u s e x p e r i e n c e , a p p e a r e d s u b s t a n t i a l l y more c o n f i d e n t i n t h e i r 1 48 o v e r a l l c o m m u n i c a t i o n and had l e s s need t o t a l k a b o u t t h e p r o b l e m s t h e y e x p e r i e n c e b e c a u s e of t h e i r h e a r i n g l o s s . They c o u l d a l s o t a l k more e a s i l y a b o u t t h e i r f e e l i n g s and e m o t i o n a l r e a c t i o n s t o c o m m u n i c a t i o n s u c c e s s and f a i l u r e , and t o f r u s t r a t i o n w i t h h e a r i n g a i d p r o b l e m s . T h i s g r e a t e r d e g r e e of i n s i g h t a l l o w e d t h e t h e r a p y t i m e f o r t h e s e two s u b j e c t s t o be f o c u s s e d more on p r e s e n t n e e d s . The s e c o n d l i m i t i n g f a c t o r i s t h e t i m e c o n s t r a i n t due t o t h e c o n t r a c t u a l n a t u r e o f t h e s t u d y . As o f M a r c h 31 1984, t h e number of t h e r a p y s e s s i o n s p e r s u b j e c t r a n g e d from two t o s i x w i t h an a v e r a g e o f f o u r . In a u r a l r e h a b i l i t a t i o n , g e n e r a l l y a t r i a l p e r i o d o f s i x t o t w e l v e weeks i s a l l o w e d b e f o r e d e c i d i n g whether improvement i s s u f f i c i e n t t o w a r r a n t f u r t h e r t h e r a p y . S e v e r a l more weeks of t h e r a p y t i m e would have a l l o w e d more i n i t i a l f i t t i n g and t r a i n i n g i n t h e t h e r a p y s e t t i n g p r i o r t o a l l o w i n g t h e s u b j e c t s t o use t h e c o m p r e s s o r f u l l - t i m e . T h i s q u i t e l i k e l y c o u l d have a v o i d e d t h e i n i t i a l d i s c o u r a g e m e n t t h a t t h e s u b j e c t s e x p e r i e n c e d when t h e y u s e d t h e c o m p r e s s o r f u l l - t i m e b e f o r e t h e y had been f i t t e d o p t i m a l l y o r i n t r o d u c e d t o t a s k s t h a t t h e y c o u l d be r e a s o n a b l y e x p e c t e d t o do a t t h e i n i t i a l s t a g e s . The m o n i t o r i n g o f t h e l e a r n i n g c u r v e s was i m p o s s i b l e i n t h e t i m e a l l o t t e d f o r t h e s t u d y b ut i t i s f e l t t h a t most s u b j e c t s a r e a t a p o i n t where t h e c o n v e n t i o n a l a i d i s s t i l l more u s e f u l o v e r a l l and t h e i r p e r f o r m a n c e w i t h t h e c o m p r e s s o r i s j u s t c a t c h i n g up w i t h t h e i r p e r f o r m a n c e w i t h t h e a i d a l o n e . 1 49 V I I - 2 Recommendations One of t h e p u r p o s e s o f t h e s t u d y under t h e government c o n t r a c t 'was t o recommend whether o r n o t t h e s e s t u d i e s s h o u l d c o n t i n u e . The i n v e s t i g a t o r s a l l a g r e e t h a t t h e y s h o u l d , w i t h t h e i m p l e m e n t a t i o n of s e v e r a l c h a n g e s m o t i v a t e d by t h e p r e s e n t s t u d y . T h e r e f o r e , t h e f o l l o w i n g r e commendations a r e made: 1. The F e d e r a l Government s h o u l d f u n d a f u r t h e r s t u d y o f t h i s d e v i c e a s t h e n e x t l o g i c a l s t e p i n an o n g o i n g r e s e a r c h and d e v e l o p m e n t p r o g r a m . T h i s f u r t h e r s t u d y s h o u l d i n c o r p o r a t e t h e c h a n g e s p r e s e n t e d h e r e i n : 2. A s t u d y w i t h a minimum o f 50 s u b j e c t s and l a s t i n g a t l e a s t 12 c a l e n d a r months i n o r d e r t o f u l f i l l a l l r e q u i r e d t a s k s . T h i s w i l l p r o v i d e a d e q u a t e t i m e f o r s u b j e c t s e l e c t i o n , o r i e n t a t i o n , f i t t i n g , t r a i n i n g and e v a l u a t i o n . 3. The s e l e c t i o n o f t h e s u b j e c t s s h o u l d be g o v e r n e d by t h e f o l l o w i n g c r i t e r i a : a) The t i m e s i n c e h e a r i n g l o s s o n s e t c o u l d v a r y i n t h e s u b j e c t s . b) S u b j e c t s s h o u l d p r e f e r a b l y be r e c r u i t e d t h r o u g h e x i s t i n g a u r a l r e h a b i l i t a t i o n p r o g r a m s , and have had e x p e r i e n c e w i t h a p p r o p r i a t e c o n v e n t i o n a l h e a r i n g a i d s . T h i s w i l l a l l o w f o r a l a r g e r r a n g e o f s u b j e c t s w h i l e m i n i m i z i n g i n a p p r o p r i a t e r e f e r r a l s . A l s o , o n l y a d u l t s s h o u l d be i n c l u d e d i n t h e s t u d y . c) The s u b j e c t s s h o u l d i d e a l l y have a c o n v e r s a t i o n p a r t n e r a t home w i t h whom t o p r a c t i c e . 4. S u i t a b l e t e s t i n g m a t e r i a l s s h o u l d be o b t a i n e d o r p r e p a r e d , 150 p o s s i b l y by m o d i f i c a t i o n of t h e MAC t e s t ( w h i c h may i t s e l f p r o v e u s e f u l f o r s u b j e c t s w i t h more h e a r i n g ) o r by c o n s t r u c t i n g them from s i m i l a r m a t e r i a l s . The s u b j e c t s s h o u l d be a b l e t o s c o r e above c h a n c e i n t h e p r e - t r a i n i n g t e s t s . The t e s t s s h o u l d be s h o r t and e a s y enough t o be done q u i c k l y . T h i s would f a c i l i t a t e t e s t i n g i n o t h e r c e n t e r s . In o r d e r t o make m e a n i n g f u l measurements, d a t a must be c o l l e c t e d more o f t e n b e c a u s e o f t h e d a i l y v a r i a t i o n i n s p e e c h c o m p r e h e n s i o n a b i l i t y . T h i s w o u l d a l s o f a c i l i t a t e t h e measurement o f t h e l e a r n i n g c u r v e w i t h t h e c o m p r e s s o r . S u b j e c t s s h o u l d be e n c o u r a g e d t o keep a d i a r y . The f r u s t r a t i o n s of t h e s u b j e c t s c a n be k e p t t o a minimum i f t h e f o l l o w i n g p r o c e d u r e i s a d o p t e d : f i r m l y e s t a b l i s h a c o m f o r t a b l e s i t u a t i o n w i t h t h e h a r d w a r e , i n s t r u c t i o n i n s m a l l g r o u p s s h o u l d f o l l o w and t h e s u b j e c t s s h o u l d be a l l o w e d t o t a k e t h e c o m p r e s s o r home o n l y a f t e r t h e y have shown improvement i n l i s t e n i n g s k i l l s and c o n f i d e n c e . The use o f t a p e d m a t e r i a l s i s a good at-home p r a c t i c e method. T h i s medium c a n be u s e d t o p r a c t i s e m o n o s y l l a b i c word s p o n d e e s , n o n - s p e e c h i t e m s s u c h a s r i s i n g and f a l l i n g t o n e s , and s t o r i e s w i t h o r w i t h o u t t h e c o r r e s p o n d i n g p r i n t e d t e x t . Some t i m e s h o u l d , a l s o be s p e n t i n s t r u c t i n g t h e c o n v e r s a t i o n a l p a r t n e r ( s ) o f e a c h s u b j e c t , i n o r d e r t o i n c r e a s e t h e s u b j e c t ' s l e a r n i n g , n o t j u s t when t h e i n v e s t i g a t o r s ( a u d i o l o g i s t s ) a r e p r e s e n t , but a t home t o o . T h i s w i l l h e l p f a c i l i t a t e t r a n s f e r o f s k i l l s a c q u i r e d i n 151 t h e r a p y t o e v e r y d a y c o m m u n i c a t i o n s s i t u a t i o n s . 11. The s t u d y s h o u l d be c a r r i e d o u t s i m u l t a n e o u s l y and c o o p e r a t i v e l y i n s e v e r a l m e t r o p o l i t a n c e n t e r s where i d e n t i f i e d p o p u l a t i o n s a r e u t i l i z i n g e x i s t i n g r e h a b i l i t a t i o n r e s o u r c e s . C e n t r e s w i t h s u c h p o p u l a t i o n s w ould i n c l u d e T o r o n t o , M o n t r e a l , V a n c o u v e r , H a l i f a x , O t t a w a , C a l g a r y , and Edmonton. W i t h t h e f u r t h e r t e s t i n g o f t h i s t e c h n i q u e , c o m m e r c i a l i z a t i o n may r e s u l t . In any c a s e , i t i s t h e s i n c e r e hope of t h e a u t h o r , and t h o s e i n v o l v e d w i t h t h e p r o j e c t t h a t t h e work w i l l be o f h e l p i n more a p p r o p r i a t e l y a i d i n g t h e s e v e r e l y h e a r i n g i m p a i r e d . 152 A P P E N D I X I P o w e r S p e c t r u m o f t h e P e r i o d i c P r o c e s s i n g . A l g o r i t h m f o r a S i n u s o i d a l I n p u t F o r a n i n p u t o f cos(wt) t h e o u t p u t b e t w e e n t a n d t n + ^ i s : V t) - co. [ - | l^ SzI + V 2 I ] + cos [ . j ^  + V l j ] C o n s i d e r i n g j u s t t h e f i r s t t e r m , a n d u s i n g : C O S ( U T ) = hie + e } we o b t a i n a r e s u l t f o r t h e o u t p u t a t a l l t i m e : V n ( t ) = i [ Mcp{in>P5(t-t ,)+t )} + e xp { l u ( 5a ( t - t )+t . ) } ] 6 ( t - t ) 6 ( t -0 n=—oo ^ n-1 n-z n n-1 J n n+l b u t — = ^ + t _ - t/2 + (n-2 ) t - J5(n-1)T « ht + - 3T / 2 = Js { t+(n-3)T} 2. n-2 and t~tn + t , = ht + ( n - l ) i - '-sCnt) = Jjt + hm - T = * s { t+ (n-2)T} So t h a t , V Q ( t ) = I eh±^ £*»in-2)i { 1 + e - ^ i " T } e ( ) 6 ( ) = Z e ^ e J 5 i u ( n - 2 ) T e - l i l i i , T { 2 c o S ( l t a ) T ) } 6( )6( ) N e g l e c t i n g m u l t i p l i c a t i v e c o n s t a n t s , t h e F o u r i e r t r a n s f o r m b e c o m e s co /- W t _ VQCOJ') •= / e ~ " V Q ( t ) dt „ . _ >siu)(n-2)T - J J I U T / K f e i i - c o ' H . t COSCSCOT) I e e I e dt / t n 153 L e t t h e i n t e g r a l be d e n o t e d by / t h e n , r = 1 riCsu-w 1) t n + i i(Jsa>-w' ) t n , J i ( W ) l e and V Q i s g i v e n b y : V n(w') = COS ( *£U)T) I e e -pr rr e sinU ^ a - a ) )hx} U v.'SuJ—u) ) = COSC^WT) e e e — j \ I e The sum i s p r o p o r t i o n a l t o I — 6(a)-u ) T T So t h a t t h e o u t p u t i s g i v e n by 7 0( U') = c o s ( ^ x ) e e I 6 (w-u>' - — ) The power s p e c t r u m = P(w') = jVQ(to') | a n d , 0 f o r (u-°° f o r (OJ-O)') (n-m) =2iTk So t h a t , 1 62(o.-cd' - — ) = 6(a)-u' - — ) (unit time) i(o)-ti)' ) T I 2 _ i(oj-a)') (n-m)x (  (cu-tu') (n-m) j*2iTk, k c l I e = I e = < n,m I Since there are no cross terms, the power spectrum i s given by the following (the other term from the i n i t i a l cosine has been included): 155 APPENDIX I_I The MAC S u b t e s t s The M i n i m a l A u d i t o r y C a p a b i l i t i e s T e s t (MAC) t e s t b a t t e r y i s a s e t o f 14 s u b t e s t s d e s i g n e d t o measure s p e e c h d i s c r i m i n a t i o n i n h a r d - o f - h e a r i n g s u b j e c t s . The t e s t i s a d m i n i s t e r e d by p l a y i n g s p e e c h o r sounds from a c a s s e t t e t a p e . Some of t h e s u b t e s t s were t o o d i f f i c u l t f o r t h e s u b j e c t s i n o u r s t u d y , a r e s u l t t h a t was c o n s i s t e n t w i t h t h e s c o r e s o f s u b j e c t s w i t h c o c h l e a r i m p l a n t s ( E d g e r t o n e t a l . , 1983). In a l l c a s e s t h e t e s t s were t r i e d , and t o p r e v e n t t h e f r u s t r a t i o n o f o u r s u b j e c t s , t h e s u b t e s t was d i s c o n t i n u e d i f t h e r e was no s c o r e a f t e r f i v e i t e m s i n t h e s u b t e s t . As d i s c u s s e d i n t h e t e x t , t h e MAC t e s t was d i v i d e d i n t o two m i n i m a c s of e q u a l l e n g t h and e q u a l d i f f i c u l t y . The s u b t e s t s a r e d e s c r i b e d b e l o w . S u b t e s t I The f i r s t o f t h e s u b t e s t s i s c a l l e d t h e Q u e s t i o n / S t a t e m e n t T e s t and a s k s t h e s u b j e c t t o i d e n t i f y w h ether t h e spoken s e n t e n c e i s a q u e s t i o n or a s t a t e m e n t . A sample p h r a s e i s "They saw t h e m o v i e " . S u b t e s t I I T h i s i s c a l l e d t h e Vowel T e s t . The s u b j e c t i s g i v e n a l i s t o f f o u r o n e - s y l l a b l e words w i t h i d e n t i c a l i n i t i a l c o n s o n a n t s and i d e n t i c a l f i n a l c o n s o n a n t s . O n l y t h e v o w e l c h a n g e s , and one o f them i s t h e one spoken from t h e t a p e . 1 56 There a r e 30 such i t e m s i n the s u b t e s t . S u b t e s t I I I The Spondee R e c o g n i t i o n T e s t ; a s e t o f 12 t w o - s y l l a b l e words p l a y e d by t h e t a p e , and r e p e a t e d by t h e s u b j e c t . T h i s t e s t was g e n e r a l l y t o o d i f f i c u l t f o r our s u b j e c t s . S u b t e s t IV The N o i s e / V o i c e T e s t ; t h e s u b j e c t i s a s k e d t o i d e n t i f y t h e sound f rom the t ape as b e i n g n o i s e , o r v o i c e . S u b t e s t V The A c c e n t T e s t : i n t h i s t e s t , t h e s u b j e c t i s a s k e d w h i c h word i n t h e spoken s e n t e n c e has t h e e m p h a s i s . A sample s e n t e n c e i s "Can you f i x i t " . S u b t e s t VI The E v e r y d a y S e n t e n c e s T e s t was a l s o g e n e r a l l y t o o d i f f i c u l t f o r t h e s u b j e c t s i n t h i s s t u d y . The s u b j e c t s a r e a s k e d t o r e p e a t a s e n t e n c e such as "They l o o k e d up a t t h e b l u e s k y " . S u b t e s t V I I The I n i t i a l Consonant T e s t i s v e r y s i m i l a r t o the vowel t e s t e x c e p t t h a t t h e v o w e l s a r e i d e n t i c a l , a s a r e t h e f i n a l c o n s o n a n t s , and t h e i n i t i a l c o n s o n a n t s a r e c h a n g e d . A g a i n , t h e s u b j e c t s a r e a s k e d t o mark on t h e i r shee t of f o u r p o s s i b i l i t i e s w h i c h one was s p o k e n . T h e r e a r e 30 such 157 i t e m s i n t h i s s u b t e s t . S u b t e s t V I I I The Spondee S a m e / D i f f e r e n t T e s t a s k s t h e s u b j e c t s t o say whether o r n o t two words sp o k e n from t h e t a p e a r e t h e same or d i f f e r e n t . T h e r e a r e 10 s u c h i t e m s i n t h e s u b t e s t . S u b t e s t IX In t h e Words i n C o n t e x t T e s t t h e s u b j e c t s a r e a s k e d t o r e p e a t o n l y t h e l a s t word i n a s e n t e n c e spoken from t h e t a p e . A g a i n , t h i s t e s t was t o o d i f f i c u l t f o r o u r s u b j e c t s . S u b t e s t X The E v e r y d a y Sounds T e s t i s a c o l l e c t i o n o f f a m i l i a r sounds s u c h as l a u g h i n g , o r g a n m u s i c , d o o r b e l l s , a t e l e p h o n e , a dog b a r k , e t c . The s u b j e c t s a r e a s k e d t o i d e n t i f y t h e sound. S u b t e s t XI The M o n o s y l l a b i c Word T e s t c o n s i s t s of 25 words w h i c h t h e s u b j e c t i s a s k e d t o r e p e a t . T h i s t e s t was a l s o g e n e r a l l y t o o d i f f i c u l t f o r t h e s u b j e c t s i n t h i s s t u d y . S u b t e s t X I I In t h e F o u r C h o i c e Spondee T e s t t h e s u b j e c t s a r e g i v e n a l i s t o f f o u r t w o - s y l l a b l e words, one o f w h i c h i s p r e s e n t e d on t h e t a p e . They a r e a s k e d t o mark t h e one t h e y h e a r . 158 S u b t e s t X I I I T h i s s u b t e s t i s much l i k e t h e v o w e l t e s t and t h e i n i t i a l c o n s o n a n t t e s t e x c e p t t h a t t h e f i n a l c o n s o n a n t i s t h e v a r i a b l e . S u b t e s t XIV T h i s t e s t i s a s p e e c h r e a d i n g t e s t w h i c h was a d m i n i s t e r e d w i t h t h e U t l e y s p e e c h r e a d i n g t e s t as a measure o f s p e e c h r e a d i n g a b i l i t y . 159 APPENDIX I I I  Random Chance S c o r e C o r r e c t i o n F o r t e s t s o f t h e " m u l t i p l e c h o i c e " t y p e , t h e number of c o r r e c t l y answered q u e s t i o n s i s not a p r o p o r t i o n a l measure of t h e number o f q u e s t i o n s t h e s u b j e c t i s s u r e o f , f o r example i f he knew n o t h i n g and randomly g u e s s e d , h i s most l i k e l y s c o r e w o u l d be Np where N i s t h e number of q u e s t i o n s on t h e t e s t and p i s l / ( # of c h o i c e s ) ; t h e d e s i r e d p r o p o r t i o n a l s c o r e would be z e r o . The most l i k e l y p r o p o r t i o n a l s c o r e can be d e r i v e d as f o l l o w s . D e f i n e N = t h e number of q u e s t i o n s on t h e t e s t , r = t h e number of q u e s t i o n s s c o r e d c o r r e c t l y , p = l / ( # of c h o i c e s ) and s = t h e number of q u e s t i o n s t h e s u b j e c t c o u l d c o r r e c t l y answer w i t h o u t g u e s s i n g . The minimum s c o r e f o r t h e s u b j e c t i s s , i . e . the q u e s t i o n s he was s u r e o f . I n a d d i t i o n he w i l l most p r o b a b l y c o r r e c t l y answer a f r a c t i o n p of t h e r e m a i n i n g N - s q u e s t i o n s . H e n c e : r = s + ( N - s ) p o r , s = ( r - N p ) / d - p ) I f we d e f i n e t h e p e r c e n t a g e q u a n t i t i e s S = 1 0 0 S / N , R = 1 0 0 r / N and P = lOOp t h e n we o b t a i n : S = ( 1 0 0 R - 1 0 0 P ) / ( 1 0 0 - P ) o r , S = R - ( l O O - R ) P / ( 1 0 0 - P ) . T h i s wou ld be t h e most l i k e l y p r o p o r t i o n a l s c o r e . I t may not be t h e mean p r o p o r t i o n a l s c o r e i f t h e d i s t r i b u t i o n i s skewed. We can e v a l u a t e t h e most l i k e l y p r o p o r t i o n a l s c o r e and the mean p r o p o r t i o n a l s c o r e from p r o b a b i l i t y t h e o r y . 160 If the s u b j e c t guessed c o r r e c t l y on m q u e s t i o n s and got a t o t a l of r c o r r e c t , then out of N - (r-m) guesses, he got m r i g h t . The p r o b a b i l i t y of doing t h i s i s p r o p o r t i o n a l to ( c f . Bevington, 1969): T./ M m,, NN-r (N-r+m) ! £(N-r+m) = p (1-p) m ! ( N - r ) ! The most l i k e l y m i s the one f o r which the p r o b a b i l i t y (or i t s logarithm) i s a maximum. Using S t e r l i n g ' s s e r i e s f o r f a c t o r i a l s ( c f . Arfken, 1970) we f i n d the maximum by s e t t i n g the d e r i v a t i v e of the l o g of the p r o b a b i l i t y equal to zero. ln ( P ) m l n ( p ) + (N-r+m) In (N-r+m) - m ln(m) + m independent terms. = l n ( p ) + ln(N-r+m) - ln(m) = 0 f o r the most l i k e l y m: ln ( p ) = In(m/(N-r+m)) or, m = (N-r)p/(1-p) T h i s i s the most l i k e l y c o n t r i b u t i o n from the random guesses so that the most l i k e l y p r o p o r t i o n a l score (s) i s given by: s = r - m = r - (N-r)p/(1-p) which i s i d e n t i c a l t o the r e s u l t d e r i v e d e a r l i e r . The mean p r o p o r t i o n a l score (s') i s an average of the scores (r - m) of a l l p o s s i b l e outcomes weighted by t h e i r r e s p e c t i v e p r o b a b i l i t i e s . These mean scores (s') were e v a l u a t e d n u m e r i c a l l y by computer f o r a l l experimental parameters and found t o d e v i a t e from the most l i k e l y scores (s) by an i n s i g n i f i c a n t amount (always l e s s than 1, making the r e l a t i v e e r r o r always l e s s than 1/N). 161 APPENDIX IV The MAC T e s t Raw D a t a As d e s c r i b e d i n C h a p t e r V I , s e v e r a l s u b t e s t s were not i n c l u d e d i n t h e a n a l y s e s s i n c e t h e t e s t s were o b v i o u s l y t o o d i f f i c u l t f o r t h e s u b j e c t s . The raw s c o r e s f o r t h e s u b t e s t s u s e d i n t h e a n a l y s e s a p p e a r i n T a b l e A.1. In t h e t a b l e , t h e f o l l o w i n g a b b r e v i a t i o n s a r e u s e d : a P r e - t e s t w i t h t h e h e a r i n g a i d c P r e - t e s t w i t h t h e c o m p r e s s o r s y s t e m a' P o s t - t e s t w i t h t h e h e a r i n g a i d c' P o s t - t e s t w i t h t h e c o m p r e s s o r s y s t e m i n c o m p l e t e t e s t The "chance s c o r e " i s t h e most l i k e l y s c o r e i f t h e s u b j e c t ' s a n s w ers a r e j u s t g u e s s e s . T a b l e A.1 The MAC T e s t Raw D a t a S u b j e c t * MAC S u b t e s t I I IV V I I V I I I X I I X I I I max. s c o r e 30 20 30 10 20 25 c h a n c e s c o r e 7.5 10 7.5 5 5 6.2 B1 a 10 13 13 9 16 9 c 6 14 11 4 9 7 a' 14 14 13 9 13 15 c* 8 12 10 4 12 13 B 2 a 11 12 10 8 16 13 c 10 10 13 8 15 15 a' 9 16 18 10 13 15 c' 10 11 7 8 19 19 B3 a c -- — -- 4 a' - - - - - - 4 4 7 c' 7 12 B4 a 15 20 13 10 16 16 c 13 17 11 8 15 11 a' 11 19 12 — 1 8 17 c' 17 17 13 -- 14 17 B5 a 3 15 — 6 c 9 16 7 5 5 5 a' 12 18 15 ' 9 10 6 c' 10 18 8 6 8 11 B6 a 6 9 11 5 7 4 c 8 8 8 6 4 10 a' 4 12 7 4 6 10 c' 5 10 7 2 3 5 B7 a 6 11 7 8 10 14 c 10 14 6 4 10 11 a' 7 15 11 6 13 14 c' 11 18 6 9 14 13 163 B i b l i o g r a p h y A h l s t r o m , K . G . , R i s b e r g , A . and L i n d h e , V . ( 1 9 6 8 ) , " E x p e r i m e n t i n L e a r n i n g t o D i s c r i m i n a t e F r e q u e n c y T r a n s p o s e d S p e e c h " , R p t . 3_6 I n s t i t u t e of E d u c a t i o n U p p s a l a U n i v . , Sweden. A r f k e n , G . ( 1 9 7 0 ) , M a t h e m a t i c a l Methods f o r P h y s i c i s t s , Academic P r e s s , New Y o r k , N . Y . B a t e , H . L . ( 1 9 8 0 ) , i n Speech P r o t o c o l s i n A u d i o l o g y , R .Rupp ( e d . ) , Grune and S t r a t t o n . B e a s l e y , D . S . , M o s h e r , N . L . and O r c h i k , D . J . ( 1 9 7 6 ) , "Use of F r e q u e n c y S h i f t e d / T i m e Compressed Speech w i t h H e a r i n g I m p a i r e d C h i l d r e n " , A u d i o l o g y , V o l . ±5 , p p . 3 9 5 - 4 0 6 . B e n n e t t , D . N . and B y e r s , V . W . ( 1 9 6 7 ) , " I n c r e a s e d I n t e l l i g i b i l i t y i n t h e H y p o c u s i c by S l o w - P l a y F r e q u e n c y T r a n s p o s i t i o n " , J . A u d . R e s . , V o l . 7 , p p . 1 0 7 - 1 1 8 . B e n n e t t , I . M . and L i n v i l l , J . G . ( 1 9 7 5 ) , "A S tudy of Time Domain Speech C o m p r e s s i o n " , J . A c o u s t . S o c . A m . , V o l . 23 , N o . 9 , p p . 7 1 3 - 7 2 1 . B e v i n g t o n , P . R . ( 1 9 6 9 ) , Da ta R e d u c t i o n and E r r o r A n a l y s i s f o r the  P h y s i c a l S c i e n c e s , M c G r a w - H i l l Book C o . New Y o r k , N . Y . B i o n d i , E . , and B i o n d i , L . ( 1 9 6 8 ) , "The S a m p l i n g of Sounds as a New Means o f M a k i n g Speech I n t e l l i g i b l e t o t h e P r o f o u n d l y D e a f " , A l t a F r e q u e n z a , V o l . 3_7 , p p . 180-191 . B i o n d i , E . and B i o n d i , L . ( 1 9 7 3 ) , "The S a m p l i n g of Sounds as a Means of M a k i n g Speech I n t e l l i g i b l e t o t h e D e a f : T h e o r i e s and R e s u l t s " , P r o c . 1973 C o n f . E l e c t r o n i c P r o s t h e s i s , U n i v . of K e n t u c k y , p p . 5 - 9 . B r a i d a , L . D . , D u r l a c h , N . I . , L i p p m a n n , R . P . , H i c k s , B . L . , R a b i n o w i t z , W . M . , and R e e d , C M . ( 1 9 7 9 ) , " H e a r i n g A i d s : A Review of P a s t R e s e a r c h on L i n e a r A m p l i f i c a t i o n , A m p l i t u d e C o m p r e s s i o n , and F r e q u e n c y L o w e r i n g " , ASHA Mono. N o . 1 9 . C a m p b e l l , R . M . , S h u l t h e i s , D . C . and B a r t o n , J . M . ( 1 9 7 6 ) , "A Compar i son o f F r e q u e n c y S p e c t r a l S h i f t i n g and Frequency D i v i s i o n as a P o s s i b l e H e a r i n g A i d " , P r o c . 1976 C o n f e r e n c e on  Systems and D e v i c e s f o r t h e D i s a b l e d , T u f t s U n i v . , New E n g l a n d Med. C e n t e r , B o s t o n . D a n i l o f f , R . G . , S h r i n e r , T . H . and Z e m l i n , W . R . ( 1 9 6 8 ) , " I n t e l l i g i b i l i t y of V o w e l s A l t e r e d i n D u r a t i o n and F r e q u e n c y " J . A c o u s t . S o c . Am. V o l . 44 , p p . 7 0 0 - 7 0 7 . D a v i d , E . E . and M c D o n a l d , H . S . ( 1 9 5 6 ) , " N o t e on P i t c h S y n c h r o n o u s P r o c e s s i n g of S p e e c h " , J . A c o u s t . S o c . A m . , V o l . 28 , p p . 1 2 6 1 -1266. 164 Denes , P . B . and P i n s o n , E . N . ( 1 9 6 3 ) , "The Speech C h a i n " , B e l l T e l e p h o n e L a b o r a t o r i e s I n c . , W a v e r l y P r e s s I n c . , B a l t i m o r e Md. E d g e r t o n , B . J . , P r i e t t o , A . and D a n h a u e r , J . L . ( 1 9 8 3 ) , " C o c h l e a r I m p l a n t P a t i e n t P e r f o r m a n c e on t h e MAC B a t t e r y " , O t o l a r y n g o l o g y C l i n i c s of N o r t h A m e r i c a , V o l . J_6 N o . 1 . E n g e l b e r g , M . W . ( 1 9 7 0 ) , A u d i o l o g i c a l E v a l u a t i o n f o r E x a g g e r a t e d  H e a r i n g L e v e l , C h a r l e s C . Thomas P u b l i s h e r , Thomas B o o k s , S p r i n g f i e l d , I l l i n o i s , U . S . A . E r b e r , N . ( 1 9 8 2 ) , " A u d i t o r y T r a i n i n g " , A l e x a n d e r Graham B e l l A s s o c i a t i o n f o r t h e D e a f . F a i r b a n k s , G . , E v e r e t t , W . L . and J a e g e r , R . P . ( 1 9 5 4 ) , "Method f o r Time o r F r e q u e n c y C o m p r e s s i o n - E x p a n s i o n of S p e e c h " , I R E . T r a n s . A u d i o , AU2 , p p . 7 - 1 2 . F a i r b a n k s , G . and Kodman,F . ( 1 9 5 7 ) , "Word I n t e l l i g i b i l i t y as a F u n c t i o n of Time C o m p r e s s i o n " , J . A c o u s t . S o c . A m . , V o l . £ 9 , p p . 6 3 6 - 6 4 1 . F l a n a g a n , J . L . and H o u s e , A . S . ( 1 9 5 6 ) , "Deve lopment and T e s t i n g of a F o r m a n t - C o d i n g Speech C o m p r e s s i o n S y s t e m " , J . A c o u s t . S o c . A m . , V o l . 28 , p p . 1 0 9 9 - 1 1 0 6 . F l e t c h e r , H . ( 1 9 2 9 ) , Speech and H e a r i n g . , Van N o s t r a n d C o . New Y o r k , N . Y . F l e t c h e r , H . ( 1 9 5 3 ) , Speech and H e a r i n g i n C o m m u n i c a t i o n , Van N o s t r a n d , P r i n c e t o n . F o u s t , K . O . and G e n g e l , R . W . ( 1 9 7 3 ) , " Speech D i s c r i m i n a t i o n by S e n s o r i n e u r a l H e a r i n g I m p a i r e d P e r s o n s u s i n g a T r a n s p o s e r H e a r i n g A i d " , S c a n d . A u d i o l . , V o l . 2 , p p . 1 6 1 - 1 7 0 . G a r v e y , W . D . ( 1 9 5 3 ) , "The I n t e l l i g i b i l i t y of A b b r e v i a t e d Speech P a t t e r n s " , The Q u a r t e r l y J o u r n a l o f S p e e c h , V o l . 3_9 , p p . 2 9 6 -306 . G r e e n , D . M . ( 1 9 7 6 ) , " A n I n t r o d u c t i o n t o H e a r i n g " , Lawrence E r l b a u m A s s o c i a t e s I n c . , H i l l s d a l e , New J e r s e y . G u t t m a n , N . and van B e r g e i j k , W . A . ( 1 9 5 9 ) , " F r e q u e n c y D i v i s i o n i n R e a l Time as a Means of C o u n t e r a c t i n g H i g h F r e q u e n c y H e a r i n g L o s s " , S o c i e t e I n t e r n a t . D ' A u d i o l , 4 t h C o n g r e s s 1958, L y o n : A u d i n ( 1 9 5 9 ) . G u t t m a n , N . , L e v i t t , H . and B e l i e f l e u r , P . A . ( 1 9 7 0 ) , " A r t i c u l a t i o n T r a i n i n g o f t h e Deaf u s i n g Low F r e q u e n c y S u r r o g a t e F r i c a t i v e s " , J . Speech H e a r i n g R e s . , V o l . J_3 , p p . 19-29 . H e n o c h , M . ( 1 9 8 2 ) , " A d u l t A u r a l R e h a b i l i t a t i o n " , P a p e r : A n n . m e e t i n g : B . C . Speech and H e a r i n g A s s . , O c t . 1 9 8 2 165 H e s s , W . J . ( 1 9 8 2 ) , " A l g o r i t h m s and D e v i c e s f o r P i t c h D e t e r m i n a t i o n of Speech S i g n a l s " , P h o n e t i c a , V o l . 39 , p p . 2 1 9 -240 . I n g h a m , K . R . ( 1 9 6 7 ) , " S p e l l e d Speech as an O u t p u t f o r Computers and R e a d i n g M a c h i n e s f o r t h e B l i n d " , T r a n s a c t i o n s on Human F a c t o r s i n E l e c t r o n i c s , V o l . HFE-8 , N o . 3 . J e f f e r s , J . and B a r l e y , M . ( 1 9 7 1 ) , " S p e e c h r e a d i n g ( L i p r e a d i n g ) " , C h a s . C . Thomas ( e d . ) , S p r i n g f i e l d , 1 1 1 . J o h a n s s o n , B . ( 1 9 6 1 ) , "A New C o d i n g A m p l i f i e r System f o r t h e S e v e r e l y H a r d of H e a r i n g " , P r o c . 3 r d I n t e r n a t i o n a l C o n g r e s s on  A c o u s t i c s , S t u t g a r t , p p . 6 5 5 - 6 5 7 . J o h a n s s o n , B . ( 1 9 6 6 ) , "The Use of t h e T r a n s p o s e r f o r t h e Management o f the Deaf C h i l d " , I n t e r n a t . A u d i o l . , V o l . 5 , p p . 3 6 2 - 3 7 3 . J o h a n s s o n , B . and S j o g r e n , H . (1965) "The E f f e c t o f Normal H e a r i n g S u b j e c t s and P r o f o u n d l y Deaf C h i l d r e n by C o d i n g V o i c e l e s s C o n s o n a n t s U s i n g F r e q u e n c y T r a n s p o s i t i o n " . P r o c . 5 t h  I n t e r n a t i o n a l C o n g r e s s on A c o u s t i c s , L i e g e . J o h n s o n , J . H . (1965) I n t r o d u c t i o n t o E l e c t r i c a l E n g i n e e r i n g , I n t . Tex tbook C o . , S c r a n t o n , P e n n s y l v a n i a . K a t z , J . ( 1 9 7 8 ) , Handbook of C l i n i c a l A u d i o l o g y , W i l l i a m s and W i l k i n s C o . B a l t i m o r e , Md . U . S . A . K l u m p p , R . G . and W e b s t e r , J . C . ( 1 9 6 1 ) , " I n t e l l i g i b i l i t y of Time Compressed S p e e c h " , J . A c o u s t . S o c . A m . , V o l . 33 , p p . 2 6 5 - 2 6 7 . K n o r r , S . G . ( 1 9 7 6 ) , " A H e a r i n g A i d f o r S u b j e c t s w i t h E x t r e e m H i g h F r e q u e n c y L o s s e s " , IEEE T r a n s . A c o u s t . , S p e e c h , S i g n a l p r o c e s s i n g , A S S P - 2 4 , p p . 4 7 3 - 4 8 0 . L e e , F . F . ( 1 9 7 2 ) , "T ime C o m p r e s s i o n and E x p a n s i o n o f Speech by t h e S a m p l i n g M e t h o d " , J . A u d . E n g . S o c , V o l . 20 , N o . 9 , p p . 7 3 8 - 7 4 2 . L i n g , D . ( 1 9 6 8 ) , " T h r e e E x p e r i m e n t s on F r e q u e n c y T r a n s p o s i t i o n " , Am. A n n . D e a f , V o l . J_3 , p p . 2 8 3 - 2 9 4 . L i n g , D . ( 1 9 6 9 ) , " Speech D i s c r i m i n a t i o n by P r o f o u n d l y Deaf C h i l d r e n U s i n g L i n e a r and C o d i n g A m p l i f i e r s " , IEEE T r a n s . A u d . E l e c t r o a c o u s t . A U - 1 7 , p p . 2 9 8 - 3 0 3 . L i n g , D . ( 1 9 7 2 ) , " A u d i t o r y D i s c r i m i n a t i o n o f Speech T r a n s p o s e d by a Sample and H o l d P r o c e s s " , i n G . F a n t ( e d . ) P r o c .  I n t e r n a t i o n a l Symposium on Speech C o m m u n i c a t i o n and P r o f o u n d  DeafnessT S t o c k h o l m ( 1 9 7 0 ) , W a s h i n g t o n : A . G . B e l l A s s o c . ( 1 9 7 2 ) . 166 L i n g , D . and D r u z , W . S . ( 1 9 6 7 ) , " T r a n s p o s i t i o n of H i g h F r e q u e n c y Sounds by P a r t i a l V o c o d i n g of t h e Speech S p e c t r u m : i t s Use by Deaf C h i l d r e n " , J . A u d . R e s . , V o l . 7 , p p . 1 3 3 - 1 4 4 . M a z o r , M . , S i m o n , H . , S c h e i n b e r g , J . and L e v i t t , H . ( 1 9 7 7 ) , " M o d e r a t e F r e q u e n c y C o m p r e s s i o n f o r t h e M o d e r a t l e y H e a r i n g I m p a i r e d " , J . A c o u s t . S o c . A m . , V o l . 62 , p p . 1 2 7 3 - 1 2 7 8 . M c G r a t h , M . and S u m m e r f i e l d , Q (1984) i n 107th m e e t i n g : A c o u s t i c a l S o c i e t y of A m e r i c a , J . A c o u s t . S o c . Am. V o l . 75 , S u p p l . 1 , S33(A) . M i n i f i e , F , D . , H i x o n , T . J . , F r e d e r i c k , W . ( 1 9 7 3 ) , Normal A s p e c t s of S p e e c h , H e a r i n g , and Language , P r e n t i c e - H a l l I n c . , Eng lewood C l i f f s , New J e r s e y . M o r g a n , H . L . and S a v i g e , J . J . ( 1 9 7 5 ) , " B a n d w i d t h C o m p r e s s i o n and E x p a n s i o n " M . S . L a b o r a t o r i e s , P . O . Box 28425 , D a l l a s T e x a s . M u s s e n , P . , R o s e n z w e i g , M . P . , A r o n s o n , E . , F e s h b a c h , S . , G e i w i t z , P . J . , G l i c k m a n , S . E . , M u r d o c k , B . B . and W e r t h e i m e r , M . ( 1 9 7 3 ) , P s y c h o l o g y : an I n t r o d u c t i o n , D . C . H e a t h & C o . , L e x i n g t o n M a s s a c h u s e t t s , T o r o n t o , L o n d o n . N a g a f u c h i , M . ( 1 9 7 6 ) , " I n t e l l i g i b i l i t y o f D i s t o r t e d Speech Sounds S h i f t e d i n F r e q u e n c y and Time i n Normal C h i l d r e n , " A u d i o l o g y V o l . ±5 , p p . 3 2 6 - 3 3 7 . O c h i a i , Y . and I z u m i t a c h i , N . ( 1 9 5 5 ) , " T i m b r e S tudy on M i s h e a r i n g Phenomena of Speech Phones i n R o t a t i o n a l S y n c h r o n o u s D i s t o r t i o n " , R e p o r t I : " M i s h e a r i n g v o w e l i c t i m b r e " , Mem. F a c . E n g . Nagoya,. V o l . 7 , p p . 4 9 - 6 0 . O c h i a i , Y . , S a i t o , S . and S a k a i , Y . ( 1 9 5 5 ) , " A r t i c u l a t i o n S t u d y of Speech Q u a l i t i e s i n R o t a t i o n a l S y n c h r o n o u s D i s t o r t i o n " , Mem. F a c . E n g . N a g o y a , V o l . 7 p p . 4 0 - 4 8 . O e k e n , F . W . ( 1 9 6 3 ) , "Can Hard of H e a r i n g P a t i e n t s S u f f e r i n g from H i g h Tone P e r c e p t i v e D e a f n e s s be Improved by F r e q u e n c y T r a n s p o s i t i o n ? " , J . I n t e r n a t . A u d i o l . , V o l . 2 , p p . 2 6 3 - 2 6 6 . P e t e r s o n , G . E . and B a r n e y , H . L . ( 1 9 5 2 ) , " C o n t r o l Methods Used i n t h e S t u d y of V o w e l s " , J . A c o u s t . S o c . A m . , V o l . 24^  ' N o . 2 , p p . 1 7 5 - 1 8 4 . R a y m o n d , T . H . and P r o u d , G . O . ( 1 9 6 2 ) , " A u d i o F r e q u e n c y C o n v e r s i o n " , A r c h . O t o l a r y n g . , V o l . 7j> , p p . 6 0 - 7 0 . R e e d , C M . , H i c k s , B . L . , B r a i d a , L . D . , D u r l a c h , N . I . (1983) " D i s c r i m i n a t i o n of Speech P r o c e s s e d by Low Pass F i l t e r i n g and P i t c h I n v a r i a n t F r e q u e n c y L o w e r i n g " , J . A c o u s t . S o c . Am. V o l . 1± , p p . 4 0 9 - 4 1 9 . R e e d e r , K . , S t r o n g , W . J . and P a l m e r , E . P . ( 1 9 7 5 ) , " L o w - F r e q u e n c y Formant Speech Codes f o r t h e S e v e r e l y / P r o f o u n d l y H e a r i n g I m p a i r e d " , J . A c o u s t . S o c . A m . , V o l . 58 , S 1 1 3 ( A ) . 1 67 S a i t o , S . , S e k i m o t o , S . and K i r i t a n i , S . (1981) " I n t e l l i g i b i l i t y of t h e F r e q u e n c y Compressed Speech and i t s A p p l i c a t i o n t o the H e a r i n g A i d s " , A n n u a l B u l l e t i n N o . 15', R e s e a r c h I n s t i t u t e of L o g o p e d i c s and P h o n i a t r i c s , U n i v . o f T o k y o , p p . 7 1 - 9 0 . S c h a f e r - V i n c e n t , K . ( 1 9 8 2 ) , " S i g n i f i c a n t P o i n t s : P i t c h P e r i o d D e t e c t i o n as a P r o b l e m of S e g m e n t a t i o n " , P h o n e t i c a , V o l . 39 , p p . 2 4 1 - 2 5 3 . S c h a r f , B . ( 1 9 7 8 ) , " C o m p a r i s o n of N o r m a l and I m p a i r e d H e a r i n g " i n S e n s o r i n e u r a l H e a r i n g Impai rment and H e a r i n g A i d s , C . L u d v i g s e n and J . B a r f o d ( e d s . ) , S c a n d . A u d i o l . S u p p l . , V o l 6 . S c h r o e d e r , M . R . , F l a n a g a n , J . L . and L u n d r y , E . A . ( 1 9 6 7 ) , " B a n d w i d t h C o m p r e s s i o n of Speech by A n a l y t i c - S i g n a l R o o t i n g " , P r o c . I E E E , V o l . 55 , p p . 3 9 6 - 4 0 1 . S c o t t , R . J . and G e r b e r , S . E . ( 1 9 7 2 ) , " P i t c h S y n c h r o n o u s Time C o m p r e s s i o n of S p e e c h " P r o c . 1972 C o n f e r e n c e on Speech C o m m u n i c a t i o n and P r o c e s s i n g , IEEE C a t . No .72 CHO 596-7 A E , p p . 6 3 - 6 5 . S h r i n e r , T . H . , B e a s l e y , D . S . and Z e m l i n , W . R . ( 1 9 6 9 ) , "The E f f e c t s of F r e q u e n c y D i v i s i o n on Speech I d e n t i f i c a t i o n i n C h i l d r e n " , J . S p e e c h . H e a r i n g R e s . V o l . J_2 , p p . 4 1 3 - 4 2 2 . S p e n s , K . E . and M a r t o n y , J . (1972) "The T r a n s p o s e r as a L i p R e a d i n g A i d " , P r o c . 1972 C o n f . Speech Comm. and p r o c e s s i n g , IEEE C a t . N o . 7 2 , CHO 596-7 A E , p p . 2 4 6 - 2 4 8 . S t e w a r t , S . E . , S t r o n g , W . J . , P a l m e r , E . P . ( 1 9 7 6 ) , " E x p e r i m e n t s on t h e I n t e l l i g i b i l i t y of Speech Codes f o r t h e S e v e r e l y H e a r i n g I m p a i r e d " , J . A c o u s t . S o c . Am. V o l . 60 , S u p p l . 1 S124 S u n d b e r g , J . ( 1 9 7 7 ) , "The A c o u s t i c s of the S i n g i n g V o i c e " , S c i e n t i f i c A m e r i c a n M a r c h 1977, p p . 8 2 - 9 1 . T h o m a s , I . B . and F l a v i n , F . E . ( 1 9 7 0 ) , "The I n t e l l i g i b i l i t y of Speech T r a n s p o s e d Downward i n F r e q u e n c y by One O c t a v e " , J . Aud E n g . S o c . V o l . J_8 , p p . 5 6 - 6 2 . T i f f a n y , W . R . and B e n n e t t , D . N . ( 1 9 6 1 ) , " I n t e l l i g i b i l i t y of Slow P l a y e d S p e e c h " , J . S p e e c h H e a r i n g R e s . , V o l . 4 , p p . 2 4 8 - 2 5 8 . U t l e y , J . ( 1 9 4 6 ) , "A T e s t of L i p R e a d i n g A b i l i t y " , J . Speech and H e a r i n g D i s o r d e r s , V o l . J J_ , p p . 109-116 . V e l m a n s , M . (1971) " A i d s f o r Deaf P e r s o n s " , U . K . P a t e n t 1340105 V e l m a n s , M . ( 1 9 7 4 ) , "The D e s i g n of Speech R e c o d i n g D e v i c e s f o r t h e D e a f " B r i t . J . A u d i o l . , V o l . 8 , p p . 1 - 5 . Z e m l i n , W . R . ( 1 9 6 6 ) , "The Use of B a n d w i d t h and Time C o m p r e s s i o n f o r t h e H e a r i n g H a n d i c a p p e d " i n E . F o u l k e ( e d . ) P r o c . o f t h e  L o u i s v i l l e C o n f . on Time Compressed S p e e c h , L o u i s v i l l e : U n i v . L o u i s v i l l e p r e s s , p p . 9 5 - 9 7 . PUBL ICAT IONS 1. B .D. C u t f o r t h , W.R. D a t a r s , R.J. G i l l e s p i e , A . J . V an S c h y n d e l , " H g ~ ftfiAsFfi - A N o v e l S t r u c t u r e w i t h U n u s u a l E l e c t r i c a l P r o p e r t i e s " , A d v . Chem S e r i e s p p . 5 6 - 6 1 ( 1 9 7 6 ) 2 . B.D. C u t f o r t h , W.R. D a t a r s , A . J . V a n S c h y n d e l , R.J. G i l l e s p i e , " E l e c t r i c a l C o n d u c t i v i t y o f L i n e a r C h a i n M e r c u r y C o m p o u n d s " , S o l i d S t a t e Comm. p p . 3 7 7 - 3 7 9 ( 1 9 7 7 ) 3. R.J. G i l l e s p i e , D. C h a r t i e r , B .D. C u t f o r t h , W.R. D a t a r s , A . J . V a n S c h y n d e l , " T h e L i n e a r C h a i n M e r c u r y Compounds H g ? fifiAsFfi a n d Hg„ Q , S b F 6 > E l e c t r i c a l C o n d u c t i v i t y , O p t i c a l R e f l e c t a n c e a n d - T h e r m o e l e c t r i c S t u d i e s " A n n . N.Y. A c a d . S c i . p p . 7 8 8 - 7 9 9 ( 1 9 7 7 ) 4 . W.R. D a t a r s , A . J . V a n S c h y n d e l , J . S . L a s s , D. C h a r t i e r , R.J. G i l l e s p i e , " M e r c u r y E x t r u s i o n f r o m L i n e a r - C h a i n M e r c u r y C o m p o u n d s " P h y s . R e v . L e t t e r s p p . 1 1 8 4 - 1 1 8 7 ( 1 9 7 8 ) 5. R.E D o e z e m a , W.R. D a t a r s , H. S c h a b e r , A . J . V a n S c h y n d e l , " F a r - I n f r a r e d M a g n e t o s p e c t r o s c o p y o f t h e L a n d a u - L e v e l S t r u c t u r e i n G r a p h i t e " P h y s . R e v . p p . 4 2 2 4 - 4 2 3 0 ( 1 9 7 9 ) 6. A . J . V a n S c h y n d e l , " M a g n e t i c F e e d b a c k a n d Quan tum O s c i l l a t i o n s i n M e t a l s " MSc . D i s s e r t a t i o n , The U n i v e r s i t y o f B r i t i s h C o l u m b i a , N a t i o n a l L i b r a r y o f C a n a d a , O t t a w a . ( 1 9 8 0 ) 7. A . V . G o l d a n d A . J . V a n S c h y n d e l , " R e d u c t i o n o f t h e S h o e n b e r g M a g n e t i c I n t e r a c t i o n b y M a g n e t i c F e e d b a c k " J . L . T . P . 44 p p . 7 3 - 8 4 ( 1 9 8 1 ) 8. A . J . V a n S c h y n d e l , " D e v e l o p m e n t a n d C l i n i c a l E v a l u a t i o n o f a F r e q u e n c y C o m p r e s s o r f o r t h e H e a r i n g I m p a i r e d " , PhD. D i s s e r -t a t i o n , The U n i v e r s i t y o f B r i t i s h C o l u m b i a , N a t i o n a l L i b r a r y o f C a n a d a , O t t a w a . ( 1 9 8 4 ) 9. A . J . V a n S c h y n d e l , N. W e i s s , A - P . B e n g u e r e l , " R e a l T i m e F r e q u e n c y C o m p r e s s i o n f o r t h e H e a r i n g I m p a i r e d " , To be p u b l i s h e d . 10 . A . J . V an S c h y n d e l , " A P r a c t i c a l V o i c e I n d e x i n g S y s t e m f o r u s e i n T a l k i n g B o o k s f o r t h e B l i n d " , To be p u b l i s h e d . 

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