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Relationship between otoadmittance and threshold measurements in a TTS paradigm with phonation Andrews, Virginia Anathalie Taylor 1973

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RELATIONSHIP BETWEEN OTOADMITTANCE AND THRESHOLD MEASUREMENTS IN A TTS PARADIGM WITH PHONATION  by VIRGINIA ANATHALIE TAYLOR ANDREWS BSc. U n i v e r s i t y o f B r i t i s h Columbia,  1971  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n the D i v i s i o n o f Audiology and Speech S c i e n c e s i n the Department o f Paediatrics  We accept t h i s t h e s i s as conforming required  to the  standard  THE UNIVERSITY OF BRITISH COLUMBIA J u l y , 1973  In presenting  t h i s thesis i n p a r t i a l fulfilment of the requirements for  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 available for reference  and study.  I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the Head of my Department or by his representatives.  It i s understood that copying or publication  of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission.  Department of  PAEDIATRICS, DIVISION OF AUDIOLOGY AND SPEECH SCIENCES  The University of B r i t i s h Columbia Vancouver 8, Canada  Abstract T h i s i n v e s t i g a t i o n s t u d i e s the r o l e o f the middle ear muscles  i n the TTS r e d u c t i o n t h a t o c c u r s when phonation  accompanies  exposure to a h i g h i n t e n s i t y low frequency pure  tone.  Changes i n a c o u s t i c admittance  middle ear. muscle  (taken as a measure o f  a c t i v i t y ) were compared w i t h changes i n  TTS, r e c o r d e d under s i m i l a r experimental c o n d i t i o n s . paradigm  c o n s i s t e d o f measuring  b e f o r e and a f t e r 5 minute tone, accompanied  The TTS  subjects' hearing thresholds  exposure to a 500 Hz, 117.5  o r n o t by phonation (humming).  dB SPL  The paradigm  was r e p e a t e d w i t h t h r e s h o l d measurement b e i n g r e p l a c e d by otoadmittance measurement; i n t h i s case admittance changes were r e c o r d e d b e f o r e , d u r i n g , and a f t e r the f a t i g u e  exposure.  The r e s u l t s show t h a t TTS from the exposure  tone  w i t h p h o n a t i o n was s i g n i f i c a n t l y l e s s than TTS from the exposure tone w i t h no p h o n a t i o n .  The e f f e c t o f phonation on TTS was  most s i g n i f i c a n t a t e a r l y post-exposure times.  No s i g n i f i c a n t  TTS d i f f e r e n c e s between males and females were found. Changes i n the two admittance components a t the b e g i n n i n g and a t the end o f exposure were s i g n i f i c a n t l y  larger  when phonation accompanied  This  the exposure  than when n o t .  f i n d i n g suggests t h a t more middle ear muscle when phonation accompanies is  a c t i v i t y occurs  exposure than when no phonation  performed. Most admittance measurements d i d n o t c o r r e l a t e  f i c a n t l y w i t h any o f the TTS measurements.  signi-  The o n l y s i g n i f i c a n t  c o r r e l a t i o n s i n d i c a t e d t h a t the s m a l l e r the middle  ear  muscle a c t i v i t y r e s u l t i n g from the f a t i g u e exposure the l a r g e r the amount o f p r o t e c t i o n p r o v i d e d as measured by d i f f e r e n c e s between TTS exposure times between the two  values  conditions.  suggests t h a t most i n d i v i d u a l s may  by  alone,  phonation,  at early post-  This finding  have middle ear muscles  t h a t c o n t r a c t weakly i n response to i n t e n s e a c o u s t i c  stimula-  t i o n alone but t h a t these muscles c o n t r a c t s i g n i f i c a n t l y when phonation accompanies the a c o u s t i c s t i m u l a t i o n . t i o n provides 5 0 0 Hz  considerable  p r o t e c t i o n of the ear from the  f a t i g u e tone, as shown by the reduced TTS  t i o n accompanies exposure.  Thus, phona-  The  when phona-  r e s u l t s a l s o suggest t h a t  middle ear muscles are a major f a c t o r i n reduced TTS p h o n a t i o n but other mechanisms such as i n e f f i c i e n t v i b r a t i o n and research  a t t e n t i o n a l f a c t o r s may  the  with  stapes  a l s o be i n v o l v e d .  More  i s necessary to determine the exact r o l e each mechan-  ism p l a y s i n the r e d u c t i o n o f TTS  with phonation.  TABLE OP CONTENTS Page ABSTRACT , .  ±±  LXST OF TABLiii> . . , . . , « « . . . «  vi.  LIST OF FIGURES . . . . . . . . . . . . v i i Chapter 1.  INTRODUCTION  1  Chapter 2 .  REVIEW OF THE LITERATURE . . . . . . .  4  2.0  Introduction  4  2.1  Effect  4  2 11  TTS  2.12  Phonation and TTS . . . .  C  • 2.2  o f Phonation on TTS. . . . .  E f f e c t o f Phonation on Sound T r a n s m i s s i o n i n the Middle E a r . 2.21  The Middle Ear Muscles (MEM) . •. Anatomy MEM A c t i v i t y MEM A c t i v i t y D u r i n g Phonation E f f e c t of MEM A c t i v i t y on Sound T r a n s mission. . . . . . .  2„22 2.3  Stapes V i b r a t i o n ,  0  , , ,  C o n t r o l o f P o s s i b l e Mechanisms Involved i n TTS R e d u c t i o n . ' . 2.31 2«32  C o n t r o l o f MEM Contract i o n During. Phonation . ,  4 6 9 9  9 11 14 15 18 20 20  C o n t r o l o f Stapes V i b r a t i o n D u r i n g Phonation . 21 e  2.33  Attention F a c t o r s and TTS Reduction . . ... . . '22 -iv-  -VPage Chapter 3 .  AIMS OF THE  Chapter 4.  EXPERIMENTAL APPARATUS AND 4.1  INVESTIGATION  . . 25  4.11  TTS I n s t r u m e n t a t i o n  4.12  Otoadmittance  4.13  Calibration  25  I n s t r u m e n t a t i o n . 27 28  4.2  Subjects. . . . . . . . . .  JO  4.3  Experiments  51  .  Chapter 5 .  PROCEDURES, . . 25  E x p e r i m e n t a l Apparatus.  . . . . . . . . . . . . .  4.31  E x p e r i m e n t a l Design  . . . . . .  3-1  4.3  Procedures. . . . . . . . . . .  34  TTS S e s s i o n s . . .' . . . . . . .  54  2  Otoadmittance  Chapter 5 .  . . 24  4,33  S e s s i o n s . . . . . 55  Data Measurement. . . . . . . . .  56  TTS Measurement Otoadmittance Measurement . . .  56 59  RESULTS.  42  5.1  TTS Data  42  5.2  Otoadmittance  5.3  Comparison Data  Data.  . . . .  o f TTS and  48  Otoadmittance  DISCUSSION  49 . . . 57  REFERENCES . . . . . . . . . . . . . . . .  67  APPENDIX . . . . . . . . . . .  71  e . . . . .  L i s t of Tables Page  Table 1.  Summary o f ANOVA. TTS as a f u n c t i o n off sex, post-exposure time ( 0 ' \ 7 . 5 " , 15"» 3 0 % 2*,  V),  and c o n d i t i o n  7 female s u b j e c t s .  (N^,. H^)  f o r 7 BKS£1?S. and  . < > . , . . . . . » . i« . . . 4-3 e  2a.  R e s u l t s o f Neuman-Keuls t e s t f o r s i g n i f l a s a a c e o f d i f f e r e n c e s between TTS f o r 7 p0st--«a'grasure times (7 male and 7 female subjects),™ » « . . . 4 - 5  2b.  R e s u l t s o f Neuman-Keuls t e s t f o r s i g n i f i c a n c e o f d i f f e r e n c e s between TTS f o r N and 1^, c o n d i t i o n s or . . . . a . . . . . . .  , 4-7  R e s u l t s o f Neuman-Keuls t e s t f o r signlliccrmce o f d i f f e r e n c e s between TTS f o r conditierres Hm and Hrr, a t the s p e c i f i e d post-exposure Wmvs, .  . 4-7  T  2c.  3.  M a t r i x o f R e s u l t s £>f Pearson Product-Moment C o r r e l a t i o n s between s p e c i f i e d TTS and (fifeadmittance v a l u e s . . . * ». «« i* • . . 51  -vi-  L i s t of Figures Figure 2.1  Page Schematic diagram o f the t e n s o r tympani .muscleo . , . . o c . . . . . . . .  10  2.2  Schematic diagram o f middle ear l i g a m e n t s and s t a p e d i u s muscle. . . . . . . . . . . . . . . . . 1 0  2.3  Movement of the s t a p e s , a) Normal stapes motion i n r e s p o n s e t o a i r - b o r n e sound, b) Movement around the l o n g a x i s o f the s t a p e s ( p o s s i b l e d u r i n g phonation) r e s u l t i n g i n reduced d i s p l a c e ment o f c o c h l e a r f l u i d , . . . . . . . . . . . . . .  ^o,  B l o c k diagram o f i n s t r u m e n t a t i o n f o r TTS procedures. . . . . . . . . . . . . . .  25  4.1 4.2  B l o c k diagram o f i n s t r u m e n t a t i o n f o r Otoadmittance procedures. . . . . . . . . . . . . . . . . . . 2^  4.3  E x p e r i m e n t a l d e s i g n and parameters. A) Design and parameters of TTS p r o c e d u r e s . . . ^2 B) D e s i g n and parameters o f Otoadmittance procedures . . . . . . . . ^2  4.4  Record o f a r e p r e s e n t a t i v e TTS procedure  4.5  Example photograph o f otoadmittance p l o t s (condition NQ).  (condition  40  4.6  R e p r e s e n t a t i v e schematic o f otoadmittance p l o t s . . 40  5.1  Comparison o f TTS (measured a t 700 Hz) a t 6 d i f f e r e n t post-exposure times f o r c o n d i t i o n s N and H . . „ „ . „  44  Comparison o f TTS d i f f e r e n c e v a l u e s (15" p o s t exposure w i t h i n i t i a l change i n G^ d u r i n g exposure . o . . . . . . . . .  c,2  T  5.2  5.3  5.4  T  Comparison o f TTS d i f f e r e n c e v a l u e s (15" p o s t exposure) w i t h f i n a l change i n G^ d u r i n g GXpO SUITS e » o i r o o 0 e t o o » « 0 * e « 6 o « «  ^  Comparison o f TTS d i f f e r e n c e v a l u e s (15" p o s t - . exposure) w i t h i n i t i a l change i n during e x p o s u r e . , . . . . . . . . . . . « . * . . . . .  ^4  -vii-  -viii-  Figure 5,5  Z§££ Comparison o f TTS d i f f e r e n c e v a l u e s (15" postexposure) w i t h i n i t i a l change .in Y during exoosure, . • o , , , t , , • • c « . . » • • • • N  55  Chapter 1 Introduction Each time a person t a l k s a l o u d he i s c o n s t a n t l y dependent  on h i s a u d i t o r y system t o monitor h i s v o c a l o u t p u t .  Thus s p e a k i n g i s i n f l u e n c e d by h e a r i n g but, as r e c e n t dence  evi-  s u g g e s t s , h e a r i n g i s a l s o i n f l u e n c e d by s p e a k i n g .  I t i s known t h a t i f we speak w h i l e l i s t e n i n g t o a sound,the sound we hear i s a l t e r e d .  But how does t h i s occur?  What  mechanisms come i n t o p l a y d u r i n g phonation and how do they change t h e sound t h a t e n t e r s the ear? When the human ear i s exposed t o any sound the a c o u s t i c energy o f the sound t r a v e l s from the e x t e r n a l a u d i t o r y meatus through the tympanic membrane, middle ear s t r u c t u r e s and c o c h l e a r f l u i d Corti.  to the h a i r c e l l s o f the Organ o f  A t the h a i r c e l l s the a c o u s t i c energy i s transformed  i n t o e l e c t r i c a l energy which i s t r a n s m i t t e d a l o n g the a u d i t o r y nerve and h i g h e r order neurons t o the c o r t e x .  This  t r a n s m i s s i o n o f sound energy i s i n f l u e n c e d by the frequency, i n t e n s i t y , and d u r a t i o n o f the sound t o which the ear i s exposed. I t has been shown ( B e l l and F a i r b a n k s , 1963)  that  a 60 second exposure t o as low an i n t e n s i t y tone as 10 dB SL a t 1,  2 , o r 4 kHz can s i g n i f i c a n t l y r a i s e the post-exposure  b e h a v i o u r a l t h r e s h o l d f o r a tone o f the same f r e q u e n c y . a post-exposure temporary t h r e s h o l d s h i f t -1-  Such  ( h e n c e f o r t h TTS)  -2i s a f u n c t i o n o f the i n t e n s i t y , d u r a t i o n , and frequency of  the exposure tone.  Thus, a h i g h i n t e n s i t y exposure tone  w i l l produce a g r e a t e r TTS than a low i n t e n s i t y exposure tone. A r e c e n t study (McBay, 1971)  has shown t h a t TTS produced by  a f i v e minute exposure to a 118 dB SPL 5 0 0 Hz tone i s reduced if  the l i s t e n e r phonates  (hums) d u r i n g the exposure.  Such  r e s u l t s i n d i c a t e t h a t i f the TTS i s decreased when phonation o c c u r s d u r i n g exposure, then phonation might a t t e n u a t e t r a n s m i s s i o n o f the exposure tone to the i n n e r e a r . tic  I f l e s s acous-  energy reaches the i n n e r e a r , l e s s f a t i g u e o f the h a i r  must o c c u r , thus TTS due to exposure i s reduced.  cells  I t i s not  c l e a r , however, what f a c t o r s cause t r a n s m i s s i o n o f sound to be a t t e n u a t e d . -,T.he sound may ear  be a t t e n u a t e d by the c o n t r a c t i o n o f middle  muscles ( h e n c e f o r t h MEM),  which o c c u r s d u r i n g or j u s t  p r i o r to p h o n a t i o n (Djupesland, 1964,  1967;  Salomon and  Starr,  1963» Shearer and Simmons, 1965)1 o r the sound t r a n s m i s s i o n may  be a l t e r e d by a change i n the mode o f s t a p e s v i b r a t i o n ,  p o s s i b l y r e s u l t i n g from a change i n the d i r e c t i o n o f s k u l l v i b r a t i o n t h a t o c c u r s d u r i n g phonation (Bekesy, I 9 6 0 , cf.  sec. 2 . 2 2 ) .  p.201;  I f , d u r i n g phonation, some or a l l o f the  a t t e n u a t i o n o f sound t r a n s m i s s i o n i s due t o MEM  contraction,  how  I t i s possible  i s the a c t i o n o f these muscles c o n t r o l l e d ?  t h a t the MEM  are d i r e c t l y i n f l u e n c e d by c o r t i c a l c o n t r o l or  it  may  be t h a t the MEM  are a c t i v a t e d r e f l e x i v e l y by a c t i v i t y  of  the l a r y n x d u r i n g and j u s t p r i o r to p h o n a t i o n .  -5-  The  general  o b j e c t i v e o f t h i s study i s to  one  of the  f a c t o r s t h a t may  TTS  i f phonation accompanies exposure to a high  'More s p e c i f i c a l l y , w i l l be of MEM  the r o l e of the MEM  investigated. activity,  be r e s p o n s i b l e  investigate  for reduction  in  i n t e n s i t y tone.  i n the r e d u c t i o n  of  TTS  U s i n g a c o u s t i c admittance as a measure  changes i n admittance and  changes i n  TTS,  r e c o r d e d under s i m i l a r experimental c o n d i t i o n s , w i l l be to r e v e a l p o s s i b l e c o r r e l a t i o n s between MEM  a c t i v i t y and  compared TTS.  Chapter 2 Review o f the L i t e r a t u r e 2«0  Introduction S e c t i o n 2.1 phenomenon and  i n c l u d e s a d i s c u s s i o n of the  TTS  a r e v i e w of experiments t h a t show some e f f e c t s  o f p h o n a t i o n on TTS.  S e c t i o n 2.2  d i s c u s s e s the e f f e c t of  p h o n a t i o n on sound t r a n s m i s s i o n i n the middle e a r . are subsections  Included  on a c t i v i t y o f the middle ear muscles and  v i b r a t i o n o f the s t a p e s .  on  Although o n l y i n d i r e c t l y r e l e v a n t  t o t h i s study a f i n a l s e c t i o n , which examines the p o s s i b l e c o n t r o l mechanisms i n v o l v e d i n TTS Included  i n S e c t i o n 2.3  ac-ti-vi-ty -and  reduction,  is  presented.  are s u b s e c t i o n s on c o n t r o l of  stapes v i b r a t i o n and  MEM  on c e n t r a l f a c t o r s i n f l u -  encing auditory f a t i g u e . 2.1  E f f e c t o f P h o n a t i o n on 2.11  TTS  TTS  I f a l i s t e n e r i s exposed to any  sound o f  s u f f i c i e n t i n t e n s i t y and d u r a t i o n h i s ears" post-exposure s e n s i t i v i t y w i l l be a l t e r e d .  T h i s change i n s e n s i t i v i t y  be measured i n terms o f a temporary s h i f t i n threshold is  (TTS).  T h i s TTS  absolute  may  hearing  or p o s t - s t i m u l a t o r y a u d i t o r y f a t i g u e  " u s u a l l y , but not always, a decrease i n t h r e s h o l d s e n s i -  t i v i t y . " (Ward, 1963i p.241) Measurement o f TTS  r e q u i r e s determination  o f pre-  exposure t h r e s h o l d , f o l l o w e d by exposure o f the same ear to the f a t i g u i n g s t i m u l u s , a f t e r which the post-exposure t h r e s h o l d -4-  '  -5-  o f t h a t e a r i s measured.  TTS i s the d i f f e r e n c e , i n dB, b e t -  ween t h e p o s t - and pre-exposure t h r e s h o l d s .  TTS t h a t  follows  a pure tone f a t i g u e s t i m u l u s g e n e r a l l y i n c r e a s e s w i t h the d u r a t i o n and f r e q u e n c y o f the s t i m u l u s u n t i l a l i m i t i n t h r e s h o l d s h i f t i s reached (Ward, 1963* B o t s f o r d , 1 9 7 1 ) .  It is  g e n e r a l l y a c c e p t e d t h a t TTS v a r i e s d i r e c t l y w i t h i n t e n s i t y o f the pure tone f a t i g u e s t i m u l u s ( i e . as i n t e n s i t y i n c r e a s e s TTS  becomes l a r g e r ) .  T h i s o c c u r s even f o r i n t e n s i t i e s below  70 dB SL i f TTS i s measured w i t h i n 5 seconds o f exposure c e s s a t i o n ( B e l l and F a i r b a n k s , 1963)« The f r e q u e n c y o f the p r e - and post-exposure  test  tone a l s o i n f l u e n c e s TTS as does the post-exposure time a t which t h r e s h o l d o f the tone i s measured.  F o r exposure  tones  o f l e s s than 80 dB SPL t h e r e s u l t i n g TTS i s maximum a t the f r e q u e n c y o f t h e exposure.  TTS from such lower  intensity  s t i m u l i i s o f s h o r t d u r a t i o n , thus measurement roust be taken s h o r t l y a f t e r c e s s a t i o n o f the exposure tone. s i t y stimulation  Higher i n t e n -  (80 dB SPL and above) produces l o n g e r l a s t i n g  TTS w i t h a maximum v a l u e o n e - h a l f o c t a v e o r more above the exposure  f r e q u e n c y ( D a v i s , e t a l , 1 9 5 0 ; E p s t e i n and Schubert,  1957; B e l l and F a i r b a n k s , 1 9 6 3 ; Rodda, 1 9 6 4 ) . A f t e r c e s s a t i o n o f the exposure tone TTS g r a d u a l l y d e c r e a s e s , i n , r o u g h l y , an e x p o n e n t i a l f a s h i o n , r a p i d l y i n the f i r s t  few seconds then g r a d u a l l y t o zero ( i e . t h e t h r e s h o l d  becomes e q u a l t o t h e pre-exposure v a l u e ) .  T h i s r e c o v e r y occurs,  f o r each s u b j e c t , a t a f a i r l y c o n s t a n t r a t e which does n o t  -6-  seem to depend on the parameters o f the f a t i g u e  stimulus  (Ward, 1 9 6 3 ) . There i s g r e a t i n t e r - s u b j e c t v a r i a b i l i t y i n the magnitude o f TTS,  produced by a g i v e n exposure, which seems  dependent on i n d i v i d u a l s u s c e p t i b i l i t y to a u d i t o r y and  n o t r e l a t e d to d i f f e r e n c e s i n a u d i t o r y t h r e s h o l d a t  exposure f r e q u e n c y (Ward, 1 9 6 3 ) . TTS  fatigue the  Intra-subject variation i n  magnitude produced by a s p e c i f i c exposure i s , however,  insignificant.  Riach,  et a l . (1964) i n v e s t i g a t e d i n d i v i d u a l  s u s c e p t i b i l i t y to a u d i t o r y f a t i g u e by g i v i n g 12  subjects  the  same h i g h i n t e n s i t y pure tone exposure 20 times over a p e r i o d o f weeks.  No  ( a t 2800 Hz)  s i g n i f i c a n t change i n the pre-exposure t h r e s h o l d was  noted d u r i n g the s e s s i o n s but t h e r e was  " t r e n d toward a s m a l l e r TTS a t the one minute post-exposure p o i n t . " (Riach, et a l . , 1964, N i x o n and  G l o r i g (1962) a l s o looked  auditory fatigue.  p.1195)  at s u s c e p t i b i l i t y to  They warned t h a t TTS  experiments must a l l o w  f o r the f a c t t h a t i f the ear does n o t have r e c o v e r y between exposures but i s s u b j e c t e d s t i m u l a t i o n before recovery may  o c c u r and 2.12  and 1971?  Luterman, 1 9 6 9 i 1970;  TTS  time  fatiguing  has o c c u r e d , cumulative e f f e c t s threshold.  Recent i n v e s t i g a t i o n s ( K a r l o v i c h  Luterman and  B e n g u e r e l and KcBay, 1972)  K a r l o v i c h , 1969;  McBay,  have shown t h a t phonation  appears to a l t e r sound t r a n s m i s s i o n K a r l o v i c h and  t o repeated  l e a d t o permanent s h i f t s i n h e a r i n g  P h o n a t i o n and  a  i n the a u d i t o r y system.  Luterman (1969) exposed f o u r normal  hearing  -7-  s u b j e c t s t o a 4000 Hz 90 dB SL f a t i g u i n g tone  f o r three  The s u b j e c t s t r a c k e d t h e i r t h r e s h o l d s a t 5656 Hz  minutes.  f o r two minutes b e f o r e and t h r e e minutes a f t e r  exposure.  D u r i n g exposure the s u b j e c t s e i t h e r r e a d a s e t passage aloud or r e a d i t s i l e n t l y .  Post-exposure  TTS was found  t o be con-  s i s t e n t l y g r e a t e r when the s u b j e c t s r e a d a l o u d than when they r e a d s i l e n t l y d u r i n g exposure.  R e s u l t s suggest  that, during  the r e a d i n g a l o u d a c t i v i t y , t r a n s m i s s i o n o f a 4000 Hz tone i s enhanced. found  I n a l a t e r study, Luterman and K a r l o v i c h (1969)  t h a t when s u b j e c t s , exposed t o a 2000 Hz 90 dB SL  tone, r e a d a l o u d d u r i n g exposure t h e y o b t a i n e d  consistently  l e s s TTS than i f they r e a d s i l e n t l y , read s i l e n t l y w h i l e a r t i c u l a t i n g , o r engaged i n r e v e r i e d u r i n g exposure. r e s u l t s suggest  t h a t , d u r i n g the r e a d i n g a l o u d  These  activity,,  t r a n s m i s s i o n o f a 2000 Hz tone t o t h e c o c h l e a i s reduced. A t h i r d study by these experimenters  exposed sub-  j e c t s t o a 1000 Hz 110 dB SPL tone f o r t h r e e minutes d u r i n g which the s u b j e c t s e i t h e r v o i c e d o r g e s t u r e d - o n l y the vowels / a / or / i / TTS  ( K a r l o v i c h and Luterman, 1970).  Post-exposure  a t 1414 Hz was s i g n i f i c a n t l y l e s s i f v o i c e d / a / o r / i /  accompanied the exposure than i f non-voiced performed.  g e s t u r e s were  As w i t h t h e 2000 Hz tone, these r e s u l t s  imply  t h a t , i f v o i c i n g accompanies exposure, the t r a n s m i s s i o n o f a 1000 Hz tone i s a t t e n u a t e d ,  K a r l o v i c h and Luterman  suggest  t h a t a t t e n u a t i o n o f low frequency tones d u r i n g phonation r e s u l t from MEM c o n t r a c t i o n , known t o occur d u r i n g  may  phonation  (Salomon and S t a r r , 19631 Shearer and Simmons, 19651  Djupesland,  -81967)i tion  and/or from i n e f f i c i e n t stapes v i b r a t i o n d u r i n g phona(Bekesy, I 9 6 0 ) . Most r e c e n t l y McBay and Benguerel (McBay, 1971?  B e n g u e r e l and McBay, 1972) used TTS s t u d i e s to i n v e s t i g a t e more c l o s e l y the e f f e c t o f phonation on sound t r a n s m i s s i o n i n t h e a u d i t o r y system.  They s u b j e c t e d l i s t e n e r s t o a 500 Hz  118 dB SPL exposure tone f o r 5 minutes d u r i n g which the l i s t e n e r hummed a t s p e c i f i e d fundamental f r e q u e n c y and i n t e n s i t y , approximated the v o c a l f o l d s w i t h o u t v o i c i n g , l i s t e n e d to a r e c o r d i n g o f humming, performed a c t i v i t i e s to e l i c i t ( n o n - a c o u s t i c a l l y ) the MEM r e f l e x e s , o r s a t q u i e t l y performi n g no t a s k .  Post-exposure TTS was measured by t r a c k i n g  t h r e s h o l d s a t 700 Hz f o r 4 minutes a f t e r the exposure tone ended.  They found t h a t "TTS from the exposure tone accompanied by p h o n a t i o n (humming) was c o n s i s t e n t l y and s i g n i f i c a n t l y l e s s than TTS from the exposure tone w i t h o u t any supplementary activity," (McBay, 1971.  p.107)  The most s i g n i f i c a n t d i f f e r e n c e s i n magnitude  o f TTS occurred  when post-exposure t h r e s h o l d was measured 10 t o 15 a f t e r exposure c e s s a t i o n .  seconds  S l i g h t decreases i n TTS were noted  when c e r t a i n a c o u s t i c r e f l e x e l i c i t i n g movements accompanied exposure ( i e . r e p e a t e d t u r n i n g o f the head, chewing, f o r c e f u l l y , and s w a l l o w i n g ) .  smiling  No s i g n i f i c a n t a l t e r a t i o n s i n  TTS occurred when s u b j e c t s l i s t e n e d t o r e c o r d e d humming or approximated the v o c a l f o l d s without humming d u r i n g exposure. In a d d i t i o n , they found t h a t phonation d u r i n g exposure was  -9-  more e f f e c t i v e i n d e c r e a s i n g TTS f o r females than f o r males. T h i s suggests t h a t females may  have more e f f i c i e n t mechanisms  f o r a t t e n u a t i n g low-frequency sound t r a n s m i s s i o n to the c o c h l e a d u r i n g phonation than have males. the h y p o t h e s i s t h a t females may males (Ward, 1 ° 6 6 ) .  T h i s a l s o supports  have more e f f i c i e n t MEM  than  F o r a more d e t a i l e d d i s c u s s i o n o f the  e f f e c t o f phonation on TTS see McBay ( 1 9 7 1 ) . 2.2  E f f e c t o f Phonation on Sound T r a n s m i s s i o n i n the Middle Ear I t has been e s t a b l i s h e d  ( c f . S e c t i o n 2.1)  that  p h o n a t i o n d u r i n g exposure to a f a t i g u i n g s t i m u l u s a l t e r s the post-exposure TTS and i t i s i m p l i e d t h a t phonation a l t e r s t r a n s m i s s i o n o f the f a t i g u i n g s t i m u l u s to the c o c h l e a , the f o l l o w i n g d i s c u s s i o n w i l l c o n s i d e r the p o s s i b l e mechanisms by which t h i s change i n middle ear sound t r a n s m i s s i o n o c c u r s . 2.21  The Middle Ear Muscles Anatomy  (MEM)  Of the two middle ear muscles, the l a r g e r  i s the t e n s o r tympani which i s about 25 mm  i n l e n g t h and  2 about 5«85 mm  i n cross section.  T h i s muscle  lies  within  a bony c a n a l p a r a l l e l w i t h and s u p e r i o r to the E u s t a c h i a n tube.  The tendon o f the muscle passes through the p o s t e r i o r  opening o f the c a n a l and i s i n s e r t e d on the manubrium below the neck of the m a l l e u s , (see F i g . 2.1) the t e n s o r tympani  On  moves the malleus m e d i a l l y and  just  contraction anteriorly,  almost a t r i g h t a n g l e s to the d i r e c t i o n o f r o t a t i o n o f the o s s i c l e s , thus i n c r e a s i n g t e n s i o n on the tympanic  membrane.  I n n e r v a t i o n i s s u p p l i e d by a branch o f the t r i g e m i n a l nerve  -10Tendon of tensor tymponi Cochleoriform process  Tensor tymponi  Septum canalis musculotubarii  Auditory tube'  Figure 2.1 Schematic diagram of the tensor tympani muscle. (from Zenilin,1968,p.383) Superior ligcment of lateral ligament of the malleus  , h e  n  }  a l , e u s  Posterior ligament of the incus  Stapedius muscle Posterior ligament Annular ligament of the stapes • Remains of the anterior ligament of the malleus  Anterior  ligornen.t  Figure 2.2 Schematic diagram of middle ear ligaments and stapedius m u s c l e  '  (from Zemlin,1968,p.380)  -11-  (Jepsen,  1963? D j u p e s l a n d , 1967; Zemlin, 19685 M j i l l e r ,  1972).  S t a p e d i u s muscle, 6 . 3 mm i n l e n g t h , i s the  The  s m a l l e s t muscle i n the human body.  I t occupies  a bony c a n a l  on t h e p o s t e r i o r v/all o f the tympanic c a v i t y and i t s tendon i n s e r t s a t the p o s t e r i o r margin o f the head o f the s t a p e s . (See F i g . 2 . 2 ) r i g h t angles chain,thus  C o n t r a c t i o n draws the stapes p o s t e r i o r l y , a t  t o the d i r e c t i o n o f movement o f the o s s i c u l a r  a l t e r i n g the movement o f the stapes  a g a i n s t the o v a l window.  Innervation  o f t h e f a c i a l nerve (Jepsen,  footplate  i s s u p p l i e d by a branch  19635 D j u p e s l a n d , 1967?  Zemlin,  1968). MEM A c t i v i t y  The two MEM c o n t r a c t i n o p p o s i t i o n  t o each o t h e r b u t the r e s u l t o f c o n t r a c t i o n i s a dampening o f o s s i c u l a r movement and an i n c r e a s e o f a c o u s t i c impedance a t the tympanic membrane. number o f ways.  C o n t r a c t i o n can be e l i c i t e d  in a  A s m a l l percentage o f i n d i v i d u a l s a r e a b l e t o  v o l u n t a r i l y c o n t r a c t t h e i r MEM  (Metz, 1951)  Reger, i 9 6 0 ?  J e p s e n , 1963? Z e m l i n , 1968) b u t , f o r most i n d i v i d u a l s , a c t i v i t y u s u a l l y r e s u l t s r e f l e x i v e l y from a c o u s t i c o r n o n - a c o u s t i c stimuli. Acoustic occurs  e l i c i t a t i o n o f MEM r e f l e x c o n t r a c t i o n  when t h e e a r i s presented  w i t h an a c o u s t i c s t i m u l u s o f  an i n t e n s i t y a t o r above the r e f l e x t h r e s h o l d . i s normally  This  threshold  between 80 dB SL and 90 dB SL f o r pure tones o f  1 2 5 Hz t o 4000 Hz (Jepsen,  1963? M i l l e r , .196lb| J e r g e r , 1 9 7 0 ) .  -12The  acoustic reflex  ( h e n c e f o r t h AR)  l o u d tone i s presented w i l l occur  to one  i n both e a r s .  to  the motor n u c l e u s  ear, r e f l e x c o n t r a c t i o n o f  The  the s u p e r i o r o l i v a r y nucleus  i s b i l a t e r a l , thus i f a MEM  r e f l e x c e n t r e i s thought to be o f the pons, j u s t v e n t r a l  o f the f a c i a l nerve, where e f f e r e n t  neurons o f the r e f l e x are l o c a t e d , w h i l e the a f f e r e n t neurons are l o c a t e d i n the d o r s a l and v e n t r a l c o c h l e a r n u c l e i  (Jepsen,  1963). H i g h e r f r e q u e n c i e s appear to e l i c i t lar  t h r e s h o l d s to lower f r e q u e n c i e s  1963? P o r t e r , 1 9 7 2 ) .  ( J e r g e r , 1970;  (1972) found t h a t narrow bands or  Peterson  and L i d e n  full  bands o f white n o i s e produced AR  a l a t e n c y of about 45  depending on the frequency nal  (Zemlin, 1968).  creased in  thresholds  dB more s e n s i t i v e than t h r e s h o l d s from pure has  and  approximately  tones.  to 150  msec  i n t e n s i t y o f the s t i m u l u s  the degree o f c o n t r a c t i o n o f the s t a p e d i u s  the c o n t r a c t i o n o f MEM  muscle,  I f the sound  continues,  g r a d u a l l y decreases to a r e s t i n g l e v e l .  I f a sound o f a d i f f e r e n t frequency traction results  sig-  As the i n t e n s i t y o f the s i g n a l i s i n -  p a r t i c u l a r , i n c r e a s e s to a maximum.  (Metz, 1 9 5 1 ) .  r e f l e x a d a p t a t i o n i s due fatigue.  Jepsen,  than pure tones i n e l i c i t i n g the  AR.  The AR  at simi-  Complex s i g n a l s such as random n o i s e ,  however, a r e more e f f i c i e n t  15  the AR  i s i n t r o d u c e d a new  con-  T h i s f i n d i n g suggests t h a t  to p r o c e s s e s  o t h e r than muscular  K a r l o v i c h e t a l . (1972) have shown t h a t MEM  contrac-  t i o n , as measured by changes i n a c o u s t i c impedance, i s maint a i n e d i f a tone or n o i s e i s presented  p u l s e d 12  dB above  -13the AR t h r e s h o l d .  The same tone o r n o i s e ,  i f presented con-  t i n u o u s l y , was found t o r e s u l t i n a decrease i n impedance ( i e . an a d a p t a t i o n that a pulsed  o f the r e f l e x ) .  stimulus  i s a more e f f e c t i v e a c t i v a t o r o f MEM  than i s a c o n t i n u o u s s t i m u l u s . a f f e c t r e f l e x adaptation who found  Such r e s u l t s suggest  Frequency o f s t i m u l a t i o n may  as shown by Brasher e t a l (1969)  that "AR s t i m u l a t e d by t h e 1000 Hz (octave band) n o i s e d i d adapt more s l o w l y than t h a t from the 4000 Hz (octave band) n o i s e . " (Brasher,  e t a l , 1 9 6 9 . p.583)  S e v e r a l i n v e s t i g a t o r s have shown MEM r e f l e x e s t o be  e l i c i t e d by n o n - a c o u s t i c p r o c e d u r e s .  Anderson (1959)  e l i c i t e d r e f l e x c o n t r a c t i o n o f the s t a p e d i u s  muscle by p u l s e d tory canal.  e l e c t r i c a l s t i m u l a t i o n o f the e x t e r n a l  tympani response ( K l o c k h o f f and Anderson,  o r response o f b o t h muscles (Djupesland, 1 9 6 4 ) .  s i m i l a r b l a s t o f a i r on the eyes r e s u l t e d i n t e n s o r  Djupesland, I 9 6 7 ) .  196l»  Touching the s k i n o f t h e a u r i c l e s w i t h  a t w i s t o f c o t t o n was found t o produce s t a p e d i u s (Djupesland, 1 9 6 7 ) .  that voluntary  A  tympani  c o n t r a c t i o n as p a r t o f a s t a r t l e response ( K l o c k h o f f ,  traction  audi-  An a i r b l a s t d i r e c t e d toward t h e e x t e r n a l meatus  e l i c i t e d tensor i960)  K l o c k h o f f and  muscle con-  Djupesland (1967) a l s o found  movements, such as t i g h t c l o s u r e o f t h e eyes,  s w a l l o w i n g , opening o f the mouth, and c l e n c h i n g  of t h e t e e t h ,  r e s u l t i n c o n t r a c t i o n o f one o r b o t h tympanic muscles. o r t u r n i n g t h e head a l s o appeared t o r e s u l t i n such  Lifting  contractions  -14-  S t a r r , 1963)0  (Salomon and the  l i t e r a t u r e d e a l i n g w i t h a c o u s t i c and  t i o n o f MEM  r e f l e x e s see D j u p e s l a n d ,  MEM MEM  F o r a more complete d i s c u s s i o n  number o f r e c e n t s t u d i e d the  (1967.  A c t i v i t y D u r i n g Phonation  contraction during  non-acoustic  electromyographic  The  Salomon and  (EMG)  occurrence of been found i n a  a c t i v i t y o f MEM  tympani was  registered.  o f phonation while others onset of phonation. 300  increased  o f the  stapedius  in  As  one  occured 4 0 msec t o 300  A l l c o n t r a c t i o n s continued  In an EMG  tensor  a t onset  msec  before  f o r up  Increased  to  activity  muscle d u r i n g v o c a l i z a t i o n f o l l o w e d  temporal p a t t e r n .  two  a c t i v i t y of his  Some c o n t r a c t i o n s occurred  msec a f t e r c e s s a t i o n of p h o n a t i o n .  (1963)  Starr  human s u b j e c t s d u r i n g v a r i o u s motor a c t i v i t i e s . s u b j e c t began to t a l k or hum  elicita-  pp.18-24).  speech a c t i v i t i e s has  investigations.  of  a similar  study w i t h c a t s Simmons found  that  " i n v o c a l i s a t i o n , middle ear muscle c o n t r a c t i o n s b e g i n about 100 msec b e f o r e a c t u a l sound i s produced and c o n s i d e r a b l y o u t l a s t the speech ( s i c ) sound? the c o n t r a c t i o n s do not appear to h a b i t u a t e ; t h e i r magnitude i s p r o p o r t i o n a l to the i n t e n s i t y of v o c a l i z a t i o n to be a n t i c i pated." (Simmons, 1 9 6 4 , p.773) Simmons i n v e s t i g a t e d s i m i l a r phenomena w i t h human subjects;  however, he d e f i n e d  o c c u r r i n g when the  subject's  stapedius  a c o u s t i c impedance a t the  drum showed a s p e c i f i e d change, t r a c t , they s t i f f e n  muscle a c t i v i t y  ( R e c a l l t h a t when MEM  the. o s s i c u l a r c h a i n ,  t r a n s f e r impedance o f the middle ear.)  as  earcon-  thus i n c r e a s i n g the When Simmons'  subjects  said  "one, two,  t h r e e " impedance changes c o n s i s t e n t w i t h  s t a p e d i u s muscle  a c t i v i t y were produced.  I n one ear, w i t h  a s t a p e d i u s muscle p a r a l y s i s , speech r e s u l t e d i n no impedance change (Simmons, 1964} and Simmons (1965)  Shearer and Simmons, 1 9 & 5 ) .  Shearer  found a c o u s t i c impedance changes  (MEM  a c t i v i t y ) to precede i n i t i a t i o n o f phonation by 65 msec to 100 msec or t o c o i n c i d e w i t h onset o f p h o n a t i o n . whether head and  To  determine  jaw movements were r e s p o n s i b l e f o r some o f  the change i n impedance the authors asked s u b j e c t s t o a r t i c u l a t e words w i t h o u t p r o d u c i n g v o i c e .  The n e g l i g i b l e impedance  changes t h a t r e s u l t e d i n d i c a t e t h a t such muscle d i d not i n t e r f e r e w i t h measurement o f MEM D j u p e s l a n d (I967) r e c o r d e d EMG  activities  activity. a c t i v i t y from v a r i o u s  muscles when h i s s u b j e c t s spoke the words " j a " and  "nei".  A l l s u b j e c t s showed i n c r e a s e d a c t i v i t y i n the o r b i c u l a r i s oculi,  s t a p e d i u s and t e n s o r tympani  muscles.  "This a c t i v i t y  seemed t o i n c r e a s e d i r e c t l y w i t h the i n t e n s i t y o f the speech." (Ibidem, p.80)  A c t i v i t y of the t e n s o r tympani began 30 msec  to 450 msec b e f o r e phonation was r e c o r d e d and l a s t e d up to 300 msec a f t e r phonation ceased. E f f e c t o f MEM E v i d e n c e t h a t MEM  A c t i v i t y on Sound T r a n s m i s s i o n  c o n t r a c t i o n has an e f f e c t on sound  trans-  m i s s i o n through the middle ear i s found p r i m a r i l y i n animal studies,  A number o f i n v e s t i g a t o r s ( W e r s a l l , 1958? Weaver  and Vernon, 1955? Simmons, 1959? and o t h e r s c i t e d i n Jepsen, 1 9 6 3 i p.221) e i t h e r measured MEM  a c t i v i t y d i r e c t l y or observed  -16-  e f f e c t s o f the a c t i v i t y on c o c h l e a r microphonics. "basis o f such s t u d i e s i t i s now attenuates 1963;  sounds below 1000  Brasher  accepted  On  t h a t MEM  Hz by up to 20 dB  the  contraction  (Jepsen,  e t a l , 1969), whereas i t e i t h e r does not  or enhances s l i g h t l y t r a n s m i s s i o n o f h i g h e r frequency Simmons (1959). a f t e r c u t t i n g e i t h e r the  effect sounds.  stapedius  or t e n s o r tympani o f c a t s , measured the c o c h l e a r  microphonic  r e s p o n s e o f t h a t ear to i n t e n s e sounds.  t h a t the  microphonic  disappeared  thus concluded  He  found  o n l y when the s t a p e d i u s had been c u t  t h a t the s t a p e d i u s has a more important  than the t e n s o r tympani i n sound t r a n s m i s s i o n . however, K e v a n i s h v i l i and G v a c h a r i a  r  role  Recently,  (1972) measured the  effect  o f t e n s o r tympani c o n t r a c t i o n s on sound t r a n s m i s s i o n i n c a t s and  found  t r a n s m i s s i o n o f 5 0 0 Hz,  t o be a t t e n u a t e d . conduction increased.  Higher  800 Hz,  and  authors  Hz  tones  f r e q u e n c i e s were not a t t e n u a t e d  o f 1800-Hz to 2000-Hz tones may The  1000  concluded  and  even have been  that, although  t e n s o r tym-  p a n i c o n t r a c t i o n does not a l t e r sound t r a n s m i s s i o n to the same e x t e n t as does s t a p e d i u s c o n t r a c t i o n , both muscles  ap-  p e a r to a c t i n a complementary f a s h i o n over the  frequency  range.  not p e r t a i n  Note, however, t h a t f i n d i n g s i n c a t s may  t o human e a r s . D i r e c t i n v e s t i g a t i o n s o f t r a n s m i s s i o n changes cannot e a s i l y be accomplished been employed.  w i t h humans^thus i n d i r e c t methods have  Reger (I960) observed  s h i f t s i n absolute  h e a r i n g t h r e s h o l d b e f o r e , d u r i n g , and a f t e r  subjects  -17-  voluntarily  c o n t r a c t e d t h e i r MHVI.  He found t h a t MEM' c o n t r a c -  t i o n i n c r e a s e d the t h r e s h o M o f h e a r i n g f o r low frequency sounds (125 Hz to 1000 Hz) and t h a t t h i s t h r e s h o l d was g r e a t e s t a t 125 Hz and 250 Hz.  shift  Borg (1968) found, i n  s u b j e c t , t h a t a $00 Hz tone 20 dB above a c o u s t i c  one (AR)  t h r e s h o l d was attenuated  reflex  by 12 to 15 dB by s t a p e d i u s %  c o n t r a c t i o n w h i l e a 1450 Hz tone 16 dB above AR t h r e s h o l d was a t t e n u a t e d no  by o n l y 0 to 6 dB.  The r e f l e x had l i t t l e o r  e f f e c t a t f r e q u e n c i e s above 2000 Hz and a t moderate  sound  (lower)  intensities. When MEM c o n t r a c t , t h e m o b i l i t y o f the o s s i c l e s  changes, thus changing the acoustic.impedance a t the eardrum as w e l l as the t r a n s f e r impedance ( t r a n s m i s s i o n istics) can,  o f the middle e a r , ^Measurement o f impedance changes  t h e r e f o r e , as mentioned above, g i v e i n f o r m a t i o n about  concurrent ved  character-  changes i n sound t r a n s m i s s i o n .  Metz (1951)  t h a t reduced sound t r a n s m i s s i o n d u r i n g human MEM  obser-  contrac-  t i o n c o u l d be measured as a change i n impedance o f the e x t e r nal  a u d i t o r y c a n a l , p r i n c i p a l l y as a r e d u c t i o n i n the a b s o r p t i o n  coefficient  with l i t t l e  by Jepsen, 1963? M i l l e r , Miller  (196lb)  or no. change i n the phase ( a l s o  cited  1958). i n v e s t i g a t e d impedance changes i n  normal ears d u r i n g a c o u s t i c e l i c i t a t i o n  o f the MEM  reflex.  He found t h a t a $00 Hz tone produced a g r e a t e r change i n impedance than a 1500 Hz tone, which supports t h a t MEM c o n t r a c t i o n a t t e n u a t e s  the hypothesis  t r a n s m i s s i o n o f low frequency  -18-  sounds more than t h a t o f h i g h e r frequency sounds. i n which M i l l e r  (1965)  A study,  i n v e s t i g a t e d admittance ( i n v e r s e o f  impedance) changes produced by MEM c o n t r a c t i o n i n c a t s and r a b b i t s , showed t h a t , on e l i c i t a t i o n o f MEM  contraction,  t h e s e animals produced impedance changes s i m i l a r t o those produced by humans. 2 . 2 2 Stapes V i b r a t i o n  I n a d d i t i o n to MEM  contraction,  a change i n t h e v i b r a t i o n mode o f the stapes may a l s o occur during phonation,  B£k6sy ( i 9 6 0 ) has shown t h a t when a sub-  j e c t i s exposed t o moderate i n t e n s i t y a i r - c o n d u c t e d  stimuli  h i s stapes r o t a t e s around a v e r t i c a l a x i s (as i n F i g , 2 , 3 a ) . He h y p o t h e s i z e d t h a t d u r i n g p h o n a t i o n the stapes movement changes t o a r o t a t i o n around i t s l o n g (as i n F i g . 2 . 3 b ) .  (horizontal) axis  T h i s change would r e s u l t i n minimal d i s -  placement o f t h e c o c h l e a r  f l u i d which, i n t u r n , would reduce  e f f i c i e n c y o f sound t r a n s m i s s i o n  t o the c o c h l e a  (Bekesy,  I 9 6 0 , pp.201-202.) As  discussed  i n S e c t i o n 2 . 3 2 , MEM c o n t r a c t i o n may  r e s u l t i n such a l t e r e d stapes v i b r a t i o n .  S i n c e MEM  contrac-  t i o n o c c u r s d u r i n g phonation, both MEM c o n t r a c t i o n and a l t e r e d s t a p e s v i b r a t i o n may r e s u l t i n decreased e f f i c i e n c y o f sound transmission  t o the c o c h l e a .  i n the r e d u c t i o n  The r o l e each mechanism p l a y s  o f sound t r a n s m i s s i o n  y e t been determined.  has, however, n o t  -19-  I I  M  w  Figure 2.3 Movement of the stapes, a) Normal stapes motion i n response to air-borne sound, b) Movement around the -long axis of the stapes (possible during phonation) resulting i n reduced displacement of cochlear f l u i d . (from Bekesy,1960,p.202)  -20-  2.3  C o n t r o l o f P o s s i b l e Mechanisms Involved 2.31  C o n t r o l o f MEM  Contraction  i n TTS  D u r i n g Phonation  anatomy o f the r e f l e x a r c through which the MEM is  incompletely  known,,  One  Reduction The  are a c t i v a t e d  p o r t i o n o f the a r c appears to  i n v o l v e a c t i v i t y from the c o c h l e a r nerve through the  dorsal  and  v e n t r a l c o c h l e a r n u c l e i to the s u p e ' r i o r - o l i v a r y complex  and  f i n a l l y to the motor n u c l e i o f the f a c i a l and  n e r v e s which i n n e r v a t e  the MEM.  the l a t e r a l lemniscus and involved  (Miller, Since  trigeminal  A l t e r n a t i v e pathways tlsrough  the i n f e r i o r c o l l i c u l u s may  also  be  1 9 7 2 ) .  the MEM  often contract  j u s t p r i o r to  the  s t a r t of phonation.^ i t seems l i k e l y t h a t c o n t r a c t i o n i s neurol o g i c a l l y a s s o c i a t e d w i t h l a r y n g e a l a c t i v i t y , such t h a t MEM  the  are a c t i v a t e d c o n c u r r e n t l y -with the' l a r y n g e a l musculature  (Shearer and  Simmons,  1965).  McCall  and Rabuzzi •  i n v e s t i g a t e d the p o s s i b i l i t y t h a t the MEM  and  (1970*  laryngeal  muscles are a c t i v i a t e d as p a r t of a r e f l e x d u r i n g  phonation.  T h e i r r e s u l t s w i t h c a t s demonstrated r e f l e x c o n t r a c t i o n s b o t h MEM  of  a s s o c i a t e d w i t h c o n t r a c t i o n o f the c r i c o t h y r o i d  muscle o f the  larynx.  • Approximation o f the v o c a l f o l d s has as the movement n e c e s s a r y to e l i c i t r e f l e x MEM T h i s a c t i v i t y , however, performed d u r i n g f a t i g u i n g tone, r e s u l t e d i n TTS from TTS  1973)  a f t e r no  K a r l o v i c h and  not  a c t i v i t y during  been suggested contraction.  exposure to a  significantly different  exposure (McBay, 1971).  Luterman (1970) compared TTS  r e s u l t s between  -21-  c o n d i t i o n s i n which vowels were 1) gestured  v o i c e d o r 2)  d u r i n g the f a t i g u e exposure.  r e s u l t i n l e s s TTS  or  They found v o i c i n g to  than the whispered or gestured  I t , t h e r e f o r e , seems u n l i k e l y t h a t v o c a l f o l d e l i c i t s MEM  whispered  condition.  approximation  c o n t r a c t i o n hut r a t h e r t h a t  " v o c a l - f o l d v i b r a t i o n i s the n e c e s s a r y c r i t i c a l f a c t o r f o r e l i c i t i n g the muscle c o n t r a c t i o n " ( K a r l o v i c h and Luterman, 1970, p.516) In a d d i t i o n , h i g h e r areas o f the c e n t r a l nervous system may  d i r e c t the MEM  to c o n t r a c t a t about the same time  as the l a r y n g e a l musculature but the n e u r a l pathways may  not  be o r g a n i z e d  As  as a d i r e c t r e f l e x between MEM  Carmel and S t a r r (1963) suggested, MEM a s s o c i a t i o n w i t h phonation may  simply  and  larynx.  contraction i n be p a r t o f complex  motor a c t s such as swallowing, yawning, e t c . t h a t i n v o l v e many c r a n i a l n e r v e s . duals  S i n c e i t i s known t h a t c e r t a i n i n d i v i -  can v o l u n t a r i l y c o n t r a c t t h e i r MEM  (Metz, 1951t  I960? Jepsen, 1963)1 i t should be remembered t h a t c o r t i c a l i n f l u e n c e over these muscles i s one mechanisms and  must be c o n s i d e r e d  t r o l t h a t occurs 2.32  during  Reger,  higher  o f the c o n t r o l  along w i t h any r e f l e x con-  phonation.  C o n t r o l o f Stapes V i b r a t i o n D u r i n g Phonation  C o n t r o l o f the mode o f v i b r a t i o n of the stapes d u r i n g phonat i o n should  a l s o be c o n s i d e r e d ,  Bekesy ( i 9 6 0 ) has  d u r i n g exposure to moderate i n t e n s i t y a i r - c o n d u c t e d  shown t h a t sounds,  s k u l l v i b r a t i o n i s maximal i n a d i r e c t i o n p a r a l l e l to a u d i t o r y meatus.  the  D u r i n g phonation, v i b r a t i o n i n t h i s d i r e c t i o n  -22i s minimal and direction.  s k u l l v i b r a t i o n becomes maximal i n the  T h i s a l t e r a t i o n i n s k u l l v i b r a t i o n may  stapes v i b r a t i o n from t h a t i n F i g u r e 2 . 3 a 2.3b  (Beklsy, I 9 6 0 ) .  vertical  change  to t h a t i n F i g u r e  A s i m i l a r s h i f t o f r o t a t i o n a l axes,  r e s u l t i n g i n l i m i t i n g transmission of excessive v i b r a t i o n s to the c o c h l e a , i s known to occur d u r i n g s t i m u l a t i o n by i n t e n s e low  1962,  frequency  s o u n d S j i ^ . 130  dB SPL  or g r e a t e r  (Ward,  1963). I t i s a l s o p o s s i b l e t h a t c o n t r a c t i o n o f MEM  s h i f t the v i b r a t i o n a l a x i s o f the s t a p e s .  Miller  might  explained  that "The stapes i s assumed to r o t a t e around i t s lower ( p o s t e r i o r ) ligament because i t i s much s t i f f e r than the a n t e r i o r ligament." ( M i l l e r , 1961a, p.l'69) F i g u r e 2.2  shows the anatomical  p o s i t i o n s o f these  C o n t r a c t i o n o f the s t a p e d i u s muscle may,  as M i l l e r  ligaments. suggests,  a l t e r r o t a t i o n o f the stapes around the s t i f f e r , p o s t e r i o r annular  ligament  a n t e r i o r and  to a r o t a t i o n around a l i n e through both  p o s t e r i o r annular  ligaments.  Such a change i n  the a x i s o f stapes v i b r a t i o n would, as p r e v i o u s l y d i s c u s s e d , reduce sound t r a n s m i s s i o n to the Thus, both MEM t i o n d u r i n g p h o n a t i o n may which, i n t u r n , may  cochlea.  c o n t r a c t i o n and a l t e r e d s k u l l v i b r a cause i n e f f i c i e n t stapes v i b r a t i o n  r e s u l t i n TTS  reduction  t h a t occurs when  p h o n a t i o n accompanies exposure. 2.33  A t t e n t i o n F a c t o r s and TTS R e d u c t i o n  A number of  i n v e s t i g a t o r s have s t u d i e d the e f f e c t v a r i a t i o n s o f mental  -23a c t i v i t y might have on a u d i t o r y  fatigue  ( s p e c i f i c a l l y TTS).  S t u d i e s by experimenters such as C o l l i n s and Capps and F r i c k e  (1965)  (1966) suggest t h a t c e r t a i n types o f mental  acti  v i t y might reduce o r i n t e n s i f y the f a t i g u i n g e f f e c t o f an exposure tone, however, a t p r e s e n t , i t i s too d i f f i c u l t t o delineate the  the mental task a s s i g n e d t o a l i s t e n e r .  Thus,  e f f e c t o f a t t e n t i o n f a c t o r s on TTS experiments must be  c o n s i d e r e d , e v e n though the c o n t r o l o f such v a r i a b l e s i s n o t yet  possible.  Chapter 3 Aims o f the I n v e s t i g a t i o n  The purpose o f t h i s r e s e a r c h r o l e o f t h e MEM i n the r e d u c t i o n  i s t o i n v e s t i g a t e the  o f TTS t h a t occurs i f phona-  t i o n accompanies exposure to a low frequency tone. ally,  Specific-  the aims a r e : 1) To i n v e s t i g a t e the e f f e c t on TTS ( r e s u l t i n g from a 5 minute exposure to a 500 Hz tone) o f phonation (humming) d u r i n g a) to compare non-humming b) t o compare  the exposure, hencet changes i n TTS between humming and conditions. the r a t e o f TTS r e c o v e r y  between  conditions. c) t o determine i f these e f f e c t s a r e d i f f e r e n t i n males and females. 2) To i n v e s t i g a t e the e f f e c t on middle ear admittance o f a 5 minute 500 Hz exposure tone accompanied or not by a humming a c t i v i t y . 3 ) To compare  and attempt t o c o r r e l a t e TTS r e s u l t s w i t h  admittance measurements,  inparticular:  a) changes i n TTS and changes i n admittance f o r each c o n d i t i o n . b) r a t e o f TTS r e c o v e r y and r a t e o f MEM r e l a x a t i o n (from admittance changes) f o r each c o n d i t i o n . c) changes i n TTS and r a t e o f MEM r e l a x a t i o n admittance changes) f o r each c o n d i t i o n . -24-  (from  Chapter 4 E x p e r i m e n t a l Apparatus .1 E x p e r i m e n t a l 4.11 diagram  and Procedures  Apparatus  TTS Instrumentation  F i g u r e 4.1 shows a b l o c k  o f t h e equipment used i n s i g n a l - g e n e r a t i o n and r e s -  p o n s e - r e c o r d i n g d u r i n g TTS procedures.  A Grason-Stadier  Model E800 Bekesy Audiometer was used f o r the p r e - and p o s t exposure  threshold tracking.  The a t t e n u a t i o n r a t e ,  by t h e s e t t i n g o f the motor speed  controlled  s w i t c h , was s e t a t 5 dB/sec  f o r sweep frequency audiograms and a t 2 , 5 dB/sec f o r f i x e d frequency threshold t r a c i n g s . than average  S i n c e a l l s u b j e c t s had b e t t e r  hearing^the 20 dB f i x e d a t t e n u a t i o n s w i t c h was  used f o r each t r a c k i n g procedure remain on t h e graph. was  so the t r a c k i n g r e c o r d would  The continuous 500 Hz exposure  tone  generated by Channel 1 frequency o s c i l l a t o r o f a Madsen  Model OB 60 Audiometer.  I n each experimental s e s s i o n , the  5 dB i n t e r v a l step a t t e n u a t o r was s e t a t the maximum output s e t t i n g o f 110 dB (=117.5 dB S P L ) . Outputs  o f both the Bekesy and Madsen  audiometers  were sent to one s e t o f earphones v i a an e x t e r n a l s w i t c h box t h a t allowed each output to be sent to e i t h e r the r i g h t o r the l e f t earphone.  The earphones were Madsen Model TDH-39 i n  MX-41/AR c u s h i o n s , s e t i n i n s u l a t e d p l a s t i c mountings on a l i g h t - w e i g h t headband. In a d d i t i o n , a B r u e l and K j a e r Type 2203 P r e c i s i o n Sound L e v e l Meter w i t h Type 1613 Octave F i l t e r was s e t up i n -25-  ] LIGHT THRESHOLD TRACKING  OSCILLATOR  INTERRUPTER  SUBJECT CONTROL SWITCH  RECORDING ATTENUATOR  1  SWITCH BOX EXPOSURE TONE  OSCILLATOR  STEP ATTENUATOR  MIXER  J  WINDOW  SUBJECT I  ro  SPEAKER  AMPLIFIER  MICROPHONE SOUND LEVEL METER  CONTROL ROOM  TEST ROOM  Figure 4.1 Block diagram of instrumentation for TTS procedures.  I  -27-  t h e t e s t i-oom to p r o v i d e s u b j e c t s w i t h v i s u a l feedback f o r m a i n t a i n i n g c o n s t a n t i n t e n s i t y d u r i n g the humming c o n d i t i o n . As shown i n F i g u r e 4.1, r e s p o n s e - r e c o r d i n g equipment was  the s i g n a l - g e n e r a t i n g and i n - t h e c o n t r o l room while ;  the s u b j e c t , c o n t r o l s w i t c h , and sound the sound  treated  t e s t room.  l e v e l meter were i n  A window p e r m i t t e d o b s e r v a t i o n  o f the s u b j e c t by the experimenter and a s w i t c h i n the c o n t r o l room p e r m i t t e d e x t e r n a l c o n t r o l of the l i g h t i n the t e s t room. The  experimenter c o u l d monitor s u b j e c t a c t i v i t y v i a a micro-  phone i n the t e s t room connected to an a m p l i f i e r and in  speaker  the c o n t r o l room. 4.12  Model 1720  Otoadmittance  Instrumentation  Otoadmittance  Meter was  the study-.  The* G r a s o n - S t a d l e r  chosen f o r t h i s p a r t o f  (The r e c i p r o c a l o f a c o u s t i c impedance w i l l  f o r t h be r e f e r r e d to as a c o u s t i c admittance.) o f the Otoadmittance  One  advantage  Meter i s t h a t i t a l l o w s separate measure-  ment o f the two admittance components, the conductance the susceptance B. e a s i e r computation impedance i s used.  hence-  A second advantage  G and  i s t h a t i t permits  o f ear drum admittance v a l u e s than i f For example; i f we  look a t the e q u i v a l e n t  e l e c t r i c a l c i r c u i t o f the combination "ear drum + ear c a n a l , " the l a t t e r i s r e p r e s e n t e d by a p a r a l l e l branch.  Knowing the  v a l u e o f the whole, one wants to o b t a i n t h a t o f the ear drum alone.  U s i n g admittances, t h i s can be done by a simple  s u b t r a c t i o n , whereas w i t h impedances the c a l c u l a t i o n i s more cumbersome.  For a d i s c u s s i o n o f the p r i n c i p a l components  o f the b r i d g e and f o r a review o f impedance and  -28admittance  r e l a t i o n s h i p s ^ s e e Grason-Stadler  Otoadmittance  Handbook 2 ( 1 9 7 3 ) . The  t o t a l G and 3 o f the ear were a m p l i f i e d , low  pass f i l t e r e d and r e c o r d e d on a H.P. 3960 I n s t r u m e n t a t i o n Recorder.  T h i s was p l a y e d back v i a an A t o D c o n v e r t e r i n t o  a PDP-12 D i g i t a l Computer f o r a n a l y s i s .  The s i g n a l was  sampled a t approximately 1 Hz, a p p r o p r i a t e l y s c a l e d , d i s p l a y e d on a T e t r o n i x Type $6kB O s c i l l o s c o p e , and was p h o t o g r a p h i c a l l y r e c o r d e d w i t h a P o l a r o i d camera (See F i g . 4 . 2 ) , D u r i n g otoadmittance  procedures, the exposure  tone  was p r o v i d e d by an I n t e r s t a t e E l e c t r o n i c s F u n c t i o n Generator Type F 3 3 .  The exposure  tone reached the ear v i a a TDH-49  earphone a t t a c h e d t o the headband t h a t a l s o h e l d the otoadmittance probe (See F i g . 4 . 2 ) . 4.13  Calibration  frequency responses  Before e x p e r i m e n t a t i o n began the  o f the earphones were determined  using  a B r i i e l and K j a e r Type 2203 P r e c i s i o n Sound L e v e l Meter w i t h Type 1613 Octave F i l t e r ,  a B r i i e l and K j a e r Type 4152  A r t i f i c i a l E a r w i t h a standard 6 c . c . NBS Coupler, a B r i i e l and K j a e r Type 1022 Beat Frequency and K j a e r Type 2305 L e v e l Recorder, the exposure  O s c i l l a t o r , and a B r i i e l The a c o u s t i c outputs o f  tone p r o d u c i n g o s c i l l a t o r - e a r p h o n e u n i t s were  a l s o determined  w i t h the above sound l e v e l meter and a r t i f i -  c i a l ear. The  i n t e n s i t y o f the exposure  tone a t the earphone  was r e c o r d e d each day o f d a t a c o l l e c t i o n .  The mean o f d a i l y  EARPHONE BEAT FREQUENCY OSCILLATOR  ATTENUATOR  PROBE  I J II  / i 1  OTOADMITTANCE METER  FILTERS and TAPE RECORDER  RECORDING INSTRUMENTATION  TAPE RECORDER  ATTENUATOR  A to D CONVERTER  PDP-12 COMPUTER  OSCILLOSCOPE and CAMERA  PLAYBACK and ANALYSIS INSTRUMENTATION  Figure 4.2 Block diagram of instrumentation for Otoadmittance procedures.  -30measurements (3*0 d u r i n g the TTS s e s s i o n s was (SD=0.28j Range=117.1 dB to 118.0  dB).  117.5  dB  The exposure  SPL  tone  of the otoadmittance s e s s i o n s was- manually a d j u s t a b l e thus was  routinely  s e t a t 117.5  dB SPL.  Other d a i l y measurements  i n c l u d e d : i n t e n s i t y c a l i b r a t i o n o f the Bekesy  audiometer  (500 Hz r e f e r e n c e ) ? c a l i b r a t i o n o f the c i r c u i t used to a m p l i f y G and B s i g n a l s ;  and c a l i b r a t i o n o f the Otoadmittance  u s i n g the 1720-1002 t e s t c a v i t i e s . test cavity  Meter  The means of the d a i l y  measurements, u s i n g the 660 Hz probe tone, were: B(mmhos)  G(mmhos)  Large C a v i t y  9.25  (SD=0.14)  0.62  (SD=0.07)  Small Cavity  1.58  (SD=0.02)  0.80  (SD=0)  Background  n o i s e i n the t e s t rooms, measured w i t h  the  B r i i e l and K j a e r equipment b e f o r e and a f t e r d a t a c o l l e c t i o n ,  was  found to be 29 dBA SPL i n the room used f o r TTS  procedures  and 27 dBA SPL i n the room used f o r otoadmittance procedures. Daily  octave band a n a l y s i s showed t h a t f r e q u e n c i e s below  250 Hz were the main components o f t h i s n o i s e . 500 Hz to 1 6 , 0 0 0 Hz never exceeded  The f r e q u e n c i e s  28 dBA SPL and 22 dBASPL  i n the TTS t e s t room and the otoadmittance t e s t room r e s p e c tively . 4.2  Subjects The s u b j e c t s were 7 male and 7 female unpaid v o l u n t e e r s between 19  and 33 y e a r s o f age.  h e a r i n g as shown byt no h i s t o r y ear  A l l s u b j e c t s had  o f ear pathology; normal  f u n c t i o n and a c o u s t i c r e f l e x e s  normal middle  r e c o r d e d from a Madsen Model  2070 E l e c t r a c o u s t i c Impedance B r i d g e ; and normal pure tone a i r - c o n d u c t i o n h e a r i n g t h r e s h o l d s ( b e t t e r than 25 dB  ISO  I 9 6 4 ) between 250 Hz and 8000 Hz as r e c o r d e d by Bekesy a u d i o metry.  Only those persons were to be i n c l u d e d who,  a t one  minute a f t e r c e s s a t i o n o f the exposure tone d u r i n g the c o n d i t i o n r e q u i r i n g no a c t i v i t y , than 1 dB  showed a TTS a t 700 Hz o f more  ( c r i t e r i a o f McBay, 1971)*  Two  male and two  female  s u b j e c t s d i d n o t f u l l y meet these TTS c r i t e r i a but were i n c l u d e d to t y p i f y one extreme o f the normal range o f TTS  and,  p o s s i b l y , otoadmittance r e s u l t s . 4.3  Experiments For  t h i s i n v e s t i g a t i o n TTS i s d e f i n e d as the d i f -  f e r e n c e between a s u b j e c t ' s mean pre-exposure t h r e s h o l d f o r a p u l s e d pure tone and h i s mean post-exposure t h r e s h o l d s for  the same tone, measured a f t e r exposure c e s s a t i o n .  TTS paradigm was, McBay ( 1 9 7 1 ) .  The  l a r g e l y , a r e p l i c a t i o n o f t h a t used by  I"t was  h y p o t h e s i z e d t h a t the otoadmittance  v a l u e s b e f o r e , d u r i n g , and a f t e r c o n t r a l a t e r a l exposure to the  f a t i g u e s t i m u l u s would be a r e a s o n a b l e measure o f the  admittance v a l u e s t h a t occur d u r i n g such a TTS 4.31  E x p e r i m e n t a l Design  paradigm.  The b a s i c d e s i g n and p a r a -  meters o f the experiments are shown i n F i g u r e 4 . 3 . TTS paradigm c o n s i s t e d o f a 2 minute pre-exposure at  700 Hz, a 5 minute exposure to a 1 1 7 . 5  The tracking  dB SPL 500  Hz  f a t i g u e tone, and a 4 minute post-exposure t r a c k i n g a t 700 Hz.  The otoadmittance paradigm was  s i m i l a r except t h a t the  THRESHOLD TRACKING  EXPOSURE:  f =700Hz  ACTIVITY: N  t]_= 2 min.  ( 1 of )  t  f =700Hz t  T  t3=  Hj  EXPOSURE • PERIOD -  PRE-EXPOSURE • PERIOD  THRESHOLD TRACKING  500Hz SPL=177.5dB t2= 5 min.  -»  <  4 min.  POSTEXPOSUREPERIOD  A. Design and parameters of TTS procedures.  CONTINUOUS RECORDING OF ADMITTANCE CHANGES  PRE-EXPOSURE OTOADMITTANCE t]=  2 min.  PRE•EXPOSURE PERIOD  EXPOSURE: f =500Hz SPL=117.5dB t2= 5 min. e  ACTIVITY:  N  Q  C 1 of )  H  Q  <  EXPOSURE PERIOD  POST-EXPOSURE OTOADMITTANCE tg=  >  4 min.  POST<—EXPOSURE PERIOD  B. Design and parameters of Otoadmittance procedures. Figure 4,3 Experimental design and parameters.  »  -33-  r e c o r d i n g o f the t r a c k e d and  threshold  d u r i n g the pre-exposure  post-exposure p e r i o d s was r e p l a c e d by a r e c o r d i n g o f the  admittance f o r the e n t i r e 11  minutes.  D u r i n g the 5 minute  exposure p e r i o d s u b j e c t s performed one o f the f o l l o w i n g activitiesi 1.  N^/NQJ  Subject  tone.  He o r she was i n s t r u c t e d n o t to  on a n y t h i n g 2. H / H I T  Q  s a t q u i e t l y and l i s t e n e d t o the  s p e c i f i c while  Subject  concentrate  the exposure tone was on.  hummed a t 125 Hz (males) o r 250 Hz  (females) i n c y c l e s o f 7-8 sec o f humming and 2-3 sec o f r e s t , as cued by the l i g h t i n the t e s t room (on=humj o f f = r e s t and i n h a l e ) .  A "moderately l o u d "  humming i n t e n s i t y o f 65 dB SPL was monitored by the s u b j e c t , who watched the sound l e v e l meter ( p l u s filter  corresponding  placed  54- 2 inches from h i s / h e r mouth.  The  conditions  (humming TTS c o n d i t i o n ) , N  t o the frequency o f humming)  (non-humming TTS c o n d i t i o n ) , H^ Q  (non-humming otoadmittance  condi-  t i o n ) , and HQ (humming otoadmittance c o n d i t i o n ) were mandat o r y f o r a l l 14- s u b j e c t s .  No two i n d i v i d u a l s were  subjected  to t h e same sequence o f c o n d i t i o n s as a p a r t i a l c o n t r o l a g a i n s t p o s s i b l e cumulative and/or s e q u e n t i a l e f f e c t s .  A L a t i n square  d e s i g n was n o t p o s s i b l e w i t h 14 s u b j e c t s and 4 c o n d i t i o n s thus the sequence o f c o n d i t i o n s was randomized f o r each subj e c t w i t h the r e s t r i c t i o n t h a t a l l s u b j e c t s were t o perform N  T  o r H J c o n d i t i o n d u r i n g the f i r s t  the TTS c r i t e r i a  ( c f . Section 4.2)  session.  This  permitted  t o be determined a t the  -34b e g i n n i n g o f e x p e r i m e n t a t i o n . Data c o l l e c t i o n was scheduled to a l l o w 24 hours o r more between s e s s i o n s f o r each s u b j e c t . 4.32  Procedures  A f t e r i n d i v i d u a l s were accepted as  subjects^ t h e y were informed o f the g e n e r a l o u t l i n e o f the experiments,and the p u r e l y v o l u n t a r y n a t u r e o f t h e i r cooperat i o n was emphasized.  Each s u b j e c t then decided which ear  was t o be exposed t o the f a t i g u e tone; 8 l e f t and 6 r i g h t e a r s were chosen.  A t each s e s s i o n the s u b j e c t was seated  c o m f o r t a b l y , then g i v e n a s e t o f i n s t r u c t i o n s TTS S e s s i o n s 1.  Sweep-frequency  (See Appendix),  A l l TTS s e s s i o n s proceded as f o l l o w s : (Bekesy) t h r e s h o l d t r a c k i n g from  250 Hz t o 8000 Hz f o r the non-exposure ear; 2.  2-3 minutes o f s i n g l e - f r e q u e n c y (700 Hz) t h r e s h o l d t r a c k i n g f o r the non-exposure ear;  3.  Sweep-frequency  t h r e s h o l d t r a c k i n g from 250 Hz t o  8000 Hz f o r the exposure e a r . 4.  2 minutes o f s i n g l e - f r e q u e n c y (700 Hz) t h r e s h o l d t r a c k i n g f o r the exposure ear (pre-exposure p e r i o d o f TTS paradigm);  5.  5 minute exposure to 117.5  dB SPL 500 Hz tone accom-  p a n i e d by s p e c i f i e d a c t i v i t i e s 6.  (exposure p e r i o d ) ;  4 minutes o f s i n g l e - f r e q u e n c y (700 Hz) t h r e s h o l d t r a c k i n g f o r the exposure ear (post-exposure p e r i o d ) .  P r o c e d u r e s 1 t o 3 p r o v i d e d s u b j e c t s w i t h p r a c t i c e i n Bekesy t r a c k i n g and served as a check f o r p o s s i b l e t h r e s h o l d a t i o n s due t o r e p e a t e d i n t e n s e exposure, p r a c t i c e ,  fluctu-  attentive-  n e s s , s t a t e o f h e a l t h , e t c . No such f l u c t u a t i o n s were  -35-  observed i n the course o f the experiments.  The humming t a s k  was e x p l a i n e d and p r a c t i c e d a t the s t a r t o f a s e s s i o n and i n s t r u c t i o n s were r e p e a t e d j u s t p r i o r t o the exposure p e r i o d . The humming a c t i v i t y was u s u a l l y l e a r n e d w i t h 5 to 10 minutes of p r a c t i c e .  With a d d i t i o n a l p r a c t i c e , even those s u b j e c t s  who i n i t i a l l y  experienced d i f f i c u l t y were a b l e t o hum a c -  ceptably. Otoadmittance S e s s i o n s  The exposure e a r , f o r these  s e s s i o n s , was always the one c o n t r a l a t e r a l t o the TTS exposure e a r . The probe tone used was 660 Hz.  A l l otoadmittance  s e s s i o n s proceded as f o l l o w s t 1. Headset p l a c e d on s u b j e c t w i t h earphone ear.  on exposure  Probe p l a c e d i n TTS exposure ear and an a i r -  t i g h t seal obtained.  U s i n g a s c e n d i n g and descending  a i r p r e s s u r e , a tympanogram was o b t a i n e d and the G (conductance) and B (susceptance) v a l u e s read from the c o r r e s p o n d i n g d i a l s a t 0mraHgO (drum l o o s e ) and +400 and -400 mm HgO (drum t i g h t ) ? 2. Pre-exposure conductance and susceptance were r e c o r d e d f o r 2 minutes; 3.  5 minute exposure to the 117.5 was accompanied  °3 SPL 500 Hz tone  by s p e c i f i e d a c t i v i t i e s w h i l e r e -  c o r d i n g o f conductance and susceptance c o n t i n u e d ; 4. Post-exposure conductance and susceptance were r e c o r d e d f o r 4 minutes. The tympanogram measurements p r o v i d e d a check o f G and B  variability  between s e s s i o n s , allowed pre-exposure  admittance  v a l u e s to be c a l c u l a t e d , and p r o v i d e d a measure o f the conductance and  susearptasiee-of the ear c a n a l t o be s u b t r a c t e d i n  the  c a l c u l a t i o n o f conductance  final  eardrum. the  and susceptance a t the  S i n c e the exposure ear r e c e i v e d a 500 Hz tone and  probe ear r e c e i v e d a. 660 Hz tone, some s u b j e c t s found i t  somewhat more d i f f i c u l t f r e q u e n c y f o r the H  Q  to hum  a t the s p e c i f i e d  c o n d i t i o n than f o r the  fundamental condition.  With p r a c t i c e , however, a l l s u b j e c t s were a b l e to hum  accept-  ably. 4.33  Data Measurement TTS Measurement  the  Figure 4.4  i s a reproduction of  e x p e r i m e n t a l 'record o b t a i n e d from the p r e - and p o s t -  exposure  t h r e s h o l d t r a c k i n g i n the TTS p r o c e d u r e s .  exposure  t h r e s h o l d was  the  20 extrema i n the pre-exposure t r a c i n g .  last  exposure  t r a c k i n g was  Pre-  o b t a i n e d by a v e r a g i n g dB v a l u e s o f The post-  averaged by marking the midpoint o f  each p e a k - t o - t r o u g h or trough-to-peak  e x c u r s i o n and  fitting  an average curve through these p o i n t s .  The o r d i n a t e s o f t h i s  curve a t the post-exposure times o f 7 . 5  sec, 15  1  min,  sec* 3© s e c ,  2 min, and 4 min were measured w i t h r e s p e c t t® the  s u b j e c t ' s pre-exposure t h r e s h o l d .  A s e r i e s o f Frenefe curves  were used to extend the post-exposure t h r e s h o l d cunre to time zero and t o o b t a i n an e x t r a p o l a t e d TTS v a l u e at. t h a t time.  S i n c e a l l s u b j e c t s were found t o have t h r e s h o l d s t h a t  l e v e l l e d o f f between 2 and 4 minutes post-exposure, &B e i g h t h TTS v a l u e was  determined f o r t h i s p o r t i o n of the post-exposure  •  FORM  CF2  A  PftlMTID Nt U.I. A.  TRACE  MASKING  TONE  70 0  Hz  20  dB  -—  dB/SEC  SISI  2.5  FREQ.  %  NAME_  c£)  L®B,  dB  0, + , -  NO. AGE  I  SEX COLOR  G.A. BY  DATE 20/6/73TIMF  1'/.. 2Vi, 5  23 M.R.  -FREQUENCY-  -10  -10  10  10  —I •jj  Pre-  20  O UJ Q  exposure  xposure  20  30  30  40  40  00 —' l i J  UJ  Q o  1  a  <  > o £  H  I 50  60  60  70  70  80  80  DC  90  100  90  TO C O N V E R T ISO R E A D I N G S TO A S A R E A D I N G S S U B T R A C T A P P R O P R I A T E " D I F F E R E N C E IN (IB" A T E A C H F R E Q U E N C Y .  100  7-5 15 3 0  A l l I.  9*.  ^ BEKESY AUDIOMETER ]H GRAS0M - STADLER COMPANY, INC. £j MODEL NO SERIAL NO.  V, 1  2 MINUTES  2  FIXED  FREQUENCY  D I F F E R E N C E IN dB (ISO V S . A S A )  125  250  500  750  1000  1500  2000  3000  4000  6000  8000  9  15  14  (12)  10  10  8.5  8.5  6  93  113  Figure 4.H Record of a representative TTS procedure (condition N™).  -3-8-  curve by a v e r a g i n g v a l u e s the curve i n t e r s e c t e d a t 2 2,5  3 min, 3 . 5  min,  min, and 4 min,  •the e i g h t post-exposure 1 min, ing  2 min,  times (0 sec, 7.5  4 min, and 2-4  the pre-exposure  TTS,  min) was  threshold.  min,  i n dB, a t each of s e c , 15  sec, 30 sec,  then obtained by  j^Note: T T S „ and N 0  subtract-  TTS ^„ H 1  r e f e r t o the v a l u e o f TTS a t the s p e c i f i e d times f o r c o n d i t i o n N,p and H of  TTS  T  respectively.  TTS-^n*  however, r e f e r s t o the v a l u e  a t the s p e c i f i e d time f o r e i t h e r c o n d i t i o n Post-exposure  or H Yj T  threshold tracings revealed, f o r a l l 1 to 2  s u b j e c t s , a r a p i d i n i t i a l TTS r e c o v e r y i n the f i r s t minutes  post-exposure  f o l l o w e d by a slower secondary  TTS  r e c o v e r y as evidenced, i n p a r t , by the t h r e s h o l d p l a t e a u between 2 and 4 minutes post-exposure. . ( T h i s secondary r e c o v e r y may  take s e v e r a l hours b e f o r e the  t h r e s h o l d i s reached.)  (sec)  pre-exposure  To i n v e s t i g a t e the r a t e of  r e c o v e r y a n i n t h measurement (it) was  TTS  initial  taken:  = h a l f - l i f e of the i n i t i a l TTS r e c o v e r y p e r i o d = time, measured from the end o f exposure, a t which the TTS v a l u e has decreased by  50%.  T T S ^ (dB) = T T S „ ( d B ) •+ T T S , _ ( d B ) 0  2  v  TTSQ„(dB) = TTS v a l u e a t zero sec  post-exposure  TTSg ,_^,.(dB) = average TTS v a l u e between 2 and 4  minutes  post-exposure, [ N o t e j ^ j j = f f o r c o n d i t i o n N,j,j -£ ^ =  for condition  Ten TTS v a l u e s from the t h r e s h o l d t r a c i n g s o f 5 randomly chosen  s u b j e c t s were remeasured  to determine measurement  -39-  reliability. was  0.85  Standard d e v i a t i o n f o r the 50 p a i r s o f v a l u e s  dB. Otoadmittance Measurement  The r e c o r d e d conductance  and susceptance v a l u e s were f e d from t h e A t o D c o n v e r t e r i n t o the computer and there the ( t y p e d i n ) ear c a n a l conductance and susceptance v a l u e s were s u b t r a c t e d .  The r e s u l t i n g  v a l u e s o f conductance and susceptance a t the eardrum were then p l o t t e d over time f o r each s u b j e c t . (  i e  *  G  a t the drum  =  B  —  at F i g u r e 4,5 plot.  G  the drum  total " canal G  r>  s  — B  total  )  canal*  ;  i s an example o f photographs o b t a i n e d f o r each  A s p e c i a l l y c o n s t r u c t e d t r a n s p a r e n c y was used t o  measure each photograph.  The measurements (as i d e n t i f i e d  i n t h e r e p r e s e n t a t i v e schematic o f the p l o t s , F i g . 4.6) 1.  G^:pre-exposure  were:  conductance ( i n mmhos) measured  15 s e c b e f o r e the s t a r t o f exposure. 2,  A G^: change i n conductance ( i n mmhos) as the exposure tone came on.  3»  J1G|,I  change i n conductance ( i n mmhos) as the  exposure tone ceased. 4. G^.: post-exposure conductance ( i n mmhos) measured 225 s e c . a f t e r t h e end o f exposure, ( i e . 15 s e c b e f o r e the end o f the 4 minute post-exposure p e r i o d . ) F o u r s i m i l a r measurements (B^, AB^, A B , and B ) were taken f  from each susceptance p l o t .  f  Although A G ^  A B„ v a l u e s were much l a r g e r on the H  n  f  A B ^ , A G , and f  p l o t s than on the N  n  -40-  Figure M.f, Representative schematic of otoadmittance 'plots.  -4-1-  p l o t s , the same methods o f measurement were used f o r both conditions. [Note: in  AG ^,  B  N  conditions N  Hf Q  e  ^ * c  and H  Q  r  e  f  e  r  ^° ^  n e  s p e c i f i e d measurements  respectively.  AG^,  B^, e t c . r e f e r  to the s p e c i f i e d measurements i n e i t h e r c o n d i t i o n NQ or HQ. AG and  AB  r e f e r t o changes i n G and B, r e s p e c t i v e l y , a t  the b e g i n n i n g and/or  end o f exposure  for either  condition  Four otoadmittance v a l u e s were remeasured otoadmittance p l o t photographs reliability. was 0,05  to determine  Standard d e v i a t i o n  mmhos.  from 5  measurement  f o r the 20 p a i r s o f v a l u e s  Chapter 5 Results  5.1  TTS Data A t h r e e f a c t o r a n a l y s i s o f v a r i a n c e (ANOVA) f o r r e p e a t e d measures (Winer,  1962,  pp.298-349)  was used t o i n v e s -  t i g a t e p o s s i b l e s y s t e m a t i c e f f e c t on TTS o f the a c t i v i t y p e r formed d u r i n g exposure and to i n d i c a t e i f t h i s e f f e c t was a f u n c t i o n o f time o f TTS measurement and/or sex o f the s u b j e c t . T h i s ANOVA f o l l o w e d a SEX (male, female) by TIME ( 0 " , 7 . 5 " , 15", 14  30",  1 ' , 2 ' , 4 ' ) by CONDITION ( N , H ) . d e s i g n i n which T  subjects  T  ( 7 males, 7 females) were t e s t e d f o r each time and  each c o n d i t i o n .  T a b l e 1 i s a summary o f t h i s a n a l y s i s .  Since  TTS from a g i v e n exposure i s known t o v a r y g r e a t l y among i n d i v i d u a l s , the c o n s i d e r a b l e v a r i a n c e a s s o c i a t e d w i t h s u b j e c t s was expected.  A l t h o u g h SEX had a n o n - s i g n i f i c a n t e f f e c t on TTS,  CONDITION and TIME each had a h i g h l y s i g n i f i c a n t e f f e c t ,  beyond  the 0 . 0 1  inter-  level.  The ANOVA r e v e a l e d a h i g h l y s i g n i f i c a n t  a c t i o n between TIME and CONDITION, however, no s i g n i f i c a n t i n t e r a c t i o n s between SEX and CONDITION, or SEX and TIME and no o v e r a l l i n t e r a c t i o n between the three f a c t o r s was found. F i g u r e 5 . 1 shows the mean v a l u e s o f TTS f o r c o n d i t i o n s N^, and H,j a t s i x post-exposure times f o r a l l s u b j e c t s . The Neuman-Keuls method (Winer,  1962,  pp.77-85)  was  used t o probe t h e n a t u r e o f the d i f f e r e n c e s between treatment ' t o t a l s f o l l o w i n g a s i g n i f i c a n t F i n the ANOVA.  A probe o f the  time e f f e c t was made to determine the s i g n i f i c a n c e o f d i f f e r e n c e s -42-  -4-3-  SEX x TIME x CONDITION Table 1: Summary of ANOVA. TTS as a function of sex, post-exposure time (0",7.5",15",30", l',2',4'), and condition (N^, H^) for 7 male and 7 female subjects. Source of Variation Between Subjects Sex Subjects Within Subjects  df  MS  13 1  154.89  12  487.02  964.28  Sex x Subjects  .1  31.75  Time x Subjects  72  9.49  Condition  1  2,099.86  Sex x Condition  1  26.97  12  56.70  -6  37.73  6  4.76  72  3.59  Condition x Subjects Time x Condition Sex x Time x Condition Time x Condition x Subjects  * p <0.05 ** p <0.01 *** p <0.001  0.32  182 6  Time  F  101.62*** 3.35  37.03*** 0.48  10.51*** 1.33  TTS  Fig.5.1 Comparison of TTS(measured at 700 Hz) at six different post-exposure times for conditions N  T  and IL^,.  -45-  between a l l 7 post-exposure times f o r both c o n d i t i o n s and a l l subjects.  A summary i s g i v e n i n Table 2 a .  The r e s u l t s  indi-  c a t e t h a t time had a h i g h l y s i g n i f i c a n t e f f e c t on TTS, i n p a r ticular?  t h a t TTS v a l u e s f o r 0 " , 7 . 5 " ,  15",  and 3 0 " times were  s i g n i f i c a n t l y d i f f e r e n t from a l l o t h e r times except t h a t TTS f o r 0 " was n o t s i g n i f i c a n t l y d i f f e r e n t from TTS f o r 7 . 5 " , t h a t TTS v a l u e s f o r 1 ' ,  2',  and  and 4 ' times were, however, n o t  s i g n i f i c a n t l y d i f f e r e n t from each o t h e r . A probe o f the c o n d i t i o n e f f e c t confirmed t h a t , as shown by the ANOVA,  had a s i g n i f i c a n t l y d i f f e r e n t  effect  on TTS from N , f o r a l l times and s u b j e c t s (see T a b l e 2 b ) . T  A f i n a l probe o f the TIME X CONDITION e f f e c t was made to o b t a i n more i n f o r m a t i o n on the e f f e c t o f c o n d i t i o n a t s p e c i f i c p o s t exposure t i m e s .  The e f f e c t o f TIME X CONDITION on TTS f o r a l l  s u b j e c t s was shown to be s i g n i f i c a n t a t the 0 . 0 1 l e v e l by the ANOVA but the Neuman-Keuls probe r e v e a l e d t h a t the e f f e c t o f c o n d i t i o n was d i f f e r e n t a t d i f f e r e n t times (See T a b l e 2 c ) . S p e c i f i c a l l y , condition on TTS from c o n d i t i o n N  had a s i g n i f i c a n t l y d i f f e r e n t T  at 0 " , 7.5"f  effect  15" and 3 0 " f o r a l l sub-  j e c t s but the e f f e c t o f c o n d i t i o n was n o t s i g n i f i c a n t l y d i f f e r e n t at 1 ' ,  2 ' , and 4 ' . A t-test f o r related  measures (Bruning and K i n t z ,  1 9 6 8 , pp.12-15) was used to determine the r e l a t i o n s h i p between conditions N  T  and  I t was shown t h a t  f o r the v a l u e s o f T T S g , ^ , ( c f . S e c . 4 . 2 ) r e s u l t s i n a s i g n i f i c a n t l y s m a l l e r average  TTS v a l u e between 2 ' and 4 '  ( 0 . 0 1 l e v e l ) than N™,  Table 2a: Results of Neuman-Keuls test for significance of differences between TTS f o r 7 post-exposure times ( 7 male and 7 female subjects ). Time T.T. 4'  202.25  1'  234.64  V  240.55  30"  317.55  15"  428.12  4'  1'  2'  30"  15"  7.5"  0"  202.35  234.64  240.55  317.55  428.12  550.57  615.10  32.39  38.30  115.30**  225.87**  348.32**  412.85**  5.91  82.91**  193.48**  315.93**  380.46**  77.00**  187.57**  310.02**  374.55**  110.57**  233.02**  297.55**  122.45**  186.98** 64.53  7. 5" 550.57  q 0.99(r,72)  3.75  q 0.99(r,72)  61.13  x^MSerror  ** p <0.01  4.27. 69.60  4.59  4.81  4.98  5.12  74.82  78.40  81.17  83.46  Condition T.T.  N  «T 973.67  T  Table 2b: Results o f Neuman-Keuls test f o r significance o f differences  1615.21  between TTS f o r N  T  and lip conditions.  641.54** q 0.99(r,12)  4.32  q 0.99(r,12)  322.01  Table 2c: Results of Neuman-Keuls test f o r significance o f differences  xJMSerror  between TTS f o r conditions  and Hj, at the specified post-  exposure times.  Time  t=0"  V  Condition T.T.  %  t=7.5"  245.29  369.81  lij, 216.84  t=15" N  T  333.73  151.38  276.74  116.89**  125.38**  q 0.99(r,72)  3.75  3.75  3.75  q 0.99(r,72)  70.35  70.35  70.35  ** p<0.01  t= 1* N  124.52**  x>lMSerror  t= 30"  108.84  N  T  207.71 97.87**  t= 2'  82.84  N  T  151.80  t= 4'  89.84  N  T  150.71  77.64  T  124.71  68.96  60.87  47.07  3.75  3.75  3.75  3.75  70.35  70.35  70.35  70.35  -48-  Another a n a l y s i s was done t o i n v e s t i g a t e the e f f e c t o f c o n d i t i o n on the i n i t i a l  A t - t e s t f o r r e l a t e d measures, performed on the h a l f - l i f e •£  and f  N  H  revealed  cantly shorter  5.2  values  t h a t the H^, c o n d i t i o n r e s u l t s i n a s i g n i f i -  i n i t i a l recovery rate  by t h e h a l f - l i f e ,  4.32).  r a t e o f TTS r e c o v e r y ( c f . Sec.  than the  (0.01  l e v e l ) , as defined  condition.  Otoadmittance Data Analysis  o f the otoadmittance d a t a i n v e s t i g a t e d the  e f f e c t o f c o n d i t i o n on middle ear admittance b e f o r e , a f t e r t h e 5 minute exposure t o a 117.5  and  The o t o a d m i t t a n c e measurements  (G^, A G^,  dB SPL 500 Hz tone.  AG^,  G^,  B^;  c f . Sec, 4*3~)  the  c o r r e s p o n d i n g measurement f o r c o n d i t i o n HQ.  B^, A'B.^, ^B^.,  f o r - c o n d i t i o n NQ were each compared w i t h t-tests for  r e l a t e d measures -vwsre ;p:erf.orined o.n the e i g h t p a i r e d values.  and f i n a l G and B v a l u e s ,  as shown by n o n - s i g n i f i c a n t  v a l u e s ( n o n - s i g n i f i c a n t a t the 0.10  level).  The o t h e r f o u r  t - t e s t s , which were s i g n i f i c a n t beyond the 0.001 vealed  level, re-  t h a t changes i n G and B a t the b e g i n n i n g and end o f  exposure were s i g n i f i c a n t l y l a r g e r d u r i n g during  sets of  I t was found t h a t c o n d i t i o n had no s i g n i f i c a n t e f f e c t  on i n i t i a l t  during,  c o n d i t i o n HQ than  c o n d i t i o n NQ. The  changes i n G and B a t the b e g i n n i n g and end o f  exposure were then compared.  When no phonation accompanied  exposure the change i n G a t the b e g i n n i n g o f exposure was s i g n i f i c a n t l y l a r g e r (0.01 6 G . > <4B .) as shown'by a M  N  l e v e l ) than the change i n B ( i e . t - t e s t f o r r e l a t e d measures.  -49A t the end o f exposure the change i n G was the  still  l a r g e r than  c o r r e s p o n d i n g change i n B but not s i g n i f i c a n t l y  When p h o n a t i o n accompanied  larger.  exposure, however, the change i n B  both a t the b e g i n n i n g and a t the end o f exposure was (0,01  cantly larger G (ie. ^ H i S  >  A G  signifi-  l e v e l ) than the c o r r e s p o n d i n g change i n  Hi  A B  Hf  >  A G  Hf^*  *  T n  f i n d i n g suggests  s  t h a t the humming c o n d i t i o n a f f e c t e d the susceptance s i g n i f i c a n t l y more than i t a f f e c t e d the conductance, 5.3  Comparison  of TTS and Otoadmittance Data In an attempt to f i n d some r e l a t i o n s h i p between TTS  and otoadmittance d a t a , a number o f Pearson product-moment c o r r e l a t i o n s were c a l c u l a t e d . ments (^G ^, N  AG  N;f  ,  A B ^ i ' i l B ^ j ) were f i r s t  measurements a t times 0", 2'-4'  Four o f the NQ c o n d i t i o n  7.5",  15"t  30",  and w i t h the h a l f l i f e t f o r N  compared w i t h TTS  1',  and H  T  T  measure-  2',  4',  and  conditions.  The  72 Pearson r v a l u e s obtained from these comparisons were a l l s m a l l and n o n - s i g n i f i c a n t , not even a t the 0.10  level.  The  two  l a r g e s t c o r r e l a t i o n c o e f f i c i e n t s werei A G AG  N f  X TTS ,  r=-0.31  X TTS ,  r=-0.30  N 2  N f  N 1  p=0.10  i f r=0.46  The d i f f e r e n c e between TTS v a l u e s f o r c o n d i t i o n s N^, and H  T  a t 0",  7.5",  15",  30",  and 1'  were c a l c u l a t e d as a  measure o f the p r o t e c t i o n g i v e n the ear by the humming c o n d i tion.  These 5 d i f f e r e n c e s were compared w i t h f o u r N  ments 0*G , Ni  ^ Nf'^ Ni* G  B  A B  Nf^*  T  h  e  0  n  l  y  s  '  t a  '  t i s  '  Q  t i c a l l  measurey  -50s i g n i f i c a n t Pearson (TTS  N 7 < 5 H  r correlation coefficient  -TTS  „) X  H 7 t 5  4G  r=0.53* *p=0.05  N i  3)  (See Table 5 TTS  The  fo 11 owing r a t i os» A l l Pearson difference  differences  were then compared w i t h the  A G^ /G ^; A G / G i  N  Nf  r correlations  was:  N f  ;  A B_ / B N±  N  i  ;  AB  as shown i n T a b l e 3,  and,  four  of the  i n F i g u r e s 5.2, The  5.3,  N i  =  admittance  1^ Ni> G  Nf "  V  (AG  V  2  (  +  A B  Ni>  _) + 2  T  These v a l u e s c o r r e l a t e d  (TTS  N 7 > 5  are graphed  v a l u e s from c o n d i t i o n  N  Q  2  v  (AB^) "Nf  a t the b e g i n n i n g of  2  = change i n admittance  values.  correla-  f o r each s u b j e c t ;  = change i n admittance exposure.  a t the end o f  weakly and n e g a t i v e l y  exposure.  w i t h the 5  The l a r g e s t c o r r e l a t i o n c o e f f i c i e n t  „- TTS  H ? >  ^Jx  AY  r=-0.51  N i  TTS was;  p<0.10  3)  (See T a b l e The  TTS  5.4.  and  following  were then c a l c u l a t e d  difference  ^  level.  P o i n t s c o r r e s p o n d i n g to t h r e e o f these c o r r e l a t i o n s  4Y,  N f  between the A G r a t i o s and the  t i o n c o e f f i c i e n t s were s i g n i f i c a n t beyond the 0.05  Y  /B  v a l u e s were l a r g e r than the c o r r e s p o n d i n g n o n - r a t i o  correlations,  4  N f  c o r r e l a t i o n c o e f f i c i e n t s were s i m i l a r i n magnitude to  c o e f f i c i e n t s o f the comparisons between the 5 TTS v a l u e s and the v a l u e s A G ^ ,  AG^,  ^ Ni* B  a  n  d  ^ Nf * B  difference  Table 3: Matrix of Results of Pearson Product-Moment Correlations between specified TTS and Otoadmittance values.  ^ \ > v TTS  N0' " H0" ,  -0.16  \ .  /  G  Nf  ^XHlf^f  N i \ ^ -0.44  \  -0.29  -0.11  \ v  S  \  -0.48  \w  -0.20  -0.31  V  -0.2o\.  -0.3o\.  -0.44  -0.37\ \.  -0.42  TrS  N15 " H15" ,l  -0.4o\^  -0.53^S. \  ^  -0.22  -0.43  TrS  N30"~ H30"  -0.36  v  \ .  -0.57*\. \ ^  \w  -0.32  -0.4l\^ \  TTS  X.  -0.35  -0.38^\  N7.5"~ H7.5"  TrS  ^ ^ i  A  / G  TrS  \ TrS  \*%f  -0.56*  \  -0.63*\. -0.50  -0.20  -0.5l\  -0.22^^ -0.15  \ .  -0.4o\v  -0.0y\v  \  -0.18  -0.39  \ .  -0.34  TrS  > v TTS  N1'~  TTS  H1'  -0.l8\v  -0.35\. -0.39  -0.37  \  v  \  v  -0.40  -0.32  p<0.10  r=0.46  p<0.02  r=0.61  *p<0.05  r=0.53  **p<0.01  r=0.66  +0.15\v  -0.57*Nw \  v  -0.40 -0.47  \w  \  -0.35  +0.02\v.  -0.33^\^ \  -0.42 -0.36^s^  -52-  TTS.  N 15 TTS H  |  5  »  Pearson r = - 0.63  Regression Line  Fig.5.2 Comparison of TTS difference values (15" post-exposure) with i n i t i a l change i n 6^ during exposure (in percentage), * p <0.05  -53-  T  N 15 - TT S H 15 T  S  dB Pearson  184  Regression  r = -  0.56  Line  Fig.5.3 Comparison of TTS difference values (15" post-exposure) with f i n a l change i n  during exposure (in percentage) * p< 0.05  -54-  • TTS difference values (15" post-exposure) Fig 5.4 Comparison of TTS dirreie • « durins exposure- (in percentage) with i n i t i a l change va B during expo n f  -55-  T T S N 15' TTS  H 15 Pearson  r  Regression  Line  Fig.5.5 Comparison of TTS difference values (15" post-exposure) with i n i t i a l change i n Y^. during exposure (in percentage)  -56The ted  A  N  into ratios, ^ Y ^ i ^ N i  5 TTS  and h Y^^. were a l s o conver-  admittance v a l u e s Y ^  difference values.  ^Nf^Nf The  2111(3  c  o  m  N 1 5  „ - TTS  H 1 5  „) X  a  AY  N i  /Y  (See  condition  ation  AG^ N  with  d  r=-0.51  N i  - 4G  N f  d i f f e r e n c e between the i n i t i a l  and  ) was  and  P<0.10  recovery  the r a t e of MEM  relax-  then undertaken.  This  f i n a l change i n G^  during  exposure was  chosen as a measure of MEM  change i n G  ( 4 Gj^) decreased s i g n i f i c a n t l y more, w i t h  N  _to . i t s ...baseline  .(G^),  than A G^,  t i v e to t h e i r r e s p e c t i v e exposure. ( 4G ^  - AG  N  This  The w f  2*,  A  baselines  r e l a x a t i o n since  found.  2*-4'  respect  , or A B^ decreased, r e l a (G^^,  B ^, N  and  G ^),  N  was  small  and  non-significant  same measure o f the r a t e o f MEM-relaxation was  and  the  H  during  Pearson r c o r r e l a t i o n c o e f f i c i e n t between  ) and "T  pared w i t h TTS  the  5.5)  Fig.  (estimated by 1^)  ( e s t i m a t e d by  e  was:  A comparison of the r a t e of i n i t i a l TTS for  r  l a r g e s t o f the n e g a t i v e , non-  s i g n i f i c a n t Pearson r c o r r e l a t i o n c o e f f i c i e n t s (TTS  P  values f o r condition N but no  T  a t times 0 " ,  (rs0.15). a l s o com30",  1*,  s i g n i f i c a n t Pearson r c o r r e l a t i o n s were  Chapter 6 Discussion Most o f the TTS r e s u l t s from the procedures  that  i n v e s t i g a t e d the e f f e c t o f phonation on TTS were i n agreement w i t h r e s u l t s o f K a r l o v i c h and Luterman (1970), who 1000  Hz f a t i g u e tone, and o f McBay (1971)f  tone.  who  A l l these i n v e s t i g a t i o n s showed thats  i n g f a t i g u e exposure smaller  post-exposure TTS  and 2) TTS  used a 5 0 0 H z  1) phonation dur-  consistently results i n a significantly than i f no phonation accompanies  exposure, f o r a l l post-exposure females?  used a  times and f o r both males and  i s a f u n c t i o n o f the post-exposure  time  a t which i t i s measured such t h a t the TTS d i f f e r e n c e between p h o n a t i o n and non-phonation  conditions  i s most s i g n i f i c a n t a t  e a r l y post-exposure t i m e s .  A minimal tendency, noted by  K a r l o v i c h and Luterman and by McBay, f o r females to e x h i b i t g r e a t e r TTS  d i f f e r e n c e s than males between phonation and  p h o n a t i o n c o n d i t i o n s was  n o t found i n t h i s study.  Differences  between procedures used i n t h i s study and those used K a r l o v i c h and Luterman (1970) ( i e , a 1000 v o c a l e f f o r t was t h e i r f i n d i n g was  not r e p e a t e d .  by  Hz. tone was  not c o n t r o l l e d f o r ; e t c . ) may  non-  explain  used; why  McBay's (1971) study a l s o  d i f f e r e d i n t h a t three phonation c o n d i t i o n s p h o n a t i o n c o n d i t i o n i n t h i s study.  were used v s . one  She found the tendency f o r  females to e x h i b i t g r e a t e r TTS d i f f e r e n c e s t o occur o n l y d u r i n g the "humming c o m f o r t a b l y " c o n d i t i o n s  w h i l e the "humming  l o u d l y " c o n d i t i o n , which most c l o s e l y approximated -57-  this  study's  -58-  H  T  and  c o n d i t i o n , r e s u l t e d i n s i m i l a r TTS d i f f e r e n c e s f o r males females.  The r e s u l t s o f t h i s study, t h e r e f o r e , do n o t  appear t o c o n f l i c t w i t h p r e v i o u s  f i n d i n g s c o n c e r n i n g sex  r e l a t e d TTS d i f f e r e n c e s . Examination o f TTS r e c o v e r y during  revealed  t h a t humming  the f a t i g u e exposure r e s u l t s i n a s i g n i f i c a n t l y  i n i t i a l TTS r e c o v e r y , humming i s performed.  shorter  i n d i c a t e d by the l v a l u e s , than i f no This shorter i n i t i a l recovery  rate f o r  the humming c o n d i t i o n would appear to support K a r l o v i c h and Luterman's (1970) p r e d i c t i o n " t h a t r e t u r n t o pre-exposure t h r e s h o l d l e v e l s would take l o n g e r f o r the voiced  conditions."  f o r the non-voiced than  ( I b i d . , 1970, p . 5 1 4 ) .  however, seems t o show a p l a t e a u o f TTS r e c o v e r y  The data, f o r the  humming c o n d i t i o n between 2' and 4* post-exposure (See F i g . 5 . 1 ) , w h i l e the c o r r e s p o n d i n g TTS curve f o r the non-humming c o n d i t i o n i s s t i l l decaying n o t i c e a b l y .  Thus, i t would be  n e c e s s a r y t o c o n t i n u e the post-exposure t r a c k i n g u n t i l the pre-exposure t h r e s h o l d l e v e l i s reached before  the above  p r e d i c t i o n c o u l d be a p p l i e d t o a complete TTS paradigm. The  otoadmittance procedures r e v e a l e d  changes i n  conductance and susceptance a t the b e g i n n i n g and a t the end o f the exposure p e r i o d to be s i g n i f i c a n t l y l a r g e r when humming accompanied the exposure.  I t i s known t h a t 1) l a r g e changes  i n impedance (thus l a r g e changes i n admittance) can r e s u l t from a l a r g e degree o f MEM a c t i v i t y  (Metz, 1951? M i l l e r ,  196la,  1965? Simmons, 1964; Shearer and Simmons, 1965; K a r l o v i c h , e t a l . ,  -59-  1972)  2)  and  MEM  c o n t r a c t i o n a t t e n u a t e s t r a n s m i s s i o n o f low  f r e q u e n c y tones by up to 20 d3 Jepsen, and  1963;  Borg, 1968;  Gvacharia, 1972).  (Simmons,  1959?  Reger, I960}  Brasher, e t a l . , 1969? K e v a n i s h v i l i  From these f a c t s , one might assume t h a t  the r e d u c t i o n o f t r a n s m i s s i o n o f the exposure tone d u r i n g the humming c o n d i t i o n c o u l d be due an assumption  to i n c r e a s e d MEM  activity.  Such  appears v a l i d but should be regarded w i t h c a u t i o n  because, a l t h o u g h humming produced  l a r g e r changes i n G and B  than no humming, these changes w i t h humming appeared n e g a t i v e thus making i n t e r p r e t a t i o n d i f f i c u l t . o f t h e s e otoadmittance  to become  A repetition  procedures, p o s s i b l y w i t h  technical  improvements, would be d e s i r a b l e to r e s o l v e the above mentioned problem. K a r l o v i c h and Luterman  (1970, p.513)  ment o f a mechanism which i n c r e a s e s the e l a s t i c component o f the impedance" to account TTS  t h a t o c c u r s i f phonation  "suspect i n v o l v e reactance  f o r the r e d u c t i o n o f  accompanies exposure.  The  "elas-  t i c r e a c t a n c e " i s the n e g a t i v e p a r t o f the r e a c t a n c e or the c a p a c i t i v e component o f the impedance.  As the a b s o l u t e v a l u e  o f t h i s r e a c t a n c e i n c r e a s e s , the a b s o l u t e v a l u e of the s u s c e p t ance component o f admittance  decreases.  Luterman's h y p o t h e s i s i s t r u e one  I f K a r l o v i c h and  should f i n d the n e g a t i v e  r e a c t a n c e to become l a r g e r o r , i n t h i s study, the p o s i t i v e susceptance exposure. In f a c t , a be reduced  to become s m a l l e r when phonation The  l a t t e r r e s u l t was  accompanies  found i n the c u r r e n t study.  t - t e s t f o r r e l a t e d measures showed susceptance by the humming c o n d i t i o n s i g n i f i c a n t l y more  to  (0.01  -60l e v e l ) than the conductance was.  Such a f i n d i n g suggests  t h a t the susceptance component o f admittance i s a f f e c t e d more than the conductance by whatever  mechanism reduces  TTS  a f t e r phonation. When no phonation accompanied t h a t the change i n conductance was  exposure  i t was  found  a t the b e g i n n i n g o f exposure  l a r g e r than the c o r r e s p o n d i n g change i n susceptance.  d i f f e r e n c e between changes i n G and B was  a l s o p r e s e n t , though  n o t s i g n i f i c a n t l y so, a t the end o f exposure i n G decreased d u r i n g exposure).  This  ( i e . the change  I t i s w e l l known t h a t  MEM  a c t i v i t y due to the a c o u s t i c r e f l e x decays d u r i n g continuous acoustic stimulation The  (Metz, 1951?  K a r l o v i c h , et a l . ,  1972).  f a c t t h a t the change i n G (but not the change i n B)  decreased d u r i n g exposure seems to be an i n d i c a t i o n o f such a r e f l e x decay.  I t may  be t h a t G i s the admittance component  most a f f e c t e d by a c o u s t i c s t i m u l a t i o n o f the  MEM.  On the o t h e r hand, when, phonation accompanied  expo-  s u r e , the changes i n susceptance d u r i n g exposure were l a r g e r than the c o r r e s p o n d i n g changes i n conductance.  S i n c e we  do  n o t know which a n a t o m i c a l p a r t s o f the middle ear c o n t r i b u t e which components o f admittance, i t i s d i f f i c u l t to e x p l a i n this finding.  I t i s p o s s i b l e t h a t the l a r g e r change i n B  r e s u l t s from an i n c r e a s e d MEM  c o n t r a c t i o n w i t h phonation, from  the change i n stapes v i b r a t i o n thought to occur w i t h phonation (Beklsy, i 9 6 0 ) ,  o r from a combination o f these and o t h e r , as  y e t u n d e f i n e d , mechanisms.  F u r t h e r r e s e a r c h , such as t h a t by  -61-  M^ller  (1961a),  Onchi ( 1 9 6 1 ) ,  and Z w i s l o c k i (1965) on e l e c t r i c a l  o r m e c h a n i c a l analogues o f the middle e a r , i s needed, F o l l o w i n g otoadmittance d a t a a n a l y s i s , the a p p a r e n t l y negative  G and B v a l u e s , d u r i n g exposure i n the humming c o n d i -  t i o n , remained a problem.  I t was thought t h a t a c o u s t i c feedback  d u r i n g the humming might have r e s u l t e d i n the n e g a t i v e S i n c e the p l o t t i n g o f G and B had i n v o l v e d a r e l a t i v e l y sampling r a t e (approximately  values. slow  1 Hz), mingograms o f the humming  c o n d i t i o n f o r each s u b j e c t were made to determine i f p e r t i n e n t i n f o r m a t i o n had been missed i n the between-sampling p e r i o d s . The  mingograms confirmed  t h a t , f o r a l l s u b j e c t s , G and B,  d u r i n g exposure accompanied by humming, f e l l below the zero mmho b a s e l i n e .  G and B d i d n o t become p o s i t i v e , however, dur-  i n g the 2-3 sec pauses between two i n t e r v a l s o f humming thus, the h y p o t h e s i s  o f a c o u s t i c feedback r e s u l t i n g i n n e g a t i v e  B v a l u e s was r u l e d out.  G and  A study i n v e s t i g a t i n g changes i n G and  B when no exposure i s presented  d u r i n g a humming a c t i v i t y might  h e l p r e s o l v e t h i s problem. S i n c e G and B d i d n o t become p o s i t i v e d u r i n g the between-humming pauses i t appeared t h a t G and B do n o t change rapidly. 1967)  I t i s known (Salomon and S t a r r , 1963;  t h a t MEM c o n t r a c t i o n s continue  p h o n a t i o n ends.  Djupesland,  up t o 300 msec a f t e r  R e s u l t s o f the c u r r e n t study  suggest t h a t  mechanisms t h a t a l t e r G and B, when phonation accompanies an i n t e n s e exposure, remain a c t i v e much l o n g e r than 300 msec a f t e r p h o n a t i o n ends.  The p o s s i b l e mechanisms i n v o l v e d were d i s c u s s e d  -62earlier  ( c f . Sec.  2.2  and  2.3)  but i t i s not known which com-  b i n a t i o n o f mechanisms reduces admittance (and r e d u c e s TTS)  therefore  when phonation accompanies exposure or which  mechanisms are r e s p o n s i b l e  f o r separate changes i n the  two  admittance components. I n the comparison o f TTS one  s i g n i f i c a n t t r e n d was  found.  and  otoadmittance d a t a only5.2  Figures  and  t h a t the l a r g e r the change i n conductance, a t the and  end  ference  5.3  show  beginning  o f exposure w i t h no humming, the s m a l l e r the TTS between humming and non-humming c o n d i t i o n s  post-exposure t i m e s ) .  dif-  (at early  In other words, the g r e a t e r the amount  of.MEM c o n t r a c t i o n , r e f l e c t e d by the change i n conductance w i t h exposure ( c o n d i t i o n N ) , Q  the  the s m a l l e r the p r o t e c t i o n  ear by the humming, r e f l e c t e d .by TTS  T h i s may  mean t h a t i f the MEM  difference  are c o n t r a c t e d  response to an a c o u s t i c s t i m u l u s  they may  exposure.  Figure  5«  2  and  values.  strongly i n  not c o n t r a c t much  more d u r i n g phonation thus humming p r o v i d e s t e c t i o n from the  given  little 5«3  extra pro-  appear to sub-  s t a n t i a t e t h i s h y p o t h e s i s i e . i n d i v i d u a l s h a v i n g the l a r g e s t amounts o f MEM  c o n t r a c t i o n , as i n d i c a t e d by percentage changes  i n conductance, have the s m a l l e s t amounts o f e x t r a p r o t e c t i o n from humming, as i n d i c a t e d by TTS verse  difference values.  a l s o h o l d s i n t h a t i n d i v i d u a l s w i t h a weak MEM  The  re-  contraction  i n response to a c o u s t i c s t i m u l a t i o n show c o n s i d e r a b l e  extra  p r o t e c t i o n from the humming c o n d i t i o n . These r e s u l t s must be c o n s i d e r e d A repeat  as  preliminary.  o f these procedures w i t h a l a r g e r p o p u l a t i o n ,  o f both  -63normals and s u b j e c t s w i t h c e r t a i n middle e a r a b n o r m a l i t i e s , might v e r i f y t h e above t r e n d o r even show more s i g n i f i c a n t correlations.  Such a study would h e l p i n d i c a t e the normal  range o f r e s u l t s from such p r o c e d u r e s and might determine whether those n o t c l o s e l y f o l l o w i n g the t r e n d e i t h e r  fall  w i t h i n normal l i m i t s o r p o s s i b l y have some undiagnosed abnorm a l i t y t h a t was n o t apparent from accepted s c r e e n i n g  techniques.  Changes i n conductance and admittance ( F i g . 5»5) were c o r r e l a t ed w i t h t h e TTS d i f f e r e n c e v a l u e s did  but changes i n susceptance  n o t show any such r e l a t i o n s h i p ( F i g . 5*4 and T a b l e 3 ) .  Further  research,  h o p e f u l l y , w i l l i n d i c a t e why t h i s o c c u r s . I f  EMG s t u d i e s were p o s s i b l e w i t h normal humans we might determine the l e v e l s o f MEM c o n t r a c t i o n t h a t r e s u l t from a c o u s t i c  stimu-  l a t i o n and from a c o u s t i c .stimulation accompanied by p h o n a t i o n . T h i s c o u l d i n d i c a t e whether changes i n TTS and admittance d u r i n g the humming c o n d i t i o n a r e due t o MEM c o n t r a c t i o n alone o r whether o t h e r mechanisms, such as a change i n stapes v i b r a tion  (Bekesy, I960), a r e i n v o l v e d . The  r e s u l t s o f t h i s study i n d i c a t e two b a s i c  types  o f MEM a c t i v i t y i n response to a c o u s t i c and t o a c o u s t i c phonatory s t i m u l a t i o n .  Some i n d i v i d u a l s show s t r o n g  a c t i v a t i o n o f t h e i r MEM w i t h l i t t l e by p h o n a t i o n d u r i n g  acoustic  further protection  the f a t i g u e exposure.  plus  provided  Most i n d i v i d u a l s ,  however, show some a c o u s t i c a c t i v a t i o n o f t h e i r MEM w h i l e phonation during  exposure p r o v i d e s  considerable  extra  protec-  t i o n o f the ear as evidenced by a s i g n i f i c a n t l y reduced TTS. The  r e s u l t s do n o t , however, r e v e a l how phonation  protects  -64-  these e a r s from i n t e n s e One  could  strongly during  low  frequency  stimulation.  h y p o t h e s i z e t h a t the MEM  phonation p l u s exposure than d u r i n g  exposure a l o n e , however, t h i s c l a i m can through f u r t h e r r e s e a r c h . of contraction t i o n , MEM  may  c o n t r a c t more  i s the  he  substantiated  Even i f i t i s shown t h a t the  same f o r phonatory and  auditory  s t i l l provide extra protection during  S i n c e we  know t h a t i n t r o d u c t i o n o f a new  acoustic  s t i m u l a t i o n i s s u f f i c i e n t to s t i m u l a t e  contraction  acoustic  (Metz, 1951;  frequency  Brasher, et a l . , 1969)  only degree  stimula-  phonation. during  renewed  MEM  i t would seem  t h a t , as shown by the c u r r e n t r e s u l t s , humming should keep the MEM  maximally c o n t r a c t e d  throughout the  exposure.  We  also  know t h a t c o n t i n u o u s s i n g l e frequency s t i m u l a t i o n , as i n non-humming c o n d i t i o n , r e s u l t s i n a decrease of REM (Metz, 1951s  Karlovich, 1972).  r a p i d the decrease i n MEM c o n d i t i o n , the g r e a t e r a Madsen (Model ZO  70)  One  activity  might expect t h a t the more  a c t i v i t y during  the TTS  the  the non-humming  produced by exposure.  Using  e l e c t r o a c o u s t i c impedance b r i d g e  with  6 subjects,  McBay (1971) found t h i s r e s u l t f o r the non-humming  condition.  For  the c u r r e n t group o f s u b j e c t s ,  consistent pattern defined  by^G^  o f decrease of MEM  - ^ G^)  however, no  a c t i v i t y was  found  (as  thus i t would appear t h a t e i t h e r  a c t i v i t y i s d i f f e r e n t i n the two  conditions  (N^ and  H) T  MEM  or  t h a t o t h e r mechanisms are i n v o l v e d d u r i n g phonation to account f o r the l a r g e r change i n admittance and phonation.  thus reduced TTS  with  -65Summary the  T h i s study was s e t up to i n v e s t i g a t e one o f  f a c t o r s t h a t may be r e s p o n s i b l e f o r TTS r e d u c t i o n t h a t  o c c u r s when phonation accompanies pure tone.  exposure t o a 500 Hz 117.5  Through the use o f admittance measurements, t h e  r o l e o f the MEM i n TTS r e d u c t i o n was i n v e s t i g a t e d . of  t h e study i n d i c a t e d 1)  dB  The r e s u l t s  thats  TTS i s a f u n c t i o n o f t h e post-exposure time a t which the t h r e s h o l d i s measured. The e a r l y post-exposure times ( 0 " , 7.5"• 15". 30") r e s u l t e d i n the l a r g e s t TTS v a l u e s .  2) TTS from the exposure tone accompanied by phonation (humming) was c o n s i s t e n t l y and s i g n i f i c a n t l y s m a l l e r than TTS from the exposure tone w i t h no supplementary activity. 3) D i f f e r e n c e s between TTS from phonation (humming) d u r i n g exposure and TTS from exposure w i t h no - supplementary a c t i v i t y were most s i g n i f i c a n t a t the e a r l y post-exposure times ( 0 " , 7.5". 15". 30"). k)  The r a t e o f i n i t i a l TTS r e c o v e r y when phonation accompanied exposure was s i g n i f i c a n t l y s h o r t e r than when no supplementary a c t i v i t y accompanied exposure.  5) There were no s i g n i f i c a n t  TTS d i f f e r e n c e s between sexes.  6) Changes i n the conductance and susceptance components o f admittance a t the b e g i n n i n g and end o f exposure were s i g n i f i c a n t l y l a r g e r when phonation accompanied exposure than when no supplementary a c t i v i t y accompanied exposure. 7) When phonation accompanied exposure the changes i n susceptance a t the b e g i n n i n g and end o f exposure were s i g n i f i c a n t l y l a r g e r than t h e c o r r e s p o n d i n g changes i n conductance. When no supplementary a c t i v i t y accompanied exposure, however, t h e changes i n conductance a t the b e g i n n i n g o f exposure were s i g n i f i c a n t l y l a r g e r than the c o r r e s p o n d i n g changes i n susceptance. 8) Changes i n conductance and susceptance a t the b e g i n n i n g and end o f exposure d i d n o t c o r r e l a t e s i g n i f i c a n t l y w i t h TTS v a l u e s measured a t any o f the post-exposure times.  -66-  9)  10)  The r a t e of MEM r e l a x a t i o n d u r i n g exposure accompanied by no supplementary a c t i v i t y d i d not c o r r e l a t e s i g n i f i c a n t l y w i t h the r a t e of i n i t i a l TTS r e c o v e r y or w i t h TTS values measured a t s e v e r a l of the post-exposure times (0", 30", 1', 2\ 2«-4'). The degree o f MEM a c t i v i t y a t the b e g i n n i n g and end o f exposure accompanied by no supplementary a c t i v i t y , measured by the percentage change i n conductance at these times, c o r r e l a t e d s i g n i f i c a n t l y with the amount of p r o t e c t i o n provided the ear by phonation (humming), measured by the d i f f e r e n c e s between TTS v a l u e s a t e a r l y post-exposure times f o r the humming and non-humming c o n d i t i o n s . From the r e s u l t s , i t was  i n d i v i d u a l s , who  have MEM  that contract strongly with  acoustic stimulation, gain l i t t l e tion  hypothesized t h a t some  e x t r a p r o t e c t i o n from phona-  (humming),during exposure, w h i l e the m a j o r i t y  d u a l s , who  have MEM  intense  of  t h a t c o n t r a c t weakly w i t h i n t e n s e  indiviacoustic  s t i m u l a t i o n , g a i n ..a . s i g n i f i c a n t amount o f p r o t e c t i o n from phonation MEM  (humming) d u r i n g  exposure.  The  r e s u l t s suggest t h a t  p l a y a major r o l e i n the a t t e n u a t i o n  of sound  t h a t o c c u r s when phonation accompanies exposure.  the  transmission Other mechan-  isms, however, i n c l u d i n g i n s u f f i c i e n t stapes v i b r a t i o n and a t t e n t i o n a l f a c t o r s , a l s o may necessary before  we  be i n v o l v e d but more r e s e a r c h  is  can determine the exact r o l e each mechanism  p l a y s i n the r e d u c t i o n  o f TTS  with phonation.  References vo  n  Bekesy, G. (I960). Experiments i n H e a r i n g (McGraw-Hill Book Co., New YorkJT"  B e l l , D.W.,  and F a i r b a n k s , G, ( 1 9 6 3 ) . "TTS Produced by LowL e v e l Tones and the E f f e c t o f T e s t i n g on Recovery," J . A c o u s t . Soc. Amer. J3j>, 1725-1731.  B e n g u e r e l , A.P. , and McBay, H.D. ( 1 9 7 2 ) . "Changes i n TTS A s s o c i a t e d w i t h Humming and Nonvocal A c t i v i t i e s , " J . A c o u s t . Soc. Amer. j)4, 1107-1114. B o t s f o r d , J.H. ( 1 9 7 1 ) . "Theory of Temporary T h r e s h o l d S h i f t , " J . A c o u s t . Soc. Amer. 4°;, 440-446. Borg, E. ( 1 9 6 8 ) . "A Q u a n t i t a t i v e Study o f the E f f e c t o f the Acous t i c S t a p e d i u s R e f l e x on Sound T r a n s m i s s i o n Through the Middle E a r o f Man," A c t a O t o - l a r y n g o l . 6 6 , 4 6 1 - 4 7 2 . B r a s h e r , P.F. , C o l e s , R.R'.A., Elwood, M.A., and F e r r e s , H.M. (1969)« "Middle E a r Muscle A c t i v i t y and Temporary T h r e s h o l d S h i f t , " I n t . A u d i o l . 8, 5 7 9 - 5 8 4 . B r u n i n g , J . L . , and"'Kiritz, "B.L. (1968). Computational Handbook of S t a t i s t i c s ( S c o t t , Foresman and Co., Glenview, Illinois), Carmel, P.W. , and S t a r r , A. ( 1 9 6 3 ) . " A c o u s t i c and Nonacoustie F a c t o r s M o d i f y i n g Middle E a r Muscle A c t i v i t y I n Waking C a t s , " J . N e u r o p h y s i o l . 2 6 , 5 9 8 - 6 1 6 . C o l l i n s , W.E., and Capps, M.J. ( 1 9 6 5 ) . " E f f e c t s o f S e v e r a l Mental Tasks on A u d i t o r y F a t i g u e , " J . A c o u s t . Soc. Amer. 21> 7 9 3 - 7 9 6 . D a v i s , H. , Morgan, C.T. , Hawkins, J . E . J r . , Galambos, R.«, and Smith, F.W. ( 1 9 5 0 ) . "Temporary Deafness F o l l o w i n g Exposure to Loud Tones and N o i s e , " A c t a O t o - l a r y n g o l . S u p p l . 88. D j u p e s l a n d , G. ( 1 9 6 4 ) . "Middle Ear Muscle R e f l e x e s E l i c i t e d by A c o u s t i c and Nonacoustic S t i m u l a t i o n , " A c t a O t o - l a r y n g o l . S u p p l . 188. ( 1 9 6 7 ) , C o n t r a c t i o n s o f the Tympanic Man ( U n i v e r s i t e t f o r l a g e t , O s l o ) ,  Museles i n  . E p s t e i n , A., and Schubert, E.D. (1957)« " R e v e r s i b l e A u d i t o r y F a t i g u e R e s u l t i n g from Exposure to a Pure To«e, A r c h . O t o l a r y n g o l , 6_5_, 17^-182. •  -67-  -68-  F r i c k e , J . E . ( 1 9 6 6 ) . " A u d i t o r y F a t i g u e and Mental J . A u d i t o r y Res, 6 , 2 8 3 - 2 8 7 . .  Activity,"  G r a s o n - S t a d l e r ( 1 9 7 3 ) . Otoadmittance Handbook 2 ( G r a s o n - S t a d l e r • Co., I n c . , Concord, Massachusetts"!. Jepsen,  0.  ( 1 9 6 3 ) . "Middle E a r Muscle R e f l e x e s i n Man," i n Modern Developments i n A u d i o l o g y , J , J e r g e r , Ed, "(Academic P r e s s Inc., New Y o r k ) ,  J e r g e r , J . (1970) <, " C l i n i c a l E x p e r i e n c e with Impedance Audiometry," A r c h . O t o l a r y n g o l . J_2, 3 1 1 - 3 2 4 . K a r l o v i c h , R.S., Gooden, R.D., and Wiley, T, (1972) "Some S p e c t r a l and Temporal Parameters o f Middle-Ear i M u s c l e R e f l e x - A c t i v a t i n g S t i m u l i A l t e r i n g TTS," J . Amer. Speech H e a r i n g A s s o c . 1 4 , 4 7 6 . , and Luterman, B.F. ( 1 9 6 9 ) . " A u d i t o r y F a t i g u e D u r i n g A r t i c u l a t i o n ," J . A c o u s t . Soc. Amer. 4_>,  786-787.  and (1970). "Application of the TTS Paradigm f o r A s s e s s i n g Sound T r a n s m i s s i o n i n t h e A u d i t o r y System D u r i n g Speech Production," J , A c o u s t . Soc. Amer. 4_, 5 1 0 - 5 1 7 . K e v a n i s h v i l i , Z. Sh., and G v a c h a r i a , Z.V. ( 1 9 7 2 ) . "On t h e Role o f the Tensor Tympani Muscle i n Sound Conduction through t h e Middle E a r , " A c t a O t o - l a r y n g o l , 231-239. Klockhoff,  I., and Anderson, H. ( 1 9 5 9 ) . "Recording o f the Stapedius R e f l e x E l i c i t e d by Cutaneous S t i m u l a t i o n (A P r e l i m i n a r y R e p o r t ) , " A c t a O t o - l a r y n g o l . 5 0 , 4 5 1 - 4 5 4 . , and (i960). "Reflex A c t i v i t y i n the Tensor Tympani Muscle Recorded i n Man (A Prel i m i n a r y Report)," Acta Oto-laryngol. £ 1 , 1 8 4 - 1 8 8 . (1961). "Middle E a r Muscle R e f l e x e s i n Man," A c t a O t o - l a r y n g o l . Suppl. 1 6 4 .  Luterman, B.F., and K a r l o v i c h , R.S. ( 1 9 6 9 ) . " F u r t h e r Observat i o n s Concerned w i t h A u d i t o r y F a t i g u e During V o c a l and Nonvocal Speech A c t i v i t i e s , " J . Acoust. Soc. Amer. 4 6 , 4 0 3 - 4 0 8 . McBay, H.D.  ( 1 9 7 1 ) . I n f l u e n c e o f Phonation on H i g h - I n t e n s i t y Sound T r a n s m i s s i o n i n the A u d i t o r y System (Master's T h e s i s , U n i v e r s i t y o f B r i t i s h Columbia, Vancouver, B.C.)  -69-  McCall,  G.N., and Rabuzzi, D.D. ( 1 9 7 0 ) . " R e f l e x C o n t r a c t i o n o f Middle E a r Muscles Secondary t o S t i m u l a t i o n o f L a r y n g e a l Nerves i n the Cat," J . Amer. Speech Hearing Assoc. 12, 446. , and (1973). "Reflex Contraction of Middle E a r Muscles Secondary t o S t i m u l a t i o n o f L a r y n g e a l Nerves," J . Speech Hearing Res. 1_6, 51-61.  Metz, 0 . ( 1 9 5 1 ) . " S t u d i e s on the C o n t r a c t i o n o f the Tympanic Muscles as I n d i c a t e d by Changes i n the Impedance o f the E a r , " A c t a O t o - l a r y n g o l . _ 9 , 3 9 7 - ^ 0 5 . M o l l e r , A.R. ( L 9 5 8 ) . " I n t r a - A u r a l Muscle C o n t r a c t i o n i n Man, Examined by Measuring A c o u s t i c Impedance o f the E a r , " Laryngoscope 68, 48-62. ( 1 9 6 1 a ) . "Network Model o f the Middle Ear,-" J . . Acoust. Soc. Amer. ^ , 1 6 8 - 1 7 6 . _ _ ( 1 9 6 1 b ) . " B i l a t e r a l C o n t r a c t i o n o f the Tympanic Muscles i n Man (examined by measuring a c o u s t i c impedance change)," Ann. O t o l . R h i n o l . L a r y n g o l . 70  735-752.  ( 1 9 6 5 ) . "An E x p e r i m e n t a l Study o f the A c o u s t i c Impedance o f the Middle E a r and i t s Transmission Properties," Acta Oto-laryngol. ( 1 9 7 2 ) . "The Middle Ear," i n Foundations o f Modern A u d i t o r y Theory, J.V. Tobias, E6~. (Academic Press Inc. New York). Nixon, J.C. and G l o r i g , A. ( 1 9 6 2 ) . "Noise-Induced Temporary T h r e s h o l d S h i f t vs Hearing L e v e l i n Four I n d u s t r i a l Samples," J . A u d i t o r y Res. 2, 125-138. Onchi, Y. (1961)'. "Mechanism o f the Middle Ear," J . Acoust. Soc. Amer. __, 7 9 4 - 8 0 5 . Peterson,  J . L . , and Liden, G. .(1972). "Some S t a t i c i s t i c s o f the S t a p e d i a l Muscle Reflex," 11, 97-114.  CharacterAudiology  P o r t e r , T.A. ( 1 9 7 2 ) . "Normative Otoadmittance Values f o r Three P o p u l a t i o n s , " unpublished paper ( d i s t r i b u t e d by Reger, S.N.- ( i 9 6 0 ) . " E f f e c t o f Middle E a r Muscle A c t i o n on C e r t a i n P s y c h o p h y s i c a l Measurements," Ann. O t o l . R h i n o l . L a r y n g o l . __5, 1179-1198.  -70-  Riach, W.D.,  E l l i o t t , D.N., and F r a z i e r , L. ( 1 9 6 4 ) . " E f f e c t o f Repeated Exposure t o High I n t e n s i t y Sound," J . Acoust. Soc. Amer. __6, 1195-H98.  Rodda, M. ( 1 9 6 4 ) . "Role o f Test Tone i n Producing Temporary T h r e s h o l d S h i f t , " Arch. O t o l a r y n g o l . 8 0 , 160-166. Salomon, G., and S t a r r , A. ( 1 9 6 3 ) . "Electromyography o f Middle E a r Muscles i n Man During Motor A c t i v i t i e s , " A c t a Neurol. Scand. 32, 161-168. „ Shearer,  W.M., and Simmons, F.B. ( 1 9 6 5 ) . "Middle E a r A c t i v i t y During Speech i n Normal Speakers and S t u t t e r e r s , " J . Speech Hearing Res. 8, 2 0 3 - 2 0 7 .  Simmons, F.B. ( 1 9 5 9 ) . "Middle E a r Muscle A c t i v i t y a t Moderate Sound L e v e l s , " Ann. O t o l . R h i n o l . L a r y n g o l . 68, 1126-1143. ( 1 9 6 4 ) . " P e r c e p t u a l T h e o r i e s o f Middle E a r Muscle F u n c t i o n , " Ann. O t o l . R h i n o l . L a r y n g o l . 21* 724-739. Ward, W.D.  (1962)". Damage R i s k C r i t e r i a f o r Line J . Acoust. Soc. Amer. J_4, 1610-1619.  Spectra,"  (.1963)"Auditory F a t i g u e and Masking," i n Modern Developments i n Audiology, J . J e r g e r , Ed, (Academic Press IncTi New Y o r k ) . ( 1 9 6 6 ) . "Temporary T h r e s h o l d S h i f t i n Males and Females," J . Acoust. Soc. Amer. 40, 4 7 8 - 4 8 5 . W e r s a l l , R« ( 1 9 5 8 ) . "The Tympanic Muscles and T h e i r R e f l e x e s , " A c t a O t o - l a r y n g o l . Suppl. 139. Wever, E.G., and Vernon, J.A. ( 1 9 5 5 ) . "The E f f e c t s o f the Tympanic Muscle R e f l e x e s Upon Sound Transmission," Acta Oto-laryngol. _5, 433-439. Winer, B.J. ( 1 9 6 2 ) , S t a t i s t i c a l P r i n c i p l e s i n Experimental Design (McGraw-Hill Book Co., New York). Zemlin,  W.R. ( 1 9 6 8 ) . Speech and Hearing Science - Anatomy and P h y s i o l o g y I P r e n t i c e - h a i l ! i n c . , Jinglewood. C l i f f s , New J e r s e y ) .  Z w i s l o c k i , J . J . ( 1 9 6 5 ) . " A n a l y s i s o f Some A u d i t o r y C h a r a c t e r i s t i c s " i n Handbook o f Mathematical Psychology V o l . I l l , R.D. Luce, e t a l . , Ed. (John Wiley and Sons, Inc., New York).  Appendix Instructions to Subjects TTS 1.  Procedures You w i l l f i r s t hear a p u l s e d tone o f low p i t c h i n your r i g h t  ( l e f t ) e a r t h a t w i l l g r a d u a l l y become  higher i n p i t c h .  P r e s s the b u t t o n as soon as you  hear the tone, then l e t go as soon as the tone d i s appears . 2. You w i l l now hear a p u l s e d tone i n your r i g h t ear  t h a t w i l l remain a t the same p i t c h .  (left)  P r e s s the  b u t t o n as soon as you hear the tone, l e t go as soon as i t d i s a p p e a r s . 3. Now i n your l e f t then Step 2.  ( r i g h t ) ear Step 1 w i l l be r e p e a t e d  P r e s s the b u t t o n when you hear the  tone, l e t go when you don't. 4.  You w i l l now hear a l o u d continuous tone i n your left  ( r i g h t ) ear f o r 5 minutes.  You w i l l be g i v e n  i n s t r u c t i o n s about what t o do d u r i n g t h i s time and w i l l g e t s u f f i c i e n t p r a c t i c e o f the a c t i v i t i e s i n volved.  D u r i n g the 5 minutes r e f r a i n from e x c e s s i v e  body movements o r unnecessary c l e a r i n g o f the t h r o a t coughing, yawning, o r swallowing.  About 10  b e f o r e the tone i s turned o f f I w i l l ?  seconds  jump on the  f l o o r to a l e r t you t o be ready f o r the next s t e p . 5. As soon as the l o u d tone i s turned o f f l i s t e n f o r ?  the  p u l s e d tone t h a t does n o t change i n p i t c h .  As  -72-  soon as you hear the p u l s e d tone^press the b u t t o n until  i t d i s a p p e a r s , then l e t go, e t c . as b e f o r e .  T h i s w i l l continue f o r 4 minutes.  Do you have any q u e s t i o n s ?  B. Otoadmittance Procedures When the probe i s p l a c e d i n one ear^you w i l l  hear  a moderately loud tone t h a t w i l l remain on f o r the d u r a t i o n of  the session.  ear,  I w i l l o b t a i n an a i r - t i g h t  seal i n that  then v a r y the p r e s s u r e w i t h i n the s e a l e d c a v i t y and  make a number o f measurements. A f t e r t h i s t i m e y o u must remain as s t i l l }  as p o s s i b l e .  Do n o t move your f e e t , arms, hands, e t c . and t r y n o t t o swallow, cough or c l e a r your t h r o a t u n t i l  I t e l l you the  s e s s i o n i s over. 1. You w i l l hear the probe tone o n l y , f o r 2 minutes. 2. F o r the next 5 minutes you w i l l a l s o hear the loud exposure tone (same as i n t h e TTS c o n d i t i o n s ) i n the  ear o p p o s i t e to t h e probe.  S i t v e r y s t i l l or  hum as d i r e c t e d , 3. When t h i s l o u d tone i s turned o f f remain v e r y for  another 4 minutes.  Wait u n t i l  still  Probe tone w i l l remain on.  a d v i s e d to move b e f o r e d o i n g s o .  Do you have any q u e s t i o n s ?  

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