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Towards an improved method of presenting the Lexiphone code and spelled speech Suen, Ching Yee 1970

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TOWARDS AN IMPROVED METHOD OF PRESENTING THE LEXIPHONE CODE -AND SPELLED SPEECH  -by  CHING JEE SUEN ~B7ScT(Eng."), "University of Hong Kong, 1966 M.Sc.(Eng.), University of Hong Kong, 1968 __A._THESIS,.5HBMITTED_IK.EARTIAL_-FULPILMENT OF THE REQUIREMENTS FOR THE DEGREE OF. .. •:.  .  MASTER OF-APPLIED -SCIENCE i n the Department of Electrical Engineering  We accept this thesis as conforming to the required standard Research Supervisor Members of Committee..  Acting Head of Department. Members of the Department o f Electrical Engineering THE UNIVERSITY OF BRITISH' COLUMBIA  May, 1970  In  presenting  this  thesis  an a d v a n c e d d e g r e e the L i b r a r y I  further  for  of  this  written  the U n i v e r s i t y  s h a l l make i t  agree  scholarly  by h i s  at  thesis  freely  that permission  purposes-may  representatives. for  of  of  Columbia,  of  Electrical  June 10th 1970  for  for extensive by  gain  shall  Engineering  Columbia  the  requirements  reference copying  of  I agree and this  that  not  copying  or  for that  study. thesis  t h e Head o f my D e p a r t m e n t  is understood  financial  The U n i v e r s i t y o f B r i t i s h V a n c o u v e r 8, Canada  British  available  be g r a n t e d  It  fulfilment  permission.  Department  Date  in p a r t i a l  or  publication  be a l l o w e d w i t h o u t  my  .ABSTRACT  T h i s t h e s i s d e s c r i b e s the e f f e c t s o f d i c h o t i c - p r e s e n t a t i o n s  on  t h e - r e a d i n g speed.of the u s e r s of the L e x i p h o n e - a r e a d i n g machine f o r the b l i n d . "delay:  The  one  d i c h o t i c presentations i n v e s t i g a t e d are:  a)  single  s i g n a l t o one e a r and.a d e l a y e d v e r s i o n o f t h i s s i g n a l t o  the o t h e r e a r ; b) m u l t i p l e d e l a y :  the same s i g n a l w i t h t h r e e i n t e r d e l a y e d  v e r s i o n s , two s i g n a l s coming to each e a r .  E x p e r i m e n t s w i t h the Lexiphone  s u b j e c t s i n d i c a t e d t h a t d i c h o t i c p r e s e n t a t i o n s (compared w i t h o r d i n a r y b i n a u r a l p r e s e n t a t i o n , i . e . without delay) brought a s i g n i f i c a n t improvement t o ' " t h e i r r e a d i n g "speed. A s i m i l a r i n v e s t i g a t i o n has also_b.een.made on..spelled speech w h i c h has been p r o p o s e d to r e p l a c e the code sounds. . The  results indi- .  c a t e d t h a t m u l t i p l e d e l a y (as has been f o u n d i n the case u s i n g the L e x i phone s u b j e c t s ) produced a l i t t l e l e s s improvement than s i n g l e d e l a y . N e v e r t h e l e s s , b o t h t h e s e two d i c h o t i c p r e s e n t a t i o n s produced an improvement on the i n t e l l i g i b i l i t y o f the m a t e r i a l .  The  e f f e c t of t h e word l e n g t h  (number o f l e t t e r s c o n t a i n e d i n a word), on the i n t e l l i g i b i l i t y speech was  a l s o a n a l y z e d , i t showed t h a t the word l e n g t h has a g r e a t  e f f e c t ; i t was length. to  f o u n d t h a t the p e r c e n t c o r r e c t n e s s d e c r e a s e s  T h i s e f f e c t . a l s o seems to be due  w i t h the word  t o the l o n g e r time r e q u i r e d  p e r c e i v e the -word.from.'the' s p e l l i n g , thus i t i s s u g g e s t e d  that' a l o n g e r  pause s h o u l d be p r o v i d e d f o r those words w i t h -a l a r g e number o f .Confusions  of s p e l l e d  o f some l e t t e r sounds were o b s e r v e d  letters.  when s p e l l e d .speech was  com-  p r e s s e d , t h e s e a r e the consonant sounds w h i c h are a r t i c u l a t e d e i t h e r a t the. -same- place- -or - i n the-same -manner.  -. - ~  :  -••--:-;'  • TABLE OF CONTENTS '. • Page ..ABSTRACT .  i i  ...TABLE OF CONTENTS. . . . . . . . . . . . . . . . . . . . . . . . . . LIST OF ILLUSTRATIONS  i i i  .  iv  LIST OF TABLES . . . . . . . . . . . . . . . . . . .  v  "ACKNOWLEDGEMENT  '  1.  INTRODUCTION  2.  SCHEMES USED TO -PRODUCE- DICHOTIC - SIGNALS AND 2.1  . . .'. . . . . .  Vi  .  1 TIME COMPRESSION .  D i c h o t i c P r e s e n t a t i o n s - Methods u s e d t o I n c r e a s e the I n t e l l i g i b i l i t y o f Sound S i g n a l s • . . . . . . . . . . .  2.2  4.  5.  . . . . . . . . . . . . . . . . . .  9  - TESTS ON THE LEXIPHONE SUBJECTS • • ... • . ... . • • • • • ''.  12  . 3.1"-  T e s t i n g ' P r o c e d u r e s and R e s u l t s  12  . 3.2  E f f i c i e n c y o f the D i c h o t i c P r e s e n t a t i o n s  TESTS ON SPELLED SPEECH • •'.'.  —  4  Time, Compression - Method used to I n c r e a s e the P r e s e n t a t i o n Rate o f Sound S i g n a l s  3.  4  T e s t i n g P r o c e d u r e s and R e s u l t s  4.2  E f f e c t o f Word Length  .4.3  C o n f u s i o n o f Some L e t t e r Sounds  APPENDIX I I REFERENCES  14 . . •'. . .  •  •  . . . . . . . . . . . . . . . .  '.CONCLUSIONS AND. DISCUSSIONS . ....... -.7  • •  . . . . ........  4.1  APPENDIX I  . . . . . . . . . . . .  ... . . .  . . . . • '.  16 18 20  ...... . . . . . . . .". . ' . 22  . . . . . . . . . . . . .  . . . . . . . .  . . . . . . . . • • • . • • - . .......... •  16  .25  . . .  .27  ..... . '•. . ... .  29  LIST OF  ILLUSTRATIONS  Figure 1.-  Page - 6  Arrangements t o Produce D i c h o t i c S i g n a l s (a) S i n g l e D e l a y .  (b) M u l t i p l e D e l a y  2  Computer Set-up f o r P r o c e s s i n g Sound S i g n a l s  3  T i m e - d e l a y e d Waveforms..  . . . . . . . . .  (a) A Waveform and i t s Delayed V e r s i o n  .  7 8  - - '—-  -  (b) . Lower Waveform b e i n g Delayed by a D i f f e r e n t Amount 4  Sound Wave Compression P r o c e s s e s  . . . . . . . .  (a) O r i g i n a l Sound Wave  10 •  . ( b ) E x p a n s i o n o f t h e Sampled Sound Wave (c) New Compressed Sound Wave o b t a i n e d on P l a y b a c k 5.  11  Waveforms o b t a i n e d from the Computer (a) The O r i g i n a l Waveform and i t s Expanded V e r s i o n  ••' ' '. '.'  for C =  . '  •  (b) The O r i g i n a l Waveform and i t s Expanded V e r s i o n for C =  6  1.5  2  Graph Showing the V a r i a t i o n o f Rate Learned V e r s u s the  " '""  :  Rate o f t h e M a t e r i a l P r e s e n t e d i n ' t h e Lexiphone Code • 15  T e s t on Two B l i n d S u b j e c t s A and B . . . . 7  Combined E f f e c t  o f the Rate o f P r e s e n t a t i o n and t h e  Word Length, on t h e P e r c e n t C o r r e c t n e s s o f S p e l l e d Speech P e r c e i v e d by the S u b j e c t s  . . . . . . . . . .  .' . .  19-  LIST OF TABLES. Table 1  Page Scores of Two Lexiphone Subjects on Code i n Percent Correctness  2  13  Average Percent Correctness Scores of Six Subjects on Spelled Speech  3  17  Overall Percent Correctness of the Words According to the Number of Letters Contained i n the Word  4  • Letter Sounds Confused  . . . . . . . . . . . . . . . . .  v  18 20  ACKNOWLEDGEMENT  • '  The author wishes to express his gratitude to' Dr. M.P. Beddoes, the supervisor of this project, for his assistance throughout the course of the work.  The author also wishes to thank Dr. E.V. Bohn for reading  the manuscript. Sincere thanks are given to Mrs. M. Beddoes for preparing the spelled speech testing materials and Miss Heather DuBois for typing the manuscript.  .  •  Thanks are also due to the National Research Council for financ i a l assistance.  1.  . 1. INTRODUCTION • At present, there are two chief means of reading that provide . information to the blind —  the talking book and Braille.  As for printed  matter,'such as private documents and correspondence, newspaper, paper money, and so forth, the blind has to seek the assistance of a sighted person.  Thus a machine of some sort that can read printed matter i s an  obvious need for the blind.  In fact, for more than half a century, there  has been much effort devoted to the development of such a machine. Unfortunately, up to the present, only a limited success has been attained and there i s still.no simple reading machine which i s easy to learn and use. Ideally, the reading machine should be easy to learn and operate, portable and cheap so that i t can be carried and owned by the individual blind user.  There i s a gap between the f i r s t two requirements and the last.  For. example, the Optophone which was proposed a long time ago"'" and i s s t i l l in use, i s cheap and portable but d i f f i c u l t to learn and operate.  There  2-4 are recognition types of machines  . which speak directly to the user, but  these machines are complicated and expensive. Although the Optophone code i s d i f f i c u l t to learn and only a slow rate could be attained, there have been many heroic attempts by. blind people to use i t and i t i s their encouragement and the assistance of many different related organizations that provide constant zeal and . assistance to the research workers i n this f i e l d .  The Lexiphone* i s a  direct translation machine which i s rather more complex than the Optophone but i t i s believed to be easier to operate.  Each letter from the Lexiphone  is represented by a short sound pattern formed by both amplitude- and frequency-modulation of a square wave. This.gives a melodious ouput with *More details about the Lexiphone can be found i n references 5-7.  : a - c h a r a c t e r i s t i c rhythm. t u n e l e s s one, It  i t has has  Although  b e e n r e p o r t e d t o be  l o n g been r e c o g n i z e d  ..type o f r e a d i n g m a c h i n e i s s i m p l e type,  the code melody f o r e a c h l e t t e r quite pleasant.  that although a direct  and  two  to  l e a r n the L e x i p h o n e code w e l l  at  about t h i r t y words p e r minute._  is still  f a r behind  From the p a s t  hundred hours spread  enough t o r e a d Although  simple  this  > ' - t w i c e t h a t o b t a i n e d w i t h the Optophone a f t e r it  translation  cheap compared w i t h the r e c o g n i t i o n  t h e maximum r e a d i n g r a t e i s s e v e r e l y l i m i t e d .  perience, i t appears to take over  is a  a  sentences  year and  i s a r e a d i n g speed  an e q u a l  t h e minimum a c c e p t a b l e  over  ex-  stories about 8  l e n g t h of t r a i n i n g  ,  r e a d i n g r a t e o f 50-60 w o r d s  9 . p e r m i n u t e s e t by C o o p e r .  To  t a t i o n o f the code sound has in  the i n t e l l i g i b i l i t y  ,bility  been proposed.  of the code.  While  t h e mechanism by w h i c h  have been o b t a i n e d w h i c h a r e m a n i f e s t e d  t h e "upper l i m i t ' F o r . the  presen-  T h i s method p r o v i d e s an  i s improved i s u n c l e a r , e x p e r i m e n t a l l y worthwhile  telligibility in  t h i s problem, a method o f d i c h o t i c  increase  intelligi-  increases i n i n -  i n a useful increase  of r e a d i n g speed. . talking  type  time i s r e q u i r e d to understand  o f r e a d i n g m a c h i n e , p r a c t i c a l l y no the output  sound.  However, a p r o b l e m  when t h e m a c h i n e comes a c r o s s w o r d s w h i c h a r e n o t  i n the s t o r e d  of the computer.  t h i s has  T h e s e w o r d s c a n be  spelled,  training  but  arises  vocabulary  the  disadvantage  3 o f . s e v e r e l y d i s r u p t i n g the  listener's  .From the l e n g t h of .direct  complexity of  the  t a l k i n g machine which s t i l l  r e d u c e t h e amount o f t r a i n i n g t i m e of decoding  the l e t t e r s  has  a spelled  the  to  ex-  r e l i e v e him  i n the case  of  of  develop  speech machine.  o f the u s e r and  as i t i s • r e q u i r e d  and  a  the problem  spelled out, i t i s worthwhile  an i n t e r m e d i a t e t y p e ' o f r e a d i n g machine - —  the t a s k  code sounds o f  the u l t i m a t e speed a t t a i n a b l e ,  u n s t o r e d w o r d s w h i c h h a v e t o be  will  thoughts.  time r e q u i r e d to l e a r n the  t r a n s l a t i o n m a c h i n e and  pense and  t r a i n of  :  This  from coding  3.  machines and y e t t h i s w i l l n o t be so e x p e n s i v e the t a l k i n g machine. on a drum o r d i s c .  as i t i s i n t h e case o f  T h i s can be done by u s i n g p r e r e c o r d e d Each r e c o r d i n g i s s u i t a b l y addressed  keyed o u t when r e q u i r e d by a l e t t e r r e c o g n i z e r . " ^  l e t t e r sounds  so t h a t i t can be  But t h e n what r e a d i n g  speed can be o b t a i n e d w i t h the s p e l l e d - s p e e c h type o f r e a d i n g machine? t h e r e d i f f i c u l t i e s i n p r o d u c i n g a h i g h r a t e o f s p e l l e d speech? word-length  Are  Does t h e  (number o f l e t t e r s c o n t a i n e d i n a word) p l a y an i m p o r t a n t  r o l e i n s p e l l e d speech i n t e l l i g i b i l i t y ? be a p p l i c a b l e t o s p e l l e d speech?  W i l l the d i c h o t i c  presentations  The answers t o these, q u e s t i o n s w i l l be  p r o v i d e d by t h e e x p e r i m e n t s d e s c r i b e d i n l a t e r s e c t i o n s o f t h i s - t h e s i s .  2. ' SCHEMES USED TO  2.1  PRODUCE DICHOTIC SIGNALS AND  TIME COMPRESSION  D i c h o t i c P r e s e n t a t i o n - Methods used to I n c r e a s e  the  Intelligibility  ..of..Sound S i g n a l s When i d e n t i c a l  s i g n a l s are p r e s e n t e d  simultaneously  to b o t h  ears  o f a l i s t e n e r through a p a i r of earphones, a s i n g l e c e n t r a l l y l o c a t e d c r a n i a l sound.image i s p e r c e i v e d .  I f a time d e l a y i s i n t r o d u c e d  intra-  to one  of  these s i g n a l s as shown i n F i g . 1 ( a ) , the s i n g l e sound image i s p e r c e i v e d shift  towards the s i d e where the s i g n a l i s l e a d i n g .  As  the amount of  -is--increased- up—to-about -0.8 -ms.., -then- t h i s , . i m a g e - i s - p e r c e i v e d t o t a l l y e i t h e r on the r i g h t or on the l e f t a c c o r d i n g i s leading.  This kind of presentation with  p r e s e n t a t i o n and  t h a t w i t h no  delay  to be  located  to which s i d e the s i g n a l  a time d e l a y i s known as  delay, the o r d i n a r y b i n a u r a l 11-13  E a r l i e r r e s e a r c h works  to  presentation.  have shown t h a t the b i n a u r a l  g i b i l i t y o f speech u n d e r a masking c o n d i t i o n of n o i s e  'dichotic  can be  intelli-  increased  by  mean's o f d i c h o t i c p r e s e n t a t i o n , .and the i n t e l l i g i b i l i t y i n c r e a s e brought by 14-19 i t has been c o n f i r m e d by v a r i o u s groups of people f o r a delay within 20 21 the r a n g e . o f 15 ms.  I t has  proves the i n t e l l i g i b i l i t y no n o i s e . .  a l s o been shown  '  t h a t time d e l a y  of r a p i d l y compressed speech even when t h e r e i s  These f i n d i n g s seem to suggest t h a t d i c h o t i c - p r e s e n t a t i o n o f  above.can a l s o be a p p l i e d to the Lexiphone code and are.not  so, i n t e l l i g i b l e when p r e s e n t e d :  Two  s i g n a l reaches each e a r . each e a r ;  t a i n e d by  The  .•  In F i g . 1 ( b ) , two  In F i g . l  and  (a), only  the  signals with a separation i n  t i m e - d e l a y e d s i g n a l s would produce a  required-conditions  . ••"  one  the purpose o f the m u l t i p l e d e l a y arrangement i s to  whether o r not m u l t i p l e -effect.  at a f a s t rate.  Fig... 1 ( b ) .  the  s p e l l e d speech which  t y p e s o f d i c h o t i c p r e s e n t a t i o n have b e e n - i n v e s t i g a t e d  arrangements appear i n F i g . 1 (a) and  time r e a c h  also.im-  of time d e l a y  test  reinforcement  on the sound s i g n a l s were  programming the PDP-9 computer,.the s e t - u p i s shown i n F i g . 2.  ob-  A program w r i t t e n f o r t h i s purpose i s shown i n Appendix I . waveforms.produced by t h i s program a r e shown i n F i g . J.  Time-delayed  6.  (t)  S (t) L  DELAY  TI  S R ( 0  r f  (a)  S (t) = S j ( t - r ) L  " S ( t ) = Sj (t) R  Si(t)  - DELAY T  DELAY  S (t) L  = S -(t - r ) (  S .(t) = Sj(t) R  1  +  +  Sj(t-TT  S (t-r i  1  Fig. 1 Arrangements to Produce Dichotic Signals: (b) Multiple Delay.  •  R  3  r  (b)  S (t)  L  DELAY  — ?  1  S (t)  1  - t  2  -r ) 3  -r ) 2  (a) Single Delay;  •A/D CONVERTER INPUT  PDP-9 COMPUTER  #1  D/A  CONVERTER #2  D/A  CONVERTER  OUTPUT  SO UNO  SOUND  SIGNAL  SIGNALS  TAPE RECORDER  Fig. 2 Computer Set-up for Processing Sound Signals.  "(a) A Waveform "and "its "Delayed Version.  (b) Lower Waveform being Delayed by a Different Amount.  Fig. 3 '.Time-delayed'Waveforms  2.2 Time Compression - Method used to Increase the Presentation Rate of Sound Signals In order to obtain materials for presentation'to the subjects at a fast rate, time compression on the sound signals i s required.  Time 22  compression of the sound signal according to the principle of Fairbanks was obtained from the PDP-9 computer using the same set-up as shown i n Fig. 2.  In this method, two processes are involved.  The f i r s t process i s to  store alternate sections of the speech waveform at a sampling time interval I  and to discard the remaining sections of the speech -waveform at- a discard  time interval of I . The second process i s to play the recorded waveform at an appropriate speed to restore the o r i g i n a l pitch of the voice.  These  two processes are described i n Fig. 4, and for the ease of i l l u s t r a t i o n , equal sampling and discard intervals have been chosen ( i . e .  I = I ). The  compression ratio (which indicates how many times higher the rate of the compressed version of the speech sample i s compared with the uncompressed speech sample) can be defined as  I  0 = _§  + I, i I s  In the case of Fig. 4, a compression ratio of 2 has been achieved. A program i s shown i n Appendix I I i l l u s t r a t i n g how this compression i s obtained from the PDP-9 computer using a sampling i n t e r v a l of 30 ms. In the spelled speech experiment, two compression ratios (l.5 and 2) were used to bring the o r i g i n a l material to 1.5 and 2 times faster.  Both  the o r i g i n a l and the resulting expanded waveforms coming out from the D/A o  converters are shown i n Fig. 5 (a) and Fig. 5 (b). The disconnected lines indicate the place where part of the waveform has been discarded. Time compression i s obtained by playing the recorded waveforms respectively at 1.5 and 2 times faster.  Fig. 4 Sound Wave Compression Processes:  (a) Original Sound Wave;  (b) Expansion of the Sampled Sound Wave; (c) New compressed Sound Wave obtained on Playback;  11.  v\  V i/V  V V A A,  vV A/ -  .-(a) The O r i g i n a l Waveform and i t s Expanded V e r s i o n f o r C = .1.5.  •  VV  v/  NV  r  /  :  9 "'  (b) The O r i g i n a l Waveform and i t s Expanded V e r s i o n .'• . f o r C =  Pig. 5  2.  Waveforms o b t a i n e d from the Computer.  12.  3.  3-1  TESTS ON  T e s t i n g P r o c e d u r e s and In order  compared w i t h the  t o see  THE  LEXIPHONE SUBJECTS  Results  how  effective  the  dichotic presentations  o r d i n a r y b i n a u r a l p r e s e n t a t i o n o f the  various reading  speeds,  t e s t s were p e r f o r m e d on  ensure t h a t the  t e s t m a t e r i a l s are  two  are  L e x i p h o n e code under  Lexiphone subjects.  reasonably, uniform  in difficulty,  To  a  23 long story  with a l i m i t e d vocabulary  Thorndike-Lorge l i s t s a computer to g i v e  was  the  chosen.  of  1 (b)) at  Tests  the  desired S  and  1) O r d i n a r y  thousand words'of  S„  the  processed  on  s i g n a l s ( a s shown i n F i g . 1 ( a )  and  K  t e s t e d speeds and  were conducted i n the  first  These m a t e r i a l s were f i r s t  h Fig.  the  were t h e n r e c o r d e d  on  a tape  recorder.  following presentations:  b i n a u r a l p r e s e n t a t i o n , i . e . when t h e r e  i s no  T=  delay or  0  ms.  2) D i c h o t i c p r e s e n t a t i o n s : T=  a) S i n g l e d e l a y : b) A  M u l t i p l e delay:  time delay  o f 0.8  in  daily life  on  the l e f t  0.8  T  ±  ms.  audio  t h i s amount o f  t o 30,  ms.,  the  = 0.3  represents  the  the  = 0.25  delay  be  ms.  experienced  r i g h t hand s i d e  been chosen because i t has  amount o f d e l a y w i l l can  and  longest  i s e i t h e r on  e a r s ) had  time delay  ms.  or  not  yet  give additional benefit.  implemented e a s i l y employing  an  line.  The ing  = 0.25  when t h e s o u n d s o u r c e  hand s i d e of  delay  and  (which  been shown t h a t a g r e a t e r Besides,  ms.  40  passages were r e c o r d e d and  50 w o r d s p e r  at  three  m i n u t e . . The  different  speeds  r a t e s o f 30 and  correspond-  40 w o r d s  per  Q  minute represent processed  the  peak r e a d i n g r a t e s o f  m a t e r i a l s were p r e s e n t e d  o u t , i n a q u i e t room and a comfortable  level  the  the Lexiphone s u b j e c t s .  i n random o r d e r .  subjects listened  The  t e s t s were  to the r e c o r d e d  The carried  materials  at  t h r o u g h a p a i r of headphones; they were i n s t r u c t e d to  13.  omit the words i f they could not catch them. After an'explanation of the testing•procedures and a run of four practice passages, the actual tests were carried out.  The scores were based on the response of 90 words i n  the middle of the passages each of which consisted of about 120 words. The scores of these tests are shown i n the following table with each figure representing the mean of five tests.  In view of the good results of  subject A, an additional test was performed on her at a rate of 60 words per minute.  The score was: 72.2$ for no delay and 98.9$ for both dichotic  presentations.  V s  - • ~2  •1 •  \^^Con^  Ko Delay . Speed(w.p.m.  :  ••  Subject A Subject B  '... " — . ...  Single Delay  .  ......,  3  -.  ....  Multiple-Delay Subject A Subject B  Subject A Subject B  30  82.9  , 57.8  96.7  64.3 ..  97.1  62.9 •  40  90.2  61.7  98.9  73.1  96.5  72.2  50  83.1  58.2 .  96.2  : 66.2  98.9  62.9  Table 1 'Scores of two Lexiphone Subjects on Code i n Percent Correctness Note: At the time of this test, subject B had been away from the code- for ..several months. • •  . . S t a t i s t i c a l analysis of the data by means of the analysis of variance  .revealed that the dichotic presentations have definite levels.of. significance. The analysis showed that there are highly significant; differences (p<0.1$) among the different presentations and there are also significant differences (p< 5$) among the speeds of presentation. ..  ..-  By comparison,' the results i n column 2 and coluEn 3.-~of"'table 1 _  show .significant improvement. • With dichotic presentation, the subjects'  14.  scores  are higher  rates.  than u s i n g normal b i n a u r a l p r e s e n t a t i o n a t a l l reading  I t also i n d i c a t e d that multiple delay  as a s i n g l e d e l a y ;  t h i s may  be due  t o some c o n f u s i o n  t i o n o f t h e same s i g n a l s e v e n t h o u g h t h e y  3.2  E f f i c i e n c y of the D i c h o t i c Fig..6  effective  c a u s e d by a r e p e t i - .  are separated  apart  i n time.  Presentations  shows t h e v a r i a t i o n o f t h e r a t e o f L e x i p h o n e c o d e  mation learned versus  the r a t e presented  The g r a p h s o f t h e d i c h o t i c p r e s e n t a t i o n s ideal  i s o n l y about as  i n the three  infor-  tested conditions.  a r e s e e n t o be c l o s e r t o t h e  c a s e o f p e r f e c t l e a r n i n g , t h e e f f e c t i s more p r o n o u n c e d i n t h e  formance o f the b e t t e r s u b j e c t  (subject A).  Thus message e f f i c i e n c y , learned  per u n i t time,  efficiency starts  per-  a s m e a s u r e d by t h e number o f w o r d s  increases with  the d i c h o t i c p r e s e n t a t i o n s .  Message  t o d e c l i n e a t t h e r a t e o f a b o u t 40 w o r d s p e r m i n u t e f o r  the b i n a u r a l p r e s e n t a t i o n . - '  Judging  efficiently  f r o m F i g . 6,  s u b j e c t A can read w i t h  t h e L e x i p h o n e more  a t a h i g h r a t e ; f o r s u b j e c t B, b e c a u s e o f . t h e  t h e r e g i o n o f 40 w.p.m., t h i s i s p r o b a b l y sentation f o r her.  d e c l i n e around '  t h e most e f f i c i e n t r a t e o f  pre-  30  Rate  Fig. 6  40  Presented  50  (w. p.m.)  Graph Showing the Variation of Rate Learned Versus the Rate of the Material Presented in the" Lexiphone Code Test on Two Blind Subjects A and B.  4.  •4.1  TESTS ON S P E L L E D SPEECH  T e s t i n g Procedures and Results In order  to f i n d  ' ••  o u t t h e e f f i c i e n c y o f s p e l l e d s p e e c h as a  medium o f c o m m u n i c a t i o n a n d t e s t t h e e f f e c t o f d i c h o t i c l i s t e n i n g pared w i t h the o r d i n a r y b i n a u r a l p r e s e n t a t i o n , The  test material consists of selected l i s t s  t e s t s were  com-  performed.  of phonetically-balanced  24 sentences. and  Each l i s t  has an average l e n g t h o f s e v e n t y - e i g h t  c o n s i s t s o f t e n sentences.  words  These l i s t s were s p e l l e d by a mature  f e m a l e s p e a k e r a t an average r a t e o f f i f t y - f o u r words p e r m i n u t e . m a t e r i a l was t h e n c o m p r e s s e d o n t h e PDP-9 c o m p u t e r t o g i v e ent  three"! d i f f e r -  r a t e s f o r p r e s e n t a t i o n , i . e . 5 4 , 8 1 , .and 1 0 8 w o r d s ..per . m i n u t e r e -  spectively. to  These m a t e r i a l s were a g a i n  obtain the three  different kinds  processed  o n t h e PDP-9 c o m p u t e r  o f p r e s e n t a t i o n , i . e . no d e l a y ,  s i n g l e d e l a y a n d m u l t i p l e d e l a y a s i t was done i n t h e L e x i p h o n e test.  S i xsubjects  students)  ( t h r e e male a n d t h r e e  who a r e n a i v e w i t h r e s p e c t  code  female u n i v e r s i t y undergraduate  t o s p e l l e d speech and compressed  speech were employed i n t h i s e x p e r i m e n t .  B o t h t h e m a t e r i a l a n d t h e con-  d i t i o n s o f p r e s e n t a t i o n were randomized i n a b a l a n c e d the  The  design  so t h a t . a l l  t e s t i n g l i s t s were c o v e r e d by a l l t h e s u b j e c t s , a l l t h e r a t e s o f p r e -  sentation and a l l the l i s t e n i n g conditions t a t i o n s : •.- no delay,-  ( i n c l u d i n g the three  presen-  .  s i n g l e delay and m u l t i p l e delay and a l s o the i n t e r -  change o f t h e s i g n a l s t o t h e r i g h t e a r and t h e l e f t  ear).  c a r r i e d Out i n a q u i e t room and t h e s u b j e c t s l i s t e n e d materials a t a comfortable  level  The t e s t s w e r e  to the recorded  through a p a i r o f headphones; they  i n s t r u c t e d "to o m i t t h e w o r d s i f t h e y  were  could not catch-them;—Before the  a c t u a l t e s t b e g a n , t h e t e s t i n g p r o c e d u r e was e x p l a i n e d  to the subjects and  each subject had a p r a c t i c e o f f i v e  o f these  lists."  The s c o r e s  tests are  shown i n T a b l e  ^"""-'--^^^ Speed  2.  Conditions  (w. p.m.  1 No  )^^~~^~^^  78.33  81  63.81  72.58  68.65  56.69  62.41  63.98  A v e r a g e fo C o r r e c t n e s s  analyzing  the  (p<0.1$). two  the  The  no  significant  of  comparing the  material  that  interchanging  r i g h t ear  are  i s highly  has  significant  significant  the  this  s i g n a l leads  r e s u l t s shown i n T a b l e 2,  give  However, a t  r a t e , i t i s not difficulty  that a trained subject i n obtaining a high  on  score  r e s u l t s at  t h e medium and  of subject  B i n the  as  the  Speech  s p e l l e d speech experiment, i t  a f f e c t at. a l l (p>50$),  m a t t e r whether the  presentations  i t i s the  (such  Spelled  d i f f e r e n t presentations  improvements at the  subject"A  the  This  may  intelligibility  of p u t t i n g the  three  signals  of  indicates  the  left  ear  be  seen  that  t e s t e d speeds  be  due  to the  (>90$) at the  (54  letters  i n t o words.  w.p.m.),  I t i s expected  difficulty  seem t o r e s e m b l e t h e  I f i t i s the  at  performance,  t h i s r a t e of p r e s e n t a t i o n .  fastest rates  of  f a c t that  t h a t a f f e c t s the  s p e l l e d s p e e c h s h o u l d , h a v e no  L e x i p h o n e code t e s t . i n the  the  i t can  lowest rate of presentation  i s o n l y a minor improvement.  t h i s low but  e f f e c t s of the  on  Delay  versa.  presentation. there  r e s u l t o i the  analysis also revealed  e a r s has  On dichotic  the  Scores of S i x Subjects  rate of presentation  t h a t i t does not or'vice  Multiple  77.68  been found t h a t  the  Single Delay .  77.66  . On  (p<5$),  Delay  3  54  108  Table 2  2  subject's  at a l l " The  results skill  c o d e t e s t ) t h a t makes d i c h o t i c p r e s e n t a t i o n s  more  18.  helpful, then i t i s very l i k e l y that subjects trained i n spelled speech w i l l be more beneficial from the dichotic presentations.  This has to be  confirmed after training a group of subjects on hearing spelled speech. 4.2  Effect of Word Length During the test, a large number of errors occurred i n those  words which contained a large number of l e t t e r s .  In view of t h i s , a  calculation was made based on the number of errors observed at different word length (the number of letters contained i n a word).  The overall,  picture of the effect of word length of the entire experiment i s shown below.  Word Length (letters) % Correctness -Table 5  3 or less 4  5  86.22 66.74 51.84  6 43.13  7  8  29.67 32.04  Overall Percent Correctness of the Words According to the Number of Letters Contained i n the Word. The combined effect of the rate ef presentation and the word  length appears in' Fig. 7.  From Table 3 and Fig. 7, i t can be seen that  the word length has a very great effect on the correctness of the response. The longer the word, the more l i k e l y that an error w i l l be made. I t must be pointed out that no. longer pause' was allowed for long words i n the.test.  This may create the situation o f ' i n s u f f i c i e n t time for the per-  c e p t i o n of, the long words from the l e t t e r s , and while the subject was ' s t i l l pondering on the long words, words of the subsequent order followed . and disruption occurred.  Thus i t i s suggested that for those words with  four or more l e t t e r s , a s l i g h t l y longer pause should follow to compensate for the.time required to perceive these words from their spelling.  run  54 w.p.m.  Y/A  81  }  3  or less  5  U NUMBER  OF  LETTERS  6 IN  A  w.p.m.  | 108 w.p.m.  7  WORD  Fig. 7 Combined Effect of the Rate of Presentation and the Word Length on / the' Percent Correctness of Spelled Speech' Perceived by the Subjects.  8  4.3  C o n f u s i o n o f Some L e t t e r During the spelled  was  Sounds speech  test,  observed i n t h e case o f compressed  e r r o r s due t o t h e c o n f u s i o n o f l e t t e r confused l e t t e r s  a r e consonants.  p r e s s e d ) was u n n o t i c e a b l e .  c o n f u s i o n o f some l e t t e r  materials.  The t o t a l  sounds i s about  number o f  5.5$.  A l l the  Confusion a t the lowest speed  The f o l l o w i n g t a b l e  sounds  (uncom-  shows how t h e l e t t e r  sounds were c o n f u s e d a c c o r d i n g t o t h e manner a n d t h e p l a c e o f a r t i c u l a t i o n of the l e t t e r  sounds.  25  Manner o f  Place of Articulation.-  Articulation  Voiced  Bilabial  Labio-dental  Lingua-alveolar  Plosive  - f(io.56)  t  :  (19)  [Z&2)\ Unvoiced  Plosive  Voiceless  (12.70K-V  • G)-—-—  L e t t e r . Sounds Confused.  (Arrow head i n d i c a t e s  e.g. t h e a c t u a l sound  •In', a n d t h e s o u n d A dotted l i n e  thedirection of  'm' i s m i s t a k e n t o b e t h e s o u n d  'd' is. m i s t a k e n as t h e s o u n d ' ' t  indicates a less  f i g u r e s i nb r a c k e t s denote fusing situation  -G) —W3i0\  G  Fricative  confusion,  y^W  -(10.-56) i  V.V  Nasal-  Table'4  Velar  towards  1  and v i c e  frequent confusing situation.  t h e percent c o n t r i b u t i o n o f each  t h e t o t a l number.of..confusions...)._  versa. The con-  21.  Table 4 i n d i c a t e s t h a t the p l o s i v e sounds a r e the m a i n l y fused  sounds.  I t also indicates that l e t t e r  sounds a r t i c u l a t e d  same m a n n e r o r a t t h e same p l a c e a r e e a s i e r t o be c o n f u s e d . --"some u n i - d i r e c t i o n a l  confusions  i n the  There a r e  w h i c h i n d i c a t e t h a t some o f t h e m c a n b e  mistaken as others, but not v i c e  versa.  . The r e a s o n t h a t t h i s k i n d o f c o n f u s i o n  occurred  —-sonants w i t h the-compressed m a t e r i a l s and n o t - w i t h s i o n i s because the d u r a t i o n o f phonation injthe^ production  con-  only i n con-  i t s uncompressed, v e r -  ( t h e l e n g t h o f time  involved  o f a s i n g l e s o u n d ) _ o f _ t h e c o n s o n a n t s o u n d s i s much 2(5 27  s h o r t e r than that o f the vowels ' duration of phonation • o f phonation process,  ' ., t h e r a t i o  o f c o n s o n a n t s a v e r a g e s t o 0.08 s e c .  a part of the l e t t e r  more- d i f f i c u l t  from the context  r  i f  those  occurred.  may b e e l i m i n a t e d b y c o r r e c t  of the m a t e r i a l , easy i d e n t i f i c a t i o n o f l e t t e r b e c a u s e some w o r d s c o n s i s t o f  among l e t t e r s .  -  facilitated  Thus i t a p p e a r s d e s i r a b l e t o  . • s u b s t i t u t e s p e c i a l s o u n d s f o r t h e more f r e q u e n t l y c o n f u s e d . a s d , t , p , ra a n d f . '  sounds  which are a r t i c u l a t e d i n  and, d i f f e r e n t i a t i o n ..of w o r d p a t t e r n s w o u l d be  t h e r e w e r e no c o n f u s i o n s  the compression  effecting a shorter  and thus confusion  o f some l e t t e r s  sounds i n s p e l l e d speech i s i m p o r t a n t . -._single l e t t e r s  During  T h i s makes t h e c o m p r e s s e d c o n s o n a n t  '-the same m a n n e r o r a t t h e same p l a c e ) confusions  ).  sound has been d i s c a r d e d  to distinguish (especially  •". A l t h o u g h  3 to 2 (the •  f o r v o w e l s a v e r a g e s t o 0.117 s e c . a n d t h e d u r a t i o n  - d u r a t i o n o f t h e . l e t t e r sound.  • guessing  i s roughly  letters  such  ,22.  5.  CONCLUSIONS AND  Prom the Lexiphone and  DISCUSSIONS  s p e l l e d speech experiments, i t has  been  found t h a t both the s i n g l e d e l a y and m u l t i p l e d e l a y d i c h o t i c p r e s e n t a t i o n s b r i n g s i g n i f i c a n t improvements to the i n t e l l i g i b i l i t y presented  through the earphones.  that d i c h o t i c presentations  The  materials  Lexiphone code t e s t s i n d i c a t e  are more h e l p f u l to the s u b j e c t who  b e t t e r s k i l l e d i n the code.  The  is  r e s u l t s of the s p e l l e d speech t e s t s r e -  semble t h a t of s u b j e c t B (the s u b j e c t who Lexiphone) i n the Lexiphone t e s t . which had  o f the  i s not  so s k i l f u l  I f i t i s the s k i l l  i n using  of the  the  subject  produced t h i s s t r o n g i n f l u e n c e , then d i c h o t i c p r e s e n t a t i o n s  would be more b e n e f i c i a l  to those who  T h i s has  on e x p e r i m e n t i n g  to be  confirmed  t r a i n e d on s p e l l e d speech.  have been t r a i n e d . o n s p e l l e d speech.  Conclusions  s u b j e c t s who  on  u s i n g o t h e r b e t t e r s k i l l e d Lexiphone u s e r s . time (over 200  have a l r e a d y been  t h i s f a c t o r may  a l s o be a r r i v e d  S i n c e i t takes a r a t h e r  long  hours o f t r a i n i n g ) to l e a r n the' code w e l l , i t would be more  d e s i r a b l e to t r a i n s u b j e c t s on s p e l l e d speech f o r t h i s purpose.  In  fact,  23 i t has  been found  , t h a t a f t e r a t r a i n i n g time o f o n l y about twenty hours,  i f words were s p e l l e d r a p i d l y enough, the whole word, r a t h e r than the v i d u a l l e t t e r s , would become the u n i t of .r  From the comments made by  t h a t a b e t t e r performance may  indi-  perception.  the s p e l l e d speech s u b j e c t s , i t i n d i c a t e s  b e - a r r i v e d ' a t w i t h more, p r a c t i c e .  The  s u b j e c t s a l s o remarked t h a t the f a s t e s t r a t e o f p r e s e n t a t i o n (108 w.p.m.) was  too f a s t f o r the p e r c e p t i o n o f the words, but  s i t u a t i o n might change a f t e r t h e y had l o n g enough time,. any  The  they a l l f e l t  that  this  been exposed to s p e l l e d speech f o r a  s u b j e c t s a l s o showed no  p a r t i c u l a r preference  to  of the l i s t e n i n g c o n d i t i o n s . / C o u n t i n g the p e r c e n t  correctness  o f the s u b j e c t s •  performance  i n words, formed from different number of letters indicates that the longer -the word, the easier errors were made, and while they were s t i l l  pondering  on the long words, other words that followed disrupted the decoding •process of the long words. Thus i t would be helpful i f a longer pause i s provided for those words containing a bigger number of l e t t e r s . Another finding of the spelled speech test i s that there are "errors caused by the confusion among the l e t t e r sounds, i n particular, the consonants.  In order to bring spelled speech into a.more useful  medium for reading machin.e._.wo,rk ^_the.__obs.er.v.ed_-Confusions...should  be re-  moved. This can be done by substituting these l e t t e r sounds with special sounds, but this has the disadvantage of learning the special sounds.  An  alternative i s to lengthen the duration of phonation of these sounds so that they become more distinguishable.  A similar effect can be achieved  b y introducing some other variables, such as loudness, accent and intonation. -It would be very useful to find out the minimum duration of phonation for the perception of the different l e t t e r sounds.  One way of doing this i s  to simulate the l e t t e r sounds on the computer and then control the duration of the. l e t t e r sounds for presentation. This w i l l not only find out the duration of phonation required for the perception of the l e t t e r sounds, _but also give an idea of- the. absolute-maximum rate of presentation of spelled speech. In this thesis, only two dichotic presentations have been investigated and the effect of the sampling period of. compression has not been considered at great depth.  I t must be pointed out that there are  other dichotic presentations which are worthwhile for further research: these include a longer single delay ( i n the range- of 20 ms. to 300  ms.)  .and: dichotic compression (presenting .the .samples ,in -the sampling interval :  to one ear and the samples i n the discarded interval to the other ear so that there i s no loss of information to the ears).  The sampling interval  i s an important factor affecting the i n t e l l i g i b i l i t y of compressed speech because i t i s related to the amount of information retained from the o r i ginally uncompressed information for presentation to the ears.  Although 20-22  this has been investigated by several research workers i n this f i e l d  '  there i s s t i l l the lack of a model for theorizing the optimum sampling interval for compression.  An investigation of this sort would be very  useful to the f i e l d of compressed speech.  I t i s l i k e l y that the optimum  sampling interval i s related to the duration of phonation of different l e t t e r sounds, the compression.ratio and the pitch of the voice. When this model has. been established, i t w i l l be easier to produce i n t e l l i g i b l e l e t t e r sounds at different speeds of presentation for the spelled speech reading machine and i t w i l l also throw some l i g h t onto better methods of dichotic presentations.  Appendix I  FLOW CHART FOR THE DELAY PROGRAM The  •  following i s a simplified  f l o w c h a r t f o r t h e d e l a y program.  Set SFC  p r i n t on t e l e t y p e 'SET DELAY'  s e t amount o f d e l a y r e q u i r e d on AC s w i t c h e s  s e t up r e g i s t e r s f o r h a n d l i n g d a t a  w a i t f o r A/D f l a g  No  —<—  Yes clear  • r e a d A/D  flag  buffer.and store  d e p o s i t t h i s sample i n o u t p u t and s t o r e i t -  i n c r e m e n t d e l a y c o u n t e r and check f o r t h e end o f b u f f e r  No Yes  reset  26.  •TITLE DELAY ./ .IODEV 10 SFC=701207 IN52=705217 OUT3U703107 OUT32=703207 SKPFLG: 705301 CLRFLG=705302 START .INIT 10,1,START . .WRITE 10,2 PRINT,3 ; .CLOSE 10 LAC (-62 /SET THE SAMPLING PERIOD = 50 US SFC /HALT, SET THE AMOUNT OF DELAY HLT /ON AC SWITCHES, PRESS CONTINUE LAS ' CMA TAD (1 DAC DEL# LAC.(DATA-1 DAC* (10 ^ DAC* (11 ONE SKPFLG JMP .-1 CLRFLG IN52 0UT31 DAC* 10 ISZ DEL JMP ONE . TWO :, SKPFLG JMP .-1 CLRFLG IN52 0UT31 DAC* 10 LAC* 11 0UT32 LAC* (10 SAD (DATA+16660 ' JMP RESET 1 LAC* (11 SAD (DATA+16660 JMP RESET2 • JMP TWO RESET 1 LAC (DATA-1 DAC* (10 JMP TWO RESET2 LAC (DATA-1 DAC* (11 JMP TWO PRINT 003002 0 .ASCII 'SET DELAY*<15> DATA .BLOCK 16665 .END START e  ;  Appendix I I FLOW CHART FOR TIME COMPRESSION PROGRAM  set the sampling period T set .the sampling interval I and the discard interval I set up a register 'R' to handle data damples i n the period ( i + 1^) * accept signal from the A / D converter and sample i t deposit i n register 'S' the samples obtained i n the period I  s  discard those samples obtained i n the next period 1^ •  output the samples contained i n register 'S' > one at a time at an interval of C T check for the l a s t sample i n register 'S' No  Yes reset register 'S' reset register 'R'  ' —  :  —'•  :  28. :. .TITLE TIME COMPRESSION, C = 2 • .IODEV 10 . •VSFCr701207 . IN52=705217 . 0UT31=703107 0UT32= 703207 SKPFLG=705301 • CLRFLG= 705302 START  ' • _, 'V'. ; : V-.:.:.  :  .V".:  :  =  •  r.::[-^r"-'  p-V\'.- " .:' .\, V• i ;  V'-V ; \ :  .INIT 10,1,START /PRINT OUT TITLE •WRITE 10,2,PRINT,10 .CLOSE 10 • • •• LAC (-62 , • SFC /SET THE SAMPLING PERIOD = 50 US RUN LAC (DATA-1 • DAC* (10 . DAC* (11 NOW SKPFLG JMP .-1 CLRFLG IN52 0UT31 - DAC* 10 • • . THERE SKPFLG JMP .-1 CLRFLG IN52 0UT31 DAC* 10 THEN LAC* 11 0UT32 LAC* (10 SAD (DATA+2257 JMP RUN • • JMP NOW ' • PRINT 010002 0 .ASCII 'TIME COMPRESSION, C=2*<15> DATA .BLOCK 2270 .END START  References 1.  d'Albe, F.  "The type-reading Optophone", Nature, V o l . 94, p. 4, 1914-  2.  Cooper, F.S. and Gaitenby, J.~ "Reading Machine Research at Raskins" in'Reading Machines f o r the Blind, Sixth Technical Session''held at the Veterans Administration Central O f f i c e , Washington, D.C. i n Jan. 1966.  3.  Cooper, F.S., Gaitenby, J . , Mattingly, I.G. and Umeda,•N."Reading Aids f o r the B l i n d :  A s p e c i a l case of Machine-to-Man  Communication",  IEEE Trans. Audio and Electroacoustics, Vol. AU-17, No. 4, 266-269, . Dec. 1969. 4.. Lee, F.F.  "Reading Machine:  from Text to Speech", IEEE Trans. Audio  and Electroacoustics, V o l . AU-17, No. 4, 275-282, Dec. 1969. 5.  Caple, G.  "The Lexiphone, a simple Reading Machine f o r the Blind,"  .:, M.A.Sc. Thesis, U.B.C.,. January 1966. 6.  Beddoes, M.P.  "An Inexpensive Reading Instrument with a Sound Output  f o r the Blind", IEEE Trans. Bio-Med. Eng., V o l . BME-15, 70-79, A p r i l 1968. 7.  Ramsey, D.  "Design of a Simple Reading Machine f o r the Blind", M..A.Sc.  Thesis, U.B.C, October 1968. 8.  Coffey, J.L. and McParland, R.R.  "The Evaluation and Standardization  of Selection and Training Procedures' f o r the B a t t e l l e . Aural Reading Device" Research Report to the Veterans Administration from the B a t t e l l e Memorial I n s t i t u t e , Columbus, Ohio, June 19639«  Cooper, F.S.  "Research on Reading Machines f o r the B l i n d " i n P.A. Zahl  • (ed.), Blindness:.  Modern Approaches to the Unseen Environment, Prince-  ton. Univ. Press, Princeton, N.J., pp. .512-543, 1950. 10.  Smith, G.C. and ' Mauch, H.A. "Summary Report on the Development  of a.  30.  Reading Machine  f o r the B l i n d " , B u l l e t i n of P r o s t h e t i c s  Research,  BPR 1 0 - 1 2 , 2 4 3 - 2 7 1 , F a l l 196911.  Licklider,  J.C.R.  the masking  "The i n f l u e n c e o f i n t e r a u r a l p h a s e r e l a t i o n s u p o n  o f speech by w h i t e n o i s e "  J . A c o u s t . S o c . Am.,  20, 150-159,  1948. 12. • H i r s h ,  I.J.  "The i n f l u e n c e  mation and i n h i b i t i o n " 13.  S c h u b e r t , E.D.  F e l d m a n n , H. delay IV.  15.  J . A c o u s t . S o c . Am.,  "Some p r e l i m i n a r y  . and i n t e l l i g i b i l i t y " 14.  o f i n t e r a u r a l p h a s e o n i n t e r a u r a l sum-  time delay  .  28, 895-901, 1956.  "The r o l e o f i n t e r a u r a l i n t e n s i t y d i f f e r e n c e s a n d t i m e  f o r signal detection  i n noise"  International Audiology, V o l .  No. 2, 29-34, 1 9 6 5 .  L e v i t t , H. a n d R i b i n e r , L.R.  Carhart, for  e x p e r i m e n t s on b i n a u r a l  J . A c o u s t . S o c . Am.,  . a r i d gain i n i n t e l l i g i b i l i t y " .16.  20, 536-544, 1948.  Raymond; T i l l m a n ,  speech  "Binaural  release  from masking  J . A c o u s t . S o c . Am.,  T.W.  and Johnson,  through i n t e r a u r a l time delay"  f o r speech  42, 601-608, 1967.  K.R..  "Release o f masking  J . A c o u s t . S o c . Am.,  42,  • No. 1, 1 2 4 - 1 3 8 , J u l y 1 9 6 7 . 17.  Carhart, tiple  Raymond; T i l l m a n ,  maskers:  T.W.  a n d G r e e t i s , E.S.  "Release from  e f f e c t s o f i n t e r a u r a l time d i s p a r i t i e s "  ibid.  mul45_, No..  2, 4 1 1 - 4 1 8 , F e b . 1969. . 18.  Carhart, tones ..Hear.  19.  Raymond; T i l l m a n ,  and spondees:  T.W.  and D a l l o s , P . J .  "Unmasking f o r pure  i n t e r a u r a l phase and time d i s p a r i t i e s "  J . Speech  R e s . , 1 1 , No. 4, 7 2 2 - 7 3 4 , D e c . 1 9 6 8 .  D i r k s , D.D.  and W i l s o n ,  R.H.  "The e f f e c t o f s p a t i a l l y s e p a r a t e d  sources on speech i n t e l l i g i b i l i t y "  J . Speech Hear.  sound  R e s . , 12', No. 1,  '5-38, M a r c h 196920.  C r a m e r , II.L.  "The i n t e l l i g i b i l i t y  o f time-compressed  speech"  Proceed-  •  '.  ' . /.' :  :  •  5  1  i  ings of the L o u i s v i l l e Conference on Time Compressed Speech, Oct. 1966. —21.  C a r r o l l , J.B. and Cramer, H.L. speech f i n a l report"  "The i n t e l l i g i b i l i t y of time-compressed  U.S. Dept. of Health, Education and Welfare,  Bureau of Research, Final Report OE 7-31-0370-271, July 1968. 22.  Fairbanks, G., Everitt, W.L. and Jaeger, J.P. "Method of time or fre- . quency compression-expansion of speech", IEEE Trans. Audio., Vol. AU-2, . 7-12, 1954.  23.  Dolch, E.E. et a l . • "Famous stories for pleasure reading", Garrard Publishing Co., Champaign, I l l i n o i s , 1955-  . .-•  24. . "1965 Revised L i s t of Phonetically Balanced Sentences (Harvard Sentences)" IEEE Trans. Audio and Electroacoustics, Vol. AU-17, No. 3, 239-246, Sept. . . 1969. ; 25.  . '  M i l l e r , G.A.  .  "Speech and Language" i n Handbook of Experimental Psycho-  . logy, S.S. Stevens (editor), p.. 794, John Wiley, 1951. 26.  Hoops, R.A.  Speech Science: Acoustics i n Speech, Charles C. Thomas  (Publisher) U.S.A., p. 68, 1969. 27. • Parmenter, C.E. and Trevino,.S.N.  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