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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 p r e s e n t i n g t h i s t h e s i s in p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r an advanced d e g r e e a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s - m a y be g r a n t e d by t h e Head o f my Depar tment o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . Depar tment o f E l e c t r i c a l Engineering The U n i v e r s i t y o f B r i t i s h C o l u m b i a V a n c o u v e r 8, Canada Date June 10th 1970 .ABSTRACT This t h e s i s d e s c r i b e s the e f f e c t s of d i c h o t i c -presentations on the-reading speed.of the users of the Lexiphone - a r e a d i n g machine f o r the b l i n d . The d i c h o t i c p r e s e n t a t i o n s i n v e s t i g a t e d are: a) s i n g l e "delay: one s i g n a l to one ear and.a delayed v e r s i o n of t h i s s i g n a l to the other ear; b) m u l t i p l e delay: the same s i g n a l w i t h three 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 ear. Experiments w i t h the Lexiphone su 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 improve-ment to'"their 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 which has been proposed to r e p l a c e the code sounds. . The r e s u l t s i n d i - . cated t h a t m u l t i p l e delay (as has been found i n the case u s i n g the L e x i -phone su 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 delay. Nevertheless, both these two d i c h o t i c p r e s e n t a t i o n s produced an improve-ment on the i n t e l l i g i b i l i t y of the m a t e r i a l . The e f f e c t of the word l e n g t h (number of l e t t e r s contained i n a word), on the i n t e l l i g i b i l i t y of s p e l l e d speech was a l s o analyzed, i t showed that the word l e n g t h has a great e f f e c t ; i t was found t h a t the percent c o r r e c t n e s s decreases w i t h the word l e n g t h . This e f f e c t . a l s o seems to be due to the longer time r e q u i r e d to perceive the -word.from.'the' s p e l l i n g , thus i t i s suggested that' a longer pause should be provided f o r those words w i t h -a l a r g e number of l e t t e r s . .Confusions of some l e t t e r sounds were observed when s p e l l e d .speech was com-pressed, these are the consonant sounds which are a r t i c u l a t e d e i t h e r a t the. -same- place- -or -in the-same -manner. :-. - ~ -••--:-;' • TABLE OF CONTENTS '. • Page ..ABSTRACT . i i ...TABLE OF CONTENTS. . . . . . . . . . . . . . . . . . . . . . . . . . i i i LIST OF ILLUSTRATIONS . i v LIST OF TABLES . . . . . . . . . . . . . . . . . . . v "ACKNOWLEDGEMENT ' V i 1. INTRODUCTION . . .'. . . . . . . 1 2. SCHEMES USED TO -PRODUCE- DICHOTIC - SIGNALS AND TIME COMPRESSION . 4 2.1 D i c h o t i c Presentations - Methods used to Increase the I n t e l l i g i b i l i t y of Sound Signals • . . . . . . . . . . . 4 2.2 Time, Compression - Method used to Increase the Presentation Rate of Sound Signals . . . . . . . . . . . . . . . . . . 9 3. - TESTS ON THE LEXIPHONE SUBJECTS • • ... • . ... . • • • • • ''. 12 . 3.1"- Testing' Procedures and Results . . . . . . . . . . . . 12 . 3.2 E f f i c i e n c y of the D i c h o t i c Presentations • • 14 4. TESTS ON SPELLED SPEECH • •'.'. . . . . . . . . . . . . . . •'. . . 16 4.1 Testing Procedures and Results • • 16 4.2 E f f e c t of Word Length . . . . . . . . . . . . . . . . 18 — .4.3 Confusion of Some L e t t e r Sounds ... . . . . . . . • '. 20 5. '.CONCLUSIONS AND. DISCUSSIONS . ...... . . . . . . . .". . ' . 22 APPENDIX I . . . . . . . - . 7 . . . . . . . . . . . . . . . . . . . . . .25 APPENDIX I I . . . . . . . . • • • . • • - . . . . . . . . . . . . . . . 2 7 REFERENCES • ..... . '•. . ... . 29 LIST OF ILLUSTRATIONS Figure Page 1.- Arrangements to Produce Dichotic Signals - 6 (a) Single Delay . (b) M u l t i p l e Delay 2 Computer Set-up f o r Processing Sound Signals . . . . . . . . 7 3 Time-delayed Waveforms.. . 8 (a) A Waveform and i t s Delayed Version . -- '—- -(b) . Lower Waveform being Delayed by a D i f f e r e n t Amount 4 Sound Wave Compression Processes . . . . . . . . 10 (a) O r i g i n a l Sound Wave • . ( b ) Expansion of the Sampled Sound Wave (c) New Compressed Sound Wave obtained on Playback 5. Waveforms obtained from the Computer 11 (a) The O r i g i n a l Waveform and i t s Expanded Version •' ' f o r C = 1.5 . ' • '. '.' (b) The O r i g i n a l Waveform and i t s Expanded Version f o r C = 2 6 Graph Showing the V a r i a t i o n of Rate Learned Versus the :" '"" Rate of the Ma t e r i a l Presented in'the Lexiphone Code • Test on Two B l i n d Subjects A and B . . . . 15 7 Combined E f f e c t of the Rate of Presentation and the Word Length, on the Percent Correctness of Spelled Speech Perceived by the Subjects . . . . . . . . . . .' . . 19-LIST OF TABLES. Table Page 1 Scores of Two Lexiphone Subjects on Code in Percent Correctness 13 2 Average Percent Correctness Scores of Six Subjects on Spelled Speech 17 3 Overall Percent Correctness of the Words According to the Number of Letters Contained in the Word 18 4 • Letter Sounds Confused . . . . . . . . . . . . . . . . . 20 v 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 finan-c 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 is 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. Un-fortunately, up to the present, only a limited success has been attained and there is still.no simple reading machine which is 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 is a gap between the first two requirements and the last. For. example, the Optophone which was proposed a long time ago"'" and is s t i l l in use, is cheap and portable but difficult 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 is difficult 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 is their encouragement and the assistance of many different related organizations that provide constant zeal and . assistance to the research workers in this field. The Lexiphone* is a direct translation machine which is rather more complex than the Optophone but i t is 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 in references 5-7. : a - c h a r a c t e r i s t i c rhythm. A l t h o u g h the code melody f o r e a c h l e t t e r i s a t u n e l e s s one, i t has been r e p o r t e d t o be q u i t e p l e a s a n t . I t has l o n g been r e c o g n i z e d t h a t a l t h o u g h a d i r e c t t r a n s l a t i o n ..type o f r e a d i n g machine i s s i m p l e and cheap compared w i t h the r e c o g n i t i o n t y p e , 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 . From the p a s t ex-p e r i e n c e , i t a p p e a r s t o t a k e o v e r two h u n d r e d h o u r s s p r e a d o v e r a y e a r t o l e a r n the L e x i p h o n e code w e l l enough t o r e a d s i m p l e s e n t e n c e s and s t o r i e s a t a b o ut t h i r t y words p e r minute._ A l t h o u g h t h i s i s a r e a d i n g speed about > ' 8 - t w i c e t h a t o b t a i n e d w i t h t h e Optophone a f t e r an e q u a l l e n g t h o f t r a i n i n g , i t i s s t i l l f a r b e h i n d t h e minimum a c c e p t a b l e r e a d i n g r a t e o f 50-60 words 9 . p e r m i n u t e s e t by Cooper. To t h i s p r o b l e m , a method o f d i c h o t i c p r e s e n -t a t i o n o f t h e code sound has been p r o p o s e d . T h i s method p r o v i d e s an i n c r e a s e i n t h e i n t e l l i g i b i l i t y o f the code. W h i l e t h e mechanism by w h i c h i n t e l l i g i -, b i l i t y i s i m p r o v e d i s u n c l e a r , e x p e r i m e n t a l l y w o r t h w h i l e i n c r e a s e s i n i n -t e l l i g i b i l i t y 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 i n a u s e f u l i n c r e a s e i n the "upper l i m i t o f r e a d i n g speed. . ' F o r . t h e t a l k i n g t y p e o f r e a d i n g machine, p r a c t i c a l l y no t r a i n i n g t ime i s r e q u i r e d t o u n d e r s t a n d the o u t p u t sound. However, a p r o b l e m a r i s e s when th e machine comes a c r o s s words w h i c h a r e n o t i n the s t o r e d v o c a b u l a r y o f t h e computer. These words c a n be s p e l l e d , b u t t h i s has the d i s a d v a n t a g e 3 : o f . s e v e r e l y d i s r u p t i n g t h e l i s t e n e r ' s t r a i n o f t h o u g h t s . .From the l e n g t h o f time r e q u i r e d t o l e a r n t h e code sounds o f a . d i r e c t t r a n s l a t i o n machine and t h e u l t i m a t e s p e e d a t t a i n a b l e , and t h e ex-pense and c o m p l e x i t y o f the t a l k i n g machine w h i c h s t i l l has t h e p r o b l e m o f u n s t o r e d words w h i c h have t o be s p e l l e d o u t , i t i s w o r t h w h i l e t o d e v e l o p 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 - — a s p e l l e d s p e e c h machine. T h i s w i l l r e d u c e the amount o f t r a i n i n g t i m e o f t h e u s e r and r e l i e v e him f r o m t h e t a s k o f d e c o d i n g the l e t t e r s as i t i s • r e q u i r e d i n t h e c a s e o f c o d i n g 3. machines and yet t h i s w i l l not be so expensive as i t i s i n the case of the t a l k i n g machine. This can be done by u s i n g prerecorded l e t t e r sounds on a drum or d i s c . Each r e c o r d i n g i s s u i t a b l y addressed so that i t can be keyed out 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 . " ^ But then what reading speed can be obtained w i t h the spelled-speech type of reading machine? Are there d i f f i c u l t i e s i n producing a high r a t e of s p e l l e d speech? Does the word-length (number of l e t t e r s contained i n a word) p l a y an important 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 ? W i l l the d i c h o t i c p r e s e n t a t i o n s be a p p l i c a b l e to s p e l l e d speech? The answers to these, questions w i l l be provided by the experiments described i n l a t e r s e c t i o n s of this- t h e s i s . 2. ' SCHEMES USED TO PRODUCE DICHOTIC SIGNALS AND TIME COMPRESSION 2.1 Di c h o t i c Presentation - Methods used to Increase the I n t e l l i g i b i l i t y ..of..Sound Signals When i d e n t i c a l signals are presented simultaneously to both ears of 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 located i n t r a -c r a n i a l sound.image i s perceived. I f a time delay i s introduced 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 perceived to s h i f t towards the side where the s i g n a l i s leading. As the amount of delay -is--increased- up—to-about -0.8 -ms.., -then- t h i s , .image-is-perceived to be located 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 according to which side the s i g n a l i s leading. This kind of presentation with a time delay i s known as 'dichotic presentation and that with no delay, the ordinary b i n a u r a l presentation. 11-13 E a r l i e r research works have shown that the binaural i n t e l l i -g i b i l i t y of speech under a masking condition of noise can be increased by mean's of d i c h o t i c presentation, .and the i n t e l l i g i b i l i t y increase brought by 14-19 i t has been confirmed by various groups of people f o r a delay within 20 21 the range.of 15 ms. I t has also been shown ' that time delay also.im-proves the i n t e l l i g i b i l i t y of r a p i d l y compressed speech even when there i s no noise.. These f i n d i n g s seem to suggest that dichotic- presentation of the above.can also be a p p l i e d to the Lexiphone code and s p e l l e d speech which are.not so, i n t e l l i g i b l e when presented at a f a s t r a t e. .• : Two types of d i c h o t i c presentation have been-investigated and the . ••" arrangements appear i n F i g . 1 (a) and Fig... 1 (b). In F i g . l (a), only one s i g n a l reaches each ear. In F i g . 1 (b), two s i g n a l s with a separation i n time reach each ear; the purpose of the multiple delay arrangement i s to t e s t whether or not multiple time-delayed s i g n a l s would produce a reinforcement -effect. The required-conditions of time delay on the sound signals were ob-tained by programming the PDP-9 computer,.the set-up i s shown i n F i g . 2. A program w r i t t e n f o r t h i s purpose i s shown i n Appendix I. Time-delayed waveforms.produced by t h i s program are shown i n F i g . J. 6. (t) DELAY S L(t) T I S R ( 0 r f (a) S L ( t ) = S j ( t - r ) "S R ( t ) = Sj (t) Si(t) - DELAY DELAY DELAY T 1 — ? r 3 SL(t) SR(t) (b) S L ( t ) = S (-(t - r 1 ) + S j ( t - T T 1 - t 2 - r 3 ) SR.(t) = Sj(t) + S i ( t - r 1 - r 2 ) Fig. 1 Arrangements to Produce Dichotic Signals: (a) Single Delay; (b) Multiple Delay. • INPUT SO UNO SIGNAL •A/D CONVERTER PDP-9 COMPUTER #1 D/A CONVERTER #2 D/A CONVERTER TAPE RECORDER OUTPUT SOUND SIGNALS 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 original 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 + I, 0 = _§ i I s In the case of Fig. 4, a compression ratio of 2 has been achieved. A pro-gram i s shown i n Appendix II 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 interval of 30 ms. In the spelled speech experiment, two compression ratios (l.5 and 2) were used to bring the original material to 1.5 and 2 times faster. Both the original and the resulting expanded waveforms coming out ofrom the D/A 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 com-pression 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 i/V v\ vV V V A A, 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. • v/ V V N V / 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 = 2. P i g . 5 Waveforms obtained from the Computer. 12. 3. TESTS ON THE LEXIPHONE SUBJECTS 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 I n o r d e r t o see how e f f e c t i v e the d i c h o t i c p r e s e n t a t i o n s a r e compared w i t h t h e 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 L e x i p h o n e code under v a r i o u s r e a d i n g speeds, t e s t s were p e r f o r m e d on two L e x i p h o n e s u b j e c t s . To e n s u r e t h a t the t e s t m a t e r i a l s a r e r e a s o n a b l y , u n i f o r m i n d i f f i c u l t y , a 23 l o n g s t o r y w i t h a l i m i t e d v o c a b u l a r y o f the f i r s t t h o u s a n d w o r d s ' o f the T h o r n d i k e - L o r g e l i s t s was c h osen. These m a t e r i a l s were f i r s t p r o c e s s e d on a computer to g i v e the d e s i r e d S and S„ s i g n a l s ( a s shown i n F i g . 1 ( a ) and h K F i g . 1 ( b ) ) a t the t e s t e d speeds and were t h e n r e c o r d e d on a t a p e r e c o r d e r . T e s t s were c o n d u c t e d i n t h e f o l l o w i n g p r e s e n t a t i o n s : 1) 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 . when t h e r e i s no d e l a y o r T = 0 ms. 2) D i c h o t i c p r e s e n t a t i o n s : a) S i n g l e d e l a y : T = 0.8 ms. and b) M u l t i p l e d e l a y : T± = 0.25 ms., = 0.3 ms. and = 0.25 ms. A time d e l a y o f 0.8 ms. ( w h i c h r e p r e s e n t s t h e l o n g e s t d e l a y e x p e r i e n c e d i n d a i l y l i f e when the sound s o u r c e i s e i t h e r on the r i g h t hand s i d e o r on t h e l e f t hand s i d e o f t h e e a r s ) had been c h o s e n because i t has n o t y e t been shown t h a t a g r e a t e r amount o f d e l a y w i l l g i v e a d d i t i o n a l b e n e f i t . B e s i d e s , t h i s amount o f t i m e d e l a y c a n be i mplemented e a s i l y e m p l o y i n g an a u d i o d e l a y l i n e . The p a s s a ges were r e c o r d e d a t t h r e e d i f f e r e n t speeds c o r r e s p o n d -i n g t o 30, 40 and 50 words p e r m i n u t e . . The r a t e s o f 30 and 40 words p e r Q m i n u t e r e p r e s e n t t h e peak r e a d i n g r a t e s o f t h e L e x i p h o n e s u b j e c t s . The p r o c e s s e d m a t e r i a l s were p r e s e n t e d i n random o r d e r . The t e s t s were c a r r i e d o u t , 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 t o the r e c o r d e d m a t e r i a l s a t a c o m f o r t a b l e l e v e l t h r o u g h a p a i r o f headphones; t h e y were i n s t r u c t e d t o 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 in the middle of the passages each of which consisted of about 120 words. The scores of these tests are shown in 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 \ ^ ^ C o n ^ Speed(w.p.m. •1 • 2 '... " — . ... . . . . . . . , 3 - . . . . . Ko Delay . Single Delay Multiple-Delay Subject A Subject B Subject A Subject B Subject A Subject B 30 40 : 50 82.9 90.2 83.1 , 57.8 61.7 58.2 . 96.7 98.9 96.2 64.3 .. 73.1 : 66.2 97.1 96.5 98.9 62.9 • 72.2 62.9 Table 1 'Scores of two Lexiphone Subjects on Code in Percent Correctness Note: At the time of this test, subject B had been away from the code- for ..several months. • • ..Statistical 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. s c o r e s a r e h i g h e r t h a n u s i n g n o r m a l 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 r e a d i n g r a t e s . I t a l s o i n d i c a t e d t h a t m u l t i p l e d e l a y i s o n l y a b out as e f f e c t i v e 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 c a u s e d by a r e p e t i - . t i o n o f t h e same s i g n a l s even though t h e y are s e p a r a t e d a p a r t i n t i m e . 3.2 E f f i c i e n c y 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 F i g . . 6 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 code i n f o r -m a t i o n l e a r n e d v e r s u s t h e r a t e p r e s e n t e d i n t h e t h r e e t e s t e d c o n d i t i o n s . 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 a r e s e e n t o be c l o s e r t o the i d e a l 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 pronounced i n the p e r -formance o f t h e b e t t e r s u b j e c t ( s u b j e c t A ) . Thus message e f f i c i e n c y , as measured by the number o f words l e a r n e d p e r u n i t t i m e , i n c r e a s e s w i t h t h e d i c h o t i c p r e s e n t a t i o n s . Message e f f i c i e n c y s t a r t s t o d e c l i n e a t t h e r a t e o f about 40 words p e r m i n u t e f o r t h e b i n a u r a l p r e s e n t a t i o n . - ' J u d g i n g f r o m F i g . 6, s u b j e c t A c a n r e a d w i t h t h e L e x i p h o n e more e f f i c i e n t l y a t a h i g h r a t e ; f o r s u b j e c t B, because o f . t h e d e c l i n e a r o u n d ' th 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 t h e most e f f i c i e n t r a t e o f p r e -s e n t a t i o n f o r h e r . 3 0 4 0 50 R a t e P r e s e n t e d (w. p.m.) Fig. 6 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. TESTS ON SPELLED SPEECH •4.1 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 ' •• I n o r d e r t o 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 ch as a medium o f c o m m u n i c a t i o n and t e s t the 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 com-p a r e d w i t h t h e 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 , t e s t s were p e r f o r m e d . The t e s t m a t e r i a l c o n s i s t s o f s e l e c t e d l i s t s o f p h o n e t i c a l l y - b a l a n c e d 24 s e n t e n c e s . 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 words and c o n s i s t s o f t e n s e n t e n c e s . 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 aver a g e 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 . The m a t e r i a l was t h e n compressed on t h e PDP-9 computer t o g i v e three"! d i f f e r -e n t r a t e s f o r p r e s e n t a t i o n , i . e . 54, 81, .and 108 words ..per .minute r e -s p e c t i v e l y . These m a t e r i a l s were a g a i n p r o c e s s e d on t h e PDP-9 computer t o o b t a i n t h e t h r e e d i f f e r e n t k i n d s 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 and m u l t i p l e d e l a y as i t was done i n t h e L e x i p h o n e code t e s t . S i x s u b j e c t s ( t h r e e male and t h r e e f e m a l e u n i v e r s i t y u n d e r g r a d u a t e s t u d e n t s ) who a r e n a i v e w i t h r e s p e c t t o s p e l l e d s p e e ch 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 the m a t e r i a l and the con-d i t i o n s o f p r e s e n t a t i o n were r a n d o m i z e d i n a b a l a n c e d d e s i g n so t h a t . a l l t h e 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 -s e n t a t i o n and a l l t h e l i s t e n i n g c o n d i t i o n s ( i n c l u d i n g t h e t h r e e p r e s e n - . t a t i o n s : •.- no delay,- 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 and a l s o t h e 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 the l e f t e a r ) . The t e s t s were 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 t o t h e r e c o r d e d m a t e r i a l s a t a c o m f o r t a b l e l e v e l t h r o u g h a p a i r o f headphones; t h e y were i n s t r u c t e d "to o m i t t h e words i f t h e y c o u l d n o t c a t c h - t h e m ; — B e f o r e t h e a c t u a l t e s t began, 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 t o the s u b j e c t s and ea c h s u b j e c t had a p r a c t i c e o f f i v e l i s t s . " The s c o r e s o f t h e s e t e s t s a r e shown i n T a b l e 2. "^""-'--^ ^^  C o n d i t i o n s Speed (w. p.m. ) ^ ^ ~ ~ ^ ~ ^ ^ 1 2 3 No D e l a y S i n g l e D e l a y . M u l t i p l e D e l a y 54 77.66 77.68 78.33 81 63.81 72.58 68.65 108 56.69 62.41 63.98 T a b l e 2 Average fo C o r r e c t n e s s S c o r e s o f S i x S u b j e c t s on S p e l l e d Speech . On a n a l y z i n g t h e r e s u l t o i t h e s p e l l e d s p e e c h e x p e r i m e n t , i t has been f o u n d t h a t t h e e f f e c t s o f t h e d i f f e r e n t p r e s e n t a t i o n s a r e s i g n i f i c a n t ( p < 5 $ ) , t h e r a t e o f p r e s e n t a t i o n o f t h e m a t e r i a l i s h i g h l y s i g n i f i c a n t ( p < 0 . 1 $ ) . The a n a l y s i s a l s o r e v e a l e d t h a t i n t e r c h a n g i n g the s i g n a l s o f t h e two e a r s has no s i g n i f i c a n t a f f e c t a t . a l l ( p > 5 0 $ ) , t h i s i n d i c a t e s t h a t i t does n o t m a t t e r w h e t h e r t h e r i g h t e a r s i g n a l l e a d s t h e l e f t e a r o r ' v i c e v e r s a . On c o m p a r i n g t h e r e s u l t s shown i n T a b l e 2, i t c a n be seen 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 g i v e improvements a t t h e t h r e e t e s t e d speeds o f p r e s e n t a t i o n . However, a t the l o w e s t r a t e o f p r e s e n t a t i o n (54 w.p.m.), t h e r e i s o n l y a m i n o r improvement. T h i s may be due t o t h e f a c t t h a t a t t h i s low r a t e , i t i s n o t the i n t e l l i g i b i l i t y t h a t a f f e c t s the p e r f o r m a n c e , but i t i s t h e d i f f i c u l t y o f p u t t i n g the l e t t e r s i n t o words. I t i s e x p e c t e d t h a t a t r a i n e d s u b j e c t on s p e l l e d s p e e c h s h o u l d , have no d i f f i c u l t y a t a l l " i n o b t a i n i n g a h i g h s c o r e ( > 9 0 $ ) a t t h i s r a t e o f p r e s e n t a t i o n . The r e s u l t s a t t h e medium and t h e f a s t e s t r a t e s seem t o r e s e m b l e t h e r e s u l t s o f s u b j e c t B i n t h e L e x i p h o n e code t e s t . I f i t i s t h e s u b j e c t ' s s k i l l ( s u c h as s u b j e c t " A i n t h e code 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 in 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 in those words which contained a large number of letters. In view of this, 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) 3 or less 4 5 6 7 8 % Correctness 86.22 66.74 51.84 43.13 29.67 32.04 -Table 5 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. It must be pointed out that no. longer pause' was allowed for long words i n the.test. This may create the situation of'insufficient time for the per-c e p t i o n of, the long words from the letters, 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 letters, a slightly longer pause should follow to compensate for the.time required to perceive these words from their spelling. r u n 54 w.p.m. Y/A 81 w.p.m. } | 108 w.p.m. 3 or less U 5 6 7 8 NUMBER OF LETTERS IN A 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. 4.3 C o n f u s i o n o f Some L e t t e r Sounds D u r i n g t h e s p e l l e d s p e e c h t e s t , c o n f u s i o n o f some l e t t e r sounds was o b s e r v e d i n the case o f compressed m a t e r i a l s . The t o t a l number o f 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 sounds i s about 5.5$. A l l the c o n f u s e d l e t t e r s a r e c o n s o n a n t s . C o n f u s i o n a t the l o w e s t s p e e d (uncom-p r e s s e d ) was u n n o t i c e a b l e . The f o l l o w i n g t a b l e shows how the 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 and t h e p l a c e o f a r t i c u l a t i o n 25 o f t h e l e t t e r sounds. Manner o f A r t i c u l a t i o n P l a c e o f A r t i c u l a t i o n . -B i l a b i a l L a b i o - d e n t a l L i n g u a - a l v e o l a r V e l a r V o i c e d P l o s i v e U n v o i c e d P l o s i v e N a s a l -V o i c e l e s s F r i c a t i v e -:f(io.56) t ( 1 9 ) y^W [Z&2)\ -(10.-56) i V.V ( 1 2 . 7 0 K - V • G)-—-— -G) G —W3i0\ Table'4 L e t t e r . Sounds C o n f u s e d . ( A r r o w head i n d i c a t e s t h e d i r e c t i o n o f c o n f u s i o n , e.g. t h e a c t u a l sound 'm' i s m i s t a k e n t o be t h e sound •In', and t h e sound 'd' i s . m i s t a k e n as t h e s o u n d ' ' t 1 and v i c e v e r s a . A d o t t e d l i n e i n d i c a t e s a l e s s f r e q u e n t c o n f u s i n g s i t u a t i o n . The f i g u r e s i n b r a c k e t s d e n o t e the p e r c e n t c o n t r i b u t i o n o f each c o n -f u s i n g s i t u a t i o n t o w a r d s t h e t o t a l number.of..confusions...)._ 21. T a b l e 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 con-f u s e d sounds. I t a l s o i n d i c a t e s t h a t l e t t e r sounds a r t i c u l a t e d i n the same manner o r a t the 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 . There a r e --"some u n i - d i r e c t i o n a l c o n f u s i o n s w h i c h i n d i c a t e t h a t some o f them can be m i s t a k e n as o t h e r s , b u t n o t v i c e v e r s a . . 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 o c c u r r e d o n l y i n c o n -—-sonants w i t h t h e - c o m p r e s s e d m a t e r i a l s and n o t - w i t h i t s uncompressed, v e r -s i o n i s because t h e d u r a t i o n o f p h o n a t i o n ( t h e l e n g t h o f time i n v o l v e d i n j t h e ^ p r o d u c t i o n o f a s i n g l e sound) _ o f _ t h e c o n s o n a n t sounds i s much 2(5 27 s h o r t e r t h a n t h a t o f t h e v o w e l s ' ., t h e r a t i o i s r o u g h l y 3 t o 2 ( t h e • ' d u r a t i o n o f p h o n a t i o n f o r v o w e l s a v e r a g e s t o 0.117 s e c . and t h e d u r a t i o n • o f p h o n a t i o n 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 . ). D u r i n g t h e c o m p r e s s i o n p r o c e s s , a p a r t o f t h e l e t t e r sound has been d i s c a r d e d e f f e c t i n g a s h o r t e r - d u r a t i o n o f t h e . l e t t e r sound. T h i s makes t h e compressed c o n s o n a n t sounds more- d i f f i c u l t t o d i s t i n g u i s h ( e s p e c i a l l y t h o s e w h i c h a r e a r t i c u l a t e d i n '-the same manner o r a t t h e same p l a c e ) and t h u s c o n f u s i o n o c c u r r e d . •". A l t h o u g h c o n f u s i o n s o f some l e t t e r s may be e l i m i n a t e d by c o r r e c t • g u e s s i n g f r o m t h e c o n t e x t o f the m a t e r i a l , e a s y i d e n t i f i c a t i o n o f l e t t e r sounds i n s p e l l e d s p e e c h i s i m p o r t a n t b e c a u s e some words c o n s i s t o f . - . _ s i n g l e l e t t e r s and, d i f f e r e n t i a t i o n ..of word p a t t e r n s w o u l d be f a c i l i t a t e d r i f t h e r e were no c o n f u s i o n s among l e t t e r s . 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 sounds 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 l e t t e r s s u c h . as d, t , p, ra and f.' -,22. 5. CONCLUSIONS AND DISCUSSIONS Prom the Lexiphone and s p e l l e d speech experiments, i t has been found that both the s i n g l e delay and multiple delay d i c h o t i c presentations bring 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 of the materials presented through the earphones. The Lexiphone code tests i n d i c a t e that d i c h o t i c presentations are more h e l p f u l to the subject who i s better s k i l l e d i n the code. The r e s u l t s of the s p e l l e d speech tests r e -semble that of subject B (the subject who i s not so s k i l f u l i n using the Lexiphone) i n the Lexiphone t e s t . I f i t i s the s k i l l of the subject which had produced t h i s strong influence, then d i c h o t i c presentations would be more b e n e f i c i a l to those who have been trained.on s p e l l e d speech. This has to be confirmed on experimenting subjects who have already been trained on s p e l l e d speech. Conclusions on t h i s f a c t o r may also be a r r i v e d using other better s k i l l e d Lexiphone users. Since i t takes a rather long time (over 200 hours of t r a i n i n g ) to l e a r n the' code well, i t would be more desir a b l e to t r a i n subjects on s p e l l e d speech for t h i s purpose. In f a c t , 23 i t has been found , that a f t e r a t r a i n i n g time of only about twenty hours, i f words were sp e l l e d r a p i d l y enough, the whole word, rather than the i n d i -v i d u a l l e t t e r s , would become the u n i t of perception. .r From the comments made by the s p e l l e d speech subjects, i t i n d i c a t e s that a better performance may be-arrived' at with more, p r a c t i c e . The subjects also remarked that the f a s t e s t rate of presentation (108 w.p.m.) was too f a s t f o r the perception of the words, but they a l l f e l t that t h i s s i t u a t i o n might change a f t e r they had been exposed to s p e l l e d speech f o r a long enough time,. The subjects also showed no p a r t i c u l a r preference to any of the l i s t e n i n g conditions./ Counting the percent correctness of the subjects• 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 letters. Another finding of the spelled speech test i s that there are "errors caused by the confusion among the letter 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 letter 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 letter sounds. One way of doing this i s to simulate the letter sounds on the computer and then control the duration of the. letter sounds for presentation. This w i l l not only find out the duration of phonation required for the perception of the letter 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 inves-tigated and the effect of the sampling period of. compression has not been considered at great depth. It must be pointed out that there are other dichotic presentations which are worthwhile for further research: these include a longer single delay (in the range- of 20 ms. to 300 ms.) .and: dichotic compression (presenting: .the .samples ,in -the sampling interval to one ear and the samples in 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. It i s l i k e l y that the optimum sampling interval i s related to the duration of phonation of different letter 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 letter sounds at different speeds of presentation for the spelled speech reading machine and i t w i l l also throw some light onto better methods of dichotic presentations. Appendix I FLOW CHART FOR THE DELAY PROGRAM • The f o l l o w i n g i s a s i m p l i f i e d flow chart f o r the delay program. Set SFC p r i n t on t e l e t y p e 'SET DELAY' set amount of delay r e q u i r e d on AC switches set up r e g i s t e r s f o r h a n d l i n g data w a i t f o r A/D f l a g No —<— Yes c l e a r f l a g • read A/D buffer.and s t o r e d e p o s i t t h i s sample i n output and s t o r e i t -increment delay counter and check f o r the end of b u f f e r No Yes r e s e t 26. •TITLE DELAY ./ .IODEV 10 SFC=701207 IN52=705217 OUT3U703107 OUT32=703207 SKPFLG: 705301 CLRFLG=705302 START .INIT 10,1,START . .WRITE 10,2ePRINT,3 ; .CLOSE 10 LAC (-62 SFC HLT 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 /SET THE SAMPLING PERIOD = 50 US /HALT, SET THE AMOUNT OF DELAY /ON AC SWITCHES, PRESS CONTINUE Appendix II  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 in the period ( i + 1^) * accept signal from the A / D converter and sample i t deposit i n register 'S' the samples obtained in the period I s discard those samples obtained i n the next period 1^ • > output the samples contained in register 'S' one at a time at an interval of CT check for the last sample i n register 'S' No Yes reset register 'S' reset register 'R' ' — : — ' • :  28. :. .TITLE TIME COMPRESSION, C = 2 -• .IODEV 10 . '• •VSFCr701207 . :_,:'V'. .V".: = • IN52=705217 . ; : V-.:.:. r.::[-^r"-' 0UT31=703107 0UT32= 703207 V ' - V SKPFLG=705301 • p-V\'.-;" -CLRFLG= 705302 .:' .\, V• i ; \: START .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, Vol. 94, p. 4, 1914-2. Cooper, F.S. and Gaitenby, J.~ "Reading Machine Research at Raskins" in'Reading Machines for the Blind, Sixth Technical Session''held at the Veterans Administration Central Office, Washington, D.C. i n Jan. 1966. 3. Cooper, F.S., Gaitenby, J., Mattingly, I.G. and Umeda,•N."Reading Aids for the Blind: A special 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, Vol. AU-17, No. 4, 275-282, Dec. 1969. 5. Caple, G. "The Lexiphone, a simple Reading Machine for the Blind," .:, M.A.Sc. Thesis, U.B.C.,. January 1966. 6. Beddoes, M.P. "An Inexpensive Reading Instrument with a Sound Output for the Blind", IEEE Trans. Bio-Med. Eng., Vol. BME-15, 70-79, April 1968. 7. Ramsey, D. "Design of a Simple Reading Machine for 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' for the Battelle. Aural Reading Device" Research Report to the Veterans Administration from the Battelle Memorial Institute, Columbus, Ohio, June 1963-9« Cooper, F.S. "Research on Reading Machines for the Blind" in 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. R e a d i n g Machine f o r the B l i n d " , B u l l e t i n o f P r o s t h e t i c s R e s e a r c h , BPR 10-12, 243-271, F a l l 1969-11. L i c k l i d e r , J.C.R. "The i n f l u e n c e o f i n t e r a u r a l phase r e l a t i o n s upon the m a s k i n g o f s p e e c h by w h i t e n o i s e " J . A c o u s t . Soc. Am., 20, 150-159, 1948. 12. • H i r s h , I . J . "The i n f l u e n c e o f i n t e r a u r a l phase on i n t e r a u r a l sum-m a t i o n and i n h i b i t i o n " J . A c o u s t . Soc. Am., 20, 536-544, 1948. 13. S c h u b e r t , E.D. "Some p r e l i m i n a r y e x p e r i m e n t s on b i n a u r a l time d e l a y . . and i n t e l l i g i b i l i t y " J . A c o u s t . Soc. 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C a r h a r t , Raymond; T i l l m a n , T.W. and D a l l o s , P . J . "Unmasking f o r pure tones and spondees: 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 . . H e a r . Res., 11, No. 4, 722-734, Dec. 1968. 19. 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 sound s o u r c e s on s p e e c h i n t e l l i g i b i l i t y " J . Speech Hear. Res., 12', No. 1, '5-38, March 1969-20. Cramer, II.L. "The i n t e l l i g i b i l i t y o f t i m e - c o m p r e s s e d s p e e c h " P r o c e e d -• '. ' : . : / . ' • 5 1 i ings of the Louisville Conference on Time Compressed Speech, Oct. 1966. —21. Carroll, J.B. and Cramer, H.L. "The i n t e l l i g i b i l i t y of time-compressed speech f i n a l report" 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 List of Phonetically Balanced Sentences (Harvard Sentences)" IEEE Trans. Audio and Electroacoustics, Vol. AU-17, No. 3, 239-246, Sept. . . 1969. . ' . -; 25. Miller, 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 in Speech, Charles C. Thomas (Publisher) U.S.A., p. 68, 1969. 27. • Parmenter, C.E. and Trevino,.S.N. "The Length of the Sounds of a Middle Westerner", American Speech, 10, 129-133, 1935. 28. Ingham, K.R. "Spelled speech as an output for computers and reading ..machines for. the blind", IEEE Trans. Human Factors i n Electronics, .Vol. HFE-8, 175-181, Sept. 1967. . 2 9 . Fairbanks, G. and Kodman, F. "Word I n t e l l i g i b i l i t y as a function of . • time compression", J. Acous. Soc. Am., 29_, 636-641, May 1957. 

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