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UBC Theses and Dissertations

Durations of acoustic segments under synchronous and delayed feedback conditions Jeffrey, Ingrid 1974

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DURATIONS OF ACOUSTIC SEGMENTS UNDER SYNCHRONOUS AND DELAYED FEEDBACK CONDITIONS by Ingrid Jeffrey B . A . , Simon Fraser Un ive r s i t y , 1972 . A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n the Department of Paediatr ics D i v i s i o n of Audiology and Speech Sciences We accept th i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA July,1974 In p resent ing 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 the requirements f o r an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree that the 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 fo r reference and study. I f u r t h e r agree tha t permiss ion fo r e x t e n s i v e copying of t h i s t h e s i s fo r s c h o l a r l y purposes may be granted by the Head of my Department or by h i s r e p r e s e n t a t i v e s . It i s understood that copying or 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 ga in s h a l l not be a l lowed without my w r i t t e n p e r m i s s i o n . Department of PCLICLL CLI^LCS The U n i v e r s i t y of B r i t i s h Columbia Vancouver 8. Canada Date Qdoltr 9* /?7</ ABSTRACT The pre s e n t study i n v e s t i g a t e s d u r a t i o n s of a c o u s t i c segments under synchronous and delayed feedback c o n d i t i o n s . Three s u b j e c t s read a passage and f o u r sentences a t t h e i r normal r a t e (NORMAL), at a slow r a t e (SLOW SAF) under synchronous feedback, and then a t a slow r a t e (SLOW DAF) and a t a maximally f a s t r a t e (FAST DAF) under delayed a u d i -t o r y feedback. The del a y used was determined f o r each s u b j e c t so i t would produce maximum speech d i s t u r b a n c e . The hypotheses under t e s t , on the b a s i s of a p i l o t study were: (a) t h a t under SLOW SAF and under delayed feedback, vowels would be prolonged p r o p o r t i o n a t e l y more than consonants, and t h a t c o n t i n u a n t s would be prolonged p r o p o r t i o n a t e l y more than o b s t r u e n t s ; and (b) t h a t c l o s e vowels would be prolonged more under SLOW SAF and open vowels more under DAF c o n d i t i o n s . P o s i t i o n i n the s y l l a b l e was expected to a f f e c t s e l e c t i v e l y i n c r e a s e s i n d u r a t i o n under DAF. The r e s u l t s , based on normalized d a t a , confirmed t h a t vowels were p r o p o r t i o n a t e l y more prolonged than con-sonants under SLOW SAF and DAF c o n d i t i o n s . Continuant consonants were p r o p o r t i o n a t e l y more prolonged than o b s t r u -ents under DAF c o n d i t i o n s but not c o n s i s t e n t l y under SLOW SAF. For the ob s t r u e n t s p r e v o c a l i c c l o s u r e was c o n s i s t e n t l y more prolonged under DAF than under SLOW SAF. The hypothesis t h a t c l o s e vowels would be prolonged more under SLOW SAF and open vowels more under DAF was not i n g e n e r a l confirmed. The study f u r t h e r i n d i c a t e d t h a t p o s i t i o n i n the s y l l a b l e not only a f f e c t e d d u r a t i o n s of segments under DAF but a l s o under SLOW SAF: Under SLOW SAF consonants i n p o s t v o c a l i c p o s i t i o n were p r o p o r t i o n a t e l y more prolonged and under DAF consonants i n p r e v o c a l i c p o s i -t i o n were p r o p o r t i o n a t e l y more prolonged. I t was a l s o found t h a t the d u r a t i o n s of vowels i n words such as f u n c t i o n words i n c r e a s e d p r o p o r t i o n a t e l y more than the d u r a t i o n of vowels i n other words and t h a t the d u r a t i o n of the vowel /u/ i n c r e a s e d p r o p o r t i o n a t e l y more than t h a t of open vowels. Moreover, /u/ o c c u r r e d more f r e q u e n t l y than other vowels i n phonetic environments i n which vowels are normally of longer d u r a t i o n . F i n a l l y , i t i s hypothesized t h a t the s y l l a b l e i s a monitored u n i t under DAF and t h a t the r e f l e x l e v e l i s i n v o l v e d i n the DAF-induced speech d i s t u r b a n c e s . TABLE OF CONTENTS Page ABSTRACT i i TABLE OF CONTENTS i v L I S T OF TABLES v i L I S T OF FIGURES v i i ACKNOWLEDGEMENT v i i i C h a p t e r 1 INTRODUCTION 1 C h a p t e r 2 LITERATURE REVIEW 5 2 . 1 I n t r o d u c t i o n 5 2 .2 E x p e r i m e n t s 5 2 . 3 D i s c u s s i o n . 18 C h a p t e r 3 AIMS OF THE INVESTIGATION . 37 C h a p t e r 4 EXPERIMENTAL APPARATUS AND PROCEDURES. . 39 4 . 1 S u b j e c t s . 39 4 .2 E x p e r i m e n t a l D e s i g n 39 4 .3 I n s t r u m e n t a t i o n and Ar rangement . . 43 4 .4 C a l i b r a t i o n 44 C h a p t e r 5 ANALYSIS OF DATA 46 5 .1 I n s t r u m e n t a t i o n 46 5.2 S e g m e n t a t i o n C r i t e r i a 47 5 .3 Segment R e j e c t i o n C r i t e r i a 52 C h a p t e r 6 RESULTS AND DISCUSSION 55 6 .1 P i l o t S tudy 55 6 .2 S c r e e n i n g S tudy . 58 i v Page 6.3 R e s u l t s o f t he M a i n E x p e r i m e n t . . . 6 2 6. 3"*" R e l a t i v e D u r a t i o n s 65 2 6.3 R e l a t i v e Change Measure . . . 65 3 6.3 R e l a t i v e Change o f Vowe l s . . 68 4 6.3 R e l a t i v e Change o f Consonan t s 79 6.3^ R e p e t i t i o n s 87 6 .4 Summary and C o n c l u s i o n s . . . . . . 9 1 BIBLIOGRAPHY 95 APPENDIX 9 8 v LIST OF TABLES Table Page I . Normal read i n g time under SAF and delays pro-ducing peaks of d i s t u r b a n c e as d e f i n e d by the d u r a t i o n - e r r o r r a t i o d e s c r i b e d i n chapter 4 . . 59 I I . Between-condition d i f f e r e n c e s i n r e l a t i v e change of vowels i n o n e - s y l l a b l e f u n c t i o n words 70 I I I . W i t h i n - c o n d i t i o n d i f f e r e n c e s i n r e l a t i v e change of ' s t r e s s e d ' long vowels and vowels i n f u n c t i o n words 71 IV. W i t h i n - c o n d i t i o n d i f f e r e n c e s i n r e l a t i v e change of ' s t r e s s e d ' vowels and / a / not i n f u n c t i o n words 7 3 V. W i t h i n - c o n d i t i o n d i f f e r e n c e s i n r e l a t i v e change of ' s t r e s s e d ' vowels 76 V I . Between-condition d i f f e r e n c e s i n r e l a t i v e change of a s p i r a t i o n a f t e r ' i n i t i a l ' v o i c e l e s s c l o s u r e 84 v i LIST OF FIGURES Fi g u r e Page 4.1 Block diagram of i n s t r u m e n t a t i o n f o r pro-ducing the delayed feedback and f o r r e c o r d -in g 43 5.1 Block diagram of i n s t r u m e n t a t i o n used to produce mingograms 46 5.2 Mingogram of p a r t of the phrase / g r i d i t i m z / 48 5.3 Mingogram of the phrase / f u l s / 49 5.4 Mingograms of the phrases /wAn/, / r A f t / , and / j u z / . . 50 5.5 Mingogram of the phrase /6s J a f t / 51 5.6 Mingogram of the sequence / r A I d A b A O A b A b o a / . . . 5 3 o o o ° 6.1 DAF-induced speech d i s t u r b a n c e ( e r r o r - d u r a t i o n r a t i o ) f o r male s u b j e c t 1, and female s u b j e c t s 2 and 3 61 6.2 Average ' t o t a l d u r a t i o n s ' of the main e x p e r i -ment sentences i n the four c o n d i t i o n s 6 3 6.3 R e l a t i o n s h i p of ' s t r e s s e d ' long vowels, 'other' vowels, and consonants i n the main experiment sentences i n the fou r c o n d i t i o n s . 6 6 6.4 R e l a t i v e change i n d u r a t i o n f o r vowels i n the SLOW SAF ( I I ) , the SLOW DAF ( I I I ) , and the FAST DAF (IV) c o n d i t i o n s w i t h r e s p e c t t o the NORMAL c o n d i t i o n 6 9 6.5 R e l a t i v e change i n ' i n i t i a l ' v o i c e l e s s c l o s u r e , ' f i n a l ' v o i c e l e s s s t o p s , ' i n i t i a l ' /m/ and ' f i n a l ' n a s a l s 81 6.6 R e l a t i v e change i n a s p i r a t i o n i n the SLOW SAF, SLOW DAF and FAST DAF c o n d i t i o n s w i t h r e s p e c t t o the NORMAL c o n d i t i o n 8 3 6.7 Number of r e p e t i t i o n s and cumulative % repe-t i t i o n s i n the FAST DAF c o n d i t i o n 8 8 v i i ACKNOWLEDGMENT I would l i k e t o express ray s i n c e r e a p p r e c i a t i o n f o r the he l p I have r e c e i v e d i n completing t h i s t h e s i s . My thanks go e s p e c i a l l y - To Dr. A-P. Benguerel without whose time and advice t h i s t h e s i s would not have been p o s s i b l e ; - To Dr. J.B. Delack, not only f o r being on my t h e s i s committee, but p a r t i c u l a r l y f o r h i s concern and i n t e r e s t always; - To Dr. R. Gregg f o r h i s time spent s e r v i n g on my committee; - To Dr. J.H. G i l b e r t and Ca r o l y n f o r t h e i r k i n d encourage-ment ; - To Dr. R.P. Gannon f o r p e r m i s s i o n to use the f a c i l i t i e s of the A u d i o - V e s t i b u l a r U n i t at Vancouver General H o s p i t a l ; - To The Psychology Department at Simon F r a s e r U n i v e r s i t y f o r the loan of the K o r t i n g tape r e c o r d e r ; - To Jim and Kathy f o r t h e i r love and understanding; - To Sharon, Pat, Lynne, Betty and M e r a l i n f o r the clo s e n e s s we shared; - To Robin f o r her work on the drawings; - To Rose and Margaret f o r t y p i n g ; - And to my s u b j e c t s f o r t h e i r p a t i e n c e and co o p e r a t i o n . C h a p t e r 1 INTRODUCTION The i m p o r t a n c e o f s e n s o r y f e e d b a c k f o r t h e smooth e x e c u t i o n o f v o l u n t a r y movements has l o n g b e en r e c o g n i z e d . I n t h e p r o d u c t i o n o f s p e e c h a number o f v o l u n t a r y movements i n v o l v i n g t h e v a r i o u s a r t i c u l a t o r s , t h e r e s p i r a t o r y mech-a n i s m , and t h e v o c a l f o l d s h a v e t o be p r e c i s e l y c o o r d i n a t e d i n t i m e . To add t o t h e c o m p l e x i t y o f s u c h a s e t o f c o -o r d i n a t e d movements, t h e n e u r a l commands f o r t h e v a r i o u s movements r e q u i r e d f o r t h e p r o d u c t i o n o f a sound c a n n o t a l w a y s be i n i t i a t e d a t t h e same p o i n t i n t i m e . The s e q u e n c e a t w h i c h i m p u l s e s w i l l be f i r e d i s d e t e r m i n e d by a number o f f a c t o r s s u c h as t h e t r a v e l l i n g t i m e r e q u i r e d by t h e i m p u l s e t o r e a c h i t s d e s t i n a t i o n , "mass o f t i s s u e t h a t has t o be moved and t h e amount o f work t h a t must be p e r f o r m e d " ( L e n n e b e r g , 1967, p. 1 0 0 ) . F u r t h e r m o r e , d u r i n g t h e p r o -d u c t i o n o f a p a r t i c u l a r s o u n d , f e a t u r e s o f l a t e r sounds may a l r e a d y be p r e s e n t . S p e e c h , i n o t h e r words, d o e s n o t c o n -s i s t o f one d i s c r e t e s e t o f c o o r d i n a t e d movements r e s u l t -i n g i n t h e p r o d u c t i o n o f a soun d t h e l e n g t h o f a phoneme f o l l o w e d by a n o t h e r , b u t c o n s i s t s o f a s e t o f d i s c r e t e n e u r a l commands w i t h a s s o c i a t e d movements c o o r d i n a t e d i n t i m e . The l e n g t h o f t h e p r o d u c t i o n u n i t o r u n i t s i n w h i c h movements a r e i n t e g r a t e d h a s been and c o n t i n u e s t o be a s u b j e c t o f i n v e s t i g a t i o n . I t has been s u g g e s t e d ( S m i t h , 1962) t h a t t h e - 2 -m o t i o n p a t t e r n s o f s p e e c h a r e c o n t r o l l e d and m o n i t o r e d by a s y s t e m o f f e e d b a c k mechanisms. W i t h t a c t i l e , k i n e s t h e t i c , bone- and a i r - c o n d u c t i o n f e e d b a c k c h a n n e l s a v a i l a b l e t o s u c h a s y s t e m , what i s t h e p r e c i s e n a t u r e o f t h e s e f e e d b a c k c h a n -n e l s , t h e i r u t i l i z a t i o n i n t h e p r o c e s s o f m o n i t o r i n g and c o n t r o l l i n g , and t h e i r r e l a t i v e i m p o r t a n c e ? By means o f i n t e r f e r e n c e w i t h t h e f e e d b a c k c h a n -n e l s , i n v e s t i g a t o r s have s o u g h t answers t o t h e s e q u e s t i o n s . A c o n s i d e r a b l e amount o f d a t a has been c o l l e c t e d a b o u t t h e a u d i t o r y f e e d b a c k mechanism. F o r example, i t has been f o u n d t h a t when b o t h bone- and a i r - c o n d u c t e d a u d i t o r y f e e d -b a c k a r e masked by h i g h i n t e n s i t y n o i s e , v o w e l s a r e c o n s i d -e r a b l y a f f e c t e d b o t h i n l e n g t h and q u a l i t y , and c o n t r o l o f t h e s o f t p a l a t e i s l o s t t o some e x t e n t . I t has a l s o b e en o b s e r v e d t h a t p i t c h i n c r e a s e s and t h a t c h a n g e s o f i n t o n a t i o n p a t t e r n s and v o i c e o c c u r u n d e r t h i s c o n d i t i o n ( L a d e f o g e d , 1967,pp. 163-164). I n t r o d u c i n g a d e l a y between t h e s p e a k e r ' s v o c a l o u t p u t and h i s a i r - c o n d u c t e d a u d i t o r y i n p u t , a method known as d e l a y e d a u d i t o r y f e e d b a c k (DAF), a l s o r e f e r r e d t o as d e l a y e d s i d e - t o n e , i s a f r e q u e n t l y e m p l o y e d method o f i n t e r -f e r e n c e , d e l a y i n g t h e u s u a l t i m e o f a r r i v a l o f t h e a u d i t o r y f e e d b a c k d u r i n g s p e e c h p r o d u c t i o n . D e p e n d i n g on t h e o c c l u d -i n g p r o p e r t i e s o f t h e h e a d s e t e a r m u f f s , t h e sound a b s o r b i n g p r o p e r t i e s o f t h e e n v i r o n m e n t , t h e l e n g t h o f t h e d e l a y , and t h e a m p l i f i c a t i o n o f t h e d e l a y e d s i g n a l , f r a g m e n t s o f un-d e l a y e d a u d i t o r y f e e d b a c k w i l l be a v a i l a b l e t o t h e s p e a k e r . - 3 -E a r l y i n v e s t i g a t o r s (Lee, 1950a, 1950b, 1951; Black, 1951; F a i r b a n k s , 1955) found t h a t DAF slows the r a t e of speech p r o d u c t i o n , i n c r e a s e s v o c a l i n t e n s i t y and funda-mental frequency, and r e s u l t s i n speech e r r o r s such as sub-s t i t u t i o n s , omissions and a d d i t i o n s ; the l a t t e r c o n s i s t p r i m a r i l y of r e p e t i t i o n s (Fairbanks and Guttman, 1958). Such DAF-induced r e p e t i t i o n s have a l s o been termed " a r t i f i -c i a l s t u t t e r " (Lee, 1951). The d e l a y has been v a r i e d e x p e r i m e n t a l l y , and maximal speech d i s t u r b a n c e has been r e p o r t e d a t 180 msec (Black, 1951), and a t 200 msec (Fairbanks, 1955). S t i l l another study r e p o r t s 180 msec to be the maximally d i s t u r b -i n g d e l a y f o r males and 270 msec f o r females (Mahaffey and Stromsta, 1965). I t might be mentioned t h a t c o n s i d e r a b l e i n d i v i d u a l d i f f e r e n c e s e x i s t i n the a b i l i t y t o cope w i t h delayed feedback as w e l l as i n the s t r a t e g i e s employed under such c o n d i t i o n s . C o n s i d e r a b l e v a r i a t i o n from s u b j e c t to s u b j e c t i n the r e s u l t i n g behaviour can be expected. Between-subject comparisons must t h e r e f o r e be viewed with c a u t i o n , p a r t i c u l a r l y s i n c e the measures employed i n most of the p a s t DAF s t u d i e s are of a very g l o b a l nature. Mea-sures of t o t a l r e a d i n g time i n r e l a t i o n to speech u n i t s such as phonemes, s y l l a b l e s , or words c o n t a i n e d i n the read pass-age i m p l i c i t l y e i t h e r assume a uniform slowing of a l l e l e -ments i n the t e s t passage o r a slowing mainly due to i n c r e a s e of a r t i c u l a t o r y e r r o r s . Only what A l l e n (1973) has termed g l o b a l r a t e , t h a t i s , the average r a t e a t which - 4 -phonemes, s y l l a b l e s , and words a r e p r o d u c e d , can be a c c o u n t -ed f o r by such m e a s u r e s . A more d e t a i l e d a n a l y s i s i s needed t o l e a r n a n y t h i n g abou t what A l l e n r e f e r r e d t o as l o c a l r a t e , t h a t i s , " the s p e c i f i c a t i o n o f segment d u r a t i o n s w i t h i n s y l l a b l e s " ( i b i d . , p . 2 2 2 ) . As A l l e n has p o i n t e d o u t , l o c a l r a t e i s p a r t l y a f u n c t i o n o f g l o b a l r a t e . How t h e n does l o c a l r a t e change as a f u n c t i o n o f g l o b a l r a t e ? L i n e a r r e l a t i o n s h i p s can be e x p e c t e d o n l y f o r a n a r r o w r ange o f tempos ( i b i d . , p . 2 2 2 ) . T h i s s t u d y p r o p o s e s t o i n v e s t i g a t e changes i n l o c a l r a t e as a f u n c t i o n o f g l o b a l r a t e , under s y n c h r o n o u s f eedback (SAF) as w e l l as under DAF. O n l y i f g l o b a l r a t e under SAF i s a l t e r e d and t h e e f f e c t s on l o c a l r a t e a r e d e -t e r m i n e d , can t h e e f f e c t s o f D A F - a l t e r e d g l o b a l r a t e on l o c a l r a t e be a s s e s s e d . Chapter 2 LITERATURE REVIEW 2.1 I n t r o d u c t i o n In t h i s s e c t i o n the p e r t i n e n t DAF experiments w i l l be b r i e f l y d e s c r i b e d i n c h r o n o l o g i c a l o r d e r . The r e s u l t s and u n d e r l y i n g assumptions of the experimenters w i l l be d i s c u s s e d i n an attempt a t a s y n t h e s i s of a v a i l a b l e i n f o r m -a t i o n as i t r e l a t e s to the DAF mechanism and p o s s i b l e u n i t s of speech p r o d u c t i o n . 2.2 Experiments A summary i n t a b l e form of the experiments t o be d e s c r i b e d i n the f o l l o w i n g pages can be found i n the appen-d i x (Appendix A ) . Lee (1950a), one of the e a r l i e s t DAF experimenters, f i r s t c a l l e d the method of DAF to the a t t e n t i o n of i n v e s t i -g a t o r s as a means of s t u d y i n g feedback p r o c e s s e s . In h i s own experiments he found t h a t some s u b j e c t s were a b l e to avo i d to some extent the e f f e c t s of DAF, presumably as a r e s u l t of being able t o c o n c e n t r a t e on other feedback sources f o r m o n i t o r i n g purposes. In one experiment Lee (1950b) r e q u i r e d h i s sub-j e c t s t o read a passage f i r s t without delay and then under DAF, while m a i n t a i n i n g a c c u r a t e speech, which he d e f i n e d as speech without r e p e t i t i o n s and speech a t an even r a t e . He suggested t h a t t h i s c o u l d be accomplished by c o o p e r a t i n g - 5 -- 6 -with the slowing down e f f e c t , i n order to "achieve the cadence demanded by the delayed feedback" ( i b i d . , p. 824). Under the DAF c o n d i t i o n s , a l l but one of h i s s u b j e c t s were found to have c o n s i d e r a b l y i n c r e a s e d t o t a l r e a d i n g times from the no-delay c o n d i t i o n . Furthermore, the longer the delay the longer the t o t a l time taken. In a second experiment (Lee, 1950b) s u b j e c t s were asked to repeat as r a p i d l y as p o s s i b l e a s i n g l e s y l l a b l e (three phonemes) 40 times. Again, the t o t a l time r e q u i r e d f o r the r e p e t i t i o n s was longer under DAF. Lee (1951) remarks t h a t h i s s u b j e c t s e i t h e r slow-ed down and spoke with i n c r e a s e d i n t e n s i t y , or when they attempted to ma i n t a i n normal speed, they h a l t e d and repe a t -ed s y l l a b l e s and con t i n u a n t sounds. Black (1951), who had been i n v e s t i g a t i n g DAF e f f e c t s independently of Lee, r e q u i r e d h i s s u b j e c t s t o read a s e r i e s of f i v e f i v e - s y l l a b l e phrases under 11 d i f f e r e n t d e l a y s . The order of p r e s e n t a t i o n of the delay c o n d i t i o n s was r o t a t e d s y s t e m a t i c a l l y among the s u b j e c t s . S u b j e c t s were i n s t r u c t e d to "speak n a t u r a l l y " ( i b i d . , p. 57). I t was found t h a t the mean d u r a t i o n of each s e r i e s of phrases i n c r e a s e d p r o g r e s s i v e l y with an i n c r e a s e i n de l a y up to a de l a y of 180 msec. With longer d e l a y s mean r e a d i n g times decreased again, without, however, approaching the s h o r t e r z e r o - d e l a y d u r a t i o n . - 7 -"The e f f e c t of i n c r e a s i n g the delay from 30 to 60 msec i s p r o p o r t i o n a t e l y g r e a t e r than the e f f e c t of any other comparable 30 msec increment w i t h i n the range of the study" ( i b i d . , p. 60). I n t e n s i t y , based on the mean of 15 peak i n t e n s i -t i e s per c o n d i t i o n (three peaks per p h r a s e ) , i n c r e a s e d p r o g r e s s i v e l y as the d e l a y i n c r e a s e d up to 270 msec. How-ever, the i n c r e a s e s were s i g n i f i c a n t o n l y up to 90 msec. A b r i e f study by Rawnsley and H a r r i s (1954) of the nature of the a r t i f i c i a l s t u t t e r r e v e a l e d , based on s p e c t r o g r a p h i c a n a l y s i s , t h a t the f i r s t s y l l a b l e to be repeated l a t e r , l a c k e d the expected t r a n s i t i o n t o the next s y l l a b l e , whereas the f i n a l repeated s y l l a b l e showed a l l the t r a n s i t i o n a l p r o p e r t i e s of the c o r r e s p o n d i n g segment under SAF. Fairbanks (1955) r e q u i r e d h i s s u b j e c t s to read a passage f i r s t without d e l a y and then a t f o u r d e l a y s p r e -sented i n random o r d e r . Each s u b j e c t was i n s t r u c t e d to "read as you u s u a l l y do" ( i b i d . , p. 335) and was f a m i l i a r -i z e d w i t h the passage and w i t h DAF p r i o r t o the experiment. R e s u l t s showed t h a t more e r r o r s (each i n s t a n c e of e r r o r r e g a r d l e s s of l e n g t h or nature was t a l l i e d as one e r r o r ) were made and longer t o t a l d u r a t i o n s with and without pauses o b t a i n e d i n the 200-msec d e l a y c o n d i t i o n than i n any other c o n d i t i o n s . V o c a l sound p r e s s u r e (mean of g r a p h i c peaks, re the same a r b i t r a r y r e f e r e n c e f o r a l l samples) was i n c r e a s e d i n the DAF c o n d i t i o n s by 10 to 12 dB on the average . There was no s u b s t a n t i a l change i n sound p r e s s u r e - 8 -i n c r e a s e s over the range of time d e l a y s s t u d i e d . S i m i l a r l y , fundamental frequency i n c r e a s e d as a f u n c t i o n of DAF, but changed l i t t l e as a f u n c t i o n o f d e l a y i n t e r v a l . The i n -crease ammounted to "about t h r e e and one-half semitones" ( i b i d . , p. 341). Fair b a n k s termed a r t i c u l a t o r y errors, and i n c r e a s e d d u r a t i o n " d i r e c t e f f e c t s " and mean sound pr e s s u r e and fundamental frequency i n c r e a s e s " i n d i r e c t e f f e c t s " ( i b i d . , p. 3 4 1 ) , on the b a s i s of t h e i r d i f f e r e n t f u n c t i o n s . In a d d i t i o n , the r a t e of a r t i c u l a t o r y e r r o r and c o r r e c t word r a t e was p l o t t e d as a f u n c t i o n of d e l a y t o a r e l a t i v e r a t e o r d i n a t e , "using the mean r a t e s f o r the un-delayed c o n d i t i o n as r e s p e c t i v e c o n s t a n t s " ( i b i d . , p. 342). I f the s u b j e c t i n c r e a s e d d u r a t i o n y e t made the same amount of e r r o r s under the v a r i o u s delay c o n d i t i o n s , the r a t e of e r r o r decreased as a f u n c t i o n o f d e l a y . I f , on the o t h e r hand, the s u b j e c t i n c r e a s e d h i s e r r o r s as a f u n c t i o n of delay w h i l e d u r a t i o n a l i n c r e a s e s remained constant, then the r a t e of e r r o r i n c r e a s e d as a f u n c t i o n of d e l a y . I f e r r o r and d u r a t i o n both were to i n c r e a s e p r o p o r t i o n a t e l y , the e r r o r r a t e f u n c t i o n would be a f l a t one. Thus, the i n t e r a c t i o n of e r r o r and d u r a t i o n i s r e f l e c t e d i n such a measure. The a c t u a l p l o t t e d f u n c t i o n r e v e a l e d t h a t e r r o r s i n c r e a s e d more at 200 msec than a t any other d e l a y . The p l o t was based on means. Study of i n d i v i d u a l r e c o r d i n g s r e v e a l e d t h a t - 9 -" t o t a l d i s t u r b a n c e i n a g i v e n sample i n v o l v e d i n many cases a seeming com-promise with the i n t e r f e r e n c e , i n which d u r a t i o n was 'traded' f o r a r t i c u l a t i o n , or v i c e v e r s a , but i n p r o p o r t i o n s t h a t v a r i e d from case to case" ( i b i d . , p. 343). The r a t i o of c o r r e c t words per time u n i t decreases i f e i t h e r t o t a l d u r a t i o n i s i n c r e a s e d , or number of c o r r e c t words decreased. In such a measure numerator and denominator do not tend to c a n c e l each o t h e r . F a i r b a n k s , t h e r e f o r e , s u g -gested the f o l l o w i n g measure of DAF d i s t u r b a n c e , however, with the o b j e c t i v e t h a t i n t e r c o m p a r i s o n of d i f f e r e n t t e x t s c o u l d be made more o b j e c t i v e l y : II W D I = C n  X WD ' t o where Wc i s o b t a i n e d number of c o r r e c t words, D n i s normal d u r a t i o n , W^. i s t o t a l number of words, and D Q i s o b t a i n e d d u r a t i o n , Dn/Wt being a constant f o r the t e x t " ( i b i d . , p. 344). The experimental data o b t a i n e d i n the p r e v i o u s l y d e s c r i b e d study (Fairbanks, 1955) were f u r t h e r t r e a t e d by F a i r b a n k s and Guttman (1958) as f o l l o w s : three a d d i t i o n a l sentences of the passage were analyzed as before and r e -s u l t s d e s c r i b e d to be i n agreement with the p r e v i o u s l y r e -p o r t e d f i n d i n g s . E r r o r s of a r t i c u l a t i o n were l o c a t e d and a s s i g n e d to one of the f o l l o w i n g c a t e g o r i e s : s u b s t i t u t i o n , o mission, a d d i t i o n , p l u s a m i s c e l l a n e o u s category. R e s u l t s showed t h a t "number of i n s t a n c e s of e r r o r v a r i e d s u b s t a n t i a l l y w i t h both d e l a y i n t e r v a l and type of e r r o r " ( i b i d . , p. 21). - 10 -The number of d i s t u r b a n c e s of c e r t a i n types were r e l a t e d t o s p e c i f i c v a l u e s of de l a y , i . e . , the types of e r r o r s were present i n d i f f e r e n t p r o p o r t i o n s f o r d i f f e r e n t d elay i n t e r -v a l s . I t i s of i n t e r e s t t h a t d u r i n g the 200-msec delay con-d i t i o n , a d d i t i o n s were most numerous, 70% being c l a s s i f i e d as r e p e t i t i o n s . The l e n g t h of e r r o r (number of phonemes omitted, s u b s t i t u t e d , e t c . , i n any one i n s t a n c e of e r r o r ) was a l s o i n v e s t i g a t e d . There were more s u b s t i t u t i o n s and r e p e t i t i o n s i n v o l v i n g two to f o u r or more phonemes and three to ten phonemes r e s p e c t i v e l y i n the 4 00 msec de l a y c o n d i t i o n than i n any oth e r c o n d i t i o n . However, e r r o r s i n v o l v i n g fewer phonemes oc c u r r e d more f r e q u e n t l y and were found to be most numerous i n the 200-msec de l a y c o n d i t i o n . A d e s c r i p t i o n of the DAF l i t e r a t u r e would not be complete without mention of the f o l l o w i n g study by Chase (1958): i n the f i r s t of two c o n d i t i o n s , Chase asked h i s s u b j e c t s t o repeat the sound [b] "as q u i c k l y as p o s s i b l e " ( i b i d . , p. 585) a t zero d e l a y , s t a r t i n g a t a gi v e n s i g n a l and s t o p p i n g a t a s i g n a l a f t e r f i v e seconds. In the second c o n d i t i o n a 216-msec delay i n t e r v a l was i n t r o d u c e d . R e s u l t s showed t h a t 15 of h i s 20 s u b j e c t s repeated the sound from two to seven more times under the d e l a y c o n d i t i o n than under the SAF c o n d i t i o n . A much more d e t a i l e d study of DAF e f f e c t s than had been c a r r i e d out up to t h i s time was attempted by Kozhevnikov and C h i s t o v i c h (1965). F i v e s u b j e c t s were r e q u i r e d to r e c i t e ten p r e v i o u s l y l e a r n e d phrases o f about 14-25 speech - 11 -sounds each twice under SAF c o n d i t i o n s and at f o u r d i f f e r e n t d e l a y s . The f o l l o w i n g parameters were recorded by means of an o s c i l l o g r a p h : c o n t a c t between l i p s , v o i c e , c o n t a c t of the tongue wi t h an a r t i f i c i a l p a l a t e at three p o i n t s i n the a l v e o l a r and a l v e o p a l a t a l r e g i o n s . A phoneme-per-second measure r e v e a l e d t h a t the 150-300 msec range produced max-imum i n c r e a s e s i n d u r a t i o n ; however, s u b j e c t s d i f f e r e d g r e a t l y from each ot h e r i n terms of the d e l a y which pro-duced maximum d i s t u r b a n c e and i n terms of the magnitude of the d i s t u r b a n c e . For one s u b j e c t almost no d u r a t i o n a l i n -creases were found. F u r t h e r a n a l y s i s was t h e r e f o r e based on the f o u r s u b j e c t s who were a f f e c t e d by DAF. An examin-a t i o n of the o s c i l l o g r a m s r e v e a l e d " m u l t i p l e c l o s i n g and opening of one and the same c o n t a c t s i n s t e a d of t h e i r one-time c l o s i n g and opening as i n the normal speech" ( i b i d . , p. 145) f o r a l l v a l u e s of d e l a y . P e r c e p t u a l l y , the r e s u l t was a sequence of open s y l l a b l e s . R e p e t i t i o n s of longer speech u n i t s were a l s o observed, the m a j o r i t y o c c u r r i n g a t a delay of 470 msec. Such a repeated longer u n i t was r e p o r t e d to have been accompanied a t times by m u l t i p l e r e p e t i t i o n s of s h o r t e r segments, i . e . , by the m u l t i p l e c l o s i n g and opening d e s c r i b e d above. F u r t h e r a n a l y s i s r e v e a l e d t h a t the d u r a t i o n s of c o n t a c t c l o s u r e and c o n t a c t opening d i d not change as a f u n c t i o n of d e l a y i n t e r v a l , but were approximately c o n s t a n t - 12 -under DAF c o n d i t i o n s . The d u r a t i o n s of c l o s u r e and opening were approximately the same. When the number of c l o s i n g -opening movements of the same c o n t a c t s i n v o l v e d i n any one i n c i d e n c e of r e p e t i t i o n (provided a t l e a s t two such c l o s -ing-opening movements o c c u r r e d i n one such i n c i d e n c e ) were counted, i t was found t h a t the number i n c r e a s e d with an i n -crease i n de l a y . T o t a l d u r a t i o n measures d i d not r e f l e c t t h i s f a c t s i n c e p r o l o n g a t i o n o f a sound was a l s o found to le a d to a decrease i n m u l t i p l e r e p e t i t i o n s . The t r a n s i t i o n from c l o s i n g to opening was found to be the onl y aspect of speech not delayed under DAF. More complex sequences of consonants (C) and vowels (V), i f a l t e r e d by DAF, were found changed as f o l l o w s : " CVC = CV + CX CCV = CX + CV CVCC = CV + CX + CX where X i s a reduced vowel" ( i b i d . , p. 156). Even i f the consonant was v o i c e l e s s , the opening of the c l o s u r e was accompanied by v o i c i n g . F i n a l vowels i n a s e r i e s of r e p e t i t i o n s were found to be of longer d u r a t i o n and to c o i n c i d e with d u r a t i o n s under normal feedback c o n d i t i o n s . The d u r a t i o n s of non-f i n a l vowels i n a s e r i e s of r e p e t i t i o n s were found t o be f a i r l y c o nstant and u n r e l a t e d to d u r a t i o n s of vowels i n normal feedback c o n d i t i o n s . In each study, i n which an attempt was made to p l a c e a value on the maximally d i s t u r b i n g d e l a y , i n d i v i d u a l d i f f e r e n c e s have been a c o n s i d e r a b l e source of v a r i a n c e . - 13 -MacKay (1968) hypothesized t h a t speech r a t e might be c o r r e l -ated w i t h the de l a y i n t e r v a l producing maximum d i s t u r b a n c e (peak s h i f t h y p o t h e s i s ) . In one of a s e r i e s of s t u d i e s he asked a d u l t s u b j e c t s t o repeat sentences a t a maximally f a s t , slow, and very slow r a t e o f speech under two de l a y c o n d i t i o n s . Number of e r r o r s ( r e p e t i t i o n s ) was chosen as the dependent v a r i a b l e . His r e s u l t s d i d not c o n f i r m the peak s h i f t h y p o t h e s i s : there were p r o p o r t i o n a t e l y fewer e r r o r s w i t h d i m i n i s h i n g r a t e s f o r both delay v a l u e s . However, i n another experiment i n the same s e r i e s of experiments when s u b j e c t s repeated sentences a t a max-imum r a t e of speech w i t h no delay and a t f i v e d e l a y v a l u e , the peak s h i f t h ypothesis was confirmed: i t was found t h a t the s u b j e c t s w i t h the f a s t e s t r a t e of speech under the SAF c o n d i t i o n e x h i b i t e d the fewest r e p e t i t i o n s under DAF. The leng t h of de l a y producing maximal d i s r u p t i o n , as c a l c u l a t e d from a c o r r e c t s y l l a b l e i n t e r v a l ( i n seconds per s y l l a b l e ) , was found to be r e l a t e d to the maximum r a t e of speech i n the SAF c o n d i t i o n . "The slower a s u b j e c t ' s maximum r a t e of speech, the longer h i s c r i t i c a l DAF i n t e r v a l . " ( i b i d . , p. 819). What l i t t l e i s known about l o c a l r a t e under DAF to t h i s date i s due p r i m a r i l y to the i n v e s t i g a t i o n s o f Huggins (1968). The t e s t m a t e r i a l i n t h i s study c o n s i s t e d of two sentences, one c o n t a i n i n g o n l y s h o r t vowels, the other c o n t a i n i n g o n l y long vowels, both preceded by a s h o r t u t t e r a n c e s e r v i n g as a frame. The s u b j e c t was f a m i l i a r i z e d - 14 -w i t h DAF p r i o r t o t h e e x p e r i m e n t a l r e a d i n g s and i n s t r u c t e d t o "speak as f l u e n t l y as s h e c o u l d , and t o t r y n o t t o p a u s e i n t h e m i d d l e o f a s e n t e n c e . " ( i b i d . , p. 5 4 ) . She had be-f o r e h e r a V.U. m e t e r and was t o l d t o m a i n t a i n t h e same c o n -s t a n t s p e a k i n g l e v e l i n b o t h , n o r m a l and d e l a y , c o n d i t i o n s . The s e n t e n c e s were r e a d 20 t i m e s a t z e r o d e l a y and t h e n o nce e a c h a t 33 v a l u e s o f d e l a y and f i n a l l y a g a i n a t z e r o d e l a y . When t h e t o t a l d u r a t i o n o f e a c h s e n t e n c e p r o d u c -t i o n was p l o t t e d as a f u n c t i o n o f d e l a y i n t e r v a l , s e v e r a l p e a k s o f d i s t u r b a n c e f o r b o t h s e n t e n c e s were e v i d e n t . The h i g h e s t p e a k s f o r t h e s e n t e n c e w i t h t h e l o n g e r s y l l a b l e s (mean s y l l a b l e d u r a t i o n 310 msec a t z e r o d e l a y ) o c c u r r e d a t a l o w e r v a l u e o f d e l a y t h a n t h e h i g h e s t peak f o r t h e s h o r t e r s y l l a b l e s e n t e n c e (mean s y l l a b l e d u r a t i o n 160 msec a t z e r o d e l a y ) . F i n e a n a l y s i s c o n s i s t e d o f m e a s u r i n g t h e d u r a t i o n o f e v e r y a c o u s t i c segment i n e a c h s e n t e n c e a t z e r o d e l a y and a t 12 v a l u e s ' o f d e l a y f r o m s p e c t r o g r a m s . I t was f o u n d t h a t " t h e d u r a t i o n o f some segments was e q u a l t o , o r e v e n s h o r t e r t h a n , t h e d u r a t i o n w i t h z e r o d e l a y " ( i b i d . , p. 5 6 ) ; (/t/ i n / s i l i / ) . The d u r a t i o n s o f u n s t r e s s e d s y l l a b l e segments t e n d e d t o r e m a i n c o n s t a n t as t h e d e l a y c h a n g e d , w h i l e t h e d u r a t i o n s o f o t h e r segments grew l i n e a r l y w i t h t h e d e l a y ( i n i t i a l and f i n a l / s / and ///, c l o s u r e o f i n i t i a l v o i c e l e s s s t o p s , / ! / and / r / i n i n t e r v o c a l i c - 15 -p o s i t i o n i n a s t r e s s e d s y l l a b l e , long vowels i n s t r e s s e d s y l l a b l e s , s h o r t vowels, i n the l a s t s y l l a b l e b e f o r e a term-i n a l j u n c t u r e ) . " S t i l l other segments had a d u r a t i o n t h a t d i d not change as the delay was changed, but was about 6 0 msecs longer than the d u r a t i o n with zero d e l a y " ( i b i d . , p. 56); (occurred with a l l phones, sometimes i n a d d i t i o n to the l i n e a r i n c r e a s e ) . A t o t a l of 48 r e p e t i t i o n s i n a l l s h o r t sentences and 19 r e p e t i t i o n s i n a l l long sentences were counted, most of which o c c u r r e d a t 180, 240, and 360 msec. Dur a t i o n of the repeated segments, which were measured and analyzed s e p a r a t e l y , c o r r e l a t e d h i g h l y w i t h l e n g t h of d e l a y . An attempt was made r e c e n t l y by F l e t c h e r and Yates (1971) to r e p l i c a t e the e a r l i e r d e s c r i b e d experiment by Chase (1958). However, F l e t c h e r and Yates used a high e r feedback l e v e l and onl y approximately the same de l a y v a l u e s . Subjects had no p r i o r experience w i t h DAF; ( i t i s not known i f the s u b j e c t s i n Chase's study were naive w i t h r e s p e c t t o DAF). S u b j e c t s were r e q u i r e d to repeat each sound c o r r e c t -l y a f t e r the experimenter and were i n s t r u c t e d to repeat the sounds as q u i c k l y as p o s s i b l e but e x a c t l y as p r a c t i c e d . Speed was termed "important" i n the i n s t r u c t i o n s and accu r -acy " v i t a l " ( F l e t c h e r and Yates, 1971, p. 75). The e x p e r i -ment was a l s o extended to i n c l u d e r e p e t i t i o n s of 19 other consonants besides [b]. R e s u l t s showed t h a t s u b j e c t s repeated sounds fewer times under DAF, a c o n t r a d i c t i o n of the r e s u l t s r e p o r t e d by Chase. - 16 -In order t o reduce f a t i g u e e f f e c t s and to see i f s i m i l a r r e s u l t s c o u l d be o b t a i n e d f o r vowels, two f u r t h e r experiments were conducted. Only 12 consonants were r e p e a t -ed i n the f i r s t one and 12 vowels i n the second one. Sub-j e c t s were gi v e n p r a c t i c e i n r e p e a t i n g the sounds as q u i c k l y as p o s s i b l e p r i o r to the experimental c o n d i t i o n . Again the sounds t e s t e d were found to be repeated fewer times under DAF. A f u r t h e r experiment was designed i n which h a l f of the s u b j e c t s were t r a i n e d to repeat sounds under SAF c o n d i t i o n s a t s i x sounds per second (mean r a t e of Chase's (1958) s u b j e c t s ) , and the ot h e r h a l f t r a i n e d to repeat sounds at three sounds per second (mean r a t e of s u b j e c t s i n the l a s t two experiments d e s c r i b e d above). Loud c l i c k s were used to pace the s u b j e c t . I t was expected t h a t f a s t s u b j e c t s would become f a s t e r under DAF and slow s u b j e c t s slower under DAF. However, no s i g n i f i c a n t d i f f e r e n c e s were found between the two groups. The r e s e a r c h e r s up to t h i s p o i n t had not i n v e s t i -gated the behaviour of a s p e c i f i p speech a r t i c u l a t o r under a u d i t o r y d e l a y . R e a l i z i n g the need f o r such a study, Sussman and Smith (1971) designed an experiment to i n v e s t i -gate such s p e c i f i c aspects of DAF behaviour. S u b j e c t s , naive w i t h r e s p e c t t o DAF, were r e q u i r e d t o repeat the c a r r i e r phrase " t h a t ' s a CVC month", i n which the vowels / i / , /e/ and / were embedded. The phrases were repeated three times each at zero delay and a t fo u r magnitudes of - 17 -d e l a y . Jaw movements of the s u b j e c t s were recorded by means of a s t r a i n - g a u g e t r a n s d u c e r . R e s u l t s were as f o l l o w s : extent of jaw opening f o r the vowels d i d not change s i g n i f i c a n t l y as a f u n c t i o n of delay c o n d i t i o n . However, v i s u a l i n s p e c t i o n of the g r a p h i c records r e v e a l e d "a s l i g h t , but r a t h e r c o n s i s t e n t , i n c r e a s e i n jaw lowering under the 300 msec delay f o r /e/ and /ae/ vowel c o n t e x t s " ( i b i d . , p. 689). D u r a t i o n of jaw a c t i v i t y f o r each vowel context was s i g n i -f i c a n t l y longer under the 100-msec c o n d i t i o n . The l o n g e s t d u r a t i o n s a t a l l values of delay were recorded f o r the / i / vowel sentence. At a delay of 400 msec, jaw a c t i v i t y again approached d u r a t i o n s recorded under zero d e l a y . Opening and c l o s i n g v e l o c i t y of jaw movements was o n l y s l i g h t l y changed as a f u n c t i o n of d e l a y . However, though not s t a t i s t i c a l l y s i g n i f i c a n t , jaw opening v e l o c i t y f o r /e/ and /ae/ was g r e a t e s t at the 3 00-msec d e l a y . For /ae / the jaw c l o s i n g v e l o c i t y as w e l l was g r e a t e s t at 300 msec d e l a y . "The c h a r a c t e r i s t i c a l l y g r e a t e r c l o s u r e v e l o c i t y d u r i n g the open vowel context was e v i d e n t o n l y f o r the normal and 100 msec delay c o n d i t i o n s . Though there was a tendency f o r jaw c l o s u r e v e l o c i t i e s t o i n c r e a s e as a f u n c t i o n of vowel openness, the a u d i t o r y delay a l t e r e d the r e l a t i v e v e l o c i t y r e l a t i o n s h i p s of opening to c l o s i n g jaw movements, such t h a t jaw opening v e l o c i t i e s were g r e a t e r under delayed feedback c o n d i t i o n s as compared to jaw c l o s i n g v e l o c i t i e s . " ( i b i d . , p. 690). Recently another attempt was made a t r e l a t i n g speech r a t e to maximally d i s t u r b i n g d e l a y . Robinson (1972) - 18 -c o n t r o l l e d s p e e c h r a t e by p r o v i d i n g e x t e r n a l p a c i n g . Sub-j e c t s were r e q u i r e d t o c o u n t a l o u d f l a s h e s o f l i g h t s and were " c a r e f u l l y i n s t r u c t e d t o e n u n c i a t e e a c h number c l e a r l y and e v e n l y and t o t r y t o make t h e number l a s t as l o n g as t h e l i g h t s t a y e d on" ( i b i d . , p. 2 ) . F i v e s e r i e s o f 50 f l a s h e s were p r e s e n t e d a t e a c h o f e i g h t d i f f e r e n t f l a s h r a t e s . W i t h i n e a c h s e r i e s t h e f l a s h r a t e was c o n s t a n t , and b e g i n n i n g w i t h f l a s h number 21 o f e a c h s e r i e s t h e s u b j e c t h e a r d h i s own v o i c e d e l a y e d . F i v e d i f f e r e n t d e l a y s were u s e d . A w h i t e - n o i s e s p e c t r u m r e s t r i c t -ed t o t h e f r e q u e n c y band o f human s p e e c h o f a b o u t 6 0 dB SPL a c c o m p a n i e d t h e a u d i t o r y f e e d b a c k s i g n a l d u r i n g t h e e n t i r e e x p e r i m e n t i n o r d e r t o mask bone c o n d u c t i o n . A n a l y -s i s c o n s i s t e d o f c o u n t i n g a r t i c u l a t o r y e r r o r s a c c o r d i n g t o a s c o r i n g s y s t e m i n w h i c h e a c h s p o k e n number had a p o t e n t -i a l e r r o r s c o r e o f t h r e e . A s i g n i f i c a n t i n t e r a c t i o n be-tween s p e e c h r a t e and d e l a y was f o u n d . A l o n g e r d e l a y p r o -d u c e d a maximum number o f e r r o r s a t a s l o w e r s p e e c h r a t e w h i l e a s h o r t e r d e l a y p r o d u c e d a maximum number o f e r r o r s a t a f a s t e r s p e e c h r a t e . The a r t i c u l a t i o n s c o r e f u n c t i o n i s a p p r o x i m a t e l y l i n e a r . 2.3 D i s c u s s i o n O b v i o u s l y , n o t a l l o f t h e r e s u l t s o b t a i n e d by t h e DAF e x p e r i m e n t e r s a r e i n a g r e e m e n t . Chase f o u n d t h a t [b] c o u l d be r e p e a t e d f a s t e r u n d e r DAF, y e t F l e t c h e r and Y a t e s - 19 -f o u n d t h e i r s u b j e c t s were r e p e a t i n g s i n g l e s p e e c h sounds fewer t i m e s u n d e r DAF. MacKay d i d n o t f i n d a 'peak s h i f t ' as a r e s u l t o f s p e e c h r a t e c h a n g e s , whereas R o b i n s o n d i d . N e i t h e r F a i r b a n k s and Guttman n o r H u g g i n s e n c o u n t e r e d t h e m u l t i p l e r e p e t i t i o n s so c h a r a c t e r i s t i c o f t h e s u b j e c t s i n t h e K o z h e v n i k o v and C h i s t o v i c h s t u d y . Sussman and S m i t h d i d n o t f i n d t h a t t h e 200-msec d e l a y v a l u e p r o d u c e d a u n i v e r s a l d i s r u p t i v e e f f e c t on a l l a s p e c t s o f jaw movement as w o u l d have been p r e d i c t e d by t h e F a i r b a n k s ' m a x i m a l d i s -t u r b a n c e f u n c t i o n s . Can t h e s e s e e m i n g l y c o n t r a d i c t o r y f i n d -i n g s be e x p l a i n e d i n terms o f d i f f e r e n t p l a y b a c k l e v e l s , s u b j e c t i n s t r u c t i o n , i n h e r e n t s u b j e c t v a r i a b i l i t y , m e a sures employed i n t h e a n a l y s i s , o r e v e n i n t e r m s o f i n t e r p r e t a t i o n o f r e s u l t s ? An a t t e m p t w i l l be made t o r e s o l v e some o f t h e d i s c r e p a n c i e s i n a r e v i e w of. some p e r t i n e n t a s p e c t s o f e x p e r i m e n t a l d e s i g n and o f t h e u n d e r l y i n g a s s u m p t i o n s o f t h e e x p e r i m e n t e r s . Amount o f a m p l i f i c a t i o n o f t h e d e l a y e d s i g n a l has been shown by Chase and G u i l f o y l e ( 1 9 6 2 ) , among o t h e r s , t o be an i m p o r t a n t v a r i a b l e i n t h e d e g r e e o f d i s t u r b a n c e p r o d u c e d by DAF, i . e . , w i t h i n c r e a s i n g i n t e n s i t y o f t h e d e l a y e d f e e d b a c k s i g n a l , i n c r e a s e s i n d i s t u r b a n c e o c c u r . However, as F a i r b a n k s (1955) has p o i n t e d o u t , some e x p e r i -m e n t e r s s u c h as B l a c k (1951) h e l d t h e i n t e n s i t y o f t h e f e e d b a c k s i g n a l a p p r o x i m a t e l y c o n s t a n t a t t h e e a r p h o n e s by e m p l o y i n g volume l i m i t e r s , whereas o t h e r s , s u c h as F a i r -b anks (1955) h i m s e l f , a m p l i f i e d t h e v o c a l o u t p u t by a - 20 -s p e c i f i e d amount by a d j u s t i n g the g a i n of the playback amp-l i f i e r . I f volume l i m i t e r s are used, an i n c r e a s e i n v o c a l i n t e n s i t y would r e s u l t i n a high e r l e v e l of undelayed f e e d -back s i n c e the a m p l i f i e d delayed s i g n a l would be l i m i t e d by the s e t t i n g of the volume l i m i t e r . In such a system a c o u s t i c segments wi t h a high e r i n t r i n s i c i n t e n s i t y are p o s s i b l y l e s s s u b j e c t to DAF i n t e r f e r e n c e than those acous-t i c segments with a lower i n t r i n s i c i n t e n s i t y . In any event, as Fairbanks (1955, p. 337) p o i n t e d out, n o n l i n e a r i t i e s of the response can be expected, though a very h i g h s e t t i n g of the volume l i m i t e r would minimize any such n o n l i n e a r i t i e s . I f , on the other hand, v o c a l output i s a m p l i f i e d by a spec-i f i e d amount and no c e i l i n g p l a c e d on the a m p l i f i e d f e ed-back s i g n a l , then v o c a l output i n t e n s i t y i s approximately l i n e a r l y r e l a t e d to feedback s i g n a l i n t e n s i t y . The d i f -f i c u l t y i n t h i s system e x i s t s i n f i n d i n g a s e t t i n g high enough not to l i m i t v o c a l output by approaching p a i n t h r e s -h o l d l e v e l s , or not to overmodulate the tape. In view of these c o n s i d e r a t i o n s can any of the above mentioned c o n f l i c t i n g r e s u l t s be e x p l a i n e d i n terms of type and amount of a m p l i f i c a t i o n ? Chase d i d not amp-l i f y h i s s i g n a l by as much as F l e t c h e r and Yates. Does t h i s imply t h a t the s u b j e c t w i t h a l e s s e r amount of delayed feedback a v a i l a b l e t o him w i l l ' s t u t t e r ' r a t h e r than pro-long? The q u e s t i o n w i l l be d i s c u s s e d below i n terms of speech p r o d u c t i o n and DAF i n t e r f e r e n c e mechanisms. Kozhevnikov and C h i s t o v i c h kept the l e v e l of the feedback - 21-s i g n a l c o n s t a n t at the earphones, but they used such a h i g h ' s e t t i n g t h a t s u b j e c t s can not be expected to have had any undelayed a u d i t o r y feedback a v a i l a b l e t o them. Kozhevnikov and C h i s t o v i c h themselves e x p l a i n e d the m u l t i -p l e r e p e t i t i o n s i n terms of the high l e v e l of feedback. However, Huggins 1 s u b j e c t performed under a l e v e l of d e l a y -ed feedback not much lower than t h a t employed i n the Kozhevnikov and C h i s t o v i c h study but d i d not produce m u l t i -p l e r e p e t i t i o n s . As Huggins p o i n t s out, t h i s type of ex-p l a n a t i o n i s inadequate. Huggins, o f f e r i n g an a l t e r n a t i v e e x p l a n a t i o n , suggested t h a t perhaps speakers of Russian per-form d i f f e r e n t l y from speakers of E n g l i s h . Yet, he remarks t h a t such a s o l u t i o n i s even l e s s l i k e l y than the s o l u t i o n based on the d i f f e r e n t i n t e n s i t i e s of the feedback s i g n a l . In view bf the l a c k of data, however, such a hypothesis remains to be t e s t e d . Huggins a r r i v e d a t the c o n c l u s i o n t h a t the most l i k e l y cause of m u l t i p l e r e p e t i t i o n s , both i n the Chase, and Kozhevnikov and C h i s t o v i c h s t u d i e s i s the se t adopted by the s u b j e c t s , i . e . , does the s u b j e c t know the purpose of the experiment? Huggins appears t o have a r r i v e d at t h i s c o n c l u s i o n because he h i m s e l f c o u l d produce such m u l t i p l e r e p e t i t i o n s at w i l l , y e t had not encountered them i n h i s s u b j e c t s . Huggins seems to be su g g e s t i n g t h a t sub-j e c t s u s u a l l y r e s i s t producing m u l t i p l e r e p e t i t i o n s . T h i s h ypothesis w i l l be debated f u r t h e r i n a d i s c u s s i o n of the u n d e r l y i n g assumptions of the experimenters. Before proceeding w i t h t h i s d i s c u s s i o n , one f u r t h e r - 22 -p o s s i b l e e x p l a n a t i o n f o r the frequent m u l t i p l e r e p e t i t i o n s i n the Kozhevnikov and C h i s t o v i c h study suggests i t s e l f . Although i t has not been c o n s i d e r e d by the experimenters mentioned thus f a r , the a r t i f i c i a l p a l a t e c o u l d have been r e s p o n s i b l e i n t h a t i t e l i m i n a t e d a p o r t i o n of the t a c t i l e feedback, thus r e d u c i n g the undelayed n e u r a l feedback a v a i l a b l e f o r c o n t r o l and c a u s i n g what Fairbanks termed ' u n c o n t r o l l e d o s c i l l a t i o n s ' . Lee conceived the speech mechanism as being "somewhat l i k e a machine gun, r e p e a t i n g a u r a l l y monitored u n i t s as long as the t r i g g e r i s h e l d down" (Lee, 1951, p. 54). He suggested t h a t the a u r a l l y monitored u n i t probably i s the s y l l a b l e , remarking t h a t DAF-induced phoneme r e p e t i -t i o n s were not observed. However, phoneme-by-phoneme mon-i t o r i n g was h y p o t h e s i z e d by Lee to take p l a c e v i a k i n e s t h e -t i c and t a c t i l e channels. Black s i m i l a r l y c o n s i d e r e d " t h a t the d u r a t i o n of the s y l l a b l e may have an important b e a r i n g upon the e f f e c t s of d elayed s i d e - t o n e " (Black, 1951, p. 58). The h y p o t h e s i s was based on the f a c t t h a t the delay of 180 msec (approximately the d u r a t i o n of the s y l l a b l e s produced by B l a c k ' s s u b j e c t s under DAF) r e s u l t e d i n the l o n g e s t r e a d i n g time. Due to the d i s p r o p o r t i o n a t e i n c r e a s e i n r e a d i n g time w i t h an i n c r e a s e i n d e l a y from 30 to 60 msec, Black d i d not exclude the p o s s i b i l i t y t h a t the phoneme may be a monitored u n i t as w e l l . - 23 -Both authors a r r i v e d at s i m i l a r c o n c l u s i o n s v i a d i f f e r e n t o b s e r v a t i o n s . Lee's hypotheses are based on the nature of the d i s t u r b a n c e i t s e l f , whereas Black a r r i v e d a t h i s c o n c l u s i o n s by r e l a t i n g s e l e c t i v e delay i n t e r v a l s to magnitude of d i s t u r b a n c e . B a s i c t o these hypotheses i s a u n i t - b y - u n i t mon-i t o r i n g system, an assumption r e i t e r a t e d by Chase: each produced speech u n i t "feeds back to the speaker and con-t r i b u t e s to the r e l e a s e of the next speech unit"(Chase,1958, p. 584). DAF a f f e c t s the m o n i t o r i n g system such t h a t each speech u n i t tends to c i r c u l a t e one or more times due to the temporal d i s c r e p a n c i e s of v o c a l output and feedback s i g n a l and "changes i n the p h y s i c a l aspects of the speech s i g n a l s themselves" ( i b i d . , p. 588). F a i r b a n k s , commenting on the i d e a of a p o s s i b l e r e l a t i o n s h i p between the maximally d i s t u r b i n g d elay i n t e r -v a l and the d u r a t i o n of c o n v e n t i o n a l speech output u n i t s such as the s y l l a b l e , remarks t h a t the data are meager, and t h a t "the c r i t e r i o n of d i s t u r b a n c e ... i s not y e t e s t a b l i s h e d " (Fairbanks, 1955, p. 342). I n f l u e n c e d by c y b e r n e t i c theory, he conceived of the speaking system as a c l o s e d c y c l e system: "A c l o s e d c y c l e system, or servosystem ... employs feedback of the output to the p l a c e of c o n t r o l , comparison of the output to the i n p u t , and such m a n i p u l a t i o n of the output-producing d e v i c e as w i l l cause the output to have the same func-t i o n a l form as the i n p u t " (Fairbanks, 1954, p. 135). - 24 -One p a r t of the system i s a comparator which r e c e i v e s the feedback s i g n a l s as w e l l as the i n p u t . Here the e r r o r s i g n a l s are c a l c u l a t e d and sent to an e f f e c t o r u n i t v i a a mixer. T h i s mixer determines the e f f e c t i v e d r i v i n g s i g -n a l , which i s then sent to the e f f e c t o r to modify the pro-cess of speech p r o d u c t i o n u n t i l the e r r o r s i g n a l i s zero. The e r r o r s i g n a l may t r a v e l s e v e r a l times around the com-p a r a t o r - m i x e r - e f f e c t o r loop being p r o g r e s s i v e l y reduced u n t i l i t equals zero. An important p a r t of the system i s a storage component which r e c e i v e s i n p u t from the compara-t o r . I t i s able to c a l c u l a t e the time at which the e r r o r w i l l reach zero. The next u n i t of in p u t can t h e r e f o r e be s t a r t e d before the e r r o r s i g n a l reaches zero, so t h a t the e f f e c t o r does not have t o wait f o r a new d r i v i n g s i g n a l . Fairbanks suggested t h a t the u n i t of c o n t r o l , r e f e r r i n g to the u n i t of speech p r o d u c t i o n c o n t r o l , should not be i d e n t i f i e d w i t h any c o n v e n t i o n a l l i n g u i s t i c u n i t s . " I t seems more l i k e l y t h a t the u n i t of c o n t r o l , although r e l a t e d to such u n i t s , i s more fundamental, and t h a t i t may c o n s i s t , at any gi v e n t i m e , o f one or a num-ber of such c o n v e n t i o n a l u n i t s , or of a f r a c t i o n of the s m a l l e s t p h o n e t i c u n i t . " (Fairbanks, 1955, p. 342). He r e f e r r e d to the u n i t as a " s e m i p e r i o d i c , r e l a t i v e l y long, a r t i c u -l a t o r y c y c l e , with a c o r r e l a t e d c y c l e of output." (Fairbanks, 1954, p. 138). Under DAF at any given time delay, the number of c o n t r o l u n i t s which have p e r i o d s c r i t i c a l l y r e l a t e d to the time delay might be i n f e r r e d from the DAF f u n c t i o n s . - 25 -C o n s i s t e n t with the above model i n which each succeeding segment depends on the feedback from the p r e -v i o u s one, Fairbanks and Guttman (1958) prese n t t h e i r view of the DAF i n t e r f e r e n c e mechanism. P e r t i n e n t to t h e i r model i s the f a c t t h a t predominatly double r e p e t i t i o n s o c c u r r e d i n t h e i r d ata. Thus, they o n l y account f o r double r e p e t i -t i o n s and c o n s i d e r t h a t the o c c a s i o n a l m u l t i p l e r e p e t i t i o n s are "uncommon ... p e r s o n - l i n k e d , and g i v e the impression of w i l d and u n c o n t r o l l e d o s c i l -l a t i o n of the v o c a l mechanism" ( i b i d . , p. 20). Fairbanks and Guttman suggest t h a t the primary form o f DAF d i s t u r b a n c e are r e p e t i t i o n s , which are d e s c r i b e d as "automatic responses to m i s i n f o r m a t i o n i n the feedback complex" ( i b i d . , p. 19). A r e p e t i t i o n a u t o m a t i c a l l y r e -s u l t s when the s u b j e c t produced segments A and B and heard A d u r i n g B, thus t r i g g e r i n g another B and t e m p o r a r i l y r e -s t o r i n g normal feedback r e l a t i o n s h i p s . I f the system were not a p e r i o d i c , s u b j e c t s would be expected to produce A B B C C D D e t c . under DAF c o n d i t i o n s . A s i m i l a r mechanism of DAF i n t e r f e r e n c e i s pro-posed by Huggins, which does, however, t r y to account f o r m u l t i p l e r e p e t i t i o n s . Huggins suggests t h a t DAF causes the c o n t r o l mechanism to l o s e i t s 'place' i n the program, i n which case "the t a r g e t a r t i c u l a t i o n of the p r e v i o u s i n s t r u c t i o n i s continued u n t i l the p l a c e i s re-found" (Huggins, 1968, p. 59). I f the c o n t r o l f i n d s i t s p l a c e - 26 -from undelayed sources o f feedback ( e i t h e r n e u r a l or bone-conducted) , then o n l y a s l i g h t l e n g t h e n i n g o c c u r s . I f , on the oth e r hand, the p l a c e i s found from the delayed a u d i t o r y feedback source, "then an e x t r a segment may be i n s e r t e d i n t o the a r t i c u l a t o r y sequence, w i t h d u r a t i o n equal to the del a y " ( i b i d . , p. 59). A necessary c o n d i t i o n f o r such i n s e r t i o n i s probably the s i m i l a r i t y of the produced and monitored delayed s i g n a l , which can o n l y occur i n a r a p i d sequence of a r t i c u l a t i o n s . I f the p l a c e i s re-found d u r i n g a slower sequence of a r t i c u l a t i o n from the delayed source, drawling w i l l o ccur. Huggins has not y e t p u b l i s h e d the promised companion paper i n which he would t r y to d i s -cover "which a r t i c u l a t o r y sequences generate most r e p e t i -t i o n s " ( i b i d . , 1968, p. 59). Thus, the above h y p o t h e s i s remains untested to date. Kozhevnikov and C h i s t o v i c h viewed the DAF-induced r e p e t i t i o n s as w e l l as the p r o l o n g a t i o n s , r e g a r d l e s s o f the c o n d i t i o n s which determine which one of these DAF-induced d i s t u r b a n c e s w i l l o c c ur, as b a s i c a l l y the same phenomenon. They d i s a g r e e d w i t h the c o n c l u s i o n of Fairbanks and Guttman t h a t speech p r o d u c t i o n u n i t s do not c o i n c i d e w i t h any known l i n g u i s t i c u n i t s . I t i s t h i s disagreement which prompted Kozhevnikov and C h i s t o v i c h to c a r r y out t h e i r own DAF i n v e s t i g a t i o n s . As has been s t a t e d p r e -v i o u s l y , Kozhevnikov and C h i s t o v i c h d i d not f i n d m u l t i p l e r e p e t i t i o n s uncommon, i n f a c t they found them t o be the most c l e a r l y expressed e f f e c t of DAF i n t h e i r data. - 27 -C l e a r l y , t h e s e r e p e t i t i o n s had t o be accounted f o r i n an e x p l a n a t i o n o f DAF i n t e r f e r e n c e . K o zhevnikov and C h i s t o v i c h , l i k e F a i r b a n k s and Guttman, found r e p e t i t i o n s o f l o n g e r u n i t s o c c u r i n g more f r e q u e n t l y a t l o n g e r d e l a y s . D i d t h e f a c t t h a t t h e r e p e a t -ed fragments were e x t r e m e l y v a r i e d n e c e s s i t a t e the c o n c l u -s i o n t h a t speech u n i t s s h o u l d not be i d e n t i f i e d w i t h any of the c o n v e n t i o n a l l i n g u i s t i c u n i t s ? K o z h e v n i k o v and C h i s t o v i c h argue t h a t because o f the v a r i a b i l i t y o f t h e s e fragments n o t h i n g can be known from t h e s e r e p e t i t i o n s . F u r t h e r m o r e , m u l t i p l e r e p e t i t i o n s were a t t i m e s superimposed on r e p e t i t i o n s o f l o n g e r f r a g m e n t s , which caused t h e above a u t h o r s t o c o n s i d e r t h a t t h e e f f e c t s may be o f a d i f f e r e n t n a t u r e . R e j e c t i n g F a i r b a n k s ' a s s u m p t i o n s , K o z h e v n i k o v and C h i s t o v i c h proposed t h e f o l l o w i n g model: t h r o u g h t h e a u t o -m a t i c a c t i v i t y o f t h e nervous c e n t e r s w h i c h c o n t r o l t h e a n t a g o n i s t i c muscles o f the l i p s , tongue, and v o c a l c h o rds a C V - s y l l a b l e i s formed. D e l a y i n g t h e a u d i t o r y feedback e x c l u d e s t e m p o r a r i l y the c o n t r o l l i n g i n f l u e n c e s o f t h e h i g h -e r nervous c e n t e r s . I n t h i s model t h e p e r i o d o f f l u c t u a t -i n g c l o s i n g - o p e n i n g movements as a r e s u l t o f DAF would be de t e r m i n e d by t h e a c t i v i t y o f t h e nervous c e n t e r s themselves and n o t by the d e l a y i n t e r v a l . Such a model was d e r i v e d by the above a u t h o r s from a number o f o b s e r v a t i o n s : the f r e q u e n t l y o b s e r v e d l a c k o f c o o r d i n a t i o n between v o c a l f o l d a c t i v i t y and a r t i c u l a t i o n was c o n s i d e r e d e v i d e n c e f o r - 28 -D A F - i n d u c e d f l u c t u a t i o n s i n p a r a l l e l l y o p e r a t i n g c e n t e r s o f a n t a g o n i s t i c m u s c l e s . T h a t DAF o c c u r s a t a r e f l e x l e v e l was d e d u c e d f r o m t h e t r a n s f o r m a t i o n o f t h e CCV s t r u c t u r e s i n t o CV s t r u c t u r e s (on t h e b a s i s o f t h e i r p r e v i o u s r e s e a r c h t h e s e same a u t h o r s h y p o t h e s i z e d , CCV s t r u c t u r e s c o n s t i t u t e one c o h e s i v e u n i t i n t h e h i g h e r c e n t e r s ) . T h u s , i t became n e c e s s a r y t o c o n s i d e r t h a t CV s t r u c t u r e s a r e b a s i c w h i l e more complex c o m b i n a t i o n s s u c h as CCV a r e made up o f CV c o m p l e x e s " o r g a n i z e d so t h a t t h e f o l l o w i n g com-p l e x b e g i n s b e f o r e t h e p r e c e d i n g one i s a b l e t o f i n i s h . " ( K o z h e v n i k o v and C h i s t o v i c h , 1965, p. 1 5 8 ) . F u r t h e r c o n f i r m a t i o n o f t h e open s y l l a b l e as a c o h e s i v e u n i t was p r o v i d e d by t h e f a c t t h a t no s l o w i n g was o b s e r v e d f r o m C t o V b u t o n l y f r o m V t o C. Sussman and S m i t h ' s f i n d i n g t h a t jaw o p e n i n g v e l o c i t y was a t t i m e s e v e n f a c i l i -t a t e d by d e l a y , whereas v e l o c i t y o f jaw c l o s i n g was s l o w e d , seems t o f u r t h e r s u b s t a n t i a t e t h e above h y p o t h e s i s ; (Sussman and S m i t h have n o t r e l a t e d t h e i r f i n d i n g s t o t h e K o z h e v n i k o v and C h i s t o v i c h m o d e l ) . I t must be c o n s i d e r e d a p o s s i b i l i t y , t h o u g h , t h a t t h e Sussman and S m i t h r e s u l t s on E n g l i s h a r e n o t s t r i c t l y c o m p a r a b l e w i t h t h e r e s u l t s o b t a i n e d on R u s s i a n . However, i f K o z h e v n i k o v and C h i s t o v i c h a r e c o r r e c t i n t h e i r a s s u m p t i o n t h a t DAF o p e r a t e s a t a r e f l e x l e v e l and t h a t t h e o p e n i n g - c l o s i n g movements a r e b a s i c t o s p e e c h p r o d u c t i o n and t h a t t h e y c a n be s t u d i e d u n d e r DAF i n t h e t e m p o r a r y a b s e n c e o f h i g h e r c o n t r o l , t h e n t h e p h o n o l o g i c a l s y s t e m o f t h e s p e a k e r w o u l d n o t be a - 29 -c r u c i a l a s p e c t . A c c e p t i n g t h e C V - s y l l a b l e as a c o h e s i v e s t r u c t u r e , i t f o l l o w s t h a t r e p e t i t i o n o f t h e same open s y l l a b l e c o n -s t i t u t e s p r e s e r v a t i o n o f t h e same s t r u c t u r e . S i n c e t h e t i m e o f e x i s t e n c e o f a s t r u c t u r e grew w i t h an i n c r e a s e i n d e l a y , i t was " n e c e s s a r y t o c o n s i d e r t h a t t h e e s s e n c e o f t h e e f f e c t o f t h e d e l a y o f an a c o u s t i -c a l s i g n a l c o n s i s t s n o t o f t h e c a l l i n g o f r e p e a t e d movements b u t i n t h e d e l a y o f t h e t r a n s i t i o n f r o m one s t r u c t u r e o f movements t o a n o t h e r . A c t u a l l y , i n t h e c a s e o f a d e l a y o f t h e a c o u s t i c a l s i g n a l man c a n a r b i t r a r i l y e i t h e r s t u t t e r o r draw o u t t h e s p e e c h . I f he h u r r i e s , s t u t t e r i n g o c c u r s ; i f he t r i e s t o s p eak s l o w l y , t h e s p e e c h i s drawn o u t . How-e v e r , r e g a r d l e s s o f what he d o e s , t h e c hange o f s t r u c t u r e s i s s l o w e d and t h e t i m e o c c u p i e d by t h e p r o n u n c i a t i o n o f t h e p h r a s e i n c r e a s e s . " ( t h i s a u t h o r ' s e m p h a s i s ) ( K o z h e v n i k o v and C h i s t o v i c h , 1965, p. 1 5 5 ) . C r u c i a l t o t h e t h e o r y p r o p o s e d by K o z h e v n i k o v and C h i s t o v i c h i s t h e f a c t t h a t t i m e o f e x i s t e n c e o f a s t r u c t -u r e (number o f r e p e t i t i o n s i n a s e r i e s ) was r e l a t e d t o t h e d e l a y i n t e r v a l . H u g g i n s s t a t e s t h a t d u r a t i o n s o f r e p e a t e d segments i n m u l t i p l e r e p e t i t i o n s i n t h e K o z h e v n i k o v and C h i s t o v i c h s t u d y were n o t r e l a t e d t o t h e d e l a y i n t e r v a l , a f i n d i n g w h i c h he c o n s i d e r e d a l o n g w i t h t h e m u l t i p l e r e -p e t i t i o n s n o t i n a g r e e m e n t w i t h h i s f i n d i n g s . I n v i e w o f t h e above a d v a n c e d h y p o t h e s i s , t h a t m u l t i p l e r e p e t i t i o n s a r e one e x p r e s s i o n o f p r o l o n g a t i o n , i t i s c r u c i a l t h a t t h e l e n g t h o f t h e m u l t i p l e r e p e t i t i o n s , and n o t e a c h segment w i t h i n t h e m u l t i p l e r e p e t i t i o n s be r e l a t e d t o t h e d e l a y - 30 -i n t e r v a l . The seeming contradiction of the Chase, and Fletcher and Yates studies might now be considered. In the former study, subjects exhibited multiple r e p e t i t i o n s ; in the l a t t e r they s l i g h t l y prolonged. Huggins' model would predict that the behaviour of Chase's subjects was governed by the delayed source of feedback, whereas the sub-jects i n the Fletcher and Yates study r e l i e d on undelayed feedback. However, Fletcher and Yates, as has been mention-ed, amplified the feedback signal more than Chase, thus reducing possible undelayed feedback. Huggins' model of undelayed feedback also includes neural feedback. We would have to assume that the Fletcher and Yates subjects r e l i e d e n t i r e l y on neural feedback. Does t h i s imply an inherent difference i n the two sets of subjects, or does i t imply that a higher l e v e l of delayed feedback causes subjects to re l y more on neural feedback? Kozhevnikov and Chistovich used a very high l e v e l of feedback, yet t h e i r subjects per-formed l i k e the Chase subjects. In view of the unusually high number of subjects i n the Fletcher and Yates study i n a l l three experiments, inherent between-subject differences does not appear to be a reasonable explanation either. Huggins, as mentioned previously, believed that the set a subject adopts i s responsible for multiple r e p e t i t i o n s . He mentioned subject knowledge of the purpose of the study as one possible explanation. I t cannot be disputed that i n s t r u c t i o n to the subject influences his attitude. Chase - 31 -s t r e s s e d a c c u r a c y a n d s p e e d . I s i t p o s s i b l e , a s H u g g i n s a p p e a r s t o be i m p l y i n g , t h a t , n o r m a l l y , s u b j e c t s r e s i s t m u l t i p l e r e p e t i t i o n s u n l e s s t h e y b e l i e v e t h a t t h i s i s t h e d e s i r e d b e h a v i o u r i n t h e s t u d y ? I t i s r e a s o n a b l e t o a s s u m e t h a t m u l t i p l e r e p e t i t i o n s c o n s i t u t e a b e h a v i o u r w i t h o u t c o n t r o l . F a i r b a n k s h a d a l r e a d y t e r m e d m u l t i p l e r e p e t i t i o n s ' u n c o n t r o l l e d o s c i l l a t i o n s ' a n d K o z h e v n i k o v a n d C h i s t o v i c h made m o r e e x p l i c i t w h a t i s m e a n t b y ' u n c o n t r o l l e d ' . I t f o l -l o w s , s i n c e e a c h s y s t e m n o r m a l l y s t r i v e s f o r c o n t r o l , t h a t s u b j e c t s c o u l d i n d e e d b y e x p e c t e d t o f i g h t a l o s s o f c o n -t r o l . A s L e e ( 1 9 5 0 a ) a l r e a d y p o i n t e d o u t , m o r e t h a n t w o m i n u t e s o f e x p o s u r e t o DAF i s p h y s i c a l l y t i r i n g . A s u b j e c t t h e n h a s t o b e e i t h e r u n a b l e t o m a i n t a i n c o n t r o l o r w i l l i n g t o l o s e c o n t r o l . D e s p i t e t h e p r e v i o u s d i s c u s s i o n , we a r e n o t n e c -e s s a r i l y c o n f r o n t e d w i t h c o n t r a d i c t o r y r e s u l t s . I f o n e a c c e p t s t h e h y p o t h e s i s o f K o z h e v n i k o v a n d C h i s t o v i c h , m u l t i p l e r e p e t i t i o n o f t h e same s t r u c t u r e c o n s t i t u t e s s l o w -i n g o f t h e s t r u c t u r e a n d p r o l o n g a t i o n o f t h e same s t r u c t u r e a l s o c o n s t i t u t e s s l o w i n g . B e c a u s e t h e r e q u i r e d t a s k i n t h e C h a s e , a n d i n t h e F l e t c h e r a n d Y a t e s e x p e r i m e n t s c o n s i s t e d o f r e p e a t i n g o n e s t r u c t u r e , r e p e t i t i o n o f t h i s o n e s t r u c t -u r e , e i t h e r f a s t o r s l o w , c o n s t i t u t e s s l o w i n g . S i n c e a t r a n s i t i o n t o a new s t r u c t u r e d i d n o t n e e d t o be a c c o m p l i -s h e d , n o t h i n g c a n b e k n o w n f r o m t h e r e s u l t s . L e t u s c o n -s i d e r t h e c a s e w h e r e t h e s u b j e c t s w o u l d b e a s k e d t o r e p e a t t w o s t r u c t u r e s s u c h a s [b] a n d [d] i n r a p i d a l t e r n a t i o n , - 32 -i t b e i n g u n d e r s t o o d t h a t an e p e n t h e t i c vowel c o u l d be p a r t o f each s t r u c t u r e , as i t i s d i f f i c u l t t o say t h e speech sound w i t h o u t such an i n s e r t i o n . The h y p o t h e s i s o f Kozhevnikov and C h i s t o v i c h would p r e d i c t the f o l l o w i n g r e -s u l t s : the s u b j e c t s i n the Chase s t u d y would have produced r a p i d l y [bbbbdddd] (any number, depending on t h e d e l a y ) , but not [bdbdbd]; whereas the s u b j e c t s i n t h e F l e t c h e r and Yates s t u d y would have produced [b"1 b"1 b d"1 d"1 d b"1 b"1 b d"1 d n d ] where an e p e n t h e t i c vowel (at t h e r e l e a s e o f t h e c l o s u r e ) c o u l d a l s o be p r o l o n g e d . Under a s e r i e s o f d e l a y s t h e r e l -a t i v e number of r e p e t i t i o n s o f a s t r u c t u r e produced by t h e former s e t of s u b j e c t s would be r e l a t e d t o t h e r e l a t i v e amount of p r o l o n g a t i o n e x h i b i t e d by the l a t t e r s e t o f sub-j e c t s . Only i f t h e Chase s u b j e c t s would produce [bdbd] i n r a p i d s u c c e s s i o n c o u l d t h e r e s u l t s o f t h e s t u d i e s be con-s i d e r e d c o n t r a d i c t o r y . Why some s u b j e c t s p r e d o m i n a n t l y e x h i b i t one t y p e of s l o w i n g b e h a v i o u r and o t h e r s u b j e c t s t h e o t h e r , o r what de t e r m i n e s t h e o c c u r r e n c e o f b o t h b e h a v i o u r s i n one s u b j e c t a t d i f f e r e n t t i m e s must remain l a r g e l y s p e c u l a t i o n u n t i l more i s known about t h e s e b e h a v i o u r s t h e m s e l v e s , u n t i l t h e i r i n t e r a c t i o n can be more p r e c i s e l y d e s c r i b e d and u n t i l we know more about t h e r e l a t i o n o f t h e s e b e h a v i o u r s t o normal r a t e o f speech and about r a t e o f speech i t s e l f . R obinson c o n c e i v e d t i m i n g i n speech as b e i n g de-pendent on t h e speech i t s e l f as opposed t o a b i o l o g i c a l l y d e t e r m i n e d rhythm. He i n t e r p r e t e d h i s f i n d i n g s as e v i d e n c e - 33 -f o r such a model. As p o i n t e d out e a r l i e r , MacKay d i d not f i n d a peak s h i f t f o r d i s t u r b a n c e with change i n r a t e under DAF. However, s i n c e MacKay only counted r e p e t i t i o n s as e r r o r s and Robinson counted a l l e r r o r s , i n c l u d i n g o missions, t h e i r r e s u l t s are not s t r i c t l y comparable. Robinson a l s o t a l l i e d " s t r i k i n g quavers w i t h i n a vowel" as e r r o r (Robin-son, 1972, p. 2). The d i f f i c u l t y w i t h such a s c o r i n g system i s to decide when a quaver i s s t r i k i n g and when i t i s not. As was al r e a d y f o r e s e e n by Chase, although he was s p e c i f i -c a l l y speaking about r e p e t i t i o n s of phoneme-sized u n i t s , a g r a p h i c speech r e c o r d i n g might be necessary to r e v e a l i f an a c t u a l r e p e t i t i o n took p l a c e (Chase, 1958, p. 589). Thus, many a c t u a l p r o l o n g a t i o n s are p o s s i b l y i n c l u d e d i n Robinson's e r r o r count and many a c t u a l r e p e t i t i o n s might have been missed. One must t h e r e f o r e view Robinson's l i n e a r a r t i c u l a t i o n score f u n c t i o n w i t h some r e s e r v a t i o n s . MacKay, having d i s c o v e r e d t h a t s u b j e c t s w i t h a slower maximum r a t e of speech showed a g r e a t e r tendency to s t u t t e r under DAF than s u b j e c t s with a f a s t e r r a t e of speech, whereas s u b j e c t s v o l u n t a r i l y d e c r e a s i n g t h e i r r a t e under DAF showed a decreased number of r e p e t i t i o n s w i t h d e c r e a s i n g r a t e , suggested d i f f e r e n t mechanisms f o r the normal speech r a t e under SAF and p r o l o n g a t i o n under DAF. A l t e r i n g r a t e under DAF must then be viewed not as a t r u e r a t e change but as a t r a d i n g of one type of slowing f o r another, keeping i n mind t h a t the p r e v i o u s l y e s t a b l i s h e d framework i n which r e p e t i t i o n s are seen as slowing of the - 34 -t r a n s i t i o n from one s t r u c t u r e to the next. Thus, wi t h an i n c r e a s e i n one slowing behaviour (prolongation) a decrease o c c u r r e d i n the other ( r e p e t i t i o n ) . I t appears t h a t the two forms of slowing are mutually e x c l u s i v e behaviours at any one time. Why s u b j e c t s with a slow maximum speech r a t e i n the SAF c o n d i t i o n should e x h i b i t more of the r e p e t i t i v e type slowing cannot be e x p l a i n e d on the b a s i s of the data a v a i l a b l e . In view of the above c o n s i d e r a t i o n s one must s e r i o u s l y r e c o n s i d e r F a i r b a n k s ' (1955) sug g e s t i o n t h a t a r t -i c u l a t o r y e r r o r ( s u b s t i t u t i o n , omission, r e p e t i t i o n ) i s the primary form of DAF d i s t u r b a n c e . In order to assess the i n t e r a c t i o n of the two types of slowing behaviour, a f i n e a n a l y s i s of l o c a l r a t e i s needed. In a d d i t i o n , g l o b a l r a t e must be v a r i e d under SAF as w e l l as under DAF and the e f -f e c t s on l o c a l r a t e assessed. I f slower rate-under DAF can be shown to e x h i b i t d i f f e r e n t slowing p a t t e r n s from slowed r a t e under SAF then MacKay's hypothesis p o s t u l a t i n g d i f f e r e n t mechanisms f o r r a t e changes under SAF as opposed to DAF can be s u b s t a n t i a t e d . A l l e n (1973) has p o i n t e d out t h a t "although speech r a t e and p h o n o l o g i c a l l e n g t h are the major determinants of most segmental d u r a t i o n " ( i b i d . , p. 222), there are neuromuscular and b i o c h e m i c a l c o n s t r a i n t s t h a t are not e n t i r e l y under the c o n t r o l of the h i g h e r nervous c e n t e r s . The i n t e r a c t i o n between p h o n o l o g i c a l l e n g t h and p h o n e t i c d u r a t i o n i s complex. A l l e n ' s diagrammatic speech p r o d u c t i o n - 35 -model c o n t a i n s a s t r u c t u r e d p h o n o l o g i c a l i n p u t i n t o an output b u f f e r . The output b u f f e r p r o v i d e s the i n p u t f o r a speech motor c o n t r o l program ( t r a n s f e r f u n c t i o n ) which determines p a r t l y the a r t i c u l a t o r movements. A l l e n sugg-e s t s t h a t when we measure the output of the system, the v a r i a b i l i t y due to segmental t i m i n g c o n t r o l e r r o r i n the motor c o n t r o l program (speech r a t e v a r i a t i o n ) can be i s o -l a t e d from p e r i p h e r a l v a r i a b i l i t y (neuromuscular and b i o -chemical c o n s t r a i n t s and measurement e r r o r ) . He proposes a s t a t i s t i c a l model to separate these v a r i a n c e components. However, t h i s model can be a p p l i e d o n l y i f the speaker attempts to keep h i s r a t e f i x e d i n the repeated p r o d u c t i o n of the same u t t e r a n c e . How does DAF f i t i n t o A l l e n ' s speech p r o d u c t i o n model? Does DAF operate on the motor c o n t r o l program? Since the segmental t i m i n g c o n t r o l takes p l a c e at t h i s l e v e l , v o l u n t a r i l y slowed speech (the segmental t i m i n g c l o c k i s v o l u n t a r i l y s e t to a slower rate) and DAF-slowed speech (DAF determines the r a t e of the c l o c k ) would e x h i b i t s i m i l a r p a t t e r n s , although perhaps g r e a t e r v a r i a b i l i t y can be expected under DAF i f i t i s assumed t h a t the c l o c k i s slowed whenever i t comes under DAF c o n t r o l and speeds up when i t escapes the DAF i n f l u e n c e ( i . e . , a f t e r a pause). A l l e n p r e d i c t s s p e c i f i c a l l y a g r e a t e r v a r i a b i l i t y of seg-ment d u r a t i o n s when a l o c a l decrease i n c l o c k r a t e takes p l a c e (during s t r e s s e d segments). Although he r e f e r s to repeated u t t e r a n c e of the same phrase keeping the r a t e - 36 -constant, i t should a l s o be t r u e i n a comparison of s t r e s s -ed segments d u r i n g v o l u n t a r i l y slowed speech i f i t i s assumed t h a t , i n both cases, slowing of the segmental t i m i n g c l o c k takes p l a c e , p r o v i d e d the r a t e of the c l o c k does not d i f f e r too much from one c o n d i t i o n t o the o t h e r . However, one cannot be c e r t a i n , even i f such a c l o c k e x i s t s , t h a t DAF operates on segmental t i m i n g c o n t r o l a t the motor con-t r o l programme l e v e l such t h a t the c l o c k i t s e l f i s slowed and l i n e a r i n c r e a s e s i n d u r a t i o n of segments r e s u l t , pro-v i d e d DAF i s e f f e c t i v e a l l the time. I t has a l r e a d y been mentioned t h a t DAF does not a f f e c t the speech p r o d u c t i o n to the same extent from one second t o the next but v a r i e s with undelayed feedback a v a i l a b l e to the speaker at a p a r t i -c u l a r moment. Furthermore, i t i s known t h a t c e r t a i n types of sounds (continuants) are more a f f e c t e d . T h i s f a c t cannot be e x p l a i n e d by a slowing of the n e u r a l c l o c k . I f DAF operates s e l e c t i v e l y on manner of a r t i c u l a t i o n , i t i s reasonable t o assume t h a t DAF i n t e r f e r e s w i t h the e x e c u t i o n of the commands a t a l e v e l below t h a t of the motor c o n t r o l program, i . e . the r e f l e x l e v e l proposed by Kozhevnikov and C h i s t o v i c h (1965). Perhaps DAF i s a c t i v e o n l y a t t h i s l e v e l or i n a d d i t i o n i n t e r f e r e s with segmental t i m i n g c o n t r o l . Study of segment d u r a t i o n s under v o l u n t a r i l y a l t e r e d r a t e and under DAF should p r o v i d e some i n s i g h t s i n t o these q u e s t i o n s . C h a p t e r 3 AIMS OF THE INVESTIGATION I n g e n e r a l , t h i s r e s e a r c h s t u d y i s d e s i g n e d t o i n v e s t i g a t e t h e d u r a t i o n s o f a c o u s t i c s p e e c h segments a t a s p e a k e r ' s n o r m a l r a t e o f s p e e c h , a v o l u n t a r i l y s l o w e d r a t e o f s p e e c h and u n d e r DAF. As has been shown ( C h a p t e r 2 ) , m e asures o f DAF d i s t u r b a n c e have been f o r t h e most p a r t o f a v e r y g l o b a l n a t u r e i n t h e p a s t . A b e t t e r u n d e r s t a n d i n g o f D A F - i n d u c e d s p e e c h d i s t u r b a n c e s b a s e d on a more d e t a i l e d a n a l y s i s c o u l d l e a d n o t o n l y t o new i n s i g h t s i n t o s p e e c h p r o d u c t i o n and t h e r o l e o f a u d i t o r y f e e d b a c k , b u t a l s o p o s s i b l y t o an u n d e r s t a n d i n g o f s t u t t e r i n g as a p a t h o l o g i c a l phenomenon. A r e v i e w o f t h e a v a i l a b l e DAF i n f o r m a t i o n as i t r e l a t e s t o s t u t t e r i n g c a n be f o u n d i n v a n R i p e r (1972, pp. 382-403). A l t h o u g h H u g g i n s (1968) c a r r i e d o u t s u c h a d e t a i l e d a n a l y -s i s , i t r e m a i n s t o be t e s t e d i f t h e p a t t e r n s h i s s u b j e c t s d i s p l a y e d u n d e r DAF a r e u n i v e r s a l l y t r u e , and f u r t h e r m o r e , i t i s n o t c l e a r w h e t h e r t h e s e p a t t e r n s a r e t y p i c a l o f a s l o w e r r a t e o f s p e e c h u n d e r SAF as w e l l as u n d e r DAF. I n o t h e r t e r m s , i f t h e y d i f f e r f r o m v o l u n t a r i l y s l o w e d s p e e c h , how do t h e y d i f f e r ? The e x p e r i m e n t r e p o r t e d h e r e i s d e s i g n e d t o i s o -l a t e t h o s e a s p e c t s o f t h e t e m p o r a l p a t t e r n i n g o f s p e e c h w h i c h a r e s p e c i f i c t o DAF. - 37 -- 38 -S p e c i f i c a l l y , the f o l l o w i n g hypotheses w i l l be t e s t e d : (a) When speech i s slowed v o l u n t a r i l y under SAF, not a l l sounds are prolonged by the same amount. The p i l o t study r e p o r t e d below i n d i c a t e s t h a t i n comparison With speech at a normal r a t e , vowels are prolonged more than consonants. W i t h i n the c l a s s ; - o f vowels, c l o s e vowels are prolonged more than open vowels. W i t h i n the c l a s s of consonants, c o n t i n u a n t s are prolonged more than o b s t r u e n t s . (b) When speech i s slowed as a r e s u l t of DAF, not a l l sounds are prolonged by the same amount. The p i l o t study i n d i c a t e s t h a t open vowels and f r i c a t i v e s are prolonged the most and t h a t p o s i t i o n w i t h i n the s y l -l a b l e and w i t h i n the sentence s e l e c t i v e l y a f f e c t s the d u r a t i o n a l i n c r e a s e s of each sound c l a s s . (c) When v o l u n t a r i l y slowed speech under SAF i s compared wit h speech under DAF, i t i s e v i d e n t , as i n d i c a t e d by the p i l o t study, t h a t slowed speech under SAF f o l -lows an o r d e r l y p a t t e r n i n which s t r e s s , degree of vowel openness and p o s s i b l y vowel l e n g t h determine d u r a t i o n a l i n c r e a s e s . On the other hand, d u r a t i o n a l i n c r e a s e s due to DAF are determined by a r t i c u l a t o r y parameters such as v o i c i n g , c l o s u r e , p o s i t i o n i n the a r t i c u l a t e d sequence as w e l l as degree of vowel open-ness . Chapter 4 EXPERIMENTAL APPARATUS AND PROCEDURES 4.1 Subj e c t s One female s u b j e c t served i n the p i l o t study and f i v e female and f i v e male s u b j e c t s served i n the main study; t h e i r ages ranged from 21 to 32 y e a r s . A l l s u b j e c t s were u n i v e r s i t y undergraduates or graduates i n the f i e l d s of L i n g u i s t i c s , Audiology and Speech Sci e n c e , or Medicine. F i v e male and two female s u b j e c t s i n the main study were naive with r e s p e c t to DAF. The p i l o t study s u b j e c t and the three remaining female s u b j e c t s had been b r i e f l y exposed to DAF i n the p a s t . The two requirements f o r the s e l e c t i o n as s u b j e c t s were evidence of bone- and a i r - c o n d u c t i o n t h r e s h o l d s w i t h i n 25 dB of 0 dB as d e f i n e d by the ISO Standard of 1964 f o r pure tones of f r e q u e n c i e s 250-4000 Hz, and n o t a b l e speech d i s t u r b a n c e under DAF. 4.2 Experimental Design The p i l o t s u b j e c t read a s h o r t connected passage ( p i l o t study passage, see Appendix B) under SAF at a normal r a t e and then at a slow r a t e . F o l l o w i n g those two r e a d i n g s , the s u b j e c t read the same passage under DAF at 200-, 180-, 220-, and again a t 200-msec d e l a y . The d e l a y producing the l o n g e s t r e a d i n g time was chosen f o r a n a l y s i s . For the SAF c o n d i t i o n the s u b j e c t was i n s t r u c t e d to read the passage - . 39 -- 40 -at her normal r a t e and then to read i t s l o w l y . No i n c t r u c -t i o n s were g i v e n f o r the DAF c o n d i t i o n s . For the main study, the h e a r i n g of a l l s u b j e c t s was screened a t the A u d i o v e s t i b u l a r U n i t of the Vancouver General H o s p i t a l to e s t a b l i s h i f s u b j e c t s ' t h r e s h o l d s f e l l w i t h i n the l i m i t s s p e c i f i e d above. The s u b j e c t s f i r s t p r a c t i s e d r e a d i n g under DAF to exclude n o v e l t y e f f e c t s . S u b j e c t s then read a s h o r t pass-age (screening passage, see Appendix C) under SAF. I f the s u b j e c t s made any a r t i c u l a t o r y e r r o r s , they were i n s t r u c t e d to read the passage again. Subjects then read the passage under DAF over a range of d e l a y s . The ra n g e ' f o r the female s u b j e c t s was 200-310 msec; the range f o r the male s u b j e c t s was 150-240 msec. The sound p r e s s u r e l e v e l a t the ear-phones v a r i e d w i t h the v o c a l output of the s u b j e c t s . The same playback s e t t i n g was used throughout the experiment. Subjects were i n s t r u c t e d not to change s t r a t e g i e s w h i l e r e a d i n g , i . e . , they were not to a l t e r n a t e l y slow down and speed up but to t r y to read as n a t u r a l l y as p o s s i b l e . The t o t a l r e a d i n g time of each s u b j e c t was determ-ined f o r the SAF and DAF c o n d i t i o n s , t i m i n g the d u r a t i o n of the recorded passage t o the nea r e s t h a l f a second with a stop watch. In a d d i t i o n , a r t i c u l a t o r y e r r o r s were count-ed. Each i n s t a n c e o f e r r o r , r e g a r d l e s s of l e n g t h or type, was t a b u l a t e d as one e r r o r . A second observer c a r r i e d out an independent a r t i c u l a t o r y e r r o r count on h a l f the sub-j e c t s f o r the purpose of checking r e l i a b i l i t y of measure-- 4 1 -ment. In t h e i r count the two observers d i d not d i f f e r by more than one e r r o r on any of the i n d i v i d u a l e r r o r s c o r e s . The two measures and the f o l l o w i n g r a t i o were p l o t t e d f o r each s u b j e c t as a f u n c t i o n of d e l a y : DAF T o t a l D u r a t i o n C o r r e c t Words Rat i o = SAF T o t a l D u r a t i o n T o t a l Words The delay a t which the h i g h e s t r a t i o o c c u r r e d f o r a p a r t i -c u l a r s u b j e c t was chosen f o r t h a t s u b j e c t as d e l a y value to be employed i n the main experiment. Subjects r e t u r n e d on a subsequent day f o r the main experiment. They were r e q u i r e d to read a s h o r t connected passage (main experiment passage, see Appendix D) i n the f o l l o w i n g f o u r c o n d i t i o n s : (a) ( C o n d i t i o n I) under SAF at a normal r a t e (NORMAL); (b) ( C o n d i t i o n II) under SAF at a v o l u n t a r i l y slowed r a t e (SLOW SAF); (c) ( C o n d i t i o n I I I ) under DAF (at the s e l e c t e d delay f o r t h a t subject) a t a slow r a t e , such t h a t the DAF paces the s u b j e c t (SLOW DAF); (d) ( C o n d i t i o n IV) under DAF (at the same delay as above) at a maximum r a t e (FAST DAF). - 42 -The SAF c o n d i t i o n s always preceded the DAF c o n d i -t i o n s i n the above o r d e r . The order of the DAF c o n d i t i o n s was r e v e r s e d f o r every second s u b j e c t . F o l l o w i n g the fou r above t a s k s , the e n t i r e proce-dure was repeated, but t h i s time the s u b j e c t was asked to read f o u r sentences, each embedded i n an i d e n t i c a l frame (main experiment sentences, see Appendix E ) . One sentence contained predominantly open back vowels (/o/ sentence), one cont a i n e d predominantly c l o s e f r o n t vowels ( / i / sentence), one contained predominantly open f r o n t vowels (/a/ sentence), and one con t a i n e d predominantly c l o s e back vowels (/u/ sentence). The fou r sentences were presented i n random order. Subject i n s t r u c t i o n s were minimal and i n f o r m a l . Subjects were t o l d , f o r the SLOW c o n d i t i o n , not to slow t h e i r speech by producing longer pauses between words, but to prolong the a c t u a l u t t e r a n c e s and to t r y to ma i n t a i n the same speed throughout. Subjects were then asked to p r a c t -i c e t h i s . I f the s u b j e c t was performing i n the r e q u i r e d manner, no f u r t h e r i n s t r u c t i o n s were g i v e n f o r t h i s t a s k . I f a s u b j e c t d i d not perform the task as i n s t r u c t e d and as p r a c t i s e d , he was asked t o repe a t the ta s k . For the SLOW DAF c o n d i t i o n the s u b j e c t was giv e n a demonstration by the experimenter of what was meant by: "Let the DAF pace you" or " c a t c h up wit h you". For the FAST DAF c o n d i t i o n sub-j e c t s were t o l d to read as r a p i d l y as p o s s i b l e and to t r y not to omit any words. - 43 -4.3 Instrumentation and Arrangement The system employed i n the p r o d u c t i o n of the synchronous and delayed feedback c o n s i s t e d of a Uher micro-phone Model M516, a K o r t i n g C o n s t e l l a t i o n 88 Model MT 3644 1/4-track tape r e c o r d e r with movable playback heads, and earphones designed f o r DAF experi m e n t a t i o n , namely such t h a t a i r c o n d u c t e d synchronous feedback i s maximally o c c l u -ded. The v o c a l output was recorded s i m u l t a n e o u s l y on a second tape r e c o r d e r ( S c u l l y Model 280-2) v i a an A l t e c 681 A LO microphone. The s u b j e c t was seated four to s i x inches from the microphones i n an IAC 1204 soundproof room. The tape r e c o r d e r s were o u t s i d e the soundproof room. The ope r a t o r was able t o observe the s u b j e c t s through a d o u b l e - g l a s s window and monitored the s u b j e c t ' s speech c o n t i n u o u s l y . S C U L L Y T A P E R E C O R D E R IN IN K O R T I N G T A P E R E C O R D E R O U T S O U N D P R O O F R O O M A L T E C M I K E U H E R M I K E F i g u r e 4.1. Block diagram of i n s t r u m e n t a t i o n f o r producing the delayed feedback and f o r r e c o r d i n g . - 44 -4.4 C a l i b r a t i o n Recordings were made on both r e c o r d e r s a t a tape speed of 7.5 inches per second on Ampex 631 p r o f e s s i o n a l tape. The r e c o r d i n g l e v e l on the S c u l l y tape r e c o r d e r was approximately 0 dB as r e g i s t e r e d on the VU meter of the r e c o r d e r . The playback l e v e l of the K o r t i n g tape r e c o r d e r at the s e t t i n g chosen was 108 dB SPL a t the earphones when a 1-kHz pure tone recorded a t 0 VU was p l a y e d back on the K o r t i n g tape r e c o r d e r . When white n o i s e recorded a t 0 VU was p l a y e d back on the K o r t i n g tape r e c o r d e r at the same s e t t i n g , the playback l e v e l a t the earphones was 95 dB SPL. Sound p r e s s u r e l e v e l was measured on a B r u e l and K j a e r Type 2203 P r e c i s i o n Sound L e v e l Meter and B r u e l and K j a e r A r t i -3 f i c i a l Ear (Type 4152) w i t h a 6 cm c o u p l e r . The p r e c i s e d e l a y s on the K o r t i n g tape r e c o r d e r were e s t a b l i s h e d as a f u n c t i o n of the playback head p o s i -t i o n . A m i l l i m e t e r s c a l e was f a s t e n e d along the path of the playback head. The earphones were p l a c e d c l o s e to the microphone. A sharp c l i c k produced a t the microphone was recorded a t 7.5 inches per second. The microphone p i c k e d up the c l i c k r e p e a t e d l y from the earphones u n t i l the c l i c k was damped. The procedure was repeated f o r ten d i f f e r e n t p o s i t i o n s of the playback head. Mingograms of the i n i t i a l c l i c k and i t s echos were then made f o r each s e t t i n g and the d i s t a n c e from c l i c k onset to f o u r t h echo onset measured i n msec. The d i s t a n c e was d i v i d e d by f o u r . The d e l a y - 4 5 -durations so obtained were p l o t t e d as a f u n c t i o n of p l a y -back head p o s i t i o n ( i n m i l l i m e t e r s ) . The delay f u n c t i o n was approximately l i n e a r and distance values along the s c a l e could be converted to delay values from t h i s graph. . Chapter ANALYSIS OF 5 DATA 5.1 Instrumentation Mingograms were made of the tape recorded speech, d i s p l a y i n g the f o l l o w i n g f o u r s i g n a l s : Channel 1 speech wave s i g n a l 2 duplex o s c i l l o g r a m 3 fundamental frequency of speech wave 4 l o g of average speech power F i g u r e 5.1 shows a schematic of the s e t up used to produce the mingograms. TAPE RECORDER F i g u r e 5.1. Block diagram of i n s t r u m e n t a t i o n used to produce mingograms. - 46 -DUPLEX OSCILLOGRAPH' TRANSPITCH-METER SPEECHPOWER-METER 0SCILL0MINK - 47 -The t a p e r e c o r d e r u s e d i n t h e above s e t u p was a REVOX Mo d e l A77. The i n p u t t o C h a n n e l s 2 and 3 was p r o -v i d e d by a F r c f i k j a e r - J e n s e n t r a n s p i t c h m e t e r . ' The i n t e n s i t y o r s p e e c h power c i r c u i t ( C h a n n e l 4) was s i m i l a r t o t h e one d e v e l o p e d by P e t e r s o n and McK i n n e y (1961). S p e e c h u t t e r a n c e s were t h e n segmented u t i l i z i n g t h e above f o u r t r a c e s on t h e mingograms. The d u p l e x o s c i l l o g r a m y i e l d e d t h e most e f f e c t i v e b a s i s f o r segment-a t i o n b e c a u s e t h e h i g h e r f r e q u e n c i e s a r e c o n v e r t e d t o a n e g a t i v e - g o i n g i n t e n s i t y c u r v e . I n a d d i t i o n , s p e c t r o g r a m s were made on a Kay S o n a g r a p h and a s c a l e f a c t o r c a l c u l a t e d t o c o n v e r t a c o u s t i c segment d u r a t i o n f r o m t h e s p e c t r o g r a m s i n t o msec. The t r a n s c r i p t i o n s y s t e m u s e d i n t h i s s t u d y i s d e s c r i b e d i n A p p e n d i x F. 5.2 S e g m e n t a t i o n C r i t e r i a V o w e l s : t h e b o u n d a r i e s o f v o w e l s c o u l d be f a i r l y a c c u r a t e l y d e t e r m i n e d by c o m p a r i s o n o f a l l f o u r t r a c e s (see F i g u r e 5 . 2 ) . Some d i f f i c u l t i e s were e n c o u n t e r e d i f t h e v o w e l was p r e c e d e d o r f o l l o w e d by / l / , / r / , /w/, / j / , /&/, o r / v / . I n t h e s e c a s e s , s p e c t r o g r a m s were made and t h e o n s e t and e n d i n g o f f o r m a n t s u s e d as s e g m e n t a t i o n c u e s . The c r i t e r i a w i l l be d i s c u s s e d b e l o w f o r t h e i n d i v i d u a l phones i n v o l v e d i n t h e a m b i g u i t i e s . - 48 -Figure 5.2. Mingogram of part of the phrase / g r i d i timz/. V / l / : the momentary decrease i n energy between a vowel and the f o l l o w i n g / l / r e f l e c t e d by a d i p i n the average speech power t r a c e , as w e l l as changes i n formant patterns on spectrograms, were used to determine the onset of / l / . I f the p r o n u n c i a t i o n was as f o l l o w s : / f u e l / , the / e / was considered as p a r t of the / l / , because / e / was not p a r t of the other occurences of /u/, whereas i n some instances of /!/ a /a/ preceded the /!/, i . e . , i n / p i p l / . - 49 -F i g u r e 5.3. Mingogram of t h e p h r a s e / f u l s / . V / r / and /&"/: Segmentation o f / r / a f t e r a vowel c o u l d u s u a l l y be made on t h e b a s i s o f s p e c t r o g r a m s . T r a n s -i t i o n was c o n s i d e r e d p a r t o f the v o w e l , making s e g m e n t a t i o n more r e l i a b l e . /&/ o c c u r r e d o n l y a f t e r a consonant and was t h u s e a s i l y segmented on t h e b a s i s o f a b r u p t changes on t h e mingograms. I n i t i a l / j / , /l/» / r / , /w/: The e n d i n g o f t h e s e phones c o u l d be c o n s i s t e n t l y d e t e r m i n e d by a change i n t h e d u p l e x o s c i l l o g r a m t r a c e as i l l u s t r a t e d i n F i g u r e 5.4. - 50 -Figure 5.4. Mingograms of the phrases /WAI-/, A A ft/, and /juz/. /&/ and /v/: Both a change i n the duplex o s c i l l o -gram t r a c e and absence of vowel formants on spectrograms were used as segmentation c r i t e r i a (Figure 5.5). - 51 -F i g u r e 5 . 5 . Mingogram of the p h r a s e / Sa J a f t / . N a s a l s : B o u n d a r i e s of n a s a l s were d e t e r m i n e d by the o n s e t and e n d i n g o f the r e g u l a r p a t t e r n which n a s a l s d i s p l a y on the speech wave t r a c e and d u p l e x o s c i l l o g r a m t r a c e . In case o f d o u b t , spec t rograms were made, on w h i c h the formants o f n a s a l s c o u l d be e a s i l y d i s c e r n e d (see F i g u r e s 5 . 2 , and 5 . 4 ) . Stop c o n s o n a n t s : B e g i n n i n g and end o f p l o s i o n c o u l d be d e t e r m i n e d f a i r l y a c c u r a t e l y from the d u p l e x o s c i l l o g r a m t r a c e ( n e g a t i v e - g o i n g i n t e n s i t y curve) i n c o n -j u n c t i o n w i t h the speech wave t r a c e . However, d e t e r m i n -a t i o n o f b e g i n n i n g o f c l o s u r e f o r i n i t i a l s t o p consonants - 52 -proved extremely d i f f i c u l t i n some cases where no energy r e g i s t e r e d a t the onset of the c l o s u r e and a pause or i n h a l -a t i o n preceded the c l o s u r e . A r b i t r a r y d e c i s i o n s had to be made i n some cases (see F i g u r e 5.2, 5.4 and 5.5). The f r i c a t i v e s : / f , s / Z , J , ^ , 9 , h / : the boundaries of these f r i c a t i v e s were d e f i n e d as the begi n n i n g and end-i n g of the n e g a t i v e - g o i n g i n t e n s i t y curve on the duplex o s c i l l o g r a m t r a c e (see F i g u r e s 5.2, 5.3, 5.4 and 5.5). 5.3 Segment R e j e c t i o n C r i t e r i a When segments were added t o the expected sequence of a r t i c u l a t i o n , these segments were not used i n a compari-son of segment d u r a t i o n s a c r o s s c o n d i t i o n s ; i . e . , i n the comparative a n a l y s i s d e s c r i b e d i n Chapter 6. Such added segments were sometimes the r e s u l t of a c o r r e c t i o n as i n the f o l l o w i n g example, where an i n c o r r e c t l y produced word (un d e r l i n e d sequence) was repeated c o r r e c t l y : /si 6e t r i e 8ri/, p a r t of the sequence "... see the three greedy teams ...". Sometimes e x t r a segments were added, not p a r t of the t e x t and u n r e l a t e d to the t e x t ( u n d e r l i n e d segments): / DsgemvhDks /, the sequence "... awesome hawk's I f the added segment was the r e s u l t of r e p e t i t i o n under DAF, the f o l l o w i n g c r i t e r i a were used to s e l e c t one occurrence of the segment f o r purposes of the comparative a n a l y s i s and r e j e c t the other occurrence or o c c u r r e n c e s : when one r e p e t i t i o n i n a s e r i e s of r e p e t i t i o n s was c o r r e c t l y a r t i c u l a t e d , g e n e r a l l y with a non-reduced vowel, even though - 53 -pe rhaps d r a w l e d , and t h e o t h e r r e p e t i t i o n s were r e d u c e d o r i n c o r r e c t l y a r t i c u l a t e d v e r s i o n s o f t h e i n t e n d e d sequence of. a r t i c u l a t i o n , e i t h e r i n t e rms o f v o w e l q u a l i t y o r v o i c -i n g e r r o r o r some o t h e r l i n g u i s t i c f e a t u r e e r r o r , t h e c o r -r e c t l y a r t i c u l a t e d i n t e n d e d a r t i c u l a t o r y sequence was s e l e c -t e d f o r t he c o m p a r a t i v e a n a l y s i s and t h e r e s t o f t h e r e p e t i t i o n o r m i s a r t i c u l a t i o n ( u n d e r l i n e d segments i n t h e f o l l o w i n g examples ) d i s c a r d e d : / g r i d i d i / ( g r e e d y ) , / pabasasasas / ( p a s s e s ) , / gakakakahazasas I / ( c a s t l e ) . I f t he r e p e a t e d sequences o f segments i n one i n s t a n c e o f r e p e t i t i o n were a r t i c u l a t e d c o r r e c t l y i n each r e p e a t e d s e q u e n c e , t he sequence w i t h the h i g h e s t s p e e c h power t r a c e was s e l e c t e d f o r t h e c o m p a r a t i v e a n a l y s i s (see F i g u r e 5.6). F i g u r e 5 . 6 . Mingogram o f t h e sequence / PAjdAbAbAbAb. 5a / . - 54 -I f o n l y one a c o u s t i c segment was r e p e a t e d b o t h t i m e s c o r r e c t l y the l a s t o c c u r r e n c e o f t h e segment was chosen f o r t h e c o m p a r a t i v e a n a l y s i s . The maximum e r r o r w h i c h may r e s u l t f rom the above r e j e c t i o n c r i t e r i a was e s t i m a t e d f o r t h e two s u b j e c t s , who r e p e a t e d most f r e q u e n t l y under DAF, as f o l l o w s : t h e sum o f the l o n g e s t a l t e r n a t i v e a c o u s t i c segments was d i v i d e d by the sum o f the a c o u s t i c segments w h i c h were n o t i n v o l v e d i n a m b i g u i t i e s p l u s t h e sum o f the s h o r t e s t a l t e r n a t i v e a c o u s -t i c segments . I n the w o r s t ca se ( s u b j e c t 1) t h e e r r o r f a c t -o r amounted t o 10%. Chapter 6 RESULTS AND DISCUSSION The re s u l t s of t h i s study w i l l be reported and d i s -cussed simultaneously i n t h i s chapter. This mode of pre-sentation was chosen because of the complex nature of the re s u l t s . The p i l o t study, the screening study, the main experiment, and the summary and conclusions are presented i n 6.1, 6.2, 6.3, and 6.4 respectively. 6.1 P i l o t Study The mingograms of the recorded p i l o t study pass-age were segmented i n the manner described i n Chapter 5. Ten phrases, beginning with the second phrase i n the pass-age (Appendix B) were analyzed i n t h e NORMAL, SLOW SAF and DAF (200 msec only) conditions. Analysis of the absolute durations of the acoustic segments revealed that, compared to the SLOW SAF condition, (1) vowels i n stressed s y l l a b l e s , except for the open vowels /ae/ and /o/, were of shorter absolute duration i n the DAF condition, the greatest difference being observable i n the close front vowels; (2) open vowels were of longer absolute duration i n the DAF condition, regardless of stress; (3) f r i c a t i v e s and voiced stops were of longer absolute duration i n the DAF condition,'the greatest difference occurring i n i n i t i a l p o s i t i o n ; - 55 -- 56 -(4) v o i c e l e s s s t o p s w e r e o f l o n g e r a b s o l u t e d u r a t i o n i n t h e DAF c o n d i t i o n , t h e g r e a t e s t d i f f e r e n c e o c c u r r i n g i n f i n a l p o s i t i o n . ' S t r e s s e d s y l l a b l e s ' w e r e d e f i n e d i n t h e p i l o t s t u d y a s t h o s e s y l l a b l e s e x p e c t e d t o c a r r y p r i m a r y s t r e s s i n t h e NORMAL S A F c o n d i t i o n , a c c o r d i n g t o E n g l i s h p h o n o l o g i c a l r u l e s . B e c a u s e s t r e s s c o u l d n o t b e d e f i n e d i n t e r m s o f E n g l i s h p h o n o l o g i c a l r u l e s i n t h e SLOW S A F a n d DAF c o n -d i t i o n s , i t w a s d e f i n e d o n l y w i t h r e f e r e n c e t o t h e NORMAL S A F c o n d i t i o n , i . e . , a v o w e l i n a s t r e s s e d s y l l a b l e i n t h e NORMAL c o n d i t i o n was c o m p a r e d a c r o s s c o n d i t i o n s a n d r e f e r -r e d t o i n a l l c o n d i t i o n s a s v o w e l i n a s t r e s s e d s y l l a b l e . T o t a l d u r a t i o n s o f t h e a n a l y z e d p h r a s e s , i . e . , t h e sum o f t h e d u r a t i o n s o f t h e a c o u s t i c s e g m e n t s o f e a c h p h r a s e , d i d n o t d i f f e r s y s t e m a t i c a l l y i n t h e SLOW S A F a n d DAF c o n d i t i o n s . T h e a c o u s t i c s e g m e n t s w e r e n o r m a l i z e d a s f o l l o w s : - R D - D ( s e g ) " 2 D ( S e g ) w h e r e , f o r a s e n t e n c e o r p h r a s e u n d e r i n v e s t i g a t i o n , RD i s t h e r e l a t i v e d u r a t i o n o f a s e g m e n t , D ( S e g ) i s t h e d u r a t i o n o f a n a c o u s t i c s e g m e n t i n t h a t s e n t e n c e o r p h r a s e , a n d Z D ( S e g ) i s t h e sum o f d u r a t i o n s o f t h e a c o u s t i c s e g m e n t s i n t h a t s e n t e n c e o f p h r a s e . B r i e f l y , RD s i m p l y r e p r e s e n t s t h e r e l a t i v e d u r a t i o n i n p e r c e n t o f a c e r t a i n s e g m e n t i n a n u t t e r a n c e f o r a s p e c i f i c c o n d i t i o n . - 57 -The so n o r m a l i z e d d a t a r e v e a l e d t h a t compared t o t h e NORMAL c o n d i t i o n , (1) t h e v o w e l s were o f l o n g e r r e l a t i v e d u r a t i o n i n b o t h t h e SLOW SAF and DAF c o n d i t i o n s ; (2) t h e s t o p s were o f s h o r t e r r e l a t i v e d u r a t i o n i n b o t h t h e SLOW SAF and DAF c o n d i t i o n s . Compared t o the SLOW SAF c o n d i t i o n , (1) v o w e l s i n s t r e s s e d s y l l a b l e s , e x c e p t f o r t he open vow-e l s /ae / and / o / , were o f s h o r t e r r e l a t i v e d u r a t i o n i n t h e DAF c o n d i t i o n ; (2) f r i c a t i v e s were o f l o n g e r r e l a t i v e d u r a t i o n i n t h e DAF c o n d i t i o n . Graphs o f t h e r e l a t i v e d u r a t i o n s o f s y l l a b l e s r e v e a l e d p a t -t e r n s w h i c h were s i m i l a r f o r t h e NORMAL and SLOW SAF c o n -d i t i o n s i n t h a t w o r d - and s e n t e n c e - s t r e s s c o r r e l a t e d w i t h l o n g e r r e l a t i v e d u r a t i o n , whereas t h e p a t t e r n s f o r t h e DAF c o n d i t i o n were u n l i k e t h o s e o f t h e NORMAL c o n d i t i o n i n t h a t f i n a l s y l l a b l e s o f t h e s e n t e n c e were o f l o n g e r r e l a t i v e d u r a t i o n r e g a r d l e s s o f s t r e s s and i n t h a t f r i c a t i v e s a c -c o u n t e d f o r t h e l o n g e r r e l a t i v e d u r a t i o n o f s y l l a b l e s r e -g a r d l e s s o f s t r e s s . I n summary, p o s i t i o n i n t h e s y l l a b l e , s t r e s s , d e -g r ee o f v o w e l openness and manner o f a r t i c u l a t i o n appear t o be p a r a m e t e r s w h i c h d e t e r m i n e changes a t a s l o w e r r a t e o f s p e e c h . I n a d d i t i o n , v o l u n t a r i l y s l o w e d s p e e c h appea r s t o d i f f e r f rom D A F - s l o w e d s p e e c h . S i n c e t h e r e s u l t s o f t h e - 58 -p i l o t study are based on the performance of one speaker only and s i n c e no attempt was made to c o n t r o l r a t e under DAF, they were c o n s i d e r e d merely hypotheses to be t e s t e d . 6 . 2 Screening Study The two d i f f e r e n t ranges of de l a y with which the two s e t s of s u b j e c t s were presented had been chosen on the b a s i s of pr e v i o u s f i n d i n g s (Mahaffey and Stromsta, 1965) , t h a t the delay producing maximum d i s t u r b a n c e was 180 msec f o r males and 270 msec f o r females. The graphs of the dur-a t i o n - e r r o r r a t i o d e s c r i b e d i n chapter 4, r e v e a l e d t h a t f o r each s u b j e c t there o c c u r r e d on the i n t e r v a l measured at l e a s t two high v a l u e s , as c a l c u l a t e d by the above-men-t i o n e d index of d i s t u r b a n c e , separated from each other by a lower v a l u e . The delay producing the higher of the two high v a l u e s was s y s t e m a t i c a l l y chosen as the delay (produc-i n g maximum dis t u r b a n c e ) f o r the main experiment. The r e s u l t s are summarized i n t a b l e I. As can be seen, the delays producing the h i g h e s t d i s t u r b a n c e v a l u e s tended to be s h o r t e r f o r males than f o r females. The average of the del a y s producing the h i g h e s t value f e l l near 200 msec. The average of the de l a y s producing the second h i g h value was 297 f o r females and 206 f o r males. Order o f de l a y p r e s e n t a t i o n may have i n f l u e n c e d which delay produced maximum d i s t u r b a n c e f o r male s u b j e c t s 3, 4, and 5. For these three s u b j e c t s the f i r s t r e a d i n g under DAF produced the maximum d i s t u r b a n c e . No such order - 59 -Subject s Reading Time i n seconds under SAF Delay i n msec producing h i g h e s t peak d i s t u r b a n c e Delay i n msec producing the second peak Female s u b j e c t s 1 25 250 290 2 (a)* 24 200 290 2 (b) 24 200 310 3 25.5 230 310 4 23.5 ' 200 310 5 22.5 200 270 Male s u b j e c t s 1 23 .5 240 200 2 28 240 170 3 21.5 170 220 4 28 180 240 5 29 170 200 * female s u b j e c t number 2 was recorded twice a t d i f f e r e n t times with the d e l a y s presented i n d i f f e r e n t o rders to check i f the measure was r e l i a b l e . Table I. Normal r e a d i n g time under SAF and d e l a y s produc-i n g peaks of d i s t u r b a n c e as d e f i n e d by the d u r a t i o n - e r r o r r a t i o d e s c r i b e d i n chapter 4. - 60 -e f f e c t s were observed f o r the remaining s u b j e c t s . Timmons (1971) observed order e f f e c t s f o r females, whereas she ob-served no order e f f e c t s f o r males. The r e s u l t s of the s c r e e n i n g study suggest t h a t perhaps order e f f e c t s are not e n t i r e l y c o n f i n e d to females. F i g u r e 6.1 shows the r e l a t i v e amount of d i s t u r b a n c e f o r the three s u b j e c t s whose r e c o r d i n g s were analyzed i n the main experiment. As can be seen, each of the t h r e e sub-j e c t s was a f f e c t e d by DAF to a very d i f f e r e n t e x t e n t . Many hypotheses have been o f f e r e d i n the p a s t to account f o r such i n d i v i d u a l d i f f e r e n c e s . Beaumont and Foss (1957) found t h a t s u b j e c t s , who had h i g h s c o r e s on t e s t s of p e r s e v e r a t i o n , were more a f f e c t e d by DAF. These authors r e l a t e d person-a l i t y v a r i a b l e s t o degree of DAF d i s t u r b a n c e . Z e l n i k e r (1971) and S a l t e r (1973), among o t h e r s , suggested t h a t a t t e n t i o n a l f a c t o r s determine the e x t e n t t o which a s u b j e c t i s a f f e c t e d by DAF, e.g., i f e i t h e r another task demands a t t e n t i o n s i m u l t a n e o u s l y or i f the DAF t a s k (reading mat-e r i a l ) i s more d i f f i c u l t (random words as opposed to p r o s e ) , DAF w i l l d i s r u p t the speech l e s s . Yates (1965) hy p o t h e s i z e d t h a t the f a c t o r which determines degree of speech d i s t u r b -ance under DAF i s the e x t e n t t o which a speaker r e l i e s on a i r c o n d u c t e d a u d i t o r y feedback f o r normal c o n t r o l of speech, assuming t h a t some speakers r e l y on the d i f f e r e n t feedback channels f o r c o n t r o l of speech to d i f f e r i n g e x t e n t s . In summary, the r e s u l t s of t h i s p a r t of the study c o n f i r m the c o n s i d e r a b l e i n d i v i d u a l d i f f e r e n c e s which e x i s t Figure 6.1. DAF-induced speech disturbance ( e r r o r - d u r a t i o n r a t i o ) f o r male subject 1, and female subjects 2 and 3. - 62 -i n r e a c t i o n to DAF, and, although the s c r e e n i n g study was not designed to answer q u e s t i o n s about the nature of DAF i n t e r f e r e n c e or about the nature of speech p r o d u c t i o n u n i t s , the r e s u l t s suggest, as Chase et a l . (1959) have suggested, t h a t the c r i t i c a l time r e l a t i o n s h i p s are perhaps the most important f a c t o r s to be examined i f the observed changes i n speech under DAF are to be e x p l a i n e d . 6.3 R e s u l t s of the Main Experiment In accordance w i t h the c r i t e r i a l i s t e d i n chapter 5, the mingograms of the main experiment passage i n the four c o n d i t i o n s were segmented f o r male s u b j e c t 1 and the mingo-grams of the main experiment sentences i n the four c o n d i -t i o n s were segmented f o r male s u b j e c t 1 and female sub-j e c t s 2 and 3. The d u r a t i o n of each a c o u s t i c segment was measured f o r every segmented u t t e r a n c e . ' T o t a l d u r a t i o n ' of a sentence or phrase was d e f i n e d as the t o t a l d u r a t i o n of the u t t e r a n c e minus the pauses and minus the r e j e c t e d segments (according to the r e j e c t i o n c r i t e r i a 0 o u t l i n e d i n chapter 5). F i g u r e 6.2 shows the average ' t o t a l d u r a t i o n s ' of the f o u r sentences i n the f o u r c o n d i t i o n s f o r the three s u b j e c t s . ' T o t a l d u r a t i o n s ' v a r i e d from s u b j e c t to s u b j e c t and from c o n d i t i o n to c o n d i t i o n . In order to e v a l u a t e i f the same speaking r a t e was maintained throughout a sentence, the a b s o l u t e d u r a t i o n s of each s y l l a b l e d i v i d e d by the num-ber of phonemes i n t h a t s y l l a b l e were graphed (see Appendix G f o r sample graphs). The graphs r e v e a l e d t h a t s u b j e c t 1 - 63 -30,000 — 25,000 — CONDITION i n i i i i r n i z i n ur iz SUBJECT I SUBJECT 2 SUBJECT 3 F i g u r e 6.2. Average ' t o t a l d u r a t i o n s ' of the main experiment sentences i n the fou r c o n d i t i o n s . - 64 -tended to mai n t a i n the same speaking r a t e throughout a sent-ence, while s u b j e c t s 2 and 3 tended to i n c r e a s e t h e i r r a t e towards the end of sentences i n the SLOW SAF and SLOW DAF c o n d i t i o n s . The ' t o t a l d u r a t i o n ' of each phrase i n the passage r e v e a l e d t h a t d u r i n g the SLOW SAF c o n d i t i o n s u b j e c t 1 tended t o slow down towards the end of the passage. In sh o r t , the speaking r a t e s v a r i e d a c r o s s s u b j e c t s and c o n d i -t i o n s and a t times w i t h i n c o n d i t i o n s . Although s u b j e c t s spoke a t t h e i r maximum r a t e i n the FAST DAF c o n d i t i o n as opposed to speaking a t t h e i r norm-a l r a t e i n the NORMAL c o n d i t i o n , i t w i l l be noted t h a t ' t o t a l d u r a t i o n 1 f o r a l l s u b j e c t s under FAST DAF was g r e a t e r than i n the NORMAL c o n d i t i o n , even though no r e p e t i t i o n s or other a d d i t i o n s to the expected sequence of a r t i c u l a t i o n were i n c l u d e d i n the ' t o t a l d u r a t i o n ' v a l u e s as p l o t t e d i n f i g u r e 6.2. I f the d u r a t i o n s of the r e p e t i t i o n s are added to the ' t o t a l d u r a t i o n ' f o r each s u b j e c t , s u b j e c t 1 e x h i -b i t s by f a r the most slowing under DAF and s u b j e c t 2 e x h i -b i t s more slowing than s u b j e c t 3. These f a c t s are mentioned here f o r two reasons. F i r s t l y , the data support the e r r o r -d u r a t i o n r a t i o as a r e l i a b l e i n d i c a t o r of degree of speech d i s t u r b a n c e produced by DAF i n t h a t the same r e s u l t s were obtained by the e r r o r - d u r a t i o n r a t i o . Secondly, the data seem to i n d i c a t e t h a t r e p e t i t i o n s and p r o l o n g a t i o n are i n -deed m a n i f e s t a t i o n s of the same phenomenon, namely slowing: s u b j e c t s who under FAST DAF do not make many r e p e t i t i o n s do not pro l o n g very much. T h i s does not answer why a - 65 -r e p e t i t i o n occurs a t one time and dra w l i n g at another, i t merely suggests the s i m i l a r i t y of the e f f e c t s i n terms of s u b j e c t r e a c t i o n . 6.3^ R e l a t i v e Durations The data were normalized as d e s c r i b e d i n the p i l o t study. The r e l a t i o n s h i p s o f ' s t r e s s e d ' long vowels as de-3 f i n e d below under 6.3 , vowels other than the ' s t r e s s e d ' long vowels ('other'vowels) , and consonants are shown i n f i g u r e 6.3 f o r the main experiment sentences i n the fou r c o n d i t i o n s . As can be seen, i n comparison w i t h the NORMAL c o n d i t i o n , vowels, p r i m a r i l y 'other'vowels tended to i n -crease i n r e l a t i v e d u r a t i o n and consonants tended to de-crease. No c o n s i s t e n t change i n r e l a t i v e d u r a t i o n o c c u r r e d f o r / a / and / £ / from c o n d i t i o n to c o n d i t i o n . Compared to the other c o n d i t i o n s , / o / tended to i n c r e a s e i n r e l a t i v e d u r a t i o n i n the FAST DAF c o n d i t i o n . In comparison w i t h the other c o n d i t i o n s , / u / c o n s i s t e n t l y i n c r e a s e d i n r e l a t i v e d u r a t i o n i n the SLOW SAF c o n d i t i o n . A d i s c u s s i o n o f these r e s u l t s , which are e s s e n t i -a l l y the same as the r e s u l t s of the data a n a l y s i s d e s c r i b e d below, w i l l f o l l o w when the l a t t e r r e s u l t s are r e p o r t e d and d i s c u s s e d . 2 6.3 R e l a t i v e Change Measure The data were a l s o normalized as f o l l o w s : - 66 -NORM- S SAF S DAF F DAF NORM. S SAF S DAF F DAF NORM. S SAF S DAF F DAF F i g u r e 6 . 3 . R e l a t i o n s h i p of ' s t r e s s e d ' long vowels, 'other' vowels, and consonants i n the main experiment sentences i n the four c o n d i t i o n s . - 67 -R C ( k ) - S D< k> V T D ( I )  R L ( K ) ~ SD(I) A TD (k) where, f o r a p a r t i c u l a r segment, RC(k) i s the r e l a t i v e i n -crease or decrease i n d u r a t i o n of an a c o u s t i c segment i n a p a r t i c u l a r c o n d i t i o n k ( I I , I I I , or IV) w i t h r e s p e c t t o the corresponding segment i n the NORMAL c o n d i t i o n , SD(k) i s the d u r a t i o n of the a c o u s t i c segment under c o n d i t i o n k, and TD(k) i s the ' t o t a l d u r a t i o n ' under c o n d i t i o n k. T h i s measure r e f l e c t s the r e l a t i v e i n c r e a s e o r decrease i n dura-t i o n of an a c o u s t i c segment compared to i t s d u r a t i o n i n the NORMAL c o n d i t i o n and normalized w i t h r e s p e c t t o the two c o r -responding ' t o t a l d u r a t i o n s ' . An RC value of 1.0 c o r r e s -ponds to no change, an RC val u e g r e a t e r than 1.0 corresponds to a r e l a t i v e i n c r e a s e and an RC value l e s s than 1.0 c o r r e s -ponds to a r e l a t i v e decrease. 'Increase' or 'decrease' w i l l be used h e r e a f t e r to r e f e r to the r e l a t i v e i n c r e a s e or de-crease c a l c u l a t e d by means of the above formula. The RC value s obtained from the a n a l y s i s of the four main experiment sentences w i l l be r e p o r t e d f o r d i f -f e r e n t s e t s o f phones s e p a r a t e l y . Any l e v e l s of s i g n i f i c a n c e mentioned i n t h i s study w i l l r e f e r to l e v e l s of s i g n i f i c a n c e e s t a b l i s h e d by t - t e s t s as f o l l o w s : * = s i g n i f i c a n t beyond the 0.05% l e v e l ** = s i g n i f i c a n t beyond the 0.02% l e v e l *** = s i g n i f i c a n t beyond the 0.01% l e v e l **** = s i g n i f i c a n t beyond the 0.005% l e v e l - 68 -6•3 R e l a t i v e Change o f V o w e l s I t became n e c e s s a r y i n the c o u r s e o f a n a l y s i s , on t h e b a s i s o f t h e i r a p p a r e n t l y d i f f e r e n t f u n c t i o n s , t o c o n -s i d e r v o w e l s i n m o n o s y l l a b i c f u n c t i o n words such as p r e p o -s i t i o n s , p r o n o u n s , and d e t e r m i n e r s , s e p a r a t e l y f rom the v o w e l s i n o t h e r w o r d s , p r i m a r i l y words b e a r i n g l e x i c a l i n -f o r m a t i o n . H e r e a f t e r ' s t r e s s e d ' v o w e l w i l l r e f e r t o v o w e l s i n s t r e s s e d s y l l a b l e s i n words o t h e r t h a n t h e m o n o s y l l a b i c f u n c t i o n w o r d s , and ' u n s t r e s s e d ' v o w e l w i l l r e f e r t o v o w e l s i n a l l o t h e r s y l l a b l e s . ' U n s t r e s s e d ' l o n g and s h o r t and ' s t r e s s e d ' l o n g and s h o r t v o w e l s were a n a l y z e d s e p a r a t e l y . F i g u r e 6.4 d i s p l a y s the r e l a t i v e change f o r t h e d i f f e r e n t g roups o f v o w e l s f o r each s u b j e c t . As can be s e e n , t h e v o w e l s i n t h e f u n c t i o n words ' i n c r e a s e d ' more t h a n any o t h e r g roup o f v o w e l s . T a b l e I I shows t h e b e t w e e n - c o n d i t i o n s t a t i s t i c a l d i f f e r e n c e s f o r v o w e l s i n f u n c t i o n words and t a b l e I I I shows t h e w i t h i n - c o n d i t i o n s t a t i s t i c a l d i f f e r e n c e s . The ' i n c r e a s e s ' f o r v o w e l s i n f u n c t i o n words i n the SLOW SAF c o n d i t i o n were s i g n i f i c a n t l y d i f f e r e n t f rom the ' i n -c r e a s e s ' i n t h e FAST DAF c o n d i t i o n and t o a l e s s e r e x t e n t f rom the ' i n c r e a s e s ' i n t h e SLOW DAF c o n d i t i o n . F u r t h e r -more , t he ' i n c r e a s e s ' f o r t he v o w e l s / u / , / o / , and / a / i n f u n c t i o n words were f r e q u e n t l y s i g n i f i c a n t l y d i f f e r e n t f rom t h e ' i n c r e a s e s ' f o r / i i / , /'6/ and ' s t r e s s e d ' v o w e l s r e s p e c t -i v e l y . Mos t o f t h e s i g n i f i c a n t d i f f e r e n c e s o c c u r r e d i n the SLOW c o n d i t i o n s . The r e l a t i v e changes f o r t h e v o w e l s /A/ and /ae/ i n f u n c t i o n words were r a r e l y s i g n i f i c a n t l y S t r e s s e d ' v o w e l s o 3.5 -3 — 2.5 -2 — i u 1.5 -I-o 0.5 -3.5 -3 — 2.5 -2 — 1.5 -I — 0.5 -3.5 -3 — a 2.5 -_K33 O 2 — 1.5 -I - m=f^ 0.5 A 6 u[ e I ] u* A' 6 6[e\] ' U n s t r e s s e d ' v o w e l s 1 I U A O u [ a l ] r it CL V o w e l s i n m CONDITION n u n c t i o n words 8 CONDITION ISC F i g u r e 6 . 4 . R e l a t i v e change i n d u r a t i o p . f o r vowe l s i n the and the FAST DAF (IV) c o n d i t i o n s w i t h r e s p e c t t o I I CONDITION ur l i p SUBJECT I ae u SUBJECT 2 SUBJECT 3 SLOW SAF ( I I ) , the SLOW DAF ( I I I ) , t he NORMAL c o n d i t i o n . - 70 -SLOW DAF FAST DAF S u b j e c t 1 NS ** SLOW SAF 2 * **** 3 ** **** T a b l e I I . B e t w e e n - c o n d i t i o n d i f f e r e n c e s i n r e l a t i v e change o f v o w e l s i n o n e - s y l l a b l e f u n c t i o n w o r d s . - 71 -SLOW SAF SLOW DAF FAST DAF / i i / v s . / u / i n f u n c t i o n w o r d s , / u / s e n t e n c e S u b j e c t 1 * **** NS 2 ** ** **** * * 3 *** NS * * * /6/ v s . /o/ i n f u n c t i o n w o r d s , / o / s e n t e n c e S u b j e c t 1 NS *** NS 2 * * * * **** **** 3 * NS NS / a / v s . /A/ and / a / i n f u n c t i o n w o r d s , / a / s e n t e n c e S u b j e c t 1 * * * "k NS NS 2 NS * NS 3 NS NS NS ' s t r e s s e d ' v o w e l s v s . / e / i n f u n c t i o n w o r d s , a l l s e n t e n c e s S u b j e c t 1 **** **** **** 2 **** **** ]vjg 3 **** **** ftjg T a b l e I I I . W i t h i n - c o n d i t i o n d i f f e r e n c e s i n r e l a t i v e change o f ' s t r e s s e d ' l o n g v o w e l s and v o w e l s i n f u n c -t i o n w o r d s . 72 -d i f f e r e n t from the r e l a t i v e changes f o r the vowel /a/. The s m a l l number of occurrences of /A/ and / f f i/ (N=3) might account f o r the n o n s i g n i f i c a n t r e s u l t s f o r these vowels. However, an a l t e r n a t i v e e x p l a n a t i o n w i l l be o f f e r e d below, when these r e s u l t s are d i s c u s s e d . In order to assure t h a t the d i f f e r e n c e between ' s t r e s s e d ' vowels and /a/ i n f u n c t i o n words was not simply due to the d i f f e r e n c e s i n vowel q u a l i t y , /%/ i n words other than f u n c t i o n words, e.g., i n / s i t e d / , were compared with ' s t r e s s e d ' vowels. The s t a t i s t i c a l r e -s u l t s , presented i n t a b l e IV, i n d i c a t e t h a t there i s r a r e l y a s i g n i f i c a n t d i f f e r e n c e i n r e l a t i v e change between / s / i n words other than f u n c t i o n words and ' s t r e s s e d ' vowels. A l l e n (1968) i n a d i s c u s s i o n of rhythmic behaviour i n motor ta s k s proposed t h a t the minimum i n t e r v a l between a c t s f o r rhythmic behaviour i n speech (beats) i s probably 300 msec and the maximum i n t e r v a l 1000 msec. I t was found i n the presen t study t h a t when the vowels i n f u n c t i o n words are examined, the speech power t r a c e on the mingograms i s as hi g h f o r these vowels as f o r the vowels which have heen c a l l e d ' s t r e s s e d ' vowels i n t h i s study. When the data are examined i n view of A l l e n ' s minimum and maximum l i m i t s , i t becomes e v i d e n t , t h a t the s u b j e c t s , at the slower r a t e s of speech and p a r t i c u l a r l y a t the very slow r a t e i n the SLOW SAF and SLOW DAF c o n d i t i o n s , lengthened vowels and i n c r e a s -ed the p h y s i c a l e f f o r t with which they were produced i n comparison w i t h the NORMAL c o n d i t i o n such, t h a t each vowel became a beat i n the rhythmic s u c c e s s i o n of speech - 73 -SLOW SAF SLOW DAF FAST DAF ' S t r e s s e d ' v o w e l s v s . / 9 / n o t i n f u n c t i o n words S u b j e c t 1 NS NS NS 2 NS *** NS 3 ** * * T a b l e I V . W i t h i n - c o n d i t i o n d i f f e r e n c e s i n r e l a t i v e change o f ' s t r e s s e d ' v o w e l s and / a / n o t i n f u n c t i o n w o r d s . - 74 -u n i t s . F u r t h e r e x a m i n a t i o n r e v e a l e d t h a t t h e i n t e r v a l s b e -tween t h e n o r m a l l y s t r e s s e d v o w e l s w o u l d have exceeded 1000 msec a t t h e s l o w e r r a t e s o f s p e e c h , t h u s n e c e s s i t a t i n g the a d d i t i o n a l b e a t s . I n o t h e r t e r m s , t h e s l o w e r the r a t e o f s p e e c h , t h e more l i k e l y w i l l a n o r m a l l y u n s t r e s s e d v o w e l be p r o l o n g e d and form a b e a t i n t h e r h y t h m i c s u c c e s s i o n o f speech u n i t s . T h i s may e x p l a i n why t h e d i f f e r e n c e s between t h e SLOW SAF and SLOW DAF c o n d i t i o n s f o r v o w e l s i n f u n c t i o n words were n o t as s i g n i f i c a n t as t he d i f f e r e n c e s between t h e SLOW SAF and FAST DAF c o n d i t i o n and why i n the FAST DAF c o n d i t i o n t h e r e s h o u l d be fewer s i g n i f i c a n t d i f -f e r e n c e s between ' s t r e s s e d ' v o w e l s and v o w e l s i n f u n c t i o n w o r d s . The e x c e p t i o n s , i . e . , t h e v o w e l s i n f u n c t i o n words w h i c h d i d n o t i n c r e a s e s i g n i f i c a n t l y i n d u r a t i o n i n com-p a r i s o n w i t h o t h e r v o w e l s , were now examined i n v i e w o f the above h y p o t h e s i s : i t was found t h a t t h e s e e x c e p t i o n s o c c u r r e d between two b e a t s (two s t r e s s e d v o w e l s ) w h i c h were n o t s e p a r a t e d from each o t h e r by more t h a n 1000 msec . I n a d d i t i o n , t h e s e e x c e p t i o n a l v o w e l s , e . g . , / A / i n / A p / and /ae / i n / a t / , o c c u r r e d i n an e n v i r o n m e n t t h a t i n the NORMAL c o n d i t i o n w o u l d c a l l f o r a s h o r t e r v o w e l . A d i s -c u s s i o n o f t h i s l a t t e r p o i n t f o l l o w s when t h e r e s u l t s o f t h e a n a l y s i s o f ' s t r e s s e d ' v o w e l s a r e d i s c u s s e d . A n a l y s i s o f t h e ' s t r e s s e d ' v o w e l s (see f i g u r e 6 .4) r e v e a l e d t h a t i n g e n e r a l /ix/ was c o n s i s t e n t l y most ' i n -c r e a s e d ' i n t h e SLOW SAF c o n d i t i o n , and more ' i n c r e a s e d ' i n t h e SLOW DAF c o n d i t i o n t h a n i n t h e FAST DAF c o n d i t i o n . - 75 -The r e v e r s e was t r u e f o r /o/, where t h e g r e a t e s t i n c r e a s e o c c u r r e d i n t h e FAST DAF c o n d i t i o n , / u / was more ' i n c r e a s e d ' t h a n any o t h e r ' s t r e s s e d ' v o w e l i n any o t h e r c o n d i t i o n w i t h t h e e x c e p t i o n o f /6/ i n t h e FAST DAF c o n d i t i o n . / u / i n / u e l / was n o t i n c l u d e d i n t h e a n a l y s i s o f / u / b e c a u s e o f t h e c o n s i s t e n t l y d i f f e r e n t b e h a v i o u r o f / u / i n t h i s e n v i r o n -ment. T a b l e V shows t h e w i t h i n - c o n d i t i o n d i f f e r e n c e s i n r e l a t i v e change f o r t h e f o u r g r o u p s o f ' s t r e s s e d ' v o w e l s . As c a n be s e e n , t h e ' i n c r e a s e s ' f o r / u / were s i g n i f i c a n t l y d i f f e r e n t f r o m ' i n c r e a s e s ' f o r t h e low v o w e l s ( p r i m a r i l y /a/) i n t h e SLOW SAF and SLOW DAF c o n d i t i o n s f o r s u b j e c t s 1 and 2. F o r s u b j e c t 3 t h i s d i f f e r e n c e r a r e l y r e a c h e d s i g n i f i c a n c e , a l t h o u g h t h e d i r e c t i o n o f t h e d i f f e r e n c e was t h e same, namely / u / was more ' i n c r e a s e d ' t h a n t h e low v o w e l s . The o n l y s i g n i f i c a n t b e t w e e n - c o n d i t i o n d i f -f e r e n c e s f o r ' s t r e s s e d ' v o w e l s ( n o t shown i n t a b l e form) were as f o l l o w s : w i t h r e s p e c t t o t h e SLOW SAF c o n d i t i o n , the, ' i n c r e a s e s ' f o r /o/ and / i / were e a c h s i g n i f i c a n t l y d i f f e r e n t f o r one s u b j e c t i n t h e FAST DAF c o n d i t i o n and / a / was s i g n i f i c a n t l y d i f f e r e n t f o r one s u b j e c t i n t h e SLOW DAF c o n d i t i o n . A n a l y s i s o f ; t h e v o w e l s i n t h e p a s s a g e s u b s t a n t i a t e d t h e a b o v e f i n d i n g s i n t h a t v o w e l s i n f u n c t i o n words ' i n -c r e a s e d ' more t h a n any o t h e r t y p e o f v o w e l and most a t t h e s l o w e s t r a t e , i . e . , i n t h e SLOW SAF c o n d i t i o n . The a v e r a g e RC v a l u e s f o r v o w e l s i n t h e p a s s a g e amounted t o 1.51 i n t h e SLOW SAF c o n d i t i o n , 1.3 8 i n t h e SLOW DAF - 76 -/ a / /?/ / i / /u/ SLOW SAF Subject 1 / a / 2 Subject 1 /5V 2 NS NS NS NS NS NS NS * NS **** **** NS * * **** NS Subject 1 / i / 2 NS * NS SLOW DAF Subject 1 / a / 2 Subject 1 /6/ 2 NS NS NS NS NS NS NS NS NS **** * * * *** ** * NS Subject 1 / ! / 2 * * NS NS FAST DAF Subject 1 / a / 2 Subject 1 75 / 2 NS NS NS NS * * * NS NS * NS * ** * NS NS NS NS NS Subject 1 / i / 2 NS NS NS Table V. W i t h i n - c o n d i t i o n d i f f e r e n c e s i n r e l a t i v e change of " s t r e s s e d 1 vowels. - 77 -c o n d i t i o n , and 1.2 0 i n the FAST DAF c o n d i t i o n . Why was /u/ more ' i n c r e a s e d ' than the other vowels and p a r t i c u l a r l y more than / a / i n the SLOW c o n d i t i o n s ? Two d i f f e r e n t answers w i l l be examined i n d e t a i l : (a) the vowel /u/ i t s e l f d i f f e r s from the other vowels such t h a t i t e x p l a i n s the g r e a t e r ' i n c r e a s e ' , (b) the environment i n which /u/ o c c u r r e d , d i f f e r e d " f r o m the environment i n which the other vowels o c c u r r e d such, t h a t i t w i l l e x p l a i n the g r e a t e r ' i n c r e a s e ' . (a) The vowel /u/ d i f f e r s , as does / i / , from / a / and /o/ i n t h a t i t has a lower i n t r i n s i c amplitude ( L e h i s t e and Peterson, 1959) and /u/ d i f f e r s from a l l other vowels i n t h a t i t i s c l o s e and back. Why /u/ should behave d i f f e r -e n t l y cannot be e x p l a i n e d i n terms of these f a c t s . (b) House and Fairbanks (1953) found t h a t v o i c i n g , manner and p l a c e of a r t i c u l a t i o n , i n t h a t o r d e r , e x e r t an i n f l u e n c e on vowel d u r a t i o n , e.g., i n v o i c e d environments vowels are g e n e r a l l y longer; when preceded and f o l l o w e d by f r i c a t i v e s , vowels are longer, whereas when preceded and f o l l o w e d by stops, vowels are g e n e r a l l y s h o r t e r ; when pre -ceded and f o l l o w e d by consonants with a b i l a b i a l p l a c e of a r t i c u l a t i o n , vowels are g e n e r a l l y s h o r t e r . A c c o r d i n g to Peterson and L e h i s t e (1960) , the i n f l u e n c e of the preceding consonant on vowel d u r a t i o n i s minimal. Chen (197 0) con-firm e d t h a t the i n c r e a s e i n vowel d u r a t i o n b e f o r e a v o i c e d consonant i s t r u e f o r o t h e r languages as w e l l . D e l a t t r e (1962) suggested t h a t the changes i n vowel d u r a t i o n are - 78 -f o r t h e most p a r t p h y s i o l o g i c a l l y c o n d i t i o n e d , i . e . , " a n t i -c i p a t i o n o f g r e a t e r e f f o r t " ( c l u s t e r s , c l o s u r e s , no v o i c i n g ) "would make one ' s h o r t e n ' t h e v o w e l " ( i b i d . , p. 1 1 4 2 ) . Chen (1970) p r o p o s e d t h a t o b s e r v e d f a s t e r t r a n s i t i o n s f r o m an open v o c a l t r a c t (vowel) t o a more c l o s e p o s i t i o n f o r a v o i c e l e s s c o n s o n a n t e x p l a i n most s a t i s f a c t o r i l y t h e s h o r t e r d u r a t i o n o f a v o w e l b e f o r e a v o i c e l e s s s t o p . When t h e / u / s e n t e n c e i s now compared w i t h t h e o t h e r s e n t e n c e s , i t i s e v i d e n t t h a t / u / a p p e a r e d more f r e q u e n t l y i n an e n v i r o n m e n t w h i c h r e s u l t s i n a s h o r t e r d u r a t i o n o f t h e v o w e l a c c o r d i n g t o t h e above f i n d i n g s . The v o w e l o c c u r r i n g l e a s t f r e q u e n t l y i n s u c h an e n v i r o n m e n t was / a / . Does t h i s i m p l y t h a t , when t h e r a t e o f s p e e c h i s d e c r e a s e d , v o w e l s i n an e n v i r o n m e n t , w h i c h r e s u l t s i n a l o n g e r v o w e l d u r a t i o n , a r e p r o l o n g e d r e l a t i v e l y more t h a n v o w e l s i n an e n v i r o n m e n t w h i c h s h o r t e n s t h e d u r a t i o n o f t h e v o w e l ? I n o t h e r t e r m s , do l o n g e r segments a t s l o w e r r a t e s o f s p e e c h t e n d t o be r e l a t i v e l y more p r o l o n g e d t h a n s h o r t e r segments? The o t h e r f a c t o f i n t e r e s t e m e r g i n g f r o m t h e an-a l y s i s o f ' s t r e s s e d ' v o w e l s was t h e c o n s i s t e n t l y g r e a t e r ' i n c r e a s e ' f o r / $ / i n t h e FAST DAF c o n d i t i o n . I n v i e w o f t h e e a r l i e r r e p o r t e d f i n d i n g s by Sussman and S m i t h (1971) t h a t jaw a c t i v i t y f o r t h e v o w e l s / i / , / e / and /ae/ was l o n g -e s t a t 100-msec d e l a y , i t i s p e r h a p s n o t t o o s u r p r i s i n g t h a t i n t h e p r e s e n t s t u d y , where l o n g e r t h a n 100-msec de-l a y s were u s e d , no c o n s i s t e n t ' i n c r e a s e s ' u n d e r DAF f o r t h e - 79 -v o w e l s / £ / , / u / and / a / were f o u n d . How, t h e n , c a n t h e c o n s i s t e n t ' i n c r e a s e s ' f o r /6/ be e x p l a i n e d ? I s i t p o s -s i b l e , t h a t f o r /6 / a l o n g e r t h a n 100-msec d e l a y i s needed t o p roduce l o n g e s t jaw a c t i v i t y ? Any h y p o t h e s i s w h i c h w o u l d a t t e m p t t o e x p l a i n s e l e c t i v e v o w e l d u r a t i o n under DAF w o u l d have t o a c c o u n t f o r t h e d i s t a n c e t h e a r t i c u l a t o r s have t o move from t h e r e s t p o s i t i o n as w e l l as f o r c r i t i c a l t i m e d e l a y s . I n t h e p r e s e n t s t u d y , v o w e l c o n t e x t , w h i c h t u r n e d o u t t o be a p o s s i b l e s o u r c e o f v a r i a t i o n o f ' i n -c r e a s e s ' f o r v o w e l s , was n o t c o n t r o l l e d w e l l enough , so t h a t no such h y p o t h e s i s c an be o f f e r e d . 4 6.3 R e l a t i v e Change o f Consonan t s I n g e n e r a l , c o n s o n a n t s t e n d e d t o be ' d e c r e a s e d ' i n t h e SLOW SAF c o n d i t i o n , whereas v o w e l s showed an ' i n -c r e a s e ' . The e f f e c t was s t a t i s t i c a l l y s i g n i f i c a n t beyond the 0.01% l e v e l w i t h one e x c e p t i o n f o r t he t h r e e s u b j e c t s . Consonan t s t ended t o be ' d e c r e a s e d ' a l s o i n t h e SLOW DAF and FAST DAF c o n d i t i o n s b u t n o t as c o n s i s t e n t l y o r as s i g n i f i c a n t l y as i n the SLOW SAF c o n d i t i o n . T h i s was a l s o t r u e f o r t h e a n a l y z e d m a i n e x p e r i m e n t p a s s a g e . I t has been s u g g e s t e d when t h e g r e a t e r ^ inc reases f o r / d / i n t h e SLOW c o n d i t i o n s were d i s c u s s e d , t h a t an e n v i r o n m e n t w h i c h r e s u l t s i n a l o n g e r segment d u r a t i o n , a l s o appea r s t o r e s u l t i n g r e a t e r ' i n c r e a s e s ' a t s l o w e r r a t e s f o r t h a t segment . The q u e s t i o n was a s k e d whe the r l o n g e r segments a t s l o w e r r a t e s o f speech t e n d t o be - 80 -r e l a t i v e l y more p r o l o n g e d t h a n s h o r t e r s egmen t s . I f t h i s i s i n f a c t t h e ca se t h e n i t w o u l d seem r e a s o n a b l e t h a t c o n s o n a n t s , i n p a r t i c u l a r n o n c o n t i n u a n t s , s h o u l d be ' d e -c r e a s e d ' o r l e s s ' i n c r e a s e d ' i n c o m p a r i s o n w i t h v o w e l s . Under DAF a number o f o t h e r f a c t o r s must be c o n -s i d e r e d . A d i s c u s s i o n f o l l o w s a f t e r t h e r e s u l t s o f t h e c o n s o n a n t a n a l y s i s a r e r e p o r t e d . I n t h e s t a t e m e n t s b e l o w , ' i n i t i a l ' and ' f i n a l ' w i l l r e f e r n o t n e c e s s a r i l y j u s t t o t h e f i r s t o r l a s t c o n s o n a n t i n t h e s y l l a b l e b u t w i l l mean p r e - o r p o s t v o c a l i c r e s p e c t i v e l y . F i g u r e 6 .5 shows t h e ave rage RC f o r ' i n i t i a l ' c l o s u r e and ' f i n a l ' s t o p s , and f o r ' i n i t i a l ' / m / and ' f i n a l ' n a s a l s . As can be s e e n , ' i n i t i a l ' c l o s u r e and ' i n i t i a l ' / m / e i t h e r ' i n c r e a s e d ' more under the DAF c o n d i t i o n s o r ' d e c r e a s e d ' l e s s t h a n i n the SLOW SAF c o n d i t i o n . , ' F i n a l ' n a s a l s c o n s i s t e n t l y ' i n c r e a s e d ' i n t h e SLOW SAF c o n d i t i o n and e i t h e r ' i n c r e a s e d ' l e s s o r ' d e c r e a s e d ' i n t h e DAF c o n d i t i o n s . As can be s e e n , no c o n s i s t e n t p a t t e r n emerged f o r t h e ' f i n a l ' v o i c e l e s s s t o p s . I t w i l l be remembered t h a t ' i n i t i a l ' c l o s u r e r e -f e r s i n t h i s s t u d y t o the c l o s u r e p a r t o f an ' i n i t i a l ' s t o p o n l y , whereas ' f i n a l ' s t o p i n c l u d e s the r e l e a s e o f t h e c l o s u r e and a s p i r a t i o n . A n a l y s i s o f t he passage r e v e a l e d t h a t ' i n i t i a l ' / b / was a l s o i n c r e a s e d under t h e DAF c o n -d i t i o n s , t h e i n c r e a s e i n t h e DAF c o n d i t i o n s b e i n g h i g h l y s i g n i f i c a n t l y d i f f e r e n t f rom t h e SLOW SAF c o n d i t i o n . I n t h e s e n t e n c e s , where no s u c h o b s e r v a t i o n was made, / b / o c c u r r e d o n l y a f t e r a c o n s o n a n t p r e v o c a l i c a l l y , whereas i n - 81 -• I n i t i a l ' v o i c e l e s s c l o s u r e SUBJECT I • i SLOW SAF | | SLOW DAF FAST DAF SUBJECT 2 1 SUBJECT 3 SUBJECT (PASSAGE) ' F i n a l ' ' I n i t i a l ' ' F i n a l ' v o i c e l e s s / m / N a s a l s s t o p s F i g u r e 6 . 5 . R e l a t i v e change i n ' i n i t i a l ' v o i c e l e s s c l o s u r e , ' f i n a l ' v o i c e l e s s s t o p s , ' i n i t i a l ' / m / and ' f i n a l ' n a s a l s . - 82 -the passage /b/ oc c u r r e d o n l y w o r d - i n i t i a l l y . F i g u r e 6.6 shows the r e l a t i v e change f o r a s p i r a t i o n a s s o c i a t e d w i t h the r e l e a s e of ' i n i t i a l ' v o i c e l e s s s t o p s . As can be seen, a s p i r a t i o n 'decreased' f o r a l l s u b j e c t s i n a l l c o n d i t i o n s . However, when between-condition d i f f e r e n c e s i n r e l a t i v e change f o r a s p i r a t i o n are examined, i t can be seen i n F i g -ure 6.6 t h a t s u b j e c t s 1 and 2 showed an even f u r t h e r 'de-crease' i n a s p i r a t i o n i n the DAF c o n d i t i o n s , whereas sub-j e c t 3 showed a l e s s e r 'decrease*. Table VI shows the s t a t i s t i c a l s i g n i f i c a n c e of these o b s e r v a t i o n s . Subject 3 d i f f e r e d f u r t h e r from s u b j e c t s 1 and 2 i n t h a t f r i c a -t i v e s were e i t h e r more 'i n c r e a s e d ' or l e s s ' d e c r e a s e d 1 i n the DAF c o n d i t i o n s than i n the SLOW SAF c o n d i t i o n ; ( s i g n i f i c a n t a t the .05% l e v e l i n the SLOW DAF c o n d i t i o n and at the .005% l e v e l i n the FAST DAJT c o n d i t i o n ) . The d i f f e r e n c e s , although i n the same d i r e c t i o n f o r s u b j e c t s 1 and 2, d i d not reach s i g n i f i c a n c e f o r these s u b j e c t s . Haggard (1971) , as quoted i n MacNeilage (1972) , found t h a t of the p o s t v o c a l i c consonants, the a b s o l u t e l y f i n a l consonants appear t o have the l o n g e s t d u r a t i o n s . In the pr e s e n t study, consonants i n t h i s p o s i t i o n were f r e q u e n t l y more ' i n c r e a s e d ' than consonants i n other p o s i -t i o n s i n the SLOW SAF c o n d i t i o n . ' F i n a l ' n a s a l s i l l u s t r a t e t h i s p o i n t , i n t h a t f o r a l l s u b j e c t s the h i g h e s t RC va l u e s f o r ' f i n a l ' n a s a l s were ob t a i n e d c o n s i s t e n t l y i n a b s o l u t e l y f i n a l p o s i t i o n . T h i s appears t o f u r t h e r c o n f i r m the impression t h a t at a slower r a t e , the normally longer - 83 -• H SLOW SAF I I SLOW DAF S 5 3 FAST DAF 0 — SUBJECT I SUBJECT 2 S U B J E C T 3 F i g u r e 6 . 6 . R e l a t i v e change i n a s p i r a t i o n i n t h e SLOW S A F , SLOW DAF and FAST DAF c o n d i t i o n s w i t h r e s p e c t t o t h e NORMAL CONDITION. - 84 -SLOW DAF FAST DAF SLOW SAF S u b j e c t 1 2 3 NS * * * * NS T a b l e V I . B e t w e e n - c o n d i t i o n d i f f e r e n c e s i n r e l a t i v e change o f a s p i r a t i o n a f t e r ' . i n i t i a l ' v o i c e l e s s c l o s u r e . - 85 -segments are 'in c r e a s e d ' more than normally s h o r t e r seg-ments, o r 'decreased' l e s s . I f t h i s impression i s t r u e , then i t would be expected t h a t under the SLOW SAF con-d i t i o n c l o s u r e would e x h i b i t the lowest RC v a l u e . T h i s was not always the case, p a r t i c u l a r l y not f o r v o i c e d c l o -sure. Furthermore, of the d i f f e r e n t c l o s u r e s one might ex-pect the b i l a b i a l c l o s u r e t o show a higher RC value under the SLOW SAF c o n d i t i o n than d e n t a l or v e l a r c l o s u r e s be-cause, as MacNeilage (1972) has p o i n t e d out, b i l a b i a l c l o s u r e can be maintained longer than d e n t a l or v e l a r c l o -sure s i n c e the tongue i n the l a t t e r c l o s u r e s i s needed i n the next a r t i c u l a t i o n . However, the expected sys t e m a t i c d i f f e r e n c e s i n r e l a t i v e change f o r the d i f f e r e n t c l o s u r e s were not found. I t appears then, t h a t , while i t i s tr u e t h a t i n the SLOW SAF c o n d i t i o n vowels are more'increased' than consonants and vowels i n an environment, i n which the vowel i s longer, more 'i n c r e a s e d ' than vowels i n an e n v i r -onment, i n which the vowel i s s h o r t e r , and a b s o l u t e l y f i n a l consonants more 'in c r e a s e d ' than consonants i n other p o s t -v o c a l i c p o s i t i o n s , i t i s not t r u e t h a t a l l normally longer segments are more 'i n c r e a s e d ' under the SLOW SAF c o n d i t i o n . Instead, p o s i t i o n i n the s y l l a b l e , v o i c i n g , and p l a c e and manner of a r t i c u l a t i o n , beyond a simple stop / co n t i n u a n t dimension f o r consonants, a l l appear to p l a y d i f f e r e n t i a l r o l e s i n determining ' i n c r e a s e s ' f o r consonants i n the SLOW SAF c o n d i t i o n . In order t o s p e c i f y the r o l e of each of the parameters, environment would have to be s t r i c t l y - 86 -c o n t r o l l e d . The f i n d i n g s of the consonant a n a l y s i s are best d i s c u s s e d , however, i n terms of r e a c t i o n to DAF. To sum-marize, ' i n i t i a l ' v o i c e l e s s c l o s u r e , ' i n i t i a l ' v o i c e d c l o -sure (not i n a c l u s t e r ) , ' i n i t i a l ' /m/ and f r i c a t i v e s showed a g r e a t e r ' i n c r e a s e ' or a l e s s e r 'decrease' i n the DAF c o n d i t i o n s than i n the SLOW SAF c o n d i t i o n . F u r t h e r a n a l y s i s r e v e a l e d t h a t b i l a b i a l c l o s u r e c o n t r i b u t e d the most to the observed d i f f e r e n c e s i n v o l v i n g c l o s u r e , i n t h a t b i l a b i a l c l o s u r e e x h i b i t e d most c o n s i s t e n t l y a high e r RC val u e under DAF than under SLOW SAF. I t must be p o i n t e d out here, t h a t the observed d i f f e r e n c e s i n r e l a t i v e change f o r ' i n -i t i a l ' c l o s u r e cannot be e x p l a i n e d i n terms of c o n s i s t e n t l y lower RC va l u e s f o r c l o s u r e s under the SLOW SAF c o n d i t i o n , but i n s t e a d the d i f f e r e n c e s must be a t t r i b u t e d to the DAF e f f e c t . I t w i l l be remembered t h a t Huggins (1968) found t h a t i n i t i a l v o i c e l e s s c l o s u r e grew l i n e a r l y w i t h d e l a y . ' I n i t i a l ' p o s i t i o n appears t o be a c r u c i a l parameter i n determining ' i n c r e a s e s ' under DAF. MacNeilage (1972) i n a d i s c u s s i o n o f c l o s e d loop c o n t r o l system i n speech con-cludes t h a t one cannot assume t h a t a u d i t o r y feedback p l a y s an important r o l e i n the c o n t r o l of running speech, but somatic sensory c o n t r o l i s co n s i d e r e d necessary f o r the i n i t i a t i o n of speech. "The command necessary f o r an a r t i c u l a t o r to reach a f i x e d s p e e c h - i n i t i a l p o s i t i o n must be c o n d i t i o n a l upon the pre-speech p o s i t i o n of t h a t a r t i c u l a t o r which no doubt v a r i e s from o c c a s i o n t o o c c a s i o n . " (ibid.,pp.44-45). - 87 -I t i s e n t i r e l y p o s s i b l e , t h a t i n the normal case t h i s i s the o n l y type of feedback needed f o r the i n i t i a t i o n of speech. I f the system under DAF, however, r e c e i v e s the normal somatic sensory feedback with r e s p e c t to a r t i c u l a t o r p o s i t i o n and a t the same time r e c e i v e s a i r - c o n d u c t e d audi-^-t o r y feedback which informs the system t h a t i t (the a i r -conducted a u d i t o r y feedback) i s at v a r i a n c e w i t h the som-a t i c sensory i n f o r m a t i o n , then h e s i t a t i o n might be expected. I f we furthermore assume t h a t once speech i s i n i t i a t e d an open loop system takes over, than i t i s p o s s i b l e t h a t under DAF the beginning of a speech u n i t should be prolonged r e l a t i v e l y more than would be expected f o r a slower r a t e of speech. T h i s does not e x p l a i n the g r e a t e r ' i n c r e a s e s ' f o r vowels. However, s i n c e vowels were more 'in c r e a s e d ' a l s o a t the slower r a t e of speech under SAF, t h i s phenomen-on cannot be a t t r i b u t e d to DAF but must be c o n s i d e r e d t y p i -c a l of a slower r a t e of speech i n g e n e r a l . 5 . . 6.3 R e p e t i t i o n s F i g u r e 6.7 shows the number of r e p e t i t i o n s of d i f -f e r e n t d u r a t i o n s f o r each s u b j e c t i n the FAST DAF c o n d i t i o n and the cumulative % r e p e t i t i o n s . The graphs r e v e a l e d t h a t l e n g t h o f the repeated segments, as d e f i n e d i n chapter 5, c o r r e l a t e d w i t h the l e n g t h of delay under which they were produced. As can be seen, s u b j e c t 1 repeated more f r e q u e n t l y than s u b j e c t 2 and s u b j e c t 2 more f r e q u e n t l y than s u b j e c t 3. I t might be mentioned here t h a t the l a t t e r 2 7 -o b 6 -i— Q. ° rr 4 -cr u CD 2 -O -I I I D U R A T I O N I 2 5 I 7 5 I 125 I 175 I 2 2 5 I 2 7 5 I 3 2 5 I 3 7 5 I 4 2 5 O 5 0 100 150 2 0 0 2 5 0 3 0 0 3 5 0 4 0 0 S I I I I I I I I I I I | I I I I 2 5 I 7 5 I 125 I 175 ' 2 2 5 I 2 7 5 ' 3 2 5 0 5 0 100 150 2 0 0 2 5 0 3 0 0 I I I 1 I 1 I 1 I 1 I 1 I I 2 5 I 7 5 I 125 I 175 I. 2 2 5 ' 2 7 5 I 0 5 0 100 150 2 0 0 2 5 0 3 0 0 100 — 2 9 0 -o P 8 0 -7 0 -tu CL UJ DC 6 0 -4 0 -C 3 0 -< 3 O 2 0 -10-0 — D U R A T I O N I 2 5 I 7 5 I 125 I 175 I 2 2 5 I 2 7 5 I 3 2 5 I 3 7 5 I 4 2 5 0 5 0 1 0 0 1 5 0 2 0 0 2 5 0 3 0 0 3 5 0 4 0 0 S U B J E C T I D e l a y u sed i n t he e x p e r i m e n t : 2 4 0 I 2 5 I 7 5 I 125 I 175 I 2 2 5 I 2 7 5 I 3 2 5 0 5 0 1 0 0 150 2 0 0 2 5 0 3 0 0 S U B J E C T 200 oo 00 I I I I I I I I I I' I I I I 2 5 I 7 5 I 125 I 175 I 2 2 5 I 2 7 5 I 0 5 0 100 150 2 0 0 2 5 0 3 0 0 S U B J E C T 3 230 F i g u r e 6 . 7 . Number o f r e p e t i t i o n s and c u m u l a t i v e % r e p e t i t i o n s i n the FAST DAF c o n d i t i o n . - 89 -f i n d i n g was a l s o t r u e f o r other a d d i t i o n s to the expected sequence of a r t i c u l a t i o n . Subject 1 e x h i b i t e d by f a r the most a d d i t i o n s u n r e l a t e d to the t e x t and r a t h e r b i z a r r e h. i n nature, e.g., /kam fa&e*-/ became /k ambagl f ep af aoa"/• In the SLOW DAF c o n d i t i o n o n l y a few i s o l a t e d r e p e t i t i o n s o c c u r r e d which i s i n agreement w i t h MacKay's (1968) f i n d i n g t h a t under DAF a t a slower r a t e r e p e t i t i o n s decrease i n number. In view of the r a r i t y w i t h which m u l t i p l e repe-t i t i o n s have been observed f o r E n g l i s h speakers under DAF by p a s t experimenters, i t might be noted here, t h a t although s u b j e c t s 2 and 3 p r i m a r i l y e x h i b i t e d double r e p e t i t i o n s , s u b j e c t 1 f r e q u e n t l y produced m u l t i p l e r e p e t i t i o n s (up to f i v e r e p e t i t i o n s i n one i n s t a n c e ) . T h i s does suggest t h a t m u l t i p l e r e p e t i t i o n s are not p e c u l i a r t o the Russian speak-ers i n the Kozhevnikov and C h i s t o v i c h (1965) study. Fur-thermore, these r e p e t i t i o n s were always, r e p e t i t i o n s of open s y l l a b l e s , which i s i n agreement wi t h the f i n d i n g s of the above authors. F i n a l l y , i t was observed t h a t when a vowel was repeated a t the b e g i n n i n g of a s y l l a b l e , e.g., / i ? i s t / , a g l o t t a l stop was i n s e r t e d , and when a vowel was repeated a f t e r a consonant, e.g., /kaham/, an /h/ was i n s e r t e d . L a r y n g e a l i z a t i o n f r e q u e n t l y preceded a vowel i n s y l l a b l e -i n i t i a l p o s i t i o n i n the DAF c o n d i t i o n s . Stromsta (1959) found t h a t s i d e - t o n e , which was d i s t o r t e d by a l t e r i n g i t s frequency components or i t s a r r i v a l phases at the two e a r s , produced a blockage i n phonation while phonating a vowel i n f a l s e t t o . Van Riper - 90 -(1971), who, l i k e many others ( f o r a review see Timmons and Boudreau,1972), c o n s i d e r n a t u r a l and a r t i f i c i a l s t u t t e r to be s i m i l a r behaviours, h y p o t h e s i z e d t h a t asynchronies i n t i m i n g of a n t a g o n i s t i c muscle groups a t the l a r y n g e a l l e v e l are r e s p o n s i b l e f o r the observed s t u t t e r . In support of such a theory, Freeman and Us h i j i m a (1974) on the b a s i s of t h e i r experiments, s t a t e : " f l u e n t u t t e r a n c e i s c h a r a c t e r i z e d by p r e -c i s e balance and t i m i n g of l a r y n g e a l abductor and adductor f o r c e s . In f l u e n t u t t e r a n c e abductor and adductor f o r c e s a c t r e c i p r o c a l l y , whereas, i n s t u t t e r e d u t t e r a n c e , t h i s r e c i -p r o c i t y i s d i s r u p t e d . In many s t u t t e r e d u t t e r a n c e s the l a t e r a l c r i c o a r y t e n o i d - g e n -e r a l l y presumed to be an adductor, w i t h the s p e c i f i c f u n c t i o n of medial compression-achieved abnormally h i g h l e v e l s o f a c t i v i t y . " ( i b i d . , p. S80). The l a r y n g e a l i z a t i o n and i n s e r t i o n o f g l o t t a l stops observed under DAF i n t h i s study and a l s o the 'decrease' i n a s p i r a -t i o n under DAF a f t e r ' i n i t i a l ' v o i c e l e s s c l o s u r e would tend to c o n f i r m t h a t the e f f e c t s of DAF on speech are not u n l i k e those of n a t u r a l or a r t i f i c i a l s t u t t e r . I t i s of p a r t i c u l a r i n t e r e s t i n t h i s r e s p e c t t h a t those s u b j e c t s most a f f e c t e d by DAF showed a g r e a t e r 'decrease' of a s p i r a t i o n under DAF than i n the SLOW SAF c o n d i t i o n , whereas the s u b j e c t l e a s t a f f e c t e d showed a l e s s e r 'decrease'. No e x p l a n a t i o n can be o f f e r e d a t t h i s time f o r the d i f f e r e n t i a l i n s e r t i o n of g l o t t a l stops and /h/. Nor can the b i z a r r e i n s e r t i o n s i n t o the expected sequence of a r t i c u l a t i o n be reasonably e x p l a i n -ed. The c o r r e l a t i o n of the d u r a t i o n s of repeated segments w i t h the de l a y under which they were produced, i s i n - 91 -agreement w i t h the f i n d i n g s r e p o r t e d by Huggins (1968). In summary, the i n v e s t i g a t i o n of i n s e r t i o n s i n t o the e x p e c t e d sequence o f a r t i c u l a t i o n s u g g e s t s t h a t (a) m i s t i m i n g a t the l a r y n g e a l l e v e l a c c o u n t s f o r some o f the speech d i s t u r b a n c e s o b s e r v e d under DAF, (b) t ime r e l a t i o n -s h i p s are a c r u c i a l a s p e c t o f b e h a v i o u r under DAF i n t h a t the d u r a t i o n s of r e p e t i t i o n s are r e l a t e d to the d e l a y under which they were produced and (c) m u l t i p l e r e p e t i t i o n s c o n s t i t u t e s a b e h a v i o u r which must i n the l a s t a n a l y s i s be e x p l a i n e d i n terms of i n d i v i d u a l d i f f e r e n c e s . " A major c h a l l e n g e t h a t i s emerging f o r r e s e a r c h e r s i n speech p h y s i o l o g y , when they use s e v e r a l s u b j e c t s i n t h e i r e x p e r -i m e n t s , i s t o d e v e l o p speech p r o d u c t i o n t h e o r i e s which take t h e s e i n d i v i d u a l d i f f e r e n c e s i n t o a c c o u n t r a t h e r t h a n i g n o r i n g t h e m . " ( M a c N e i l a g e , 1972 ,pp. 22 -23) . 6.4 Summary and C o n c l u s i o n s T h i s s tudy has examined and compared speech a t a normal r a t e and a t a slow r a t e under synchronous feedback and speech under DAF a t b o t h a slow and m a x i m a l l y f a s t r a t e . I t was found t h a t c o n s i d e r a b l e i n d i v i d u a l d i f f e r -ences e x i s t i n terms of the degree of speech d i s t u r b a n c e produced i n the s u b j e c t s under DAF. A r e c i p r o c a l r e l a t i o n -s h i p between p r o l o n g a t i o n and r e p e t i t i o n , i . e . , the more o v e r a l l p r o l o n g a t i o n , the fewer the r e p e t i t i o n s , e x i s t e d o n l y when r a t e was v a r i e d under DAF. A t a maximum r a t e , s u b j e c t s who p r o l o n g e d more a l s o r e p e a t e d f r e q u e n t l y . In o t h e r t e r m s , i t was not t r u e t h a t the s u b j e c t who r e p e a t e d - 92 -most f r e q u e n t l y , showed the l e a s t amount of o v e r a l l p r o -l o n g a t i o n . R e p e t i t i o n s a t the maximum r a t e under DAF ap-peared t o be r e l a t e d t o the del a y under which they were produced. While the h y p o t h e s i s t h a t under SLOW SAF vowels are prolonged more than consonants was s u b s t a n t i a t e d , i t co u l d not be confirmed t h a t under SLOW SAF w i t h i n the c l a s s of vowels, c l o s e vowels are prolonged more than open vow-e l s . The hy p o t h e s i s t h a t under SLOW SAF c o n t i n u a n t con-sonants are prolonged more than o b s t r u e n t s was a l s o not s u b s t a n t i a t e d . The hypothesis t h a t under DAF vowels and f r i c a t i v e s are prolonged the most and t h a t p o s i t i o n w i t h i n the s y l l a b l e a f f e c t s the d u r a t i o n i n c r e a s e s of each sound c l a s s s e l e c t -i v e l y was confirmed. The hypothesis t h a t speech under SLOW SAF would d i f f e r from speech under DAF was s u b s t a n t i a t e d i n t h a t under DAF open back vowels, f r i c a t i v e s , i n i t i a l v o i c e l e s s c l o -sure and a l l i n i t i a l b i l a b i a l c l o s u r e was r e l a t i v e l y more prolonged then under SLOW SAF whereas under SLOW SAF con-sonants i n f i n a l p o s i t i o n were r e l a t i v e l y more prolonged than under DAF. I t had a l s o been hypothesized t h a t s t r e s s would determine r e l a t i v e amount of p r o l o n g a t i o n under SLOW SAF. I t was found t h a t under SLOW SAF and under SLOW DAF and to a l e s s e r extent under FAST DAF each s y l l a b l e formed a beat i n the rhythmic s u c c e s s i o n of speech u n i t s , i . e . , there - 93 -a r e no u n s t r e s s e d segments a t v e r y s low r a t e s o f speech. The b eat m a n i f e s t s i t s e l f i n r e l a t i v e i n c r e a s e s i n d u r a t i o n o f t h e vowel i n the s y l l a b l e and i n c r e a s e d speech power i n comparison w i t h speech a t a normal r a t e . Thus, n o r m a l l y u n s t r e s s e d segments, e.g., f u n c t i o n words, a t a v e r y slow r a t e i n c r e a s e r e l a t i v e l y more i n d u r a t i o n t h a n n o r m a l l y s t r e s s e d segments. I n v i e w o f t h e d i s c u s s i o n (Chapter 2 ) , i t can be r e a s o n a b l y assumed t h a t s l o w i n g a t a v o l u n t a r i l y slowed r a t e under SAF i s not due t o s l o w i n g a t a r e f l e x l e v e l , i . e . , a p e r i p h e r a l l e v e l , b u t r a t h e r t h a t such a v o l u n t a r y s l o w i n g must t a k e p l a c e a t a c e n t r a l l e v e l , such as t h e motor c o n t r o l programme l e v e l proposed by A l l e n (1973). When t h e r a t e i s slowed under DAF by c o m p l y i n g w i t h t h e DAF e f f e c t , s l o w i n g can be s a i d t o be v o l u n t a r y as w e l l . Thus, s i m i l a r i t i e s i n t h e r e s u l t i n g b e h a v i o u r might be e x p e c t e d . A t a m a x i m a l l y f a s t r a t e under DAF no v o l u n t a r y s l o w i n g t a k e s p l a c e . Any s l o w i n g must be a t t r i b u t e d t o t h e DAF e f f e c t . One m ight assume t h a t t h e d i f f e r e n c e s i n speech b e h a v i o u r under SLOW SAF and under DAF a r e a t t r i b u t -a b l e t o d i f f e r e n c e s i n t h e l e v e l a t which s l o w i n g t a k e s p l a c e . I f one assumes t h a t v o l u n t a r y r a t e changes a r e de-t e r m i n e d a t a c e n t r a l l e v e l , t h a n th e o b s e r v e d d i f f e r e n c e s between v o l u n t a r i l y slowed speech and DAF-slowed speech might be a t t r i b u t a b l e t o i n t e r f e r e n c e a t t h e r e f l e x l e v e l , w h i l e o b s e r v e d s i m i l a r i t i e s m ight be a t t r i b u t a b l e e i t h e r t o i n t e r f e r e n c e a t a c e n t r a l l e v e l , o r a l s o t o r e f l e x l e v e l - 94 -i n t e r f e r e n c e , i f r e f l e x l e v e l i n t e r f e r e n c e i s s i m i l a r i n these r e s p e c t s (from the p o i n t of view of r e s u l t s ) to cen-t r a l i n t e r f e r e n c e . In any event, one cannot deny t h a t the r e f l e x l e v e l i s i n v o l v e d i n DAF-induced changes i n the speech behaviour, e s p e c i a l l y i n view of the involvement of the l a r y n x as evidenced by f r e q u e n t l a r y n g e a l i z a t i o n under DAF. The p r e v o c a l i c r a t h e r than p o s t v o c a l i c slowing observed under DAF and not under SLOW SAF seems to i n d i c a t e t h a t the s y l l a b l e i s a monitored u n i t i n speech p r o d u c t i o n under DAF; once speech i s i n i t i a t e d , i t i s a b l e to procede towards i t s c o n c l u s i o n , the next i n t e r f e r e n c e being n o t i c e -a b l e a g a i n a t the i n i t i a t i o n o f the next speech u n i t . 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"The E f f e c t s o f A u d i t o r y Feedback as a F u n c t i o n o f F r e q u e n c y , I n t e n s i t y , T i m e , and S e x , " De T h e r a p i a V o c i s e t L o q u e l a e IJE, 2 3 3 - 2 3 5 . - 97 -PETERSON, G., and L E H I S T E , I . ( 1 9 6 0 ) . " D u r a t i o n o f S y l l a b l e N u c l e i i n E n g l i s h , " J . A c o u s t . S o c . Amer. 32, 693-703. PETERSON, G.E., and McKINNEY, N.P. ( 1 9 6 1 ) . "The Measurement o f S p e e c h Power," P h o n e t i c a ]_, 65. RAWNSLEY, A . I . , and HARRIS, J.D. ( 1 9 5 4 ) . " C o m p a r a t i v e A n a l y s i s o f N o r m a l S p e e c h and S p e e c h w i t h D e l a y e d S i d e - T o n e by Means o f Sound S p e c t r o g r a m s , " Med. Res. L a b . Rep. No. 248, B u r e a u o f M e d i c i n e and S u r g e r y , Navy D e p t . P r o j . NM 003 041.56.03, 13, No. 9. ROBINSON, G.M. ( 1 9 7 2 ) . "The D e l a y e d A u d i t o r y F e e d b a c k E f f e c t i s a F u n c t i o n o f S p e e c h R a t e , " J . Exp. P s y c h o l . 95, 1-5. SALTER, D. ( 1 9 7 3 ) . " C a p a c i t y and D e l a y e d S p e e c h , " B r . J . P s y c h o l . 6_4, 193-198. SMITH, K.U. ( 1 9 6 2 ) . D e l a y e d S e n s o r y F e e d b a c k and B e h a v i o u r (W.B. S a u n d e r s Co., P h i l a d e l p h i a & L o n d o n ) . STROMSTA, C P . (1959.) " E x p e r i m e n t a l B l o c k a g e o f P h o n a t i o n by D i s t o r t e d S i d e t o n , " J . S p e e c h H e a r i n g Res. 2, 286-301 SUSSMAN, H.M., and SMITH, K.U. ( 1 9 7 0 ) . "Jaw Movements u n d e r D e l a y e d A u d i t o r y F e e d b a c k , " J . A c o u s t . S o c . Amer. 5fJ, 685-691. TIMMONS, B.A. ( 1 9 7 1 ) . "Sex as a F a c t o r I n f l u e n c i n g S e n s i t i -v i t y t o D e l a y e d A u d i t o r y F e e d b a c k , " P e r c e p t u a l and M o t o r S k i l l s 32, 82*4-826. TIMMONS, B.A.,.and BOUDREAU,J.P. ( 1 9 7 2 ) . " A u d i t o r y F e e d -b a c k as a M a j o r F a c t o r i n S t u t t e r i n g , " J . S p e e c h H e a r i n g D i s . 3_7, 476-484. VAN RIPER, C. (-1971) . The N a t u r e o f S t u t t e r i n g ( P r e n t i c e -H a l l , I n c . , E n g l e w o o d C l i f f s , N . J . ) . YATES, A . J . ( 1 9 6 5 ) . " D e l a y e d A u d i t o r y F e e d b a c k and Shadow-i n g , " Q u a r t . J . Exp. P s y c h o l . 1_7, 125-131. ZELNIKER, T. ( 1 9 7 1 ) . " P e r c e p t u a l A t t e n u a t i o n o f an I r r e l e -v a n t A u d i t o r y V e r b a l I n p u t as M e a s u r e d by an I n v o l u n t a r y V e r b a l R e s p o n s e i n a S e l e c t i v e - A t t e n t i o n Task,". J . Exp. P s y c h o l . 87, 52-56. - 98 -Number of Delay Level or Gain of Error and Duration Experimenter Subjects in msec. feedback signal Measures Lee (1950b) 5 0,40,140,280 unspecified (high Total duration enough to produce sub-stantial disturbance Black (1951) 22 0 to 300 in 85-90 dB at earphones Mean of total duration 30 msec. increments Fairbanks 16 0,100,200, 30 dB above an arbitrary a) total instances of error, (1955) 400,800 reference b) total duration c) rate of instance of error, d) correct word rate, e) total word rate f) error word rate Fairbanks and" Guttman (1958) (based on Fairbanks (1955) experiments) a) classification of errors according to type, b) number of phonemes per error Chase (1958) 20 0,216 20 dB above the vocal Number of times [b] was output repeated in 5 sec. Kozhevnikov 5 0,100,210, 115 dB at earphones a) phonemes per sec., and Chistovich 300,470 b) duration of repeated (1965) syllables and of segments within syllables, c) number of repetitions in any one instance of repe-tition. Number of Delay Level or Gain of Error and Duration Experimenter Subjects i n msec. feedback signal Measures MacKay 1968 a) 13 200,263 45 dB above vocal a) Number of repetitions output per syllable b) 13 0,100,150,200, 45 dB above vocal b) Total duration 263,375,524,750 output Number of correct syllables Huggins (1968) 1 0,80-400 i n 10 35 dB above vocal a) total duration msec increments output (70-75 dB b) number of repetitions speaking level) c) acoustic segment dur-ations Fletcher and 50 i n 200 35 dB above vocal Number of times a par-Yates (1971) experiments I, output ticular sound was II and I I I , 48 repeated i n 5 seconds in experiment IV. Sussman and 4 0,100,200,300, unspecified (high Extent of Smith (1971) 400 enough to mask bone- a) jaw opening conducted feedback) b) jaw velocity during opening and closing c) duration of jaw activity Robinson 4 0,200,225,250, unspecified (feedback Number of errors (1972) 275,300 signal was accompanied by "pink" noise masker) Appendix B P i l o t Study Passage [Once upon a time], a number of mice c a l l e d a meeting, to decide upon the best means of ridding themselves of a cat that had k i l l e d so many of them. Various plans were talked about, but none of them chosen. A young mouse came forward, and said that a b e l l should be hung round the tyrant's neck. Then they would a l l hear the cat coming, and so be able to escape. The suggestion was received with pleasure by a l l , u n t i l a thoughtful old mouse got up and said, "I consider the plan a very clever one. But I should l i k e to know, who i s going to put the b e l l on the cat?" [It i s easier to make a suggestion than to carry i t out.] The sentences i n brackets served as frame and were not analyzed. The passage was broken up into the following phrases for purposes of analyses: Phrase 1 . a number of mice c a l l e d a meeting, Phrase 2 . to decide upon the best means Phrase 3 . of ridding themselves of a cat Phrase 4. that had k i l l e d so many of them. Phrase 5 . Various plans were talked about, Phrase 6 . but none of them chosen. Phrase 7 . A young mouse came forward, - 1 0 1 -- 1 0 2 -P h r a s e 8. a n d s a i d t h a t a b e l l s h o u l d b e h u n g r o u n d t h e t y r a n t ' s n e c k . P h r a s e 9. T h e n t h e y w o u l d a l l h e a r t h e c a t c o m i n g , a n d s o b e a b l e t o e s c a p e . P h r a s e 1 0 . T h e s u g g e s t i o n w a s r e c e i v e d w i t h p l e a s u r e b y a l l . P h r a s e 1 1 . u n t i l a t h o u g h t f u l o l d m o u s e g o t u p a n d s a i d , P h r a s e 1 2 . " I c o n s i d e r t h e p l a n a v e r y c l e v e r o n e . " P h r a s e 1 3 . B u t I s h o u l d l i k e t o know, who i s g o i n g t o p u t t h e b e l l o n t h e c a t ? " Appendix C Screening Passage We know the shocks are p a i n f u l ; we have t r i e d them on o u r s e l v e s and we know t h a t they h u r t . But i t i s s t r e s s f u l f o r the person who does the shocking too. You may have used shock s u c c e s s f u l l y w i t h a hundred k i d s , but you are s t i l l apprehen-s i v e about i t ; you always t h i n k t h a t maybe t h i s k i d w i l l be the exce p t i o n ; maybe you w i l l h u r t him and i t won't do any good. But then when you shock him and you see the s e l f - d e s t r u c t i v e behaviour stop, i t i s tremendously rewarding. - 103 -Appendix D Main Experiment Passage [Some time ago, a group of mice c a l l e d a meeting to d ecide upon a good means of r i d d i n g themselves permanently of t h a t awful k i l l e r c a t.] Many a p l a n was t a l k e d over, when an i n s i g n i f i c a n t l i t t l e mouse came forward and remarked t h a t they should t i e a b e l l around the t y r a n t ' s neck. Then i n f u t u r e they would hear t h a t c r a f t y f e l i n e approach and so be ab l e to escape. The su g g e s t i o n was r e c e i v e d w i t h much p l e a s u r e , u n t i l a t h o u g h t f u l mouse s a i d , "I c o n s i d e r the whole p l a n a c l e v e r one. But I should l i k e to know, who w i l l p u t the b e l l on the c a t ? " [ I t i s e a s i e r to make a suggestion than to c a r r y i t out.] The sentences i n b r a c k e t s served as frame and were not a nalyzed. The passage was broken up i n t o the f o l l o w i n g phrases f o r purposes of a n a l y s i s : Phrase 1: Many a p l a n was t a l k e d over, Phrase 2: when an i n s i g n i f i c a n t l i t t l e mouse came forward Phrase 3: and remarked t h a t they should t i e a b e l l around the t y r a n t ' s neck. Phrase 4: Then i n f u t u r e they would hear t h a t c r a f t y f e l i n e approach - 104 -- 105 -Phrase 5: and so be abl e to escape. Phrase 6: The suggestion was r e c e i v e d w i t h much p l e a s u r e , Phrase 7: u n t i l a t h o u g h t f u l mouse s a i d , Phrase 8: "I c o n s i d e r the whole p l a n a c l e v e r one. Phrase 9: But I should l i k e to know, who w i l l put the b e l l on the c a t ? " Appendix E Main Experiment Sentences Sentence 10 " [ I n an average t h e a t e r a c t o r s are working /o/ on a scene j u s t l i k e the f o l l o w i n g : ] E n t h r a l l e d Maud's c a u t i o u s daughter pauses, f o r the ch a l k scrawl on the w a l l t a l k s of awesome hawk's claws. [ I t i s q u i t e c l e a r t h a t such scenes must be c a r e f u l l y executed.]" Sentence 11 " [ I n an average t h e a t e r a c t o r s are working / i / on a scene j u s t l i k e the f o l l o w i n g : ] Seated i n between l e a f y t r e e s the keen Ea s t G r e e n v i l l e people see the three greedy teams each r e t r e a t s p e e d i l y . [ I t i s q u i t e c l e a r t h a t such scenes must be c a r e f u l l y executed.]" Sentence 12 " [ I n an average t h e a t e r a c t o r s are working / a / on a scene j u s t l i k e the f o l l o w i n g : ] At h a l f p a s t one the calm f a t h e r passes gas masks up the s h a f t a f t e r the c a s t l e s t a f f rushed up the path. [I t i s q u i t e c l e a r t h a t such scenes must be c a r e f u l l y executed.]" - 106 -- 107 -Sentence 13 " [ I n an average t h e a t e r a c t o r s are working on /u/ a scene j u s t l i k e the f o l l o w i n g : ] Soon the two f o o l s who choose crude t o o l s l o s e to the smooth snoops who use goof-proof r u l e s to shoot snooker p o o l . [ I t i s q u i t e c l e a r t h a t such scenes must be c a r e f u l l y e x e c uted.]" The sentences i n b r a c k e t s served as frame and were not analyzed. Appendix F Symbols used i n the Study Consonants B i l a b i a l L a b i o - Dental and Palato- Pala- Velar G l o t t a l Dental Al v e o l a r Alveolar t a l Plosives p,b Nasals m Laterals F r i c a t i v e s p F r i c t i o n l e s s Continuants and Semi-vowels w f,v t , d e,8/s,z j , ^ Vowels front back close i u i o e o e e A O ae v open a D i a c r i t i c a l Marks: = unreleased ( = s y l l a b i c = v o i c i n g • ' =• stress v 0 = breath h = a s p i r a t i o n - 108 -Appendix' G 6 0 0 — 1 3 6 II 14 16 2 0 2 2 2 4 2 7 3 0 3 3 3 8 4 0 4 2 4 6 4 8 51 5 3 5 8 6 3 6 7 6 9 71 2 5 10 13 15 19 21 2 3 2 6 2 9 3 2 3 7 3 9 41 4 5 4 7 5 0 5 2 5 7 6 2 6 6 6 8 7 0 7 4 NORMAL FAST DAF SLOW SLOW DAF Subject 1 , Sentence 12 - 109 -- 110 -4 0 0 — M S E C , 1 3 6 II 14 16 20 22 24 27 30 33 38 4 0 42 46 4 8 51 53 58 63 67 6 9 71 S Y L . - - - - - - -2 5 10 13 15 19 21 23 26 29 32 37 39 41 4 5 4 7 50 52 57 62 66 68 70 74 NORMAL FAST DAF SLOW SLOW DAF Subject 2, Sentence 12 - I l l -5 0 0 4 0 0 3 0 0 -2 0 0 1 0 0 — M S E C . 0 . S Y L . 3 6 | , | , , . | i | • |- . | i | i | i | i 14 16 2 0 2 2 2 4 2 7 3 0 3 3 3 8 4 0 4 2 4 6 4 8 51 5 3 5 8 6 3 6 7 6 9 71 2 5 10 13 15 19 21 2 3 2 6 2 9 3 2 3 7 3 9 41 4 5 4 7 5 0 5 2 5 7 6 2 6 6 6 8 7 0 7 4 N O R M A L — F A S T D A F — S L O W — S L O W D A F S u b j e c t 3, Sentence 12 - 112 -7 0 0 — M S E C . 0 — | i | . | , | , | i | I | , | . | i | i | i | I 4 6 9 13 15 19 2 4 2 9 3 2 3 5 3 7 41 4 6 4 8 51 5 4 5 9 6 3 6 6 6 9 7 2 7 5 S Y L . - - - - - - - - -3 5 8 12 14 18 2 3 2 8 31 3 4 3 6 4 0 4 5 4 7 5 0 5 3 5 8 6 2 6 5 6 8 71 7 4 7 8 N O R M A L F A S T D A F S L O W S L O W D A F Subject 1, Sentence 13 - 113 _ 5 0 0 — 4 0 0 — 3 0 0 — 2 0 0 - \ - \ 1 0 0 — -A V/ \ A V I V / \\ i I M S E C . 0 — SYL. I |• i | I | i | i | I | ' | • ' | i | 1 | 1 | I 4 6 9 13 15 19 2 4 2 9 3 2 3 5 3 7 41 4 6 4 8 51 5 4 5 9 6 3 6 6 6 9 7 2 7 5 3 5 8 12 14 18 2 3 2 8 31 3 4 3 6 4 0 4 5 4 7 5 0 5 3 5 8 6 2 6 5 6 8 71 7 4 7 8 N O R M A L F A S T D A F S L O W S L O W D A F •Subject 2, Sentence 13 - i i U -600 — M S E C | I | I | I | I | I | I | I | I | I | I | I | I 4 6 9 13 15 19 24 29 32 35 37 4J 46 48 51 54 59 63 66 69 72 7! SYL. 3 5 8 12 14 18 23 28 31 34 36 40 45 47 50 53 58 62 65 68 71 74 78 NORMAL FAST DAF SLOW SLOW DAF Subject 3, Sentence 13 400 — | I I I | I I I I | I I I I | I II I | I I I I | I I I I | I I I I | I I I I | I I I I | I I I I | I I I I | I I I I | I I M | I I I I | I SEG. I 5 10 15 20 25 30 35 40 45 50 55 60 65 70 Subject 1, Sentence 12 NORMAL FAST DAF 

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