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Journal of S peech and Hea ring Research, INGHAMET AL.,Volume 26, 579-587 , De cem ber 1983

T H E E F F E C T O F M A N I P U L A T I N G P H O N A T I O N D U R A T I O N O NS T U T T E R I N G ~ T

R O G E R J . IN G H A M J A C K MO N T G O ME R Y L O U IS E U L L IA N AI Cumberland College of Health Sciences, Sydne!t,Australia| Two single-subject e xperim ents with two adult stutterers we re condu cted to assess the effect of changing the frequencv of|p h on a t i o n in te rva ls tha t were shorte r o r g rea te r than p resc r ibed dura t ions dur ing spon taneous speech . Both sub jec ts m odif ied] t h e f requency o f p resc r ibed phona t ion in tervals and showed changes in the f requency o f these in te rva ls tha t were pos i t ive ly| r e la t e d to decreases and inc reases in s tu t ter ing frequency . A percep tua l ana lys is o f the snb jec ts ' speech qual i ty dur ing phona-| t i o n con tro l cond i tions showed tha t when s tu tte ring frequency was reduced , l i steners cou ld de tec t changes in the speech]q ua li ty , of both subjects ; how ever, only one subject 's speech during these conditions w as describ ed as nonnorrnal sounding. Th ek therapeu tic and theor etical implications of these findings are discussed,

O n e o f t h e p a r a d o x e s c o n c e r n i n g t h e b e h a v i o r a l l yo r i e n t e d s t u t t e r i n g t h e r a p i e s i s t h a t , in s p i t e o f t h e i r e m -p h a s e s o n m e a s u r e m e n t a n d r e p l i c a b l e o p e r a t i o n s , t h ec e n t e r p i e c e s o f m a n y t r e a t m e n t s a r e v a g u e l y d e s c r i b e dt e c h n i q u e s w h o s e r e p l i c a b i l i t y d e p e n d s o n c l i n ic i a nj u d g m e n t ( I n g h a m , 19 7 5; I n g h a m & L e w i s , 19 78 ). M a n yo f t h e s e t e c h n i q u e s a r e d e r i v a t i v e s o f G o l d i a l n o n d ' s( 19 6 5) p r o c e d u r e f o r in d u c i n g " p r o l o n g e d s p e e c h " v i aD A F . T h e q u e s t i o n a b l e r e p l i c a b i li t y o f t h is p r o c e d u r ew a s c l e a r l y r ec o g n i z e d b y G o l d i a m o n d . F o r n o t o n l y d i dh e p o i n t o u t t h a t D A F m a y b e u n n e c e s s m T t o a c h i e v ep r o l o n g e d s p e e c h ( G o l d i a l n o n d , 1 9 6 7 ) , b u t a l s o d u r i n gD A F c o n d i t i o n s h e i d e n t i f i e d a t l e a s t t h r e e o t h e r " c o m -p e t i n g " p a t t e rn s : v o i c e l o w e r i n g , p r o p r i o c e p t i v e i n -c r e a s e , a n d t u n i n g o u t . I n d e e d , i t w a s n e c e s s a r y f o r t h ec l i n i c i a n t o i n s t r u c t t h e s u b j e c t o n t h e m o s t a p p r o p r i a t es p e e c h c h a r a ct e r is t i cs t o e n s u r e t h e a p p e a r a n c e o f t h ed e s i r e d s p e e c h p a t t e r n . T h u s , o n i n s p e c t i o n , t h i s e s s e n -t i a l l y b e h a v i o r a l t r e a t m e n t r e s t s o n r e l a t i v e l y i l l - d e f i n e do p e r a t i o n s . T h i s i s n o t t o d e n y t h e p o s s i b i l i t y t h a t s u c hc l i ni c ia n j u d g m e n t s m i g h t b e m a n a g e d r e l i a b l y - - T h ef a c t i s, h o w e v e r , t h i s h a s n o t b e e n d e m o n s t r a t e d .

T h e s u b s e q u e n t v a r i a t i o n s o n G o l d i a m o n d ' s p r o c e d u r ea l s o r e l y o n v a g u e l y d e f i n e d o p e r a t i o n s b a s e d o n c l i n i -c i a n j u d g m e n t s , i n d e e d , t h e l a b e l s f o r so m e o f th e c u r -r e n t o p e r a t i o n s , s u c h a s " g e n t l e c o n t a c t s , " " s m o o t h e ds p e e c h , " " r a t e c o n t r o l , " a n d " b r e a t h s t r e a m m a n a g e -m e n t , " w e r e a p p l i e d t o t e c h n i q u e s t h a t f l o u r i s h e d d u r -i n g t h e 1 9 4 0 s ( c f . , B e n d e r & K l e i n f e l d , 1 9 3 8 ; H a h n ,1 9 41 ) . T h e d e c l i n e i n u s e o f e a r l i e r v e r s i on ~ o f t h e s et e c h n i q u e s w a s p r o b a b l y l a r g e l y d u e to t h e i r l a ck o fs p e c i f i c i t y a s w e l l a s t o t h e u n c o n t r o l l e d f a s h i o n i nw h i c h t h e y w e r e a d m i n i s t e r e d . S o m e j u s t if i a b l e c la i m sf o r o p e r a t i o n a l r e p l i c a b i l i t y o f s o m e o f th e s e t e c h n i q u e ss h o u ld b e p o s s i bl e w i t h e q u i p m e n t d e s c r i b e d b y A g-h e l l o ( 1 9 75 ) a n d W e b s t e r ( 1 9 77 ) f o r p r o d u c i n g " e a s y o n -s e t s " w i t h i n t h e s p e e c h o f s t u t t e r e rs . H o w e v e r , t o d a t et h e r e h a v e b e e n n o d a t a - b a s e d d e m o n s t r a t i o n s o f t h e e f -f e c t s o f t h i s e q u i p m e n t o n s t u t t e r i n g .

A r g u a b l y , G o l d i a m o n d ' s ( 1 9 6 5 ) r e s e a r c h w a s t h e m a i ns t i m u l u s f o r t h e r e c e n t l y r e v i v e d i n t e r e s t i n r e s p i r a t i o n ,p h o n a t i o n , a n d a r t i c u l a t o r y f a c t o r s i n s t u t t e r i n g r e s e a r c h .T h i s w a s e x p r e s s e d m o s t v i s ib l y i n th e r e s e a r c h p r o g r a mo f A d a m s a n d c o l l e a g u e s o n a e r o d y n a m i c a s p e c t s o f st n t-t e r e r s ' s p e e c h b e h a v i o r ( A d a m s , 1 9 74 ). I t w a s a ls o l i n k e dw i t h t h e e m p h a s i s t h a t W i n g a t e ( 1 9 6 9, 1 9 7 0 , 19 7 6 )p l a c e d o n t h e r o l e o f m o d i f i e d v o c a l i z a t i o n w i t h i n t h e" a r t i f i c i a l " f l u e n c y p r o d u c e d d u r i n g d i f f e r e n t c o n d i t i o n s .S i n c e a l t e r e d v o c a l i z at i o n i m p l i c a t e d p h o n a t o lT b e h a v i o r( i n s p i t e o f W i n g a t e ' s 1 9 79 a s s e r t i o n s t o t h e c o n t r a r y ) , itw a s a h n o s t i n e v i t a b l e t h a t t h is a s p e c t O f s p e e c h s h o u l df o r m a c e n t r a l e l e m e n t i n t h e r e s e a r c h t h a t e m e r g e d i nth i s a re a .E x t e n s i v e r e s e a r c h h a s s h o w n t h a t i n c r e a s e d p h o n a -t i on t i m e i s p r o m i n e n t a m o n g t h e v a r i a b l e s t ha t c h a n g ed u r i n g D A F c o n d i t i o n s . S u b s e q u e n t r e s e a r c h s u g g e s t e dt h a t p h o n a t i o n - t i m e m o d i f i c a t i o n w a s a l s o n e c e s s a l - y t oe f f e c t s p r o d u c e d b y s i n g i n g ( C o l c o r d & A d a m s , 1 9 7 9 ) ,r e d u c e d s p e a k i n g r a t e ( H e a l e y & A d a m s , 1 9 8 1 ) , a n d , t o al e s s e r e x t e n t , c h o r u s r e a d i n g ( A d a m s & R a m i g , 1 9 8 0 ) .Y e t , in s p i t e o f t h i s i n t e r e s t i n p h o n a t i o n t i m e , n o d i r e c ta t t e m p t h a s b e e n m a d e t o a s s e s s t h e e f f e c t s o n s t u t t e r i n go f m a n i p u l a t i n g t h is v a r i a b l e . S o m e t a n g e n t i a l a p -p r o a c h e s h a v e b e e n m a d e v i a s t u d ie s t h a t h a v e u s e d o r a lr e a d i n g p a s s a g e s c o n t a i n i n g v a r i o u s p r o p o r t i o n s o f p o -t e n t i a l ly v o ic e d s p e e c h ( c f . , A d a ln s & R e i s , 1 9 7 1 , 1 9 7 4 ) .B u t t h e e x t e n t t o w h i c h p h o n a t i o n - t i a n e c h a n g e s m a y a f -f e c t s t u t t e r i n g h a s n o t b e e n e s t a b l i s h e d .

I t w a s a g a i n s t t h i s b a c k g r o u n d t h a t t h e p r e s e n t s t u d yw a s d e s i g n e d . T h e p r i n c i p a l o b j e c t i v e w a s t o s e e k a r e p -l i c a b le p r o c e d u r e f o r m a n i p u l a t i n g s t u t te r e r s ' p h o n a t i o nt i m e i n o r d e r t o p r o v i d e a m o r e c o n t r o l l e d c l i n i ca lm e t h o d f o r m o d i f y i n g s t u t t e ri n g . T h i s s t u d y s t e n n n e d d i -r e c t l y f r o m th e n e e d t o o p e r a t i o n a l i z e o n e o f t h e m o s to b v i o u s s p e e c h p a r m n e t e r s t h a t i s a l t e r e d d u r i n g p r o -l o n g e d s p e e c h - - t h a t is , p h o n a t i o n d u r a t i o n . S p e c i f i ca l l y ,t h e p u r p o s e w a s t o a s se s s t h e e f f e c t o f m a n i p n l a t i n g t h ef r e q u e n c y o f m i n i l n a l d u r a t io n s o f p h o n a t io n i n t he s p o n-

(~ 1 9 83 , A m e r ic an S p e e c h -L a ng u a g e -H e a rin g A s so c ia tion 5 7 9 0 0 9 , 2 -4 6 8 5 / 8 3 /2 6 0 4 - 0 5 7 9 5 0 1 . 0 0

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580 Journal o f Speech and Hearing Research 26 579-587 Dec emb er 1983taneous speec h of two adult stutterers in order to (a) de-termine whether subjects could establish control overthe fr equen cy of these phonatio n intervals, and (b) mea-sure the association between that control and changes inthe fr eque ncy of stuttering. An additional purpos e was toevaluate the p ercep tual qu ality of each siabjeet's spee chduring phonation interval control conditions.

M E T H O DS u b j e c t s a n d A p p a r a t u s

The subjects were two male stutterers who were on awaiting list for stuttering therapy. Subject P.A. (52 years)and Subject S.L. (19 years) had received treatment 10years earlier. Their previous treatment, which had notsucceeded in eliminating their stuttering, involved theuse of a prolonged speech procedure in a program simi-lar to that described by Ingham and Andrews (1973).Both subjects' stutterings could be categorized withinthe kernel characteristics of Wingate' s (1964) defini tionof stuttering.

Througl~out the experiment each subject was seated inan experimental sound-treated room. A microphone, aCounter Display Unit, an oscilloscope (Gould OS4000),and a Phonation Interval Monitor and Feedback Unitwere also located in the same room. Each subject wasmonitored and recorded auditorily from a control room.The control room monitoring facilities included a dataprinter (Newport 810), a tone feedback unit, tape record-er (TEAC A-7300), and a dual button-press electroniccounter. The experimenter (L.U.) counted, on line, syl-lables judged as stuttered or nonstuttered using the elec-tronic counter.

The recording and feedback assembly arrangements inthe experfinental room enabled each subject's "phona-tion interval" counts to be illuminated on the subject'sCount er Dis play Unit for 10 s at the end o f each minute.That score, along with syllables and stutterings countedeach minute, were registered concurrently on the controlroom data printer.Phona tion interval (PI) recording an d feedb ack sys-tem. Each subject's phonation was registered through aminiature accelerometer (Koningsberg Type, A 1-4)hous ed to fit on the surface of the throat, slightly bel owthe thyroid prominence. The accelerometer signal wasfed to a Phonation Interval Monitor and Feedback Unit3Briefly, the Unit accepts a signal which is fed to a bridgeamplifier and then filtered so that, generally, the fre-quency range 200-1000 Hz is accepted for phonationinterval comparison. The intensity and frequency rangeof the a ccept ed signal may be adjusted to ignore non-phonated signals. The duration of the accepted phona-tion signal is then compared with a preset durationinterval. If the pho nation signal is less than a presc ribed

1The circuit diagram for this unit is available on request fromthe senior author.

duration, then a "phonation interval" (PI) count is re-corded. The PI signal counts are stored for delivery tothe subject's Counter Display Unit and the control roomdata printer. Each PI count signal also could activate a50-ms, 750-Hz tone. Thus, wh ene ver an interval of pho-nation was registered as less than a prescribed duration,the subject could instantly receive a tone and a PI count.

Each accepted phonation signal and its activated pre-scribed duration signal were displayed in dual-channelcontinuous-roll function on the digital storage oscillo-scope. This gave the subject the option of viewin g online an analog depiction of his phonated response andcomparing it with a depiction of the prescribed duration.The oscilloscope display also permitted the experi-menter to set a threshold activation level for the phona-tion signal. This was determined innnediately after theaccelerometer was attached to the subject's throat andbefore each treatment session. The experimenter re-quested the subject to make a variety of physical move-ments, mainly vigorous head movements and swallowingactions followed by soft-voiced counting, to ensure thatthe "phonation signal" was essentially voice-related.Pe rc e p tua l ana ly s i s s y s t e m . A perceptual analysis(Ingham & Packman, 1978) was made of speech samplesobtained from conditions in which the subjects' fi'e-quency of phonation intervals of prescribed durationswas reduced. Four audio recordings containing speechsamples were heard individua lly by four groups of 20 lis-teners. The listeners were essentially naive; they wereneither clinicians nor students training in the field ofspeech and language pathology. They were aged "20-45years.

P r o c e d u r eEach subject spoke spontaneously in 5-rain trials sepa-

rated by l-rain rest periods. After four trials, the subjectrested for 10 rain. Each subject completed at least 12 butno more than 48 trials d uring any day of the e xperiment.The experimental design required each subject to com-plete a different series of four nontrea tment trials (Aconditions) and four treatanent trials (B- or B+ condi-tions). Three data measures were obtained throughouteach of the experimental conditions: percentage sylla-bles stuttered (%SS), syllables spoken per minute (SPM),and PI counts per rain. (Recall that the PI counts wereintervals of phonat ion that were le ss than a prescribedduration.)Stage One experimental procedure. The experimentalprocedures were designed to assess whether subjectscould modify the frequency of PI counts during spon-taneous speech when receiving PI count feedback andinstructions to reduce these counts. A concurrent pur-pose was to assess the effect of modifying prescribed PIcounts on stuttering. The effect of these phonation-modif ying procedure s was evaluat ed in a series of ABAexperimental conditions involving systematic increasesin the phonation interval necessary for a PI count.During the first A condition the PI duration setting

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was 50 ms. 2 Eac h subject spoke spont aneo usly for four5-min trials while the frequency o f PI counts was re-corded. The subject was not fed back information abouthis PI counts. In the succeeding B- condition the sub-jeet received auditory and visual feedback of each PIcount; each interval o f phona tion less tha n 50 ms acti-vated the tone signal and recorded a count on theCounter Display Unit. At the begi nning of this and allother B- condition trials, the subject was instructed totry to reduce the number of PI counts per rain to below50% of the mean counts per rain recorded during the Acondition. This figure was displayed on the CounterDisplay Unit. In addition, the subject was able tomonitor the oscilloscope's dual signals. This permittedhim to observe the association between duration inter-vals in his phonation signal and an activated 50-msinterval. Consequently, in each B- condition the subjectreceived three sources of feedback to assist him to mod-ify PI counts: the tone signal, counter display, and oscil-loscope signal display.

The instructions to the subject preceding the B- con-dition involved considerable care to ensure that noexplicit instructions were provided about a particularmanner o f speaking that should be used to reduce PIcounts. The subjeet was told only how the equipmentoperated with respect to the duration of throat-surfacevibration. A series of vowel utterances were requested,and these we re frozen on the oscilloscope's dual channeldisplay. This was used to demonstrate the relationshipbetween the subject's voice signal duration and the pre-scribed duration. Recall from the previous description ofthe oscilloscope display that the onset of the pho natedsignal, which was displayed on one channel, also acti-vated a comparison-time signal (prescribed duration) onthe second channel. The subject was informed that anyof his signal durations that we re less than the prescribedduration would also activate the counter and the feed-back tone. To ensure that the subject was not instructedinadvertently about using a particular speech pattern,the counter and tone activation were demonstrated bytapping the aecelerometer and indicating (on the oscil-loscope display) that signals which would activate a PIcount also produced a tone burst and a count on theCounter Display Unit. The subject then was informed ofthe maximum num ber of PI counts he should produce by

2Throughout this study the phonation intervals were mea-sured in 50-ms units. There were three reasons for choosing thisunit size. First, changes in PIs needed to exceed the maximmnphonation duration measurement error; spectrographic analysisshowed that this error was 28 ms. Secondly, the unit size waschosen to correspond to the duration intervals typically used inprocedures designed to produce prolonged speech via delayedauditory feedback. Recall that Goldiamond's (1965) procedureused 50-, 100-, 150-, 200-, and 250-ms delay levels in order tomodify phonation via prolonged speech--Ostensibly, eachdelay level represented the duration of extended voice signalthat was required to prevent disruptive feedback. Finally, theunit duration was shorter than mean vowel durations producedby normal speakers and stutterers (see Brayton & Conture,1978; Klich & May, 1982).

INGHAM ET AL.: Manipulating Phonation Duration 581the end of each minute. This figure was at tachedalongside the PI counter on the Counter Display Unit.

The criterion for establishing that a subject could mod-ify his PI counts was a mean num ber of PI counts duringthe B - condition that was 50% of the mean number of PIcounts across the eight A condition trials. If PI controlwas not demonstrated during the 50-ms PI level, thenthe next A/B-/A sequence was introduced using a100-ms duration level and replication of the a bove men-tioned procedures. Again, if PI control was not obtained,then the next A/B-/A sequence was introduced with a PIlevel of 150 ms. These procedures continued until (a) PIcontrol was established or (b) the initial A eondition PIcounts were not 10% greater than those obtained in thefinal A conditions of a previous A /B-/ A sequence.

This stepwise experimental design requires commentsince it would appear that any identified "treahnent ef-fect" might be confounded. The first potential confound-ing effect involves learning. Because the subject may beexposed to increasingly larger PI counts, his control overthese may- result simply from learning to alter phonationlength, rather than being caused by a particular PI dura-tion level. It would seem that the most logical control forthis variable wo uld be ascertaining a treatment effect at aparticular PI duration level, then reintroducing the pre-ceding PI duration level (that is, 50 ms less), and check-ing that a treatment effect still did not obtain at thatlevel. The difficulty with this proe edur e is that if atreatment effect is obtained at the shorter PI duration, ittoo may be due to learning rather than associated withthe particular PI level. In this event, the subject'sstrategy for reducing PI counts could be to use the longintmwals of phona tion lea rned at the pre vious level. Thepresent design was preferred since the primary purposewas to determine whether the subject could manipulatea duration level. The second potential confound is thefixed number of 5-min trials in each experimental "run."It is customary to allow subjects to demonstrate a datatrend over variable trials when employing single-subjectexperimental designs. However, this becomes exceed-ingly difficult when more than one data measure is mon-itored. F or this reason, a fixed nmnb er of trials (four) percondition was preferred, and any ambiguity in the datatrends was regard ed as reflecting the abs ence of a treat-ment effect (Hersen & Barlow, 1976).Stage Two experimental procedure. The first experi-mental stage was designed to identify a PI level that thesubject could modify. The second experimental stagethen was introduced to assess the effect on stutteringwhen the subject manipulated his PI fiequencies rela-tive to his base rate PI level. This was carried out usingeither a B- /B +/B -/ B+ or B+ /B- /B+ /B- experimentaldesign. In this experiment the subject received the threesources of PI feedback throughout all conditions (i.e.,tone, counter display, and oscilloscope). However, in B-conditions the subject was instructed to reduce his PIcounts pe r rain to 50% of the A conditi on mean PI countsper rain, In the B+ conditions the subjeet was instructedto increase his PI counts per rain to 50% above his Acondition mean PI counts per rain. The A condition PI

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582 Journal of Speech and Hearing Research 26 579-587 Dec emb er 1983count in this ease was obtained from the first A conditionin the Stage One experiment.

Once again a treatment effect was considered to haveoccurr ed only if the subject's mea n P I counts for four5-min trials were either 50% abov e (in the ease of B+conditions) or 50% below (in the ease of B - conditions)the A condition mean PI level. In other words, the pre-scribed PI level during the first B- condition was iden-tical to the PI level which (by necessity) yielded a treat-ment effect in the Stage One experiment. If PI countcontrol was not demonstrated in the first B-/B/B-/B+(or vice versa) sequence, then the PI level was increasedby 50 ms and a new sequence introduced. This was pre-ceded by an A condition in order to establish the B - andB+ PI criterion levels. This procedure was repeated fora maximum of three occasions.Perceptual analgsis. Subsequent to both experiments,recorded smnples of each subject's stutter-flee speechwere selected for two purposes: (a) to assess whetherperceptual differences were evident in each subject'sspeech during B- conditions relative to A conditions,and (b) to assess whether listeners described speechseanples drawn from B - conditions as normal or non-normal sounding.The procedure for (a) involved selecting smnples fromA and B- conditions that enabled sample pairs, matchedfor num ber of words, to be organi zed so that listenersheard pairs drawn from same or different conditions. Tenpairs of samples w ere obtained from same conditions(i.e., both from B - or both from A conditions) and 10pairs from different conditions (i.e., A and B- condi-tions). This pro duce d two sets of tape rec orded samples.Tape One contained 9.0 sample pairs from Subject P.A.,with 2 of the 20 pairs repea ted at the end for reliabilityassessment. This recorded material was followed by asimilar set of 22 pairs of samples from Subject S.L. Thenum ber of words in each sample r anged from 11 to 21 forP.A. and 27 to 48 for S.L. Tape One contained samplesfrom B-100 ms conditions for P.A. and B-150 ms condi-tions for S.L. Tape Two was identical to Tape One ex-cept that it contained B-50 ms condition sanlples for P.A.(14-20 words per sample) and a repeat o f the B-150 mscondition samples for S.L.

The pro cedur e for (b) involved selectin g l-rainstutter-flee Salnples from both subjects' speech duringB- conditions and equivalent samples from normalspeakers of the sa me age and sex as each subject. Aclinician determined that neither control subject evi-denced a speech or language problem and had not re-ceived treatment for such a problem. Each sample wasjudged as stuttel~free by two independent clinicians anddid not contain identifying content. Tape Three wasprepared so that listeners heard the following four l-rainsamples: Subject P.A. from B-100 ms conditions (176 syl-lables), P.A,'s control (175 syllables), Subject S.L. fromB-150 ms conditions (151 syllables), S.L.'s control (156syllables). Tape Four was prepared so that the listenersheard the following samples: S.L.'s control, S.L., P.A.'scontrol samples fi'om Tape Three, plus P.A.'s samplefi'om B-50 ms conditions (174 syllables). Thus, Tape

Four contained only one sample that distinguished itfrom Tape Three, thereby permitting intergroup listenerreliability to be diseer ned for three of the four samples.

Each tape was heard individually through headsets byone gro up of 9,0 listeners. T hus, 80 listeners w ere in-volved in this part of the study. For Tape s One and Two,the listeners were read aloud instructions which askedthem to decide whether the samples in a pair weredrawn from "same" or "different" speaking conditions.The listeners to Tapes Three and Four were asked todecide whether each sample was obtained from a normalor nonnormal sounding speaker. Thus, for Tapes Threeand F our it was possible to derive a count, out of 20, ofthe num ber of listeners who judged a sample to be froma nmanal speaker.

ReliabilityThe reliabi lity of the data measures obtained in Stages

One and Two experiments involved an assessment of (a)the accuracy of the P honation Interval Monitor andFeedback Unit in identifying prescribed intervals ofphonation, and (b) the reliability of %SS and SPM scoresfrom both speakers.

The calibration of the Phonation Interval Monitor andFeedbac k Unit was checked during the course of the ex-periment by two separate procedures. In the first, aseries o f 750-Hz signals of prescri bed dm-ation were fedto the unit, which permitted interval detections within-+2 ms. The second was obtained by an'anging ~br one ofthe two subjects and a third, P.S., to produce a series ofvowels of varying duration while f itted with the phona-tion modification equipme nt. (The perfor mance of P.S. isdescri bed in the Discussion.) The duration of eachvowel production was recorded fi 'om the PhonationInterval Monitor and Feedback Unit on oscillographicdisplay. The duration of each signal was read off andthen compared with the duration derived independentlyfrom spectrographic print outs (Voice Identification Unit,Model 700) using the average duration in the 250-1000-Hz range. Twelve oscilloscope-measured samplesfor Subject S.L. ranged 180-750 ms. The spectrographicmeasures were identical for six and differed by 10-25 msfor the other six. Fourteen similar samples from SubjectP.S. were measured at 175-900 ms on the oscilloscope.The spectrograph measures were identical for eight butdiffered by 10-25 ms for the other six. These differencesare of some concern, but average on-off measuring pointson spectrographs are expected to have close rather thanexact correspondence with the phonation signal on-offmeasuring points (Peterson & Lehiste, 1960).The reliability o f %SS and SPM scores was estinlatedby obtaining syllable and stuttering counts made by aninde pen dent clinician fi'om recordin gs of each subject.The clinician was provided with two 5-rain-trial record-ings from each of the expe riment al conditions in eachexperiment. The recordings were selected randomly,and the clinician was not familiar with their source. Thescores obtained by the second clinician were converted

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t o % S S a n d S P M s c o r e s a n d a r e d i s p l a y e d w i t h i n t h e r e -s u l ts f i g u r e s ( s e e F i g u r e s 1 - 3 , s h o w n l a t er ) f o r e a c h s u b -j e c t . T h e t r e n d o f t h e s e c o n d c l i n i c i a n ' s ( r e r a t e d ) s c o r e ss h o w s a p a t t e r n c o n s i s t en t w i t h t h e t r e n d p r o d u c e d b yt h e e x p e r i m e n t e r ' s o r i g i n a l s c o r e s .

T h e r e l i a b il i t y o f t h e p e r c e p t u a l a n a l ys i s p r o c e d u r ew a s i n v e s t i g a t e d b y (a ) i n d e p e n d e n t m e a s u r e s o f t h e e x -p e r i m e n t e r ' s s y l l a b le c o u n t s a n d t i m i n g f o r s a m p l e s , a n d( b) b e t w e e n - l i s t e n e r c o m p a r i s o n s o f j u d g m e n t s m a d e o ns o m e o f t h e s a m p l e s . I n a d d i t i o n , o n l y r e l i a b l e l i s t e n e r sw e r e u s e d i n th e p e r c e p t u a l a n a l y s i s i n v e s t ig a t i o n o fs i m i l a r i t i e s o r d i f f e r e n c e s b e t w e e n s a m p l e p a i r s . " R e l i -a b l e l i s t en e r s " w e r e j u d g e s w h o s e s e c o n d j u d g m e n t s o nb o t h r e p e a t e d s m n p l e p a ir s f r o m b o t h s u b j e ct s o n T a p e sO n e a n d T w o w e r e i d e n t i e a l .

A l l w o r d e o u n t s o n t h e s m n p l e s f o r T a p e s O n e a n dT w o w e r e a g r e e d u p o n b y a n i n d e p e n d e n t c l i n i c i a n , a n dd i f f e r e n c e s i n t h e t i m e s o f b o t h s a m p l e s i n a p ai r w e r ec o n f i r m e d b y t h e s a m e c l i n i c i a n a s n o t e x c e e d i n g 3 s .T h e l - r ai n s a m p l e s w e r e c h e c k e d b y an i n d e p e n d e n tc l i n i c i a n f o r s y l l a b l e e o u n t s , a n d n o n e d i f f e r e d f r o m t h ee x p e r i m e n t e r ' s c o u n t s b y m o r e t h a n 8 % .T h e l i s t e n e r - g r o u p s ' j u d g m e n t r e l i ab i l i ty o n T a p e O n ea n d T a p e T w o w a s e s t i m a t e d f r o m j u d g m e n t s f o r i d e n t i-c a l s a m p l e s f r o m S u b j e c t S . L . t h a t a p p e a r e d o n b o t ht a p e s . T h e l i s t e n e r s t o T a p e O n e c o n f i d e n t l y i d e n t i f i e dt h e d i f f e r e n t c o n d i t i o n s a m p l e s f o r t h i s s u b j e e t , a n d t h ise f f e c t w a s r e p e a t e d b y t h e l i s t e n e r s t o T a p e T w o . T h el - r a i n s a m p l e s o n T a p e s T h r e e a n d F o u r a l s o c o n t a i n e did e n t i c a l s a m p le s fo r S . L . , S . L . ' s c o n t ro l , a n d P . A . ' s c o n -t ro l . T h e p e r c e n t a g e o f " n o ~ T n a l" j u d g m e n t s f o r t h e t w ol i s t e n e r g r o u p s a r e s h o w n i n T a b l e 1 , w h i e h i n c l u d e s a l lf i n d i n g s f o r t h is p a r t o f t h e p e r c e p t u a l a n a l y s i s s t u d y .T h e s e d a t a s ho w t h a t t h e T a p e T h r e e a n d T a p e F o u r l is -t e n e r g r o u p s w e r e r e a s o n a b l y c o n s i s t e n t i n t h e i r j u d g -m e n t s o f t h e n o r m a l c y o f P . A . 's c o n t r o l , S . L ., a n d S . L ' sc o n t r o l . H o w e v e r , f e w e r l i s t e n e r s j u d g e d S . L ' s c o n t r o l ' ss p e e c h t o b e n o r m a l s o u n d i n g w h e n c o m p a r e d w i t hP . A 2 s c o n t ro l . N e v e r t h e l e s s , i t i s e v i d e n t t h a t b o t h l is -t e n e r g r o u p s r e g a r d e d t h e s p e e c h o f S.L.'s c o n t r o l a sm u c h m o r e n o r m a l s o u n d i n g t h a n t h e s p e e c h f r o m S . L .

TABLE 1. Total (n) and percentage (%) of lis teners to TapesT h re e a n d F o u r w h o m a d e ju d g m e n t s o f " n o rm a l" o n l - r a insamp les of the speec h of subjects an d their controls.Tape three Tape .four(N = 20) (N = 20)n % n %

P.A. (B-5 0) 15 75P.A. (B - 100) 19 95P.A.'s Control 19 95 18 90S.L. (B - 150) 0 0 0 0S.L.'s Control 16 80 12 60

R E S U L T ST h e r e s td t s o f t h e S t a g e O n e a n d T w o e x p e r i m e n t a l

INGHAM ET AL. : Manipulat ing Phonation Duration 58 3p r o c e d u r e s f o r b o t h s u b j e c t s a r e s h o w n g r a p h i c a l l y a n dr e v e a l d a t a p a t t e r n s t h a t a r e c o n s i s t e n t w i t h e f f e c t s a t -t r i b u t a b l e t o p h o n a t i o n i n t e r v a l m o d i f i c a t i o n .

S u b j ec t P . A .T h e r e s ul t s o f t h e S t a g e O n e e x p e r i m e n t a l p r o e e d u r ef o r t h i s s u b j e c t a r e s h o w n i n F i g u r e 1 . F r o m t h e d a t a

d i s p l a y i t c a n b e o b s e r v e d t h a t t h e s u b j e c t ' s b a s e r a t e P Ic o u n t d u r i n g 5 0 - m s d u r a t i o n m e a s u r e m e n t ( c o n d i t i o nA S 0) r a n g e d b e t w e e n a p p r o x i m a t e l y 2 . 5 a n d 1 . 5 p e r m i n .W h e n f e e d b a c k a n d i n s t r u e t i o n s w e r e p r o v i d e d d u r i n gB - 5 0 c o n d i t i o n s , P . A . r e d u c e d t h a t f r e q u e n c y o f P I i n t e r -v a l s t o b e l o w 5 0 % o f t h e i n i t ia l A 5 0 l e v e l m e a n . P I e o n -t r o l w a s r e g a r d e d a s e s t a b l i s h e d b y e v i d e n c e i n t h e f i n a lA S 0 c o n d i t i o n t h a t t h e s u b j e c t ' s P I c o u n t r e t u r n e d t o ar a t e c o n s i s t e n t l y a b o v e t h e B - 5 0 l e v e l . I t c a n a l so b e o b -s e r v e d t h a t a c o n c o m i t a n t t r e n d o c c u r r e d i n t h e s u b j e c t ' ss t u t t e r i n g f r e q u e n c y , w i t h o u t e v i d e n c e o f a n a ss o c i a t e dr e d u c t i o n i n s p e e c h r a t e .

2 5 0.E== 1 5 0_=~ 5 0

l O1 = o

~ = ~ 0

3,c_

g = 1g,_~ o

S U B J E C T R A ,A 5 0 B - 5 0F

1 I l l I i I IF I V E M I N U T E T R I A L S

A 5 0

. - - - . 3 ~ ~ J 3

O r i g i n a l s c c c e so R e r a t e d s c o r e s

I t t

FIGURE 1. Freq uenc y o f phonation intervals (PI counts) lessthan 50 ins , percentage of s tuttered syllables (%SS), and sylla-bles pe r min (SPM ) for Subject P.A. during AS0/B-50/A50 con-ditions o f the Stage One ex perim ent.

T h e f i n d in g s f r o m t h e S t a g e T w o e x p e r i m e n t a l p r o c e -d u r e f o r P .A . a r e s h o w n i n F i g u r e 2 . I n t h e i n i t i a l p a r t o ft h i s e x p e r i m e n t t h e c r i t e r i o n r e d u c t i o n i n P I c o u n t s d u r -i n g B - 5 0 w a s a c h i e v e d , b u t t h e r e c i p r o c a l c r i t e r i o n d u r -i n g B + 5 0 c o n d i t i o n s w a s n o t r e a c h e d . ( R e c a l l t h a t t h e" ' -" n o t a t i o n s i g n i f i e s t h a t t h e s u b j e c t w a s r e q u i r e d t or e d u c e h i s P I c o u n t s b e l o w 5 0 % o f t h e A c o n d it i o n m e a nP I e o u n t s , a n d t h e "+" n o t a t i o n s i g n i f i e s t h a t t h e s u b j e c tw a s r e q u i r e d t o i n c r e a s e h i s P I c o u n t s 5 0 % a b o v e t h e Ac o n d i t i o n m e a n P I c o u n ts .) A s u b s e q u e n t r e p l ic a t i on o ft r e a t m e n t c o n d i t i o n s c o n f i r m e d t h i s d a t a t r e n d . H o w -e v e r , i t c a n a l s o b e n o t e d t h a t t h e s u b j e c t ' s % S S s c o r e sf o l l o w e d t h e s a m e g e n e r a l t r e n d a s t h e P I c o u n t s . W h e nt h e P I l e v e l w a s s e t a t 1 0 0 m s , a n i n c r e a s e i n P I c o u n t s

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584 Journal of Speech and Hearing Research 26 579-587 Dec emb er 1983SUBJECT P.A,

2 50 AeO B-e0 B'I'50B*50 B+50 A I O 0 B ' I O 0 A I 0 0 B'IO0 B + I 0 0 i ~ 1 0 B B + l O 0 A I 0 0

t o o _ ~ 5 0 1o

m~=nu ~ o

~o_ 20 ~ o R e r o t e d~ Scores. _ S g ie _ ~ . . . . . ,. - .~ , , , . ~ , , , - m . , , " ~ ' , , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

FIVE MINUTE TRIALSFIGURE 2. Frequency of phonation intervals (PI counts) of lessthan 50 ms (A50 and B -50 conditions) and 100 ms (AI00,B - 1 0 0 and B+ 100 conditions), percentage of stuttered syllables(%SS), and syllables per rain (SPM) for Subject P.A. during theStage Two experiment.

dutifully followed (see A100). Across the followingA100/B-100/A100 conditions sequence, the subject onceagain displayed evi dence of PI control and also revealedan equivalent effect on his stuttering frequency. Duringthe subsequent B- 100/B+ 100/B- 100/B+ 100 conditions,P.A. showed a pattern of PI scores that was consis tentwith the criterion levels required within the experiment.The subject's %SS scores also decreased, ahnost to 0,during all B- 100 trials and increased above the A condi-tion level during all B+ 100 trials.

The results from Subject P.A. were consonant with theaims of this study. The subject was consisten tly able toreduce and increase his PI counts appropriately duringfeedback conditions. In addition, there was clear evi-dence that his fr equenc y of stuttering was associatedwith manipulations in PI counts.The majority of listener judgments from those listenersidentified as rel iable in evaluating Subject P.A. 's

AJB-50 condition sample pairs and his A/B-100 samplepairs are shown in Table 2. A Chi-Square Test (Siegel,1956) of the distribution of the majority of listener judg-ments shows that the listeners were able to distinguishconfidently between stutter-free A condition and B-50condition samples but that they failed to make the samedistinction between A and B-100 condition samples.

The listener judgments of normalcy from the 1-minsamples from P.A. during B -5 0 or B- 100 conditions areshown in Table 1. They indicate that P.A.'s speech qual-ity under B-50 and B-100 conditions definitely did notsound abnormal. However, sl ightly fewer l istenersjudged this speech to be nonnaI during B-50 conditions,a difference which is consistent with the distinction thatother listeners made between samples obtained fromB-50 and A conditions for this subject. The counterpartfigures from P.A.'s control are generally similar to thoseproduced for P.A., especially during B -5 0 conditions. Inshort, it would appear that only the B-50 condition al-tered the subject's mann er of speaking, but three quar-ters of the listeners still perce ived his s peech as normalsounding.

Subject S .L .The results for the Stage One and Two experimental

procedures with S.L. are shown in Figure 3. The StageOne procedures began with an abbreviated A50 condi-tion, which showed virtually zero PI counts. Con-sequently, the A100 condit ion was introduced im-mediately. However, the subject's 100-ms PI levelcounts also were relatively infrequent. During B-100conditions the subject's PI counts were reduce d from theinitial A100 level but continued virtually unchangedduring the subseq uent A1O0 condition. On the followingday the PI level was increased to 150 ms, and over thesubsequent A150/B-150/A150 conditions the subject'sresponse pattern was consistent with PI control. It willbe ob serv ed that over each of the B conditions in StageOne, the subject's %SS scores were generally substan-tially less than those produced during A conditions (the

TABLE ~2. Majority listener judgments of "same" or "different" to sample pairs drawn from Aand B conditions for both subjects. Subject P.A.'s speech samples were drawn from A and B- 50conditions (20 sample pairs) and A and B-100 conditions (20 sample pairs). Subject S.L.'s soan-ples were drawn from A and B-50 conditions (20 sample pairs).Origin of sample Origin of samplepair conditions pair conditionsfor P.A. for S.L.

A/B -50 A/B -100 A/B -50(N = 9 listeners) (N = 14 listeners) (N = 15 listeners)Listeners"judgments Same Different Same Different Same Different"Same" 10 1 7 4 7 0"Different" 0 9 3 6 3 10

X = 16.4 (p < .001) X = 2.0 (N.S.) X = 11.6 (p < .001)

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INGHAM ET AL.: Manipulating Phonation Duration 585

D - o o 3

S U B J E C T S .L .S t a g e O n eAISO AIOO 13-100 A{0O AlS0 B-E50 AIS0I . .

0 ~ ~

.E 3 0 I_~o. 20!- - ~ I I

~-~ o , - , , ~ , . ~ ,, ,-~, , ,F I V E M I N U T E T R I A L S

S t a g e T w oAlSO Bd-15OB-150E1150 -15o AlS0

~ oL / !

O r i g i n a l= '~ [ ~ I S c o r e s

I 0 IO i i i I i im ~ l i t i ( i i l l ~ i i i

FIGURE 3. Frequency of phonation intervals (PI counts) of lessthan 50 ms (A50 condition), 100 ms (A100 and B-100 condi-tions), and 150 ms (A150, B-150 and B+150 conditions); per-centage of stut tered syllables (%SS), and syllables per rain(SPM) for Subject S.L. during the Stage One and Stage Twoexperiments.

exception is the second A100 condition). There was alsono evidence that the reduced stuttering was related toreduced speech rate.The data obtained from Subject S.L. during the StageTwo experimental procedures are shown in Figure 3 andpresent a relatively straightforward pattern. His datashow that the PI counts were able to be manipulated inaccordance with the prescribed criteria levels. In addi-tion, with the exceptio n of an ambiguous trend acrossA150 and B-150 conditions, the subject's %SS scoresshow a pattern which is virtually identical to thatachieved with the PI scores.

One of the most unexpe eted features of S.L.'s data wasthe change in stuttering frequency between the StageOne and Two experiments. By comparing the %SSscores at the begi nning of each of these experiments, itean be seen that S.L. increased his stutterings by roughly100% (note that the %SS scales on Figure 3 for StageOne and Two experiments are different). S.L.'s stutter-ing appeared to worsen over the course of the study, butthis trend did not confound the effects that may be at-tributed to the manipulation of experimental conditions.Like the first subject, S.L.'s data were consistent withthe experiment's aims. S.L. showed he was able to re-duce his PI counts during B- conditions and that thesereductions were associated with decreased stuttering.During B+ conditions the subject's stutterings also in-creased, beeoming generally more frequent than thoseproduced during nonfeedbaek conditions.

The majority of listener judgments from listeners iden-tified as reliable in evaluating Subject S.L.'s A/B-150condition sample pairs on Tape One are shown in Table2. A Chi-Square Test of the distribution of judgmentsshows that the listeners were able to distinguish be-tween stutter-free A and B-150 eondition samples. The

listener judgments of normalcy from the 1-min samplesby S.L. and S.L.'s control are shown in Table 1: Theyindicate that S.L.'s speech quality in B-150 was defi-nitely not normal sounding. In summary, it is evidentthat S.L.'s speech during B-150 eonditions was dis-tinetly different from his usual speech and also not nor-real sounding.

Speech Rate ReassessmentThe experimental procedure with both subjects madeit necessary to collect SPM data that included stuttered

syllables. Thus, any improvement in speech-rate duringreduc ed %SS scores may have bee n an artifact of themeasurement methodology. To test whether reduced%SS scores were associated with reduced speeeh rate,part of the data from both subjects was reas sessed forSPM scores that excluded stutterings. The A100/B-100/A100 phase for Subject P.A. (see Figure 2) andthe A150/B- 150/A150 phase for Subject S.L. (see Figure3) were reassessed by the experimenter so that each se-quence of I0 (or more) stutter-free syllables within eachtrial was timed. The revised stutter-free SPM scores andthe during-exper iment scores are shown in Figure 4. Thedata trends from these phases show that reduced stutter-ing by both subjects was probably not associated with areduction in speech rate.

!~

P . A ,A 1 0 0 B - 1 0 0 A 1 0 0

25 O

', p - o o , ~ ~ ~ ~ O ~ O1 5 0

J . . . " "

& L .A 1 5 0 B - 1 5 0 A 1 5 0

,,~o . d2 5 0 ~ O

0 k O r i g i n a lS c o r e s- " S t u t t e r -f r e e S P MS c o r e s

FIGURE 4. Comparison between SPM scores, including stutter-ings, and SPM scores calculated without stutterings, during ex-perimental phases for both subjects.

D I S C U S S I O NThe results of this experim ent s hould not surprise

those familiar with the effects of altered speakin g pat-terns on stuttering. The existing evidence on the effectsof both DAF-assisted and unassisted prolonged spe echalmost compels the conclusion that the fluency-produci ng effeets of these procedures rely upon in-ereases in the durat ion of intervals of voicing or phona-tion. However, there are some important differences in

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5 8 6 Journal of Speech and Hearing Research 26 5 7 9- 5 87 D e c e m b e r 1 98 3t h e p r o c e d u r e d e s c r i b e d i n t h is e x p e r i m e n t t h a t m a k es o m e o f t h e f i n d i n g s u n e x p e c t e d . T h e f i r s t i s t h a t t h ep r o c e d u r e b y w h i c h p h o n a t i o n m o d i f i ca t i o n w a sa c h i e v e d i s t h e f i r s t a p p l i c a t i o n o f a m e t h o d f o r o b t a i n i n gr e l i a b l e c o n t r o l o v e r t h e f r e q u e n c y o f r e l a t i v e ly s h o r ti n t e r v a l s o f p h o n a t i o n t i m e . a I t d i f f e r s f r o m D A F a n do t h e r " s t r a t e g i e s " f o r p r o d u c i n g f l u e n c y - i n d u c i n g p a t -t e r n s i n t h a t o n l y o n e s p e c i f i c d i m e n s i o n o f t h e s p e e c hs i g n a l w a s b r o u g h t u n d e r c o n t r o l . M o r e o v e r , t h e p r o c e -d u r e a p p e a r s t o b e r e p l ic a b l e . T h e s e c o n d u n e x p e c t e df i n d i n g w a s t h e e f f e c t p r o d u c e d o n s t u t te r i n g f r e q u e n c yo f b o t h i n c r e a si n g a n d d e c r e a s i n g t h e f r e q u e n c y o f i n te r -v a l s o f p h o n a t i o n . T h e s e d a t a s t r o n g l y s u g g e s t t h a t s t u t-t e r i n g f r e q u e n c y m a y b e b r o u g h t u n d e r r e l a t i v e l y t i g h tc o n t ro l b y m a n i p u l a t i n g t h is d i m e n s i o n o f sp e e c h .

T h e r e a r e m a n y p o t e n t i a l s o u r c e s o f v a r i a n c e i n t h iss t u d y t h a t n e e d i n v e s t i g a t i o n b e f o r e i t c a n b e c o n c l u d e dt h a t p h o n a t i o n i n t e r v a l m a n i p u l a t i o n w i l l c o n t r o l s t u t t e r -i n g . F i r s t , a n d m o s t i m p o r t a n t , i s t h e c o n c e p t u a l i s s u ea s s o c i a t e d w i t h t h i s t y p e o f e x p e r i m e n t a l d e s i g n a n d i t sf i n d i n g s . T h a t i s, a n y d e m o n s t r a t i o n o f a n a p p a r e n t r e l a -t i o n s h i p b e t w e e n t w o v a r i a b l e s d o e s n o t e x c l u d e t h ep o s s i b i l i t y t h a t o t h e r v a r i a b l e s c o u l d b e n e c e s s a r y ( e v e np e c u l i a r l y n e c e s s a r y t o t h e s e s u b j e c t s ) t o p r o d u c e c o r r e -l a t e d v a r i a t io n . F o r e x a m p l e , i t is n o t c o m p l e t e l y c l e a rw h a t a s p e c t o f t h e p r o c e d u r e s u s e d i n th i s s t u d ya c h i e v e d t h e p h o n a t i o n - t i m e m a n i p u l a t i o n . T h e m o s to b v i o u s p o s s i b i l i t y i s t h a t t h e s p e c i f i c p r e s c r i b e d p h o n a -t i o n i n t e r v a ls m a y h a v e b e e n u n r e l a t e d t o t h e d u r a t i o n st h a t t h e s u b j e c t s a c t u a l l y u s e d t o c o n t r o l t h e i r P I c o u n t sd u r i n g t h e t r e a t m e n t c o n d i t io n s . I n t h e m o s t e x t r e m ee a s e t h e s u b j e c t s c o u l d h a v e r e s o r t e d t o s i n g i n g . I n a n ye v e n t , s u c h u n u s u a l s p e e c h b e h a v i o r d o e s n o t a p p e a r toe x p l a i n t h e s e f i n d i n g s .

T h e p e r c e p t u a l a n a l y se s o f b o t h s u b j e c ts ' s p e e c h q u a l-i t y d u r i n g B - c o n d i t i o n s r e v e a l s w i d e l y d i f f e r e n t f i n d-i n g s . T h e r e i s n o e v i d e n c e t h a t s u b j e c t P . A . a d o p t e d a nu n u s u a l w a y o f s p e a k i n g to r e d u c e h i s P I c o u nt s . H ee v i d e n t l y u s e d a p e r c e p t u a l l y d i f f e r e n t m a n n e r o f s p e ak -i n g i n B - 5 0 c o n d i t io n s b u t n o t d u r i n g B - 1 0 0 c o n d i-t i o ns . F u r t h e r m o r e , t h e m a j o r i t y o f l i s t e n e r s s e e m t oh a v e r e g a r d e d h i s s p e e c h a s n o r m a l s o u n d i n g . B y c o n -t r a s t , S u b j e c t S . L . d o e s s e e m t o h a v e u s e d a n u n u s u a ls p e e c h p a t t e r n d u r i n g B - 1 5 0 c o n d i t i o n s .

aS inee th is s tudy was com ple ted , a num ber o f techn ical ahdmethodolog ica l changes have been made to the p rocedure de -sc r ibed he re . The p r inc ipa l change has been a sh if t f rom a"hard-wired" to a compute r ized techn ique fo r the ana lys is o fduration components in speech behavior. A software programhas been deve loped b y the sen io r au thor and co l leagues a t theUnivers i ty o f Wash ing ton w hich p rov ides bo th ana lys is andfeedbac k from four dimensions of the spee ch s ignal: the au diblesignal, the phonated s ignal, the nonphonated audible s ignal,a n d n o n a u d ib le in t e rv a l s . T h i s t e c h n iq u e a l s o p e rm i t s t h eleng th o f s igna ls f rom each o f these d im ens ions to be p resc r ibedfor both analysis and feedback. I n oth er words, it has the advan-tage ov er the sys tem desc r ibed in the p resen t s tudy o f enab l ingpossible control o ver excessiv ely long, as well as short, dura-tions in the s ignal. It is anticipated that this will provide a moreu s e f u l a n d s o p h i s t i c a te d t e c h n i q u e f o r m a n i p u l a t i n g a n dmonito r ing a speech pa t te rn .

F u r t h e r m o r e , t h e i n c r e a s e d s u t t t e r i n g s d u r i n g B +c o n d i ti o n s m a y h a v e r e s e m b l e d s t u tt e r in g s b u t s h a r e dn o t h i n g w i t h t h e s t u t t e r i n g b e h a v i o r s p r o d u c e d d u r i n gn o n t r e a t m e n t c o n d i t i o n s . A g a i n , i n a n e x t r e m e c a s e ," f a k e d s t u t t e r i n g s " c o u l d h a v e b e e n u s e d t o i n c r e a s e P Ie r r o r co u n t s. H o w e v e r , t h i s m a y h a v e b e e n p a r t ia l l y c o n -t r o l l ed s i n c e t h e e x p e r i m e n t e r a n d a n i n d e p e n d e n t c li n i-c i a n w e r e i n s t r u c t e d t o c o u n t o n l y t h o s e e v e n t s t h a t t h e yp e r c e i v e d t o b e s t u t t e r i n g s .

O n e i m p o r t a n t s o u r c e o f v a r i a n c e i n t h e p r e s e n t s t u d yi s t h e f a m i l i a r i t y t h a t t h e s e s u b j e c t s h a d w i t h " p r o l o n g e ds p e e c h . " A s i n d i c a t e d , b o t h s u b j e c t s h a d r e c e i v e d t r e a t -m e n t b y t h is m e t h o d 1 0 y e a r s e a r l ie r . I t i s p o s s i b l e t h a tc e r t a i n s k i l ls a c h i e v e d i n t h e c o u r s e o f t h a t t h e r a p y c o u l db e i n v o k e d a s a n e n t i r e e x p l a n a t i o n f o r t h e s e r e s u l t s.T h e p r i n c i p a l l i m i t a t i o n i n t h a t e x p l a n a t i o n i s t h a t t h e r ew a s n o c o n s i s t e n t p e r c e p t u a l e v i d e n c e t h a t t h e s e " s k i l l s "w e r e b e i n g u s e d - - a t l e a s t n o t i n a w a y t h a t d i s ti n c t i v e lyc h a n g e d P.A.'s m a n n e r o f s p e a k in g . N e v e r t h e l e s s , e v e ni f t h e s u b j e c t s w e r e m a k i n g u s e o f e a r l i e r t r a i n in g , t h a td o e s n o t i n v M i d a t e t h e o b s e r v e d e f f e ct s . I t m a y s i m p l yb e t h e e a s e t h a t s u c h e f f e c t s a re a c h i e v e d m o r e e a s i l y b yt r e a t e d s u b j e c t s . I t i s n o t e w o r t h y t h a t t h e r e s e a r c h e r s 'e x p e r i e n c e i n a p p l y i n g t h is p h o n a t i o n m o d i f i c a t io n p r o -c e d u r e w i t h o t h e r s u b j e c t s s u g g e s t s t h a t t r e a t n a e n t h i s -t o r y m a y n o t b e a n i m p o r t a n t v a r i a b l e . H o W e v e r , s o m ei n i t i a l t r i a l s w ' i t h s o m e s u b j e c t s h a v e s h o w n t h a t v e r yl o n g P I l e v e l s m a y b e n e e d e d b e f o r e P I e r r o r c o n tr o l i sa c h i e v e d . S u b j e c t P . S ., w h o p r o v i d e d d a t a f o r p h o n a t i o ni n t e r v a l t e s t i n g ( s e e R e l i a b i l i t y ) , f a i l e d t o d i s p l a y P Ie r r o r c o n t r o l a t e a c h 5 0 - m s l e v e l u p t o a n d i n c l u d i n g 4 5 0m s . U n f o r t u n a t e l y t h e s u b j e c t 's s c h o o l c la s s s c h e d u l ep r e v e n t e d h i m f r o m c o n t i n u i n g i n t h e p r e s e n t e x p e r i -m e n t . P . S . w a s a n e x t r e m e l y s e v e r e s t u t t e r e r ( b o t h i nf r e q u e n c y a n d d u r a t i o n o f s t u t t e ri n g s ) a n d h a d n o t p r e v i -o u s l y r e c e i v e d t h e r a p y .

I n c o n c l u s i o n , t h e f i n d i n g s f r o m t h i s s t u d y s u g g e s t t h a ti t i s p o s s i b l e t o m a n i p u l a t e t h e f r e q u e n c y o f p h o n a t i o ni n t er v a l s b y m e a n s o f v a r io u s m o d e s o f f e e d b a c k a n d t h a ti n c r e a s e s o r d e c r e a s e s i n t h e f r e q u e n c y o f s o m e i n t e r v a l so f p h o n a ti o n m a y p r o d u c e c o r r e l a t e d c h a n g e s i n s tu t t er -i n g f r e q u e n c y . T h e f i n d i n g s o f t h i s s t u d y a l s o i n d i c a t et h e p o s s i b i l i t y o f d e v e l o p i n g a c l in i c a l l y u s e f u l a n dr e p l i c a b l e t e c h n i q u e f o r t r e a t i n g s t u t t e ri n g . C u r r e n t r e -s e a r c h i s b e i n g d i r e c t e d t o w a r d s r e f i n i n g t h i s p r o c e d u r ea n d i s o l a ti n g t h e c o n s t i t u e n t s o f a n y r e l a t i o n s h i p b e -t w e e n t h e f i ' e q u e n e y o f c e r t a i n p h o n a t i o n i n t e r v a l s a n ds tu t t e r in g .

A C K N O W L E D G M E N T SThis s tud y was supported by a grant from the National H ealthand Medical Researc h Co uncil of Ausla'a lia (Gran t No. 74/345).The assis tance of Ken Noreross and Hel en Southwood in theconduc t of different aspects of this s tu dy is gratefully acknowl-edged .

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Requests for reprints should be sent to Roger J. Ingham,School of Commu nicat ion Disorders, Cumb erl and College ofHealth Sciences, P.O. Box 170, Lideombe, NSW, Australia,2141.