JOURNAL
OF COMMUNICATION
DISORDERS
8 (1975).
141-155
VARIABLES AFFECTING STUTTERER’S INITIAL REACTIONS TO DELAYED AUDITORY FEEDBACK BRYAN
’
D. BURKE
New South Wales College of Paramedical Studies, School of Speech Therapy, Camperdown. New South Wales 2050, Australia
Twenty male stutterers (7- 18 years) described pictures under delayed auditory feedback (DAF). Delay was varied from 0 to 300 msec in 50 msec steps. There was a significant interaction between delay time, age and initial disfluency in terms of disfluent words but not speech rate. Young stutterers (7-12 years) were generally more affected by DAF than older stutterers (13-18 years). Under DAF high disfluent stutterers showed reduced disfluency, whereas low disfluent stutterers either showed little or no change or became more disfluent. Delays of 5&150 msec tended to have an ameliorative effect on stuttering. Conflicting results were obtained when the same subjects repeated short sentences under DAF. The majority of stutterers were fluent when repeating the sentences under no delay, but stuttering increased under DAF. Current explanations of the DAF effect and feedback theories of stuttering do not readily account for these results.
Introduction Although delayed auditory feedback (DAF) generally has an ameliorative effect on stuttering, investigators have consistently reported large individual differences in stutterers’ initial reactions to DAF (see Soderberg, 1968, 1969). Factors that contribute to this intersubject variability include the severity of stuttering under normal conditions (Naylor, 1953; Nessel, 19.58; Soderberg, 1959; Lotzmann, 1961; Zerneri, 1966; Ham and Steer, 1967) and the magnitude of the delay interval (Soderberg, 1959; Lotzmann, 1961). Other experiments conducted with nonstutterers have shown that young children (4-9 years) experience greater speech disruption under DAF than older children and adults (MacKay, 1968; Buxton, 1969; see also Waters, 1968). Contradictory results obtained in earlier studies (Chase et al., 1961; Ratner, Gawronski and Rice, 1964; see also Smith and Tierney, 1971) now appear to be attributable to the use of a single delay time. MacKay (1968) and Buxton (1969) reported that the delay interval producing maximal speech disruption varies at different ages. Since comparable developmental evidence is not available for stutterers, the present study investigated the effects of DAF on the speech of pre-adolescent (7- 12 years) and adolescent (13- 18 years) stutterers. A secondary aim of the study was to reexamine individual differences in stutterers’ reaction to DAF as a function of initial disfluency and delay time. In the course of this investigation data were obtained from two different speech tasks-reproducing simple sentences and giving extemporaneous descriptions of pictures. 0 American Elsevier Publishing
Company,
Inc.,
1975
141
142
BRYAN
D. BURKE
Method Subjects The subjects were 20 male stutterers with normal hearing (less than 25 dB SL at 250, 1000 and 4000 Hz), aged between 7 years, 7 months and 18 years, 1 month. Equipment All testing was conducted in a two-room recording suite. The subject spoke into a microphone (Neumann, Model U67) located approximately 30 cm from the mouth. This distance was held constant by the use of a microphone boom and headrest. The microphone and associated pre-amplifier (Radio Mechanical Engineers , Model 50Al) were connected to a tape recorder (Ampex, Model AG-350) and a delayed feedback system. The DAF system consisted of a custom-built delay unit, amplifier (Grason-Stadler speech audiometer, Model 162) and earphones (Telephonic TDH-39 mounted in an Auraldome soundattenuating headset). An automatic gain control amplifier (Amalgamated Wireless Australia, Model 2658250) held the output of the DAF unit constant at approximately 100 dB SPL in the delayed and undelayed feedback conditions. Procedure Subjects were tested under seven randomly presented DAF conditions (0,50,100, 150, 200, 250 and 300 msec delay) on two occasions. A period of 1-12 weeks separated the two testing sessions. In the first session a sentence reproduction task (cf. MacKay, 1968) was used while the second session involved giving spontaneous descriptions of pictures (cf. Soderberg, 1959). Sentence reproduction. Subjects reproduced five 8 word sentences under each of the delays. The sentences and experimental instructions were prerecorded and played back through the subject’s earphones. The subject listened to two presentations of a sentence and then repeated it aloud “. . at the same speed and with the same care you normally use.” Picture description. Subjects described two pictures under each of the delays. The prerecorded instructions told subjects to speak for 1 minute giving a literal description of the people and situation shown in each picture. The pictures were projected on to a rear projection screen 120 cm square. The period of time the picture was exposed (and hence the time the subject spoke) was controlled by the experimenter. Any unfilled pause exceeding 5 seconds was regarded as “timeout” and added to the period for that trial. If it became obvious that the subject had stopped speaking prematurely he was prompted by the experimenter. Prior to the administration of the DAF conditions subjects practiced the experimental task by either reproducing five sentences or describing two pictures
STUTTERER’S
INITIAL
REACTIONS
TO DELAYED
AUDITORY
FEEDBACK
143
under synchronous auditory feedback (SAF). A further SAF condition was administered before and after the delay conditions to assess changes in speech performance over the course of the session. Speech Analysis The dependent variables investigated were speech rate (number of words spoken per minute) and the percentage of disfluent words (relative to the total number of words spoken). Words involving any one of the following disfluencies were identified on a verbatim typescript of the tape: interjections, repetitions (including words repeated in the course of revision), blocks and gross misarticulations. In addition incomplete phrases were scored as disfluencies in the picture description task, while substitutions, omissions and reordering errors were counted in the sentence reproduction task. The experimenter’s reliability in identifying disfluencies was determined by restoring two complete subject records (10% of the data). The correlation between the total number of disfluencies identified on the two occasions was r = 0.94, indicating that a satisfactory degree of reliability had been achieved. The time taken to repeat a sentence was determined to the nearest 0.1 set from a sound level recorder (Bruel and Kjaer, Type 2305). A stopwatch was used to determine speaking times in the description task.
Results Sentence Reproduction Analysis of the disfluency data showed that 11 of the 20 subjects tested did not stutter (i.e., repeat or block) when reproducing sentences in the no delay conditions (practice of 0 msec delay). Since these “fluent” subjects were unequally distributed across the four age groups (7-9, 10-12, 13-15, and 16-18 years), the effects of stuttering severity and age were seriously confounded. Although no formal analysis of these results will be presented, performance in the sentence reproduction and picture description studies will be compared in a later section. Picture Description Subjects were allocated to one of four groups based on their age and disfluency in the experimental practice conditions (see Procedure). Stutterers with more than 23% disfluencies were arbitrarily classified as “high disfluent” and those with fewer disfluencies as “low disfluent. ” The mean disfluency of the resulting groups was 7-12 low disfluent-13.5%; 7-12 high disfluent-39.4%; 13-18 low disfluent-15.4%; and 13-18 high disfluent-36.7%.
BRYAN
LOW
ol
, PI9 OAF
I
0
D. BURKE
DISFLUENT
I
I
100
1
HIGH
L
200
I
DELAY Fig. 1.
I
,
300
P,. OAF
-
1 0
DISFLUENT -
7-12
-
13-13
1
.
0
100
0
200
1
I
300
msec
Mean speech rate of groups of stutterers (differing in age and disfluency) under DAF.
describing
pictures
Performance in the SAF conditions administered before and after the delay conditions was evaluated using a two-way (groups X conditions) analysis of variance with repeated measures on one factor (Winer, 1962, p. 302). These analyses showed that there were no significant changes in either speech rate or disfluency over the course of the experimental session for any of the groups. Separate four-way (disfluency X age X delays X trials) analyses of variance with repeated measures on two factors (Winer, 1962, p. 350) were conducted on the speech rate and disfluency data. The trials main effect and each of the interactions involving trials did not reach significance in either analysis, indicating that performance was similar when subjects described the two pictures in each condition. Therefore, only the mean results for the two speaking trials will be presented here. Speech rate. The mean speech rate for each of the groups in the delay conditions is shown in Fig. 1. The analysis of variance revealed no significant
STUTTERER’S
INITIAL
REACTIONS
TO DELAYED
AUDITORY
FEEDBACK
14.5
effects attributable to age, but there were significant differences in the effects of the delay conditions on the two disfluency groups (F = 4.84; df = 7,112; P < 0.001). Figure 1 shows that the speech rate of the low disfluent groups was significantly higher than that of the high disfluent groups in the nodelay (pre-DAF and 0 delay) conditions. Under DAF the speech rate of the low disfluent groups decreased as the delay interval was increased; delays of 50 and 100 msec produced a marked reduction in speech rate, while subsequent delays produced smaller decreases. By contrast the speech rate of the high disfluent groups increased in the 50 msec condition; 100 msec delay resulted in a speech rate only slightly below that of the no delay conditions, but with longer delays there was a further reduction in speech rate. Figure 2 shows the mean percentage of disfluent words produced DisJuency. in each of the conditions. There were significant differences in the effects of the delay conditions on the two disfluency groups (F = 2.98;df = 7,112;P < O.OOl), together with a significant interaction between age, disfluency and delay (F = 3.20; df = 7,112; P < 0.01). The differential effects of the delay conditions on the two low disfluency groups can be seen in Fig. 2. With 50 msec delay the 7-12 group showed a reduction in disfluency, but with longer delays there was a corresponding increase in disfluency. The 13-18 group showed reduced disfluency with 100 and 200 msec delay; delays of 50, 150 and 250 msec resulted in approximately the same level of disfluency as the undelayed conditions and 300 msec delay produced a slight increase in disthrency. By contrast, delay had an ameliorative effect on the speech of the high disfluent groups, with the 7-12 group showing greater gains in fluency than the 13-18 group. The 7-12 group showed improved fluency under all delays, but 50 and 100 msec produced the greatest improvement. The 13- 18 group experienced improved fluency under all delays with the exception of 300 msec delay. For this group the greatest reduction in disfluency occurred with delays of 50 and 150 msec. Effects of DAF on individual stutterers. The data were also examined to determine the optimal delay interval for each stutterer. Lotzmann (196 1) measured changes in speech performance under DAF relative to normal speech performance and then used these values to determine the “optimal” delay interval for individual stutterers. The method used here was to obtain ratios of delay to no delay (pre-DAF) performance based on the speech rate and percent fluent word data. Thus the direction and extent of changes in speech fluency and rate could be determined. The delay intervals producing maximal changes (both positive and negative) for the 20 stutterers are shown in Table 1. A maximal positive change was defined as the delay interval producing the largest fluency and speech rate ratios and a maximal negative change as the delay producing the smallest ratio values.
146
BRYAND.BURKE LOW
.s
Dl SF LUENT
HIGH
DI SfLUENT
t
DELAY-mscc
Fig. 2.
Mean percentage of disffuent words produced by groups of stutterers (differing disfluency) describing pictures under DAF.
in age and
Inspection of Table 1 shows that six low disfluent stutterers experienced considerable positive changes in fluency. Of the remaining stutterers in this group, two, (1,3) showed a slight gain in fluency, one (2) showed reduced fluency and one (15) showed no change under any of the delays. These dhanges in fluency were usually accompanied by a reduction in speech rate. High disfiuent stutterers generally made marked gains in fluency; however, one subject (11) showed reduced fluency under all delays. The improvement in fluency achieved by the high disfluent stutterers was not accompanied by consistent changes in speech rate. For example, subject 18 showed a dramatic increase in speech rate but the remaining subjects showed only slight changes. For those stutterers showing a positive DAF effect, six showed greatest improvement with 50 msec delay, seven with 100 msec and two with 150 msec delay. Examination of the deIays producing maximal negative changes provides further evidence of the ameliorative effects of delay on high disfluent stutterers. Six high disfluent stutterers showed improved fluency with atf delays (i.e. * no negative effect), two (4, f 5) showed no change and two ( i1,19) showed reduced
STUTTERER’S
INITIAL
REACTlONS
TO DELAYED
AUDITORY
FEEDBACK
TABLE 1 in Maximal Changes (Positive and Negative) in the Spontaneous Individual Stutterers.
Delay Intervals Resulting
147
Speech of
__Positive DisfluencyAge group Low 7-12
Low 13-18
High 7-12
High 13-18
Subject 1 2 3 5 10 12 13 16 17 20 4 6 7 8 9 11 14 I5 18 19
(Some subjects (identified
Negative82. Dinnan, J.G., McGuinness, E., Perrin, L. Auditory feedback-stutterers versus non-stutterers. J. Learning Dis., 1970, 3, 209213. Goldiamond, I. Stuttering and fluency as mampulatable operant response classes. In L. Krasner and L.P. Ullman (Eds.), Research in behavior modtfication. New York: Holt, Rinehart and Winston, 1965, pp. 106-156. Goldman-Eisler, F. The determinants of the rate of speech output and their mutual relations. J. Psychosom. Res., 1956, 1, 137-143. Gregory, H.H. Stuttering and auditory central nervous system disorder. J. Speech Hearing Res., 1964, 7, 335-341. Gruber, L. Sensory feedback and stuttering. J. Speech Hearing Dis., 1965, 30, 378-380. Ham, R. E. Certain effects of alterations in the auditory feedback of speech defectives and normals. Doctoral Dissertation, Purdue University, 1957. Ann Arbor, Mich.: University Microfilms, 55-236. Ham, R. E., Steer, M.D. Certain effects of alterations in auditory feedback. Folia Phoniat., 1967,13, 53-62. Lane, H., Tranel, B. The Lombard sign and the role of hearing in speech. J. Speech Hearing Res., 1971, 14, 677-709. Lotzmann, V.G. Zur anwendung variierter Verziigerungstzeiten bei balbuties. Folia Phoniat., 1961, 13, 276-3 12. MacKay, D.G. Metamorphosis of a critical interval: Age-linked changes in the delay in auditory feedback that produces maximal disruption in speech. /. Acoust. Sot. Am., 1968,43,8 11-821. MacKay, D.G. How does language familiarity influence stuttering under delayed auditory feedback? Percept Motor Skills, 1970, 30, 655699. Martin, J. E. The signal detection hypothesis and the perceptual defect theory of stuttering. J. Speech Hearing Dis., 1970, 35, 252-255. Mysak, E. D. A servo-theory model for speech therapy. J. Speech Hearing Dis., 195~, 24, 144-149. Mysak, E. D. Servo-theory and stuttering. J. Speech Hearing Dis., 1960, 15, 188-195. Mysak, E.D. Speech pathology and feedback theory. Springfield, Ill.: Charles C Thomas, 1966.
154
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D. BURKE
Naylor, R.B. A comparative study of methods of estimating Dis., 1953, 18, 3G37.
severity of stuttering. J. Speech Hearing
Nessel, E. Die verziigerte Sprachriickkopplung (Lee-Effekt) bei Stotterern. Folia Phoniar., 1958, 10, 199-204. Perkins, W.H. Physiological studies. In J.G. Sheehan (Ed.) Srurtering: research und rherapy, New York: Harper and Row, 1970, pp. 188-239. Prim, D., Walton W. Effects of monaural and binaural DAFupon the speech of stutterers in relation to responses on a dichotic listening task. Paper presented at American Speech and Hearing Association, Annual Convention, Chicago, 197 1. Ratner, S.C., Gawronski, J.J., Rice, F.E. The variable of concurrent activity in the language of children: The effects of delayed auditory feedback. Psychol. Rec., 1964, 14, 47-56. Rousey, C.L., Goetzinger, D. P., Dirks, D. Sound localization ability of normal, stuttering, neurotic and hemiplegic subjects. A.M.A. Arch. Gen. Psychiur., 1959, 1, 6W45. Shearer, W.M. Speech: Behavior of middle ear muscles during stuttering. Science, 1966, 152, 1280. Shearer, W.M., Simmons, F.B. Middle ear activity during speech in normal speakers and stutterers.J. Speech Hearing Res., 1965, 8, 203-207. Sklar, B. A feedback model of the stuttering problem-an engineer’s view. J. Speech Hearing Dis., 1969, 34, 226-230. Smith, K.U., Tierney, D. Delayed speech feedback and age. J. Speech Hearing Res., 1971, 14, 214-219. Soderberg, G. A. A study of the effects of delayed sideone onfour aspecrs of stutterer’s speech during oral reading and sponraneous speaking. Doctoral Dissertation, Ohio State University. Ann Arbor, Mich.: University Microfilms, 1960, 60-796. Soderberg, G.A. Delayed auditory feedback and stuttering. J. Speech Hearing Dis., 1968, 33, 26@267. Soderberg, G.A. Delayed auditory feedback and the speech of stutterers: A review of studies. J. Speech Hearing Dis., 1969, 34, 2C-29. Stromsta, C.P. A methodology related to the determination of the phase angle of bone-conducted speech sound energy of stutterers and non-shmerers. Doctoral Dissertation, Ohio State University, 1956. Ann Arbor, Mich.: University Microfilms, 562755. Stromsta, C.P. An investigation of the localization of inter-aural clicks and the reading times of stutterers and non-stutterers under monaural sidetone conditions. Technical Report, Ohio State University, PHS Grant NB 03541-03, National Institutes of Health, August, 1964. Stromsta, C. P. Averaged evoked responses of stutterers and non-stutterers as a function of inter-aural time relationships. Technical Report, Ohio State University, PHS Grant NB-03541-03, National Institutes of Health, September, 1965. Van Riper, C. The nature of stutlering. Englewood Cliffs, N.J.: Prentice-Hall, 1971. Waters, J.E. A theoretical and developmental investigation of delayed speech feedback. Gener. Psychol. Monogr. I 1968, 78, 3-54. Webster, R.L., A behavioral analysis of stuttering: Treatment and theory. In Calhoun, Adams and Mitchell(Eds.),Innovarive treafmenfmethodsinpsychopathology. New York: Wiley, inpress. Webster, R.L., Lubker, B.B. Interrelationships among fluency producing variables in stuttered speech. J. Speech Hearing Res., 1968, 11, 754-766. Webster, R.L., Schumacker, S.J., Lubker, B.B. Changes in stuttering frequency as a function of various intervals of delayed auditory feedback. J. Abnorm. Psych., 1970, 75, 45-49. Winer, B.J. Statistical principles in experimenta/ design. New York: McGraw-Hill, 1962. Wingate, M.E. Effect on stuttering of changes in audition. 1. Speech Hearing Res., 1970, 13, 861-873. Wolf, A. A., Wolf, E.G. Feedback processes in the theory of certain speech disorders. Speech Pathol. Ther., 1959, 2, 48-55.
STUTTERER’S
INITIAL
REACTIONS
TO DELAYED
Yates, A.J. Recent empirical and theoretical approaches normal subjects Yates, A.J. Behavior Zerneri, L. Tentatives du begaiement.
AUDITORY
to the experimental
FEEDBACK
manipulation
and stutterers. Behav. Res. Ther., 1963, 1, 95-l 19. therapy. New York: Wiley, 1970, pp. 118-122. d’application de la voix retardee (“delayed auditory feedback”) J. Franc. Orl., 1966, 15,415-418.
155
of speech in
dam la therapie
OF COMMUNICATION
DISORDERS
8 (1975).
141-155
VARIABLES AFFECTING STUTTERER’S INITIAL REACTIONS TO DELAYED AUDITORY FEEDBACK BRYAN
’
D. BURKE
New South Wales College of Paramedical Studies, School of Speech Therapy, Camperdown. New South Wales 2050, Australia
Twenty male stutterers (7- 18 years) described pictures under delayed auditory feedback (DAF). Delay was varied from 0 to 300 msec in 50 msec steps. There was a significant interaction between delay time, age and initial disfluency in terms of disfluent words but not speech rate. Young stutterers (7-12 years) were generally more affected by DAF than older stutterers (13-18 years). Under DAF high disfluent stutterers showed reduced disfluency, whereas low disfluent stutterers either showed little or no change or became more disfluent. Delays of 5&150 msec tended to have an ameliorative effect on stuttering. Conflicting results were obtained when the same subjects repeated short sentences under DAF. The majority of stutterers were fluent when repeating the sentences under no delay, but stuttering increased under DAF. Current explanations of the DAF effect and feedback theories of stuttering do not readily account for these results.
Introduction Although delayed auditory feedback (DAF) generally has an ameliorative effect on stuttering, investigators have consistently reported large individual differences in stutterers’ initial reactions to DAF (see Soderberg, 1968, 1969). Factors that contribute to this intersubject variability include the severity of stuttering under normal conditions (Naylor, 1953; Nessel, 19.58; Soderberg, 1959; Lotzmann, 1961; Zerneri, 1966; Ham and Steer, 1967) and the magnitude of the delay interval (Soderberg, 1959; Lotzmann, 1961). Other experiments conducted with nonstutterers have shown that young children (4-9 years) experience greater speech disruption under DAF than older children and adults (MacKay, 1968; Buxton, 1969; see also Waters, 1968). Contradictory results obtained in earlier studies (Chase et al., 1961; Ratner, Gawronski and Rice, 1964; see also Smith and Tierney, 1971) now appear to be attributable to the use of a single delay time. MacKay (1968) and Buxton (1969) reported that the delay interval producing maximal speech disruption varies at different ages. Since comparable developmental evidence is not available for stutterers, the present study investigated the effects of DAF on the speech of pre-adolescent (7- 12 years) and adolescent (13- 18 years) stutterers. A secondary aim of the study was to reexamine individual differences in stutterers’ reaction to DAF as a function of initial disfluency and delay time. In the course of this investigation data were obtained from two different speech tasks-reproducing simple sentences and giving extemporaneous descriptions of pictures. 0 American Elsevier Publishing
Company,
Inc.,
1975
141
142
BRYAN
D. BURKE
Method Subjects The subjects were 20 male stutterers with normal hearing (less than 25 dB SL at 250, 1000 and 4000 Hz), aged between 7 years, 7 months and 18 years, 1 month. Equipment All testing was conducted in a two-room recording suite. The subject spoke into a microphone (Neumann, Model U67) located approximately 30 cm from the mouth. This distance was held constant by the use of a microphone boom and headrest. The microphone and associated pre-amplifier (Radio Mechanical Engineers , Model 50Al) were connected to a tape recorder (Ampex, Model AG-350) and a delayed feedback system. The DAF system consisted of a custom-built delay unit, amplifier (Grason-Stadler speech audiometer, Model 162) and earphones (Telephonic TDH-39 mounted in an Auraldome soundattenuating headset). An automatic gain control amplifier (Amalgamated Wireless Australia, Model 2658250) held the output of the DAF unit constant at approximately 100 dB SPL in the delayed and undelayed feedback conditions. Procedure Subjects were tested under seven randomly presented DAF conditions (0,50,100, 150, 200, 250 and 300 msec delay) on two occasions. A period of 1-12 weeks separated the two testing sessions. In the first session a sentence reproduction task (cf. MacKay, 1968) was used while the second session involved giving spontaneous descriptions of pictures (cf. Soderberg, 1959). Sentence reproduction. Subjects reproduced five 8 word sentences under each of the delays. The sentences and experimental instructions were prerecorded and played back through the subject’s earphones. The subject listened to two presentations of a sentence and then repeated it aloud “. . at the same speed and with the same care you normally use.” Picture description. Subjects described two pictures under each of the delays. The prerecorded instructions told subjects to speak for 1 minute giving a literal description of the people and situation shown in each picture. The pictures were projected on to a rear projection screen 120 cm square. The period of time the picture was exposed (and hence the time the subject spoke) was controlled by the experimenter. Any unfilled pause exceeding 5 seconds was regarded as “timeout” and added to the period for that trial. If it became obvious that the subject had stopped speaking prematurely he was prompted by the experimenter. Prior to the administration of the DAF conditions subjects practiced the experimental task by either reproducing five sentences or describing two pictures
STUTTERER’S
INITIAL
REACTIONS
TO DELAYED
AUDITORY
FEEDBACK
143
under synchronous auditory feedback (SAF). A further SAF condition was administered before and after the delay conditions to assess changes in speech performance over the course of the session. Speech Analysis The dependent variables investigated were speech rate (number of words spoken per minute) and the percentage of disfluent words (relative to the total number of words spoken). Words involving any one of the following disfluencies were identified on a verbatim typescript of the tape: interjections, repetitions (including words repeated in the course of revision), blocks and gross misarticulations. In addition incomplete phrases were scored as disfluencies in the picture description task, while substitutions, omissions and reordering errors were counted in the sentence reproduction task. The experimenter’s reliability in identifying disfluencies was determined by restoring two complete subject records (10% of the data). The correlation between the total number of disfluencies identified on the two occasions was r = 0.94, indicating that a satisfactory degree of reliability had been achieved. The time taken to repeat a sentence was determined to the nearest 0.1 set from a sound level recorder (Bruel and Kjaer, Type 2305). A stopwatch was used to determine speaking times in the description task.
Results Sentence Reproduction Analysis of the disfluency data showed that 11 of the 20 subjects tested did not stutter (i.e., repeat or block) when reproducing sentences in the no delay conditions (practice of 0 msec delay). Since these “fluent” subjects were unequally distributed across the four age groups (7-9, 10-12, 13-15, and 16-18 years), the effects of stuttering severity and age were seriously confounded. Although no formal analysis of these results will be presented, performance in the sentence reproduction and picture description studies will be compared in a later section. Picture Description Subjects were allocated to one of four groups based on their age and disfluency in the experimental practice conditions (see Procedure). Stutterers with more than 23% disfluencies were arbitrarily classified as “high disfluent” and those with fewer disfluencies as “low disfluent. ” The mean disfluency of the resulting groups was 7-12 low disfluent-13.5%; 7-12 high disfluent-39.4%; 13-18 low disfluent-15.4%; and 13-18 high disfluent-36.7%.
BRYAN
LOW
ol
, PI9 OAF
I
0
D. BURKE
DISFLUENT
I
I
100
1
HIGH
L
200
I
DELAY Fig. 1.
I
,
300
P,. OAF
-
1 0
DISFLUENT -
7-12
-
13-13
1
.
0
100
0
200
1
I
300
msec
Mean speech rate of groups of stutterers (differing in age and disfluency) under DAF.
describing
pictures
Performance in the SAF conditions administered before and after the delay conditions was evaluated using a two-way (groups X conditions) analysis of variance with repeated measures on one factor (Winer, 1962, p. 302). These analyses showed that there were no significant changes in either speech rate or disfluency over the course of the experimental session for any of the groups. Separate four-way (disfluency X age X delays X trials) analyses of variance with repeated measures on two factors (Winer, 1962, p. 350) were conducted on the speech rate and disfluency data. The trials main effect and each of the interactions involving trials did not reach significance in either analysis, indicating that performance was similar when subjects described the two pictures in each condition. Therefore, only the mean results for the two speaking trials will be presented here. Speech rate. The mean speech rate for each of the groups in the delay conditions is shown in Fig. 1. The analysis of variance revealed no significant
STUTTERER’S
INITIAL
REACTIONS
TO DELAYED
AUDITORY
FEEDBACK
14.5
effects attributable to age, but there were significant differences in the effects of the delay conditions on the two disfluency groups (F = 4.84; df = 7,112; P < 0.001). Figure 1 shows that the speech rate of the low disfluent groups was significantly higher than that of the high disfluent groups in the nodelay (pre-DAF and 0 delay) conditions. Under DAF the speech rate of the low disfluent groups decreased as the delay interval was increased; delays of 50 and 100 msec produced a marked reduction in speech rate, while subsequent delays produced smaller decreases. By contrast the speech rate of the high disfluent groups increased in the 50 msec condition; 100 msec delay resulted in a speech rate only slightly below that of the no delay conditions, but with longer delays there was a further reduction in speech rate. Figure 2 shows the mean percentage of disfluent words produced DisJuency. in each of the conditions. There were significant differences in the effects of the delay conditions on the two disfluency groups (F = 2.98;df = 7,112;P < O.OOl), together with a significant interaction between age, disfluency and delay (F = 3.20; df = 7,112; P < 0.01). The differential effects of the delay conditions on the two low disfluency groups can be seen in Fig. 2. With 50 msec delay the 7-12 group showed a reduction in disfluency, but with longer delays there was a corresponding increase in disfluency. The 13-18 group showed reduced disfluency with 100 and 200 msec delay; delays of 50, 150 and 250 msec resulted in approximately the same level of disfluency as the undelayed conditions and 300 msec delay produced a slight increase in disthrency. By contrast, delay had an ameliorative effect on the speech of the high disfluent groups, with the 7-12 group showing greater gains in fluency than the 13-18 group. The 7-12 group showed improved fluency under all delays, but 50 and 100 msec produced the greatest improvement. The 13- 18 group experienced improved fluency under all delays with the exception of 300 msec delay. For this group the greatest reduction in disfluency occurred with delays of 50 and 150 msec. Effects of DAF on individual stutterers. The data were also examined to determine the optimal delay interval for each stutterer. Lotzmann (196 1) measured changes in speech performance under DAF relative to normal speech performance and then used these values to determine the “optimal” delay interval for individual stutterers. The method used here was to obtain ratios of delay to no delay (pre-DAF) performance based on the speech rate and percent fluent word data. Thus the direction and extent of changes in speech fluency and rate could be determined. The delay intervals producing maximal changes (both positive and negative) for the 20 stutterers are shown in Table 1. A maximal positive change was defined as the delay interval producing the largest fluency and speech rate ratios and a maximal negative change as the delay producing the smallest ratio values.
146
BRYAND.BURKE LOW
.s
Dl SF LUENT
HIGH
DI SfLUENT
t
DELAY-mscc
Fig. 2.
Mean percentage of disffuent words produced by groups of stutterers (differing disfluency) describing pictures under DAF.
in age and
Inspection of Table 1 shows that six low disfluent stutterers experienced considerable positive changes in fluency. Of the remaining stutterers in this group, two, (1,3) showed a slight gain in fluency, one (2) showed reduced fluency and one (15) showed no change under any of the delays. These dhanges in fluency were usually accompanied by a reduction in speech rate. High disfiuent stutterers generally made marked gains in fluency; however, one subject (11) showed reduced fluency under all delays. The improvement in fluency achieved by the high disfluent stutterers was not accompanied by consistent changes in speech rate. For example, subject 18 showed a dramatic increase in speech rate but the remaining subjects showed only slight changes. For those stutterers showing a positive DAF effect, six showed greatest improvement with 50 msec delay, seven with 100 msec and two with 150 msec delay. Examination of the deIays producing maximal negative changes provides further evidence of the ameliorative effects of delay on high disfluent stutterers. Six high disfluent stutterers showed improved fluency with atf delays (i.e. * no negative effect), two (4, f 5) showed no change and two ( i1,19) showed reduced
STUTTERER’S
INITIAL
REACTlONS
TO DELAYED
AUDITORY
FEEDBACK
TABLE 1 in Maximal Changes (Positive and Negative) in the Spontaneous Individual Stutterers.
Delay Intervals Resulting
147
Speech of
__Positive DisfluencyAge group Low 7-12
Low 13-18
High 7-12
High 13-18
Subject 1 2 3 5 10 12 13 16 17 20 4 6 7 8 9 11 14 I5 18 19
(Some subjects (identified
Negative82. Dinnan, J.G., McGuinness, E., Perrin, L. Auditory feedback-stutterers versus non-stutterers. J. Learning Dis., 1970, 3, 209213. Goldiamond, I. Stuttering and fluency as mampulatable operant response classes. In L. Krasner and L.P. Ullman (Eds.), Research in behavior modtfication. New York: Holt, Rinehart and Winston, 1965, pp. 106-156. Goldman-Eisler, F. The determinants of the rate of speech output and their mutual relations. J. Psychosom. Res., 1956, 1, 137-143. Gregory, H.H. Stuttering and auditory central nervous system disorder. J. Speech Hearing Res., 1964, 7, 335-341. Gruber, L. Sensory feedback and stuttering. J. Speech Hearing Dis., 1965, 30, 378-380. Ham, R. E. Certain effects of alterations in the auditory feedback of speech defectives and normals. Doctoral Dissertation, Purdue University, 1957. Ann Arbor, Mich.: University Microfilms, 55-236. Ham, R. E., Steer, M.D. Certain effects of alterations in auditory feedback. Folia Phoniat., 1967,13, 53-62. Lane, H., Tranel, B. The Lombard sign and the role of hearing in speech. J. Speech Hearing Res., 1971, 14, 677-709. Lotzmann, V.G. Zur anwendung variierter Verziigerungstzeiten bei balbuties. Folia Phoniat., 1961, 13, 276-3 12. MacKay, D.G. Metamorphosis of a critical interval: Age-linked changes in the delay in auditory feedback that produces maximal disruption in speech. /. Acoust. Sot. Am., 1968,43,8 11-821. MacKay, D.G. How does language familiarity influence stuttering under delayed auditory feedback? Percept Motor Skills, 1970, 30, 655699. Martin, J. E. The signal detection hypothesis and the perceptual defect theory of stuttering. J. Speech Hearing Dis., 1970, 35, 252-255. Mysak, E. D. A servo-theory model for speech therapy. J. Speech Hearing Dis., 195~, 24, 144-149. Mysak, E. D. Servo-theory and stuttering. J. Speech Hearing Dis., 1960, 15, 188-195. Mysak, E.D. Speech pathology and feedback theory. Springfield, Ill.: Charles C Thomas, 1966.
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Naylor, R.B. A comparative study of methods of estimating Dis., 1953, 18, 3G37.
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Nessel, E. Die verziigerte Sprachriickkopplung (Lee-Effekt) bei Stotterern. Folia Phoniar., 1958, 10, 199-204. Perkins, W.H. Physiological studies. In J.G. Sheehan (Ed.) Srurtering: research und rherapy, New York: Harper and Row, 1970, pp. 188-239. Prim, D., Walton W. Effects of monaural and binaural DAFupon the speech of stutterers in relation to responses on a dichotic listening task. Paper presented at American Speech and Hearing Association, Annual Convention, Chicago, 197 1. Ratner, S.C., Gawronski, J.J., Rice, F.E. The variable of concurrent activity in the language of children: The effects of delayed auditory feedback. Psychol. Rec., 1964, 14, 47-56. Rousey, C.L., Goetzinger, D. P., Dirks, D. Sound localization ability of normal, stuttering, neurotic and hemiplegic subjects. A.M.A. Arch. Gen. Psychiur., 1959, 1, 6W45. Shearer, W.M. Speech: Behavior of middle ear muscles during stuttering. Science, 1966, 152, 1280. Shearer, W.M., Simmons, F.B. Middle ear activity during speech in normal speakers and stutterers.J. Speech Hearing Res., 1965, 8, 203-207. Sklar, B. A feedback model of the stuttering problem-an engineer’s view. J. Speech Hearing Dis., 1969, 34, 226-230. Smith, K.U., Tierney, D. Delayed speech feedback and age. J. Speech Hearing Res., 1971, 14, 214-219. Soderberg, G. A. A study of the effects of delayed sideone onfour aspecrs of stutterer’s speech during oral reading and sponraneous speaking. Doctoral Dissertation, Ohio State University. Ann Arbor, Mich.: University Microfilms, 1960, 60-796. Soderberg, G.A. Delayed auditory feedback and stuttering. J. Speech Hearing Dis., 1968, 33, 26@267. Soderberg, G.A. Delayed auditory feedback and the speech of stutterers: A review of studies. J. Speech Hearing Dis., 1969, 34, 2C-29. Stromsta, C.P. A methodology related to the determination of the phase angle of bone-conducted speech sound energy of stutterers and non-shmerers. Doctoral Dissertation, Ohio State University, 1956. Ann Arbor, Mich.: University Microfilms, 562755. Stromsta, C.P. An investigation of the localization of inter-aural clicks and the reading times of stutterers and non-stutterers under monaural sidetone conditions. Technical Report, Ohio State University, PHS Grant NB 03541-03, National Institutes of Health, August, 1964. Stromsta, C. P. Averaged evoked responses of stutterers and non-stutterers as a function of inter-aural time relationships. Technical Report, Ohio State University, PHS Grant NB-03541-03, National Institutes of Health, September, 1965. Van Riper, C. The nature of stutlering. Englewood Cliffs, N.J.: Prentice-Hall, 1971. Waters, J.E. A theoretical and developmental investigation of delayed speech feedback. Gener. Psychol. Monogr. I 1968, 78, 3-54. Webster, R.L., A behavioral analysis of stuttering: Treatment and theory. In Calhoun, Adams and Mitchell(Eds.),Innovarive treafmenfmethodsinpsychopathology. New York: Wiley, inpress. Webster, R.L., Lubker, B.B. Interrelationships among fluency producing variables in stuttered speech. J. Speech Hearing Res., 1968, 11, 754-766. Webster, R.L., Schumacker, S.J., Lubker, B.B. Changes in stuttering frequency as a function of various intervals of delayed auditory feedback. J. Abnorm. Psych., 1970, 75, 45-49. Winer, B.J. Statistical principles in experimenta/ design. New York: McGraw-Hill, 1962. Wingate, M.E. Effect on stuttering of changes in audition. 1. Speech Hearing Res., 1970, 13, 861-873. Wolf, A. A., Wolf, E.G. Feedback processes in the theory of certain speech disorders. Speech Pathol. Ther., 1959, 2, 48-55.
STUTTERER’S
INITIAL
REACTIONS
TO DELAYED
Yates, A.J. Recent empirical and theoretical approaches normal subjects Yates, A.J. Behavior Zerneri, L. Tentatives du begaiement.
AUDITORY
to the experimental
FEEDBACK
manipulation
and stutterers. Behav. Res. Ther., 1963, 1, 95-l 19. therapy. New York: Wiley, 1970, pp. 118-122. d’application de la voix retardee (“delayed auditory feedback”) J. Franc. Orl., 1966, 15,415-418.
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of speech in
dam la therapie
