JOURNAL
OF COMMUNICATION
DISORDERS
9 (1976), 269-279
JAW MECHANICS DURING RELEASE OF THE STUTTERING MOMENT: SOME INITIAL OBSERVATIONS AND INTERPRETATIONS Department
JOHN M. HUTCHINSON of Speech Pathology and Audiology, Idaho State Vniversiry, Pocatello, Idaho 83209 KENNETH L. WATKIN
Speech Physiology Laboratory, University of Washington, Seattle, Washington 98195
As a part of a larger study (Hutchinson and Watkin, 1974), this investigation was undertaken to examine jaw mechanics during the release of stuttering moments. Six adult subjects (four stutterers, ranging in severity, and two normal talkers) read a series of sentences containing phonetic sequences requiring jaw depression. Strain-gauge transducers were employed to record articulatory movement. Only those stutterings occurring immediately prior to and during jaw opening were studied. The results confirmed generally faster jaw velocities for the opening and closing gestures, which was interpreted to suggest that the spindle motor system is maximally active to preserve synchrony in on-going vocal tract events following the dysfluency. In cases where an asynchrony between vocalization and jaw opening was noted, it was suggested that imprecision in predicting voice onset resulted in articulatory-laryngeal incoordination. It would appear from these interpretations that the clinical efficacy of the “pull out” procedure results from reduced demands on the gamma loop system and facilitation of articulatorylaryngeal synchrony through reduced supraglottal velocities.
Introduction For many years, clinicians have identified in descriptive terms the unusual and inappropriate articulator-y adjustments that accompany secondary stuttering patterns. Logically, therapeutic procedures designed to minimize these articulatory disturbances have emerged (Van Riper, 1963, 1973). One particular procedure widely used in this symptom-modification approach is the “pull out”, which is employed to effect a “slow shift in motoric sequences rather than sudden ballistic ones” (Van Riper, 1973, p. 3 12). Presumably, the pull out and other variants of this basic technique provide the stutterer with a more normal means of releasing the stuttering moment and achieving an appropriate transition to subsequent articulatory gestures. In view of these rather well-developed clinical procedures, one might assume that the dynamics of articulator movement, particularly during the release of a stuttering moment, are well understood. However, except for some cursory clinical descriptions, peripheral articulatory mechanics accompanying the release of stuttering have not been investigated. This is unfortunate since research of this type would appear warranted in any effort to explain the facilitative effects of such B American
Elsevier Publishing
Company,
Inc.,
1976
269
270
JOHN M. HUTCHINSON
and KENNETH
L. WATKIN
therapeutic techniques as the pull out or any other procedures that have demonstrated clinical success in reducing aberrant articulatory movements in stutterers. In addition, such data may add to our understanding of the motor control of stuttering. However, as Abbs and Netsell (1973) have properly cautioned, rushes to judgment regarding speech motor control are hazardous without proper consideration of peripheral mechanics. With the advent of modem strain-gauge transducer applications to the study of articulator movement (Abbs and Gilbert, 1973), a very sensitive and efficient on-line procedure is available for studying peripheral speech system disturbances in stutterers. Accordingly, the present study was undertaken, as a part of a larger investigation (Hutchinson and Watkin, 1974), in an effort to provide some preliminary documentation of the articulatory deviations that accompany the release of stuttering behaviors.
Method Subjects Four adult male stutterers (two mild, one moderate-to-severe, and one severe) and two normal adult male talkers served as subjects in this experiment. Instrumentation Superior-inferior movement of the jaw and antero-posterior deflections of the upper and lower lips were recorded with a system of strain-gauge transducers (Abbs and Gilbert, 1973). The cantilevers were positioned on the midline of the lips and jaw using a nontoxic adhesive. The strain-gauge signals were properly amplified and written out using an optical oscillograph. Preliminary testing of the strain gauges indicated faithful response characteristics within the amplitude, velocity, and acceleration ranges studied. Bench calibrations of the transducers were completed for each experimental session. A throat microphone was employed to obtain an audio signal on the oscillograms. Speech Stimuli Each subject read two sets of test sentences. The first contained a variety of consonant vowel sequences requiring large jaw excursions (/re/ sequence). The second consisted of consonant-vowel sequences requiring lip rounding/lip protrusion gestures (/u/ sequence). However, for purposes of this investigation, only dysfluencies occurring prior to and during phonetic sequences involving extensive jaw opening were studied. This restriction was adopted because such jaw gestures are relatively discrete with large amplitudes, which permits ease of measurement.
JAW MECHANICS
DURING
RELEASE
In addition, current normative literature than that for other articulators.
OF THE STUTTERING
on jaw mechanics
MOMENT
271
is far more complete
Procedure All subjects were seated at a table with the head positioned in a cephalostat to minimize artifact from general head movement. They were instructed to read the experimental sentences in a natural fashion regardless of dysfluency. The sentences were presented to the subjects by flashcards at regular intervals. Simultaneous audio and video tape recordings were made to assist in segmenting the oscillograms. The principal analysis strategy involved visual inspection of the stuttering patterns and determination of the deviations in articulatory behavior by comparisons with the patterns exhibited by normal subjects. Results and Discussion The stutterers produced a total of 21 stutterings immediately prior to or during low mid and low back vowels (16 during the /ae/ sequence and 5 during the /u/ sequence). Examination of the articulator mechanics associated with the release of these stutterings revealed two major differences in the temporal sequencing of jaw movement during release of the stuttering moment. Preservation of Temporal Sequencing Through Increased Jaw Velocity Visual inspection of the jaw velocity patterns during release of the stuttering moment suggested abnormally high opening and closing speeds in many instances. Figure 1 displays typical jaw function by Normal Talker #l (Fig. la) and an example of exaggerated average jaw velocities as exhibited by Stutterer #2 (Fig. lb). The average jaw velocity computed for the opening gesture was 57.67 mm/set for the stutterer as compared with 24.25 mrn/sec for the normal talker. Similarly, the closing gesture was associated with velocities of 67.83 and 28.60 mmlsec, respectively. Although not all stuttering moments were associated with such rapid gestures, the number was judged sufficient to warrant some measure of central tendency. Therefore, jaw velocities were calculated for all dysfluencies recorded prior to or during the vowel /a~/. Only these 16 stutterings were evaluated because the jaw velocities calculated were associated with a common vowel. In addition, jaw velocities were determined for the same phonetic sequences produced by the normal talkers. The mean opening and closing jaw velocities as well as the standard deviations are summarized in Table 1. In general, the stutterers exhibited much faster speeds than the normal talkers, regardless of whether or not the
272
JOHN
M. HUTCHINSON
and KENNETH
L. WATKIN
stuttering occurred on a single consonant-vowel sequence (CV) or on a blend (CCV or CCCV). The standard deviations also indicate much greater variability in the stutterer’s behavior. However, r-tests were computed for the total sample of opening and closing velocities. Both tests confirmed significantly more rapid velocities in the group of stutterers at the 0.01 level of confidence [opening velocity: t&s = 2.52; closing velocity: t&s = 2.72; to,99(36) = 2.441. Aside from the support these data lent to the clinical observation of a rapid, “ballistic” release of the stuttering block, insight can be gained regarding general processes of speech motor control operative during such dysfluencies. A reexamination of the results revealed that in all instances where an abnormally rapid jaw opening velocity was recorded, the mandible was initially in a relatively elevated position. In nearly all of these dysfluencies, anticipatory jaw depression was noted (Hutchinson and Watkin, 1974), but the downward excursion of the jaw may have been arrested and its extent markedly reduced during the major part of the block, thereby relegating the jaw to a relatively high “hold” position. Such was the case as seen in Fig. lb where the jaw remained elevated throughout the block and was
-
200 msec
U.LIP
L.LIP,. 7 JAW a=24.25
AUD.
mm&c
JAW MECHANICS
JAW
DURING
\
/
RELEASE
OF THE STUTTERING
,’
MOMENT
1
ST. 2
(b)
Fig. 1.
213
Oscillographic records of lip and jaw movement for (a) Normal Talker #l uttering the sentence, “I had splashed him” and (b) with an - Stutterer #2 uttering the same sentence audible prolongation of thefricative /s/. OV refers to average opening velocity. CV refers to average closing velocity.
TABLE 1 Means and Standard Deviations for Average Opening and Closing Jaw Velocities (in mm&) Recorded During Production of Low Vowels by Stutterers and Normals. The Velocities Reported for Stutterers Were Taken During Release of a Stuttering Moment ~.______. Normals Stutterers
Single consonant-vowel Opening velocity Closing velocity
sequence
Consonant blend-vowel Opening velocity Closing velocity
sequence
Total Opening velocity Closing velocity
X
SD
X
SD
43.07 45.04
25.08 20.55
29.36 36.20
7.13 13.26
46.47 56.62
17.67 31.72
29.13 33.35
9.23 6.63
44.71 50.83
21.03 26.50
28.13 34.33
7.33 9.20
274
JOHN
M. HUTCHINSON
and KENNETH
L. WATKIN
actually raised further before the jaw opening gesture appeared. This may be contrasted to the stuttering pattern seen in Fig. 2. Here a sizeable jaw opening was achieved at the onset of the block (points A to B). With this larger initial displacement, the amplitude demanded upon release of the block was reduced. Consequently, the final opening velocity was only 39.00 mm/set, which is much closer to the average reported for normal speakers. These data might be interpreted in light of Abbs’ (1973) observation that the gamma motor feedback system appears to play a significant role in control of the temporal patterning of muscle force. By inference, his work has established that gamma participation “seems to operate most clearly under conditions where temporal synchrony in conjunction with large values of displacement, velocity, and acceleration are demanded” (p. 198). Accordingly, failure to achieve complete jaw depression during a stuttering moment would require greater gamma participation in order to achieve acceptable jaw displacements within the time constraints available following release of the block. Therefore, dependence on
Fig. 2.
Oscillographic record of Stutterer #l uttering the sentence, “Tantalizing aromas captured us,” with a silent prolongation of the stop ik/. Points A to B refer to an initial jaw opening gesture followed by a relatively stable jaw position prior to release of the stuttering and continued jaw depression beginning at point C. ?% refers to average opening velocity. CV refers to average closing velocity.
JAW MECHANICS
DURING
RELEASE
OF THE STUTTERING
MOMENT
215
gamma system feedback would appear critical as a compensatory mechanism to preserve normal or near normal temporal sequencing of jaw movements subsequent to the dysfluency. Disruptions in Temporal Sequencing of Jaw Movement The preservation of near normal jaw synchrony during release of the stuttering moment was not always observed. In several instances (n = 9), a discernible incoordination between jaw movement and onset of vocalization was noted. In some cases, full jaw displacement w,as markedly delayed, as seen in Fig. 3a, b. During the word “saturation,” the normal talker (Fig. 3a) achieved full jaw excursion approximately 180 msec after the onset of vocalization and prior to the Its/ se g ment. However, Stutterer #3 achieved full excursion about 240 msec after the onset of phonation during the/q/ segment. Interestingly, the onset of vocalization was preceded by repeated jaw depressions. However, these earlier gestures were not accompanied by proper voice onset. Moreover, temporal delay was also observed for the jaw displacement accompanying the diphthongal vowel /eV in the word “saturation,” which occurred 380 msec following onset of vocalization and during the production of/s/. This is in contrast to the normal talker who achieved full jaw excursion during the vocalic segment, roughly 240 msec following the onset of phonation. An abnormally premature jaw deflection was also recorded and depicted in Fig. 4. Examination of the word “tamed” in Fig. 4a, as produced by Normal Talker #2, reveals completion of the jaw opening gesture during the vocalic segment, approximately 70 msec following the onset of phonation. However, Stutterer #4 evidenced full jaw excursion 60 msec prior to the onset of phonation (see Fig. 4b). In all instances where disturbances in the coordination of vocalization and jaw opening were noted, the dysfluency was associated with a failure to initiate phonation at the proper moment. A possible interpretation of this observation may be extracted from the work of Folkins and Abbs (1974), who suggested that “the motor control of the laryngeal musculature is sensitive to sensory feedback from supraglottal articulators” (p. 11). If this supposition is accurate, the consequences of supraglottal feedback may not be readily actualized during moments of stuttering since vocal fold function is not properly time-locked with articulatory events. The failure to initiate phonation at the proper moment may be a function of abnormally high vocal fold tension, which impedes vibratory onset, a phenomenon that has been documented by the work of Conture et al. (1974) and Freeman and Ushijima (1974). Some support for the view that stutterers experience difficulty in initiating phonation with proper temporal precision was provided by the work of Adams and Hayden (1974). Their discovery that a group of stutterers were significantly less
216
-
IT
u. LIP , \, --. \ \I \, 1
200
I.82
m5ec
mm
/T I
\
I
-._,-_----\--/-
\
---
11
,4
,
L,-,,----
‘Lf
\
I\ \I V
‘:
’ ”
Il.OGrnm L. LIP, ,c r\ II .-‘v.2---,__.-.-.-.-.-./ J’ ! i! ; \, v\j
.
I
\i
,
r\ *, I , 1,
I r,
L,._._._.,!
‘\ ,Q.J ‘4
JAW
&WI
,’
P.
k
(b)
Fig. 3. Oscillographic
records for (a) Normal Talker #2 uttering the sentence, “The wick lacked saturation” and (b) Stutterer #3 producing the same sentence with a silent prolongation of the vowel /z/ in the word “saturation.”
l---i
200
-
msec
200
T
mxx
r‘, ;
1.85mm
u. LIP
\\ L--J
L. LIP -.---.__
-_I
\( AUD.
(b)
Fig. 4.
ST. 4 Oscillographic records for (a) Normal Talker #2 uttering the sentence, “Tuberculosis has been tamed” and (b) Stutterer #4 producing the same sentence with a silent prolongation of the stop It/ in the word “tamed.”
278
JOHN
M. HUTCHINSON
and KENNETH
L. WATKIN
proficient than normal speakers in synchronizing vocalization with pure tones of varied duration suggests that some stutterers exhibit diminished laryngeal control. If laryngeal control is reduced, it would follow that supraglottal asynchronies would appear regardless of the extent of oral sensory feedback, simply because the stutterer may have difficulty predicting phonation. On the one hand, the stutterer may anticipate the onset of vocalization and initiate a proper jaw gesture. However, mechanical factors, pehaps due to increased vocal fold tension, prevent the anticipated onset of vibration. The result is premature jaw depression. Conversely, vocal fold vibration may be activated earlier than expected and the jaw lags so far behind that even exaggerated opening force will not achieve immediate synchrony. Mechanics
of the Pull Out Technique
As mentioned previously, clinical use of the “pull out” procedure is designed to reduce articulator velocity and assure a gradual release from the moment of stuttering. The efficacy of this procedure may result from a reduced demand upon gamma system feedback to achieve proper synchrony since high velocity and high acceleration gestures are eliminated. In addition, the prolongation of an articulatory posture with reduced offset velocity may, at a conscious level, facilitate synchronous motor commands to the laryngeal and articulatory systems. Conclusions If a feedback relationship between vocal fold function and supraglottal dynamics does exist, the following conclusions appear warranted. In the case of stuttering moments where the release is associated with a successful synchrony of jaw depression and onset of vocalization, the stutterer would appear to make maximal use of gamma feedback to increase jaw velocity, thereby assuring adequate jaw amplitude and preservation of subsequent temporal sequencing. In short, the jaw “catches up” with the associated on-going vocal tract events. Those stuttering moments characterized by an asychrony between vocalization and jaw movement appear to be associated with an imprecision in initiating phonation. Therefore, any hypothesized feedback relationship between supraglottal events and laryngeal control would appear diminished during some stuttering moments. The resultant lack of predicability regarding voice onset may precipitate incoordination between laryngeal and articulatory events. References Abbs, J. H. The influence of the gamma motor system on jaw movements during speech: a theoretical framework and some preliminary observations. J. Speech Hearing Res., 1973, 16, 17~.ZOO.
JAW MECHANICS
Abbs,
DURING
RELEASE
OF THE STUTTERING
MOMENT
279
J. H., Gilbert B. N. A strain-gauge transduction system for lip and jaw motion in two dimensions: design criteria and calibration data. J. Speech Hearing Res., 1973, 16, 248-256. Abbs, J. H., Netsell, R. An interpretation of jaw acceleration during speech as a muscle forcing function. J. Speech Hearing Res., 1973, 16, 421425. Adams, M. R., Hayden, P. Stutterers’ and nonstutterers’ ability to initiate and terminate phonation during nonspeech activity. Paper presented at the American Speech and Hearing Association Convention, Las Vegas, 1974. Conture, E. G., McCall, G. N., Brewer, D. W. Laryngeal activity during the moment of stuttering: some preliminary observations. Paper presented at the American Speech and Hearing Association Convention, Las Vegas, 1974. Freeman, F. J., Ushijima, T. The stuttering larynx: an EMG, fiber-optic study of laryngeal activity accompanying the moment of stuttering. Paper presented at the American Speech and Hearing Association Convention, Las Vegas, 1974. Folkins, J. W., Abbs, J. H. Lip and jaw motor control during speech: responses to resistive loading of the jaw. J. Speech Hearing Res., 1975, 18, 207-220. Hutchinson, J. M., Watkin, K. W. A preliminary investigation of lip and jaw coarticulation in stutterers. Paper presented at the American Speech and Hearing Association Convention, Las Vegas, 1974. Van Riper, C. Speech correction: principles and mefhods. Englewood Cliffs, N. J.: Prentice-Hall, 1963. Van Riper, C. The treatment ofstuttering. Englewood Cliffs, N. J.: Prentice-Hall, 1973.
OF COMMUNICATION
DISORDERS
9 (1976), 269-279
JAW MECHANICS DURING RELEASE OF THE STUTTERING MOMENT: SOME INITIAL OBSERVATIONS AND INTERPRETATIONS Department
JOHN M. HUTCHINSON of Speech Pathology and Audiology, Idaho State Vniversiry, Pocatello, Idaho 83209 KENNETH L. WATKIN
Speech Physiology Laboratory, University of Washington, Seattle, Washington 98195
As a part of a larger study (Hutchinson and Watkin, 1974), this investigation was undertaken to examine jaw mechanics during the release of stuttering moments. Six adult subjects (four stutterers, ranging in severity, and two normal talkers) read a series of sentences containing phonetic sequences requiring jaw depression. Strain-gauge transducers were employed to record articulatory movement. Only those stutterings occurring immediately prior to and during jaw opening were studied. The results confirmed generally faster jaw velocities for the opening and closing gestures, which was interpreted to suggest that the spindle motor system is maximally active to preserve synchrony in on-going vocal tract events following the dysfluency. In cases where an asynchrony between vocalization and jaw opening was noted, it was suggested that imprecision in predicting voice onset resulted in articulatory-laryngeal incoordination. It would appear from these interpretations that the clinical efficacy of the “pull out” procedure results from reduced demands on the gamma loop system and facilitation of articulatorylaryngeal synchrony through reduced supraglottal velocities.
Introduction For many years, clinicians have identified in descriptive terms the unusual and inappropriate articulator-y adjustments that accompany secondary stuttering patterns. Logically, therapeutic procedures designed to minimize these articulatory disturbances have emerged (Van Riper, 1963, 1973). One particular procedure widely used in this symptom-modification approach is the “pull out”, which is employed to effect a “slow shift in motoric sequences rather than sudden ballistic ones” (Van Riper, 1973, p. 3 12). Presumably, the pull out and other variants of this basic technique provide the stutterer with a more normal means of releasing the stuttering moment and achieving an appropriate transition to subsequent articulatory gestures. In view of these rather well-developed clinical procedures, one might assume that the dynamics of articulator movement, particularly during the release of a stuttering moment, are well understood. However, except for some cursory clinical descriptions, peripheral articulatory mechanics accompanying the release of stuttering have not been investigated. This is unfortunate since research of this type would appear warranted in any effort to explain the facilitative effects of such B American
Elsevier Publishing
Company,
Inc.,
1976
269
270
JOHN M. HUTCHINSON
and KENNETH
L. WATKIN
therapeutic techniques as the pull out or any other procedures that have demonstrated clinical success in reducing aberrant articulatory movements in stutterers. In addition, such data may add to our understanding of the motor control of stuttering. However, as Abbs and Netsell (1973) have properly cautioned, rushes to judgment regarding speech motor control are hazardous without proper consideration of peripheral mechanics. With the advent of modem strain-gauge transducer applications to the study of articulator movement (Abbs and Gilbert, 1973), a very sensitive and efficient on-line procedure is available for studying peripheral speech system disturbances in stutterers. Accordingly, the present study was undertaken, as a part of a larger investigation (Hutchinson and Watkin, 1974), in an effort to provide some preliminary documentation of the articulatory deviations that accompany the release of stuttering behaviors.
Method Subjects Four adult male stutterers (two mild, one moderate-to-severe, and one severe) and two normal adult male talkers served as subjects in this experiment. Instrumentation Superior-inferior movement of the jaw and antero-posterior deflections of the upper and lower lips were recorded with a system of strain-gauge transducers (Abbs and Gilbert, 1973). The cantilevers were positioned on the midline of the lips and jaw using a nontoxic adhesive. The strain-gauge signals were properly amplified and written out using an optical oscillograph. Preliminary testing of the strain gauges indicated faithful response characteristics within the amplitude, velocity, and acceleration ranges studied. Bench calibrations of the transducers were completed for each experimental session. A throat microphone was employed to obtain an audio signal on the oscillograms. Speech Stimuli Each subject read two sets of test sentences. The first contained a variety of consonant vowel sequences requiring large jaw excursions (/re/ sequence). The second consisted of consonant-vowel sequences requiring lip rounding/lip protrusion gestures (/u/ sequence). However, for purposes of this investigation, only dysfluencies occurring prior to and during phonetic sequences involving extensive jaw opening were studied. This restriction was adopted because such jaw gestures are relatively discrete with large amplitudes, which permits ease of measurement.
JAW MECHANICS
DURING
RELEASE
In addition, current normative literature than that for other articulators.
OF THE STUTTERING
on jaw mechanics
MOMENT
271
is far more complete
Procedure All subjects were seated at a table with the head positioned in a cephalostat to minimize artifact from general head movement. They were instructed to read the experimental sentences in a natural fashion regardless of dysfluency. The sentences were presented to the subjects by flashcards at regular intervals. Simultaneous audio and video tape recordings were made to assist in segmenting the oscillograms. The principal analysis strategy involved visual inspection of the stuttering patterns and determination of the deviations in articulatory behavior by comparisons with the patterns exhibited by normal subjects. Results and Discussion The stutterers produced a total of 21 stutterings immediately prior to or during low mid and low back vowels (16 during the /ae/ sequence and 5 during the /u/ sequence). Examination of the articulator mechanics associated with the release of these stutterings revealed two major differences in the temporal sequencing of jaw movement during release of the stuttering moment. Preservation of Temporal Sequencing Through Increased Jaw Velocity Visual inspection of the jaw velocity patterns during release of the stuttering moment suggested abnormally high opening and closing speeds in many instances. Figure 1 displays typical jaw function by Normal Talker #l (Fig. la) and an example of exaggerated average jaw velocities as exhibited by Stutterer #2 (Fig. lb). The average jaw velocity computed for the opening gesture was 57.67 mm/set for the stutterer as compared with 24.25 mrn/sec for the normal talker. Similarly, the closing gesture was associated with velocities of 67.83 and 28.60 mmlsec, respectively. Although not all stuttering moments were associated with such rapid gestures, the number was judged sufficient to warrant some measure of central tendency. Therefore, jaw velocities were calculated for all dysfluencies recorded prior to or during the vowel /a~/. Only these 16 stutterings were evaluated because the jaw velocities calculated were associated with a common vowel. In addition, jaw velocities were determined for the same phonetic sequences produced by the normal talkers. The mean opening and closing jaw velocities as well as the standard deviations are summarized in Table 1. In general, the stutterers exhibited much faster speeds than the normal talkers, regardless of whether or not the
272
JOHN
M. HUTCHINSON
and KENNETH
L. WATKIN
stuttering occurred on a single consonant-vowel sequence (CV) or on a blend (CCV or CCCV). The standard deviations also indicate much greater variability in the stutterer’s behavior. However, r-tests were computed for the total sample of opening and closing velocities. Both tests confirmed significantly more rapid velocities in the group of stutterers at the 0.01 level of confidence [opening velocity: t&s = 2.52; closing velocity: t&s = 2.72; to,99(36) = 2.441. Aside from the support these data lent to the clinical observation of a rapid, “ballistic” release of the stuttering block, insight can be gained regarding general processes of speech motor control operative during such dysfluencies. A reexamination of the results revealed that in all instances where an abnormally rapid jaw opening velocity was recorded, the mandible was initially in a relatively elevated position. In nearly all of these dysfluencies, anticipatory jaw depression was noted (Hutchinson and Watkin, 1974), but the downward excursion of the jaw may have been arrested and its extent markedly reduced during the major part of the block, thereby relegating the jaw to a relatively high “hold” position. Such was the case as seen in Fig. lb where the jaw remained elevated throughout the block and was
-
200 msec
U.LIP
L.LIP,. 7 JAW a=24.25
AUD.
mm&c
JAW MECHANICS
JAW
DURING
\
/
RELEASE
OF THE STUTTERING
,’
MOMENT
1
ST. 2
(b)
Fig. 1.
213
Oscillographic records of lip and jaw movement for (a) Normal Talker #l uttering the sentence, “I had splashed him” and (b) with an - Stutterer #2 uttering the same sentence audible prolongation of thefricative /s/. OV refers to average opening velocity. CV refers to average closing velocity.
TABLE 1 Means and Standard Deviations for Average Opening and Closing Jaw Velocities (in mm&) Recorded During Production of Low Vowels by Stutterers and Normals. The Velocities Reported for Stutterers Were Taken During Release of a Stuttering Moment ~.______. Normals Stutterers
Single consonant-vowel Opening velocity Closing velocity
sequence
Consonant blend-vowel Opening velocity Closing velocity
sequence
Total Opening velocity Closing velocity
X
SD
X
SD
43.07 45.04
25.08 20.55
29.36 36.20
7.13 13.26
46.47 56.62
17.67 31.72
29.13 33.35
9.23 6.63
44.71 50.83
21.03 26.50
28.13 34.33
7.33 9.20
274
JOHN
M. HUTCHINSON
and KENNETH
L. WATKIN
actually raised further before the jaw opening gesture appeared. This may be contrasted to the stuttering pattern seen in Fig. 2. Here a sizeable jaw opening was achieved at the onset of the block (points A to B). With this larger initial displacement, the amplitude demanded upon release of the block was reduced. Consequently, the final opening velocity was only 39.00 mm/set, which is much closer to the average reported for normal speakers. These data might be interpreted in light of Abbs’ (1973) observation that the gamma motor feedback system appears to play a significant role in control of the temporal patterning of muscle force. By inference, his work has established that gamma participation “seems to operate most clearly under conditions where temporal synchrony in conjunction with large values of displacement, velocity, and acceleration are demanded” (p. 198). Accordingly, failure to achieve complete jaw depression during a stuttering moment would require greater gamma participation in order to achieve acceptable jaw displacements within the time constraints available following release of the block. Therefore, dependence on
Fig. 2.
Oscillographic record of Stutterer #l uttering the sentence, “Tantalizing aromas captured us,” with a silent prolongation of the stop ik/. Points A to B refer to an initial jaw opening gesture followed by a relatively stable jaw position prior to release of the stuttering and continued jaw depression beginning at point C. ?% refers to average opening velocity. CV refers to average closing velocity.
JAW MECHANICS
DURING
RELEASE
OF THE STUTTERING
MOMENT
215
gamma system feedback would appear critical as a compensatory mechanism to preserve normal or near normal temporal sequencing of jaw movements subsequent to the dysfluency. Disruptions in Temporal Sequencing of Jaw Movement The preservation of near normal jaw synchrony during release of the stuttering moment was not always observed. In several instances (n = 9), a discernible incoordination between jaw movement and onset of vocalization was noted. In some cases, full jaw displacement w,as markedly delayed, as seen in Fig. 3a, b. During the word “saturation,” the normal talker (Fig. 3a) achieved full jaw excursion approximately 180 msec after the onset of vocalization and prior to the Its/ se g ment. However, Stutterer #3 achieved full excursion about 240 msec after the onset of phonation during the/q/ segment. Interestingly, the onset of vocalization was preceded by repeated jaw depressions. However, these earlier gestures were not accompanied by proper voice onset. Moreover, temporal delay was also observed for the jaw displacement accompanying the diphthongal vowel /eV in the word “saturation,” which occurred 380 msec following onset of vocalization and during the production of/s/. This is in contrast to the normal talker who achieved full jaw excursion during the vocalic segment, roughly 240 msec following the onset of phonation. An abnormally premature jaw deflection was also recorded and depicted in Fig. 4. Examination of the word “tamed” in Fig. 4a, as produced by Normal Talker #2, reveals completion of the jaw opening gesture during the vocalic segment, approximately 70 msec following the onset of phonation. However, Stutterer #4 evidenced full jaw excursion 60 msec prior to the onset of phonation (see Fig. 4b). In all instances where disturbances in the coordination of vocalization and jaw opening were noted, the dysfluency was associated with a failure to initiate phonation at the proper moment. A possible interpretation of this observation may be extracted from the work of Folkins and Abbs (1974), who suggested that “the motor control of the laryngeal musculature is sensitive to sensory feedback from supraglottal articulators” (p. 11). If this supposition is accurate, the consequences of supraglottal feedback may not be readily actualized during moments of stuttering since vocal fold function is not properly time-locked with articulatory events. The failure to initiate phonation at the proper moment may be a function of abnormally high vocal fold tension, which impedes vibratory onset, a phenomenon that has been documented by the work of Conture et al. (1974) and Freeman and Ushijima (1974). Some support for the view that stutterers experience difficulty in initiating phonation with proper temporal precision was provided by the work of Adams and Hayden (1974). Their discovery that a group of stutterers were significantly less
216
-
IT
u. LIP , \, --. \ \I \, 1
200
I.82
m5ec
mm
/T I
\
I
-._,-_----\--/-
\
---
11
,4
,
L,-,,----
‘Lf
\
I\ \I V
‘:
’ ”
Il.OGrnm L. LIP, ,c r\ II .-‘v.2---,__.-.-.-.-.-./ J’ ! i! ; \, v\j
.
I
\i
,
r\ *, I , 1,
I r,
L,._._._.,!
‘\ ,Q.J ‘4
JAW
&WI
,’
P.
k
(b)
Fig. 3. Oscillographic
records for (a) Normal Talker #2 uttering the sentence, “The wick lacked saturation” and (b) Stutterer #3 producing the same sentence with a silent prolongation of the vowel /z/ in the word “saturation.”
l---i
200
-
msec
200
T
mxx
r‘, ;
1.85mm
u. LIP
\\ L--J
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\( AUD.
(b)
Fig. 4.
ST. 4 Oscillographic records for (a) Normal Talker #2 uttering the sentence, “Tuberculosis has been tamed” and (b) Stutterer #4 producing the same sentence with a silent prolongation of the stop It/ in the word “tamed.”
278
JOHN
M. HUTCHINSON
and KENNETH
L. WATKIN
proficient than normal speakers in synchronizing vocalization with pure tones of varied duration suggests that some stutterers exhibit diminished laryngeal control. If laryngeal control is reduced, it would follow that supraglottal asynchronies would appear regardless of the extent of oral sensory feedback, simply because the stutterer may have difficulty predicting phonation. On the one hand, the stutterer may anticipate the onset of vocalization and initiate a proper jaw gesture. However, mechanical factors, pehaps due to increased vocal fold tension, prevent the anticipated onset of vibration. The result is premature jaw depression. Conversely, vocal fold vibration may be activated earlier than expected and the jaw lags so far behind that even exaggerated opening force will not achieve immediate synchrony. Mechanics
of the Pull Out Technique
As mentioned previously, clinical use of the “pull out” procedure is designed to reduce articulator velocity and assure a gradual release from the moment of stuttering. The efficacy of this procedure may result from a reduced demand upon gamma system feedback to achieve proper synchrony since high velocity and high acceleration gestures are eliminated. In addition, the prolongation of an articulatory posture with reduced offset velocity may, at a conscious level, facilitate synchronous motor commands to the laryngeal and articulatory systems. Conclusions If a feedback relationship between vocal fold function and supraglottal dynamics does exist, the following conclusions appear warranted. In the case of stuttering moments where the release is associated with a successful synchrony of jaw depression and onset of vocalization, the stutterer would appear to make maximal use of gamma feedback to increase jaw velocity, thereby assuring adequate jaw amplitude and preservation of subsequent temporal sequencing. In short, the jaw “catches up” with the associated on-going vocal tract events. Those stuttering moments characterized by an asychrony between vocalization and jaw movement appear to be associated with an imprecision in initiating phonation. Therefore, any hypothesized feedback relationship between supraglottal events and laryngeal control would appear diminished during some stuttering moments. The resultant lack of predicability regarding voice onset may precipitate incoordination between laryngeal and articulatory events. References Abbs, J. H. The influence of the gamma motor system on jaw movements during speech: a theoretical framework and some preliminary observations. J. Speech Hearing Res., 1973, 16, 17~.ZOO.
JAW MECHANICS
Abbs,
DURING
RELEASE
OF THE STUTTERING
MOMENT
279
J. H., Gilbert B. N. A strain-gauge transduction system for lip and jaw motion in two dimensions: design criteria and calibration data. J. Speech Hearing Res., 1973, 16, 248-256. Abbs, J. H., Netsell, R. An interpretation of jaw acceleration during speech as a muscle forcing function. J. Speech Hearing Res., 1973, 16, 421425. Adams, M. R., Hayden, P. Stutterers’ and nonstutterers’ ability to initiate and terminate phonation during nonspeech activity. Paper presented at the American Speech and Hearing Association Convention, Las Vegas, 1974. Conture, E. G., McCall, G. N., Brewer, D. W. Laryngeal activity during the moment of stuttering: some preliminary observations. Paper presented at the American Speech and Hearing Association Convention, Las Vegas, 1974. Freeman, F. J., Ushijima, T. The stuttering larynx: an EMG, fiber-optic study of laryngeal activity accompanying the moment of stuttering. Paper presented at the American Speech and Hearing Association Convention, Las Vegas, 1974. Folkins, J. W., Abbs, J. H. Lip and jaw motor control during speech: responses to resistive loading of the jaw. J. Speech Hearing Res., 1975, 18, 207-220. Hutchinson, J. M., Watkin, K. W. A preliminary investigation of lip and jaw coarticulation in stutterers. Paper presented at the American Speech and Hearing Association Convention, Las Vegas, 1974. Van Riper, C. Speech correction: principles and mefhods. Englewood Cliffs, N. J.: Prentice-Hall, 1963. Van Riper, C. The treatment ofstuttering. Englewood Cliffs, N. J.: Prentice-Hall, 1973.
