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Vibrotactile magnitude production scaling: A method for studying sensory-perceptual responses of stutterers and fluent speakers
J. FLUENCY DISORD. 10 (1985), 69-75
VIBROTACTILE MAGNITUDE PRODUCTION SCALING: A METHOD FOR STUDYING SENSORY-PERCEPTUAL RESPONSES OF STUTTERERS AND FLUENT SPEAKERS DONALD FUCCI, LINDA PETROSINO, and DANIEL HARRIS
PETER GORMAN,
School of Hearing and Speech Sciences Ohio University, Athens, Ohio
The method of vibrotactile mangitude production scaling was used to determine the tactile sensory-perceptual integrity for the dorsum of the tongue and thenar eminence of the right hand for 10 fluent speakers and 10 stutterers. It was discovered that both groups performed the task in a similar manner for the thenar eminence of the hand (a nonoral structure) but in a dissimilar manner for the tongue (an oral structure). From these data, it is suggested that the stutterers may maintain a different internal sensory-perceptual process for the tactile system involved in the speech process. The possibility exists that stuttering, for some, may be an “internal disorder” of the tactile-proprioceptive feedback mechanism that is directly involved in speech production.
INTRODUCTION Several researchers, through the utilization of oral stereognostic forms, have investigated the idea that stuttering behavior may be attributed to a disturbance in the integrity of the oral tactile sensory-perceptual system. Jensen et al. (1975) studied the oral sensory-perceptual integrity of stutterers by using a battery of tests, including oral form discrimination, two-point discrimination, interdental and intraoral weight discrimination, and interdental thickness discrimination. The oral form recognition measure from this test battery required the subjects to identify forms placed in the mouth by pointing to a picture of all forms used. The results of this test procedure did not show any statistical differences between the oral sensory-perceptual integrity of stutterers, compared with nonstutterers. Ringel et al. (1968, 1970) devized an oral form procedure in which two forms are placed in the mouth successively and a same-different judgeAddress University,
correspondence to Donald Athens, OH 45701.
Fucci,
8 1985 by Elsevier Science Publishing Co., Inc. 52 Vanderbilt Ave.. New York, NY 10017
School
of Hearing
and Speech
Sciences,
Ohio
69 0094-730X/85/$03.30
70
D. FUCCI
et al.
ment is made. This procedure, unlike that of Jensen et al. (1975), did not require the aid of the visual modality. In 1975, Hutchinson and Ringel tested the oral sensory-perceptual integrity of six stutterers, employing the oral form procedure divized by Ringel et al. (1968, 1970), and found that stutterers performed “within normal limits.” In 1981, Martin et al. performed two additional experiments to investigate the oral stereognostic abilities of stutterers. In their first experiment oral form discrimination of 20 stutterers and 20 nonstutterers was assessed by using the same-different paradigm of Ringel et al. (1968, 1970). In their second experiment, oral form discrimination of 20 stutterers and 20 nonstutterers was assessed by using form identification through the visual modality (Jensen et al., 1975). In both instances the stutterers made more errors in correct form identification than the nonstutterers. The few experimental attempts at comparing stutterers and nonstutterers with respect to oral stereognostic form identification do not lead to results that are in total agreement. This situation may be attributed to the combinations of forms used, the reliance on visual integrity in some instances, different retention times of the forms in the mouth, and the nature of the stimuli themselves. A stimulus method for studying the human tactile sensory mechanism, which has several advantages over the use of two-dimensional, static oral stereognostic forms, is that of controlled vibration. One advantage of using controlled vibration is that it provides the experimenter with greater flexibility over the actual stimulus, which can be varied in terms of frequency, intensity, and time. A recent focus in the vibrotactile literature has been on the use of a suprathreshold magnitude production scaling task as a measure of oral sensory-perceptual ability at a central level. A series of studies have been performed in which vibrotactile magnitude production scaling has been utilized on the tongue to assess the perceptual integrity of the oral tactile sensory system (Fucci and Petrosino, 1983a,b,c). The purpose of the present investigation was to use the vibrotactile magnitude production scaling technique as a viable way to assess the tactile sensory-perceptual integrity of a group of stutterers compared with a group of fluent speakers, and to compare oral and nonoral magnitude production scaling results obtained from both groups. METHODS Subjects Two groups of volunteer subjects were employed, and consisted of 10 fluent speakers and 10 stutterers. The mean ages for the fluent speakers and for the stutterers was 19 yr and 23 yr respectively. All subjects reported a history free of neurologic disorders, medication, and oral or facial
VIBROTACTILE
MAGNITUDE
PRODUCTION
SCALING
pathologies. Subjects also were matched for educational level to within 2 yr of the highest grade attained, with all subjects having completed at least 2 yr of college. An oral-peripheral examination was performed on all subjects. Occlusion, bite, and dentition were within normal limits for all subjects. All stutterers reported a history of at least 10 yr of fluency problems. Stuttering severity was judged by three speech pathologists in terms of frequency of stuttering and duration of blocks that occurred during 5 min of conversational speech. Total agreement was obtained between the judges resulting in the stuttering group being categorized as having three mild, four moderate, and three severe stuttering individuals. All 10 stutterers reported therapy experiences lasting two consecutive years or longer.
Procedure The vibrotactile instrumentation used in this study consisted of a stimulus unit and a measurement unit. The stimulus unit was composed of a sine wave generator, an experimenter controlled variable attenuator, a subject controlled variable attenuator, an audio amplifier, a power amplifier, a preamplifier, and an electromagnetic minivibrator with a probe-contactor extension. The pulsed vibratory signal generated had a 50% duty cycle (on 500 msec, and off 500 msec), with a rise and decay time of 100 msec. The measurement unit included a calibrated accelerometer, a cathode follower, a microphone amplifier, and a voltmeter. A detailed description of the vibrotactile equipment and procedures can be found in a review by Fucci et al. (1982). The body sites tested were the anterior midline section of the dorsum of the tongue and the thenar eminence of the right hand. The order of testing the tongue and thenar eminence was counterbalanced between subjects. All 20 subjects were treated in the same manner. Each subject was seated in an adjustable chair and asked to place the structure to be tested against the bottom of a rigidly mounted plastic disk. A hole in the center of the disk provided access for the probe-contactor extension of the vibrator to the test site. The contactor on the end of the probe had an area of 0.128 cm*, and there was a l-mm gap between the contactor and the rigidly mounted plastic disk. The psychophysical method of magnitude production was used to establish suprathreshold magnitude functions for the tongue and hand. This method was selected because it has been shown to be very stable (Zwislocki and Goodman, 1980) and because it facilitates testing the tongue in that the subject can respond by manually adjusting a variable attenuator rather than by providing a verbal numerical response (magnitude estimation) that would be difficult with the tongue in test position. The pro-
D. FUCCI
72
et al.
cedure used did not incorporate a standard modulus. A number of investigators have indicated that the use of a standard reference can have a profound effect on the shape of the resulting magnitude function by interfering with the natural absolute magnitude scales that individuals have internalized (Zwislocki and Goodman, 1980). The magnitude production task was performed at the frequency of 250 Hz. The subject was presented with a random series of six numbers (5, 10, 15, 20, 25, 30) and was asked to adjust the “magnitude” of the stimulus that he was feeling on the test structure to the number being presented. The subject controlled attenuator consisted of a smooth, unmarked knob (120 dB variable potentiometer) having no visual or mechanical cues. The experimenter was in control of a master attenuator that could be used to vary the actual stimulus amplitude with respect to the position of the subject’s attenuator knob (Zwislocki and Goodman, 1980). The numbers chosen for scaling were held to six because of adaptability and fatigue effects, which appear to be more acute for the tongue than they are for some of the other mechanoreceptor systems that have been studied (Fucci and Crary, 1979). Three runs of the randomized series of six numbers were presented to each subject at each test site. The first run was discarded and the geometric means of the second and third runs were accepted as the produced amplitudes for that body location (Verrillo et al., 1969). The results of the magnitude production task were recorded in millivolts and converted to displacement in decibels with regard to a 1-k peak. Power function exponents were then derived from the decibel values. RESULTS
AND DISCUSSION
The power function exponents for the group of stutterers were 0.87 for the tongue and 0.68 for the thenar eminence. The power function exponents for the group of fluent speakers were 0.70 for the tongue and 0.68 for the thenar eminence. All values are expressed in terms of power. The values for the thenar eminence were the same for both groups of subjects. The value for the tongue was greater for the stuttering group than it was for the fluent speakers. It appears, then, that the stutterers and nonstutterers in this particular study performed the vibrotactile magnitude scaling task in a similar manner for the thenar eminence (a nonoral structure), but in a dissimilar manner for the midline dorsum of the tongue (an oral structure). Results of the study were supportive of the use of the vibrotactile magnitude production scaling technique as a way to study the sensory-perceptual integrity of stutterers. The stuttering group employed in this study provided power function values that were identical to those of the fluent speakers for the nonoral structure only. These power function values are compatible with those already established for the thenar eminence of the
VIBROTACTILE
MAGNITUDE
PRODUCTION
SCALING
right hand of normal speaking individuals (Fucci and Petrosino, 1983a, b, c). The power function value established for the group of stutterers on the lingual dorsal surface is somewhat higher than that for the group of fluent speakers. The value established for the group of fluent speakers is compatible with those already established for the tongue of normal speaking individuals (Fucci and Petrosino, 1983a, b, c). The different power function value obtained for the lingual dorsal surface of the stutterers, when compared with the fluent speakers, tends to reinforce the results of earlier investigations, which indicate different responses from defective speaking populations for oral form discrimination (Bishop et al., 1973; Martin et al., 1981). In 1980, Zwislocki and Goodman performed a series of studies using psychophysical magnitude scaling, from which they concluded that individuals, at a very early age, devize within themselves an absolute scaling mechanism. This mechanism is then used throughout life to “measure” those environmental factors evolving around numerical scaling. Assuming that such an internal mechanism exists, it appears that the stuttering group in the present study showed a different absolute internal system for scaling of the tonge than did the fluent speakers. It is interesting to note, however, that the scaling behavior of the stutterers for the nonoral structure was the same as that of the fluent speakers for the nonoral structure. Many researchers view stuttering basically as being an internal disorder of the auditory, tactile-proprioceptive feedback mechanisms directly concerned with speech production. The recent data of Martin et al. (1981) concerning the abilities of stutterers to perceive accurately with the tongue forms placed in the oral cavity suggest such a disordered feedback explanation for stuttering. From the results of the present study, it does appear that the stutterers used a different internal scale for the tongue than for the hand. The fluent speakers did not appear to use different internal criteria for the tongue and hand. The performance difference between groups may be attributed to differences in basic internal sensory-perceptual function, organization, or both. Whatever the case, the suggestion is that some differences exist between stuttering and fluent speakers in the central processes that are rudimentary to speech production. Suggestions have been made from this study, as well as others, that stutterers and fluent speakers may have different mechanisms or different ways of controlling the sensory-perceptual aspects of speech production. However, it is premature to conclude that there is a distinct demarcation between the sensory-perceptual processes of fluent and nonfluent speakers. A broader and more cautious interpretation must take behavioral tendencies of individuals into account. The power function exponent of 0.87 established for the lingual dorsal surface of the stutterers is considered to be reflective of a more conservative scaling behavior than is the exponent of 0.70 established for the lingual dorsal surface of the fluent
74
D. FUCCI et al.
speakers. The higher exponent resulted from the fact that the stutterers, as a group, used a narrower range of intensity adjustments to perform the scaling task on the tongue than the fluent speakers (Stevens and Greenbaum, 1966). With respect to the hand, both groups used a relatively similar range of intensity adjustments to scale the six numbers provided for the scaling task. Informal observation of the behavior of the stutterers in the experimental situation led to the impression that, in general, they exhibited a more conservative approach to the lingual scaling task. The stutterers, when compared with the fluent speakers, were slower and more deliberate in their scaling responses. They showed concern about performing the task correctly and required verbal confirmation that their responses were appropriate. A generalized impression of stutterers being slower and perhaps more cautious as a decision making group has been previously suggested (Van Riper, 1971; Woods, 1977). This cautious behavior was much less noticeable when scaling of the thenar eminence was being performed by the stuttering group. The psychophysical method of vibrotactile magnitude production scaling, like the methods that use the stereognostic forms, at present, can be used to study the tactile sensory-perceptual system involved in speech activities only while it is in a static postural state. Ideally, this system should be tested during the speaking process itself. The establishment of means for measuring oral sensation and perception during the dynamics of speaking is needed for the purpose of better understanding the role of oral sensory-perceptual responses in stuttering behavior.
REFERENCES Bishop,
M.E.,
production, 257-266.
Ringel, R.L.. and House, and deafness.
Journal
A.S. Orosensory of Speech and Hearing
perception, Research,
speech 1973, 16,
Fucci, D. and Crary, M.A. Oral vibrotactile sensation and perception: State of the art. In: N. Lass (ed.), Speech and Language: Advances in basic research and practice,
vol. 2. New
York:
Academic
Press,
1979.
Fucci, D. and Petrosino, L. Lingual vibrotactile sensation magnitudes: Comparison of suprathreshold responses in men and women. Perception and Psychophysics, 1983a, 33, 93-95. Fucci, D. and Petrosino, L. Lingual vibrotactile sensation magnitudes: Comparison of suprathreshold responses for the tongue and hand. The Journal of the Acoustical Society of America, 1983b, 74, 351-353. Fucci, D. and Petrosino, L. Lingual vibrotactile sensation magnitudes: Comparison of suprathreshold responses for three different age ranges. Perceptual and Motor Skills, 1983c, 57, 31-38. Fucci, D., Petrosino, L., Wallace, D., and Small, L.H. Modification of instrumentation for research on lingual vibrotactile sensitivity: Elimination of the
75
tongue clamping procedure.
Review
of ScientijTc
Instruments,
1982, 53, 1294-
1296.
Hutchinson, stuttering
J.M. and Ringel, R.L. The effect of oral sensory deprivation on behavior. Journal of Communication Disorders, 1975, 8, 249-258.
Jensen, P.J., Sheehan, J.G., Williams, W.N., and LaPointe, L.L. Oral sensory perceptual integrity of stutterers. Folia Phoniatrica, 1975, 17, 38-45. Martin, R.R., Lawrence, B.A., Haroldson, S.K., and Gunderson, D. Stuttering and oral stereognosis. Perceptual and Motor Skills, 1981, 53, 155-162. Ringel, R.L., Burk, K.W., and Scott, C.M. Tactile perception: Form discrimination in the mouth. British Journal of Disorders of Communication, 1968, 3, 150-155.
Ringel, R.L., House, A.S., Burk, K.W., Dolinsky, J.P., and Scott, C.M. Some relations between orosensory discrimination and articulatory aspects of speech production. Journal of Speech and Hearing Disorders, 1970, 35, 3-11. Stevens, S.S. and Greenbaum, H.B. Regression effect in psychophysical ment. Perception and Psychophysics, 1966, 1, 439-446. Van Riper, C. The Nature 1971.
of Stuttering.
Englewood
judge-
Cliffs, NJ: Prentice-Hall,
Verrillo, R.T., Fraioli, A.J., and Smith, R.L. Sensation magnitude of vibrotactile stimuli. Perception and Psychophysics, 1969, 6, 366-372. Woods, Human
C.L.
Dimensions
Communication
of the stutterer Disorders,
stereotype.
Australian
Journal
of
1977, 5, 119-125.
Zwislocki, J and Goodman, D. Absolute dation. Perception and Psychophysics,
scaling of sensory magnitudes: 1980, 28, 28-38.
A vali-
VIBROTACTILE MAGNITUDE PRODUCTION SCALING: A METHOD FOR STUDYING SENSORY-PERCEPTUAL RESPONSES OF STUTTERERS AND FLUENT SPEAKERS DONALD FUCCI, LINDA PETROSINO, and DANIEL HARRIS
PETER GORMAN,
School of Hearing and Speech Sciences Ohio University, Athens, Ohio
The method of vibrotactile mangitude production scaling was used to determine the tactile sensory-perceptual integrity for the dorsum of the tongue and thenar eminence of the right hand for 10 fluent speakers and 10 stutterers. It was discovered that both groups performed the task in a similar manner for the thenar eminence of the hand (a nonoral structure) but in a dissimilar manner for the tongue (an oral structure). From these data, it is suggested that the stutterers may maintain a different internal sensory-perceptual process for the tactile system involved in the speech process. The possibility exists that stuttering, for some, may be an “internal disorder” of the tactile-proprioceptive feedback mechanism that is directly involved in speech production.
INTRODUCTION Several researchers, through the utilization of oral stereognostic forms, have investigated the idea that stuttering behavior may be attributed to a disturbance in the integrity of the oral tactile sensory-perceptual system. Jensen et al. (1975) studied the oral sensory-perceptual integrity of stutterers by using a battery of tests, including oral form discrimination, two-point discrimination, interdental and intraoral weight discrimination, and interdental thickness discrimination. The oral form recognition measure from this test battery required the subjects to identify forms placed in the mouth by pointing to a picture of all forms used. The results of this test procedure did not show any statistical differences between the oral sensory-perceptual integrity of stutterers, compared with nonstutterers. Ringel et al. (1968, 1970) devized an oral form procedure in which two forms are placed in the mouth successively and a same-different judgeAddress University,
correspondence to Donald Athens, OH 45701.
Fucci,
8 1985 by Elsevier Science Publishing Co., Inc. 52 Vanderbilt Ave.. New York, NY 10017
School
of Hearing
and Speech
Sciences,
Ohio
69 0094-730X/85/$03.30
70
D. FUCCI
et al.
ment is made. This procedure, unlike that of Jensen et al. (1975), did not require the aid of the visual modality. In 1975, Hutchinson and Ringel tested the oral sensory-perceptual integrity of six stutterers, employing the oral form procedure divized by Ringel et al. (1968, 1970), and found that stutterers performed “within normal limits.” In 1981, Martin et al. performed two additional experiments to investigate the oral stereognostic abilities of stutterers. In their first experiment oral form discrimination of 20 stutterers and 20 nonstutterers was assessed by using the same-different paradigm of Ringel et al. (1968, 1970). In their second experiment, oral form discrimination of 20 stutterers and 20 nonstutterers was assessed by using form identification through the visual modality (Jensen et al., 1975). In both instances the stutterers made more errors in correct form identification than the nonstutterers. The few experimental attempts at comparing stutterers and nonstutterers with respect to oral stereognostic form identification do not lead to results that are in total agreement. This situation may be attributed to the combinations of forms used, the reliance on visual integrity in some instances, different retention times of the forms in the mouth, and the nature of the stimuli themselves. A stimulus method for studying the human tactile sensory mechanism, which has several advantages over the use of two-dimensional, static oral stereognostic forms, is that of controlled vibration. One advantage of using controlled vibration is that it provides the experimenter with greater flexibility over the actual stimulus, which can be varied in terms of frequency, intensity, and time. A recent focus in the vibrotactile literature has been on the use of a suprathreshold magnitude production scaling task as a measure of oral sensory-perceptual ability at a central level. A series of studies have been performed in which vibrotactile magnitude production scaling has been utilized on the tongue to assess the perceptual integrity of the oral tactile sensory system (Fucci and Petrosino, 1983a,b,c). The purpose of the present investigation was to use the vibrotactile magnitude production scaling technique as a viable way to assess the tactile sensory-perceptual integrity of a group of stutterers compared with a group of fluent speakers, and to compare oral and nonoral magnitude production scaling results obtained from both groups. METHODS Subjects Two groups of volunteer subjects were employed, and consisted of 10 fluent speakers and 10 stutterers. The mean ages for the fluent speakers and for the stutterers was 19 yr and 23 yr respectively. All subjects reported a history free of neurologic disorders, medication, and oral or facial
VIBROTACTILE
MAGNITUDE
PRODUCTION
SCALING
pathologies. Subjects also were matched for educational level to within 2 yr of the highest grade attained, with all subjects having completed at least 2 yr of college. An oral-peripheral examination was performed on all subjects. Occlusion, bite, and dentition were within normal limits for all subjects. All stutterers reported a history of at least 10 yr of fluency problems. Stuttering severity was judged by three speech pathologists in terms of frequency of stuttering and duration of blocks that occurred during 5 min of conversational speech. Total agreement was obtained between the judges resulting in the stuttering group being categorized as having three mild, four moderate, and three severe stuttering individuals. All 10 stutterers reported therapy experiences lasting two consecutive years or longer.
Procedure The vibrotactile instrumentation used in this study consisted of a stimulus unit and a measurement unit. The stimulus unit was composed of a sine wave generator, an experimenter controlled variable attenuator, a subject controlled variable attenuator, an audio amplifier, a power amplifier, a preamplifier, and an electromagnetic minivibrator with a probe-contactor extension. The pulsed vibratory signal generated had a 50% duty cycle (on 500 msec, and off 500 msec), with a rise and decay time of 100 msec. The measurement unit included a calibrated accelerometer, a cathode follower, a microphone amplifier, and a voltmeter. A detailed description of the vibrotactile equipment and procedures can be found in a review by Fucci et al. (1982). The body sites tested were the anterior midline section of the dorsum of the tongue and the thenar eminence of the right hand. The order of testing the tongue and thenar eminence was counterbalanced between subjects. All 20 subjects were treated in the same manner. Each subject was seated in an adjustable chair and asked to place the structure to be tested against the bottom of a rigidly mounted plastic disk. A hole in the center of the disk provided access for the probe-contactor extension of the vibrator to the test site. The contactor on the end of the probe had an area of 0.128 cm*, and there was a l-mm gap between the contactor and the rigidly mounted plastic disk. The psychophysical method of magnitude production was used to establish suprathreshold magnitude functions for the tongue and hand. This method was selected because it has been shown to be very stable (Zwislocki and Goodman, 1980) and because it facilitates testing the tongue in that the subject can respond by manually adjusting a variable attenuator rather than by providing a verbal numerical response (magnitude estimation) that would be difficult with the tongue in test position. The pro-
D. FUCCI
72
et al.
cedure used did not incorporate a standard modulus. A number of investigators have indicated that the use of a standard reference can have a profound effect on the shape of the resulting magnitude function by interfering with the natural absolute magnitude scales that individuals have internalized (Zwislocki and Goodman, 1980). The magnitude production task was performed at the frequency of 250 Hz. The subject was presented with a random series of six numbers (5, 10, 15, 20, 25, 30) and was asked to adjust the “magnitude” of the stimulus that he was feeling on the test structure to the number being presented. The subject controlled attenuator consisted of a smooth, unmarked knob (120 dB variable potentiometer) having no visual or mechanical cues. The experimenter was in control of a master attenuator that could be used to vary the actual stimulus amplitude with respect to the position of the subject’s attenuator knob (Zwislocki and Goodman, 1980). The numbers chosen for scaling were held to six because of adaptability and fatigue effects, which appear to be more acute for the tongue than they are for some of the other mechanoreceptor systems that have been studied (Fucci and Crary, 1979). Three runs of the randomized series of six numbers were presented to each subject at each test site. The first run was discarded and the geometric means of the second and third runs were accepted as the produced amplitudes for that body location (Verrillo et al., 1969). The results of the magnitude production task were recorded in millivolts and converted to displacement in decibels with regard to a 1-k peak. Power function exponents were then derived from the decibel values. RESULTS
AND DISCUSSION
The power function exponents for the group of stutterers were 0.87 for the tongue and 0.68 for the thenar eminence. The power function exponents for the group of fluent speakers were 0.70 for the tongue and 0.68 for the thenar eminence. All values are expressed in terms of power. The values for the thenar eminence were the same for both groups of subjects. The value for the tongue was greater for the stuttering group than it was for the fluent speakers. It appears, then, that the stutterers and nonstutterers in this particular study performed the vibrotactile magnitude scaling task in a similar manner for the thenar eminence (a nonoral structure), but in a dissimilar manner for the midline dorsum of the tongue (an oral structure). Results of the study were supportive of the use of the vibrotactile magnitude production scaling technique as a way to study the sensory-perceptual integrity of stutterers. The stuttering group employed in this study provided power function values that were identical to those of the fluent speakers for the nonoral structure only. These power function values are compatible with those already established for the thenar eminence of the
VIBROTACTILE
MAGNITUDE
PRODUCTION
SCALING
right hand of normal speaking individuals (Fucci and Petrosino, 1983a, b, c). The power function value established for the group of stutterers on the lingual dorsal surface is somewhat higher than that for the group of fluent speakers. The value established for the group of fluent speakers is compatible with those already established for the tongue of normal speaking individuals (Fucci and Petrosino, 1983a, b, c). The different power function value obtained for the lingual dorsal surface of the stutterers, when compared with the fluent speakers, tends to reinforce the results of earlier investigations, which indicate different responses from defective speaking populations for oral form discrimination (Bishop et al., 1973; Martin et al., 1981). In 1980, Zwislocki and Goodman performed a series of studies using psychophysical magnitude scaling, from which they concluded that individuals, at a very early age, devize within themselves an absolute scaling mechanism. This mechanism is then used throughout life to “measure” those environmental factors evolving around numerical scaling. Assuming that such an internal mechanism exists, it appears that the stuttering group in the present study showed a different absolute internal system for scaling of the tonge than did the fluent speakers. It is interesting to note, however, that the scaling behavior of the stutterers for the nonoral structure was the same as that of the fluent speakers for the nonoral structure. Many researchers view stuttering basically as being an internal disorder of the auditory, tactile-proprioceptive feedback mechanisms directly concerned with speech production. The recent data of Martin et al. (1981) concerning the abilities of stutterers to perceive accurately with the tongue forms placed in the oral cavity suggest such a disordered feedback explanation for stuttering. From the results of the present study, it does appear that the stutterers used a different internal scale for the tongue than for the hand. The fluent speakers did not appear to use different internal criteria for the tongue and hand. The performance difference between groups may be attributed to differences in basic internal sensory-perceptual function, organization, or both. Whatever the case, the suggestion is that some differences exist between stuttering and fluent speakers in the central processes that are rudimentary to speech production. Suggestions have been made from this study, as well as others, that stutterers and fluent speakers may have different mechanisms or different ways of controlling the sensory-perceptual aspects of speech production. However, it is premature to conclude that there is a distinct demarcation between the sensory-perceptual processes of fluent and nonfluent speakers. A broader and more cautious interpretation must take behavioral tendencies of individuals into account. The power function exponent of 0.87 established for the lingual dorsal surface of the stutterers is considered to be reflective of a more conservative scaling behavior than is the exponent of 0.70 established for the lingual dorsal surface of the fluent
74
D. FUCCI et al.
speakers. The higher exponent resulted from the fact that the stutterers, as a group, used a narrower range of intensity adjustments to perform the scaling task on the tongue than the fluent speakers (Stevens and Greenbaum, 1966). With respect to the hand, both groups used a relatively similar range of intensity adjustments to scale the six numbers provided for the scaling task. Informal observation of the behavior of the stutterers in the experimental situation led to the impression that, in general, they exhibited a more conservative approach to the lingual scaling task. The stutterers, when compared with the fluent speakers, were slower and more deliberate in their scaling responses. They showed concern about performing the task correctly and required verbal confirmation that their responses were appropriate. A generalized impression of stutterers being slower and perhaps more cautious as a decision making group has been previously suggested (Van Riper, 1971; Woods, 1977). This cautious behavior was much less noticeable when scaling of the thenar eminence was being performed by the stuttering group. The psychophysical method of vibrotactile magnitude production scaling, like the methods that use the stereognostic forms, at present, can be used to study the tactile sensory-perceptual system involved in speech activities only while it is in a static postural state. Ideally, this system should be tested during the speaking process itself. The establishment of means for measuring oral sensation and perception during the dynamics of speaking is needed for the purpose of better understanding the role of oral sensory-perceptual responses in stuttering behavior.
REFERENCES Bishop,
M.E.,
production, 257-266.
Ringel, R.L.. and House, and deafness.
Journal
A.S. Orosensory of Speech and Hearing
perception, Research,
speech 1973, 16,
Fucci, D. and Crary, M.A. Oral vibrotactile sensation and perception: State of the art. In: N. Lass (ed.), Speech and Language: Advances in basic research and practice,
vol. 2. New
York:
Academic
Press,
1979.
Fucci, D. and Petrosino, L. Lingual vibrotactile sensation magnitudes: Comparison of suprathreshold responses in men and women. Perception and Psychophysics, 1983a, 33, 93-95. Fucci, D. and Petrosino, L. Lingual vibrotactile sensation magnitudes: Comparison of suprathreshold responses for the tongue and hand. The Journal of the Acoustical Society of America, 1983b, 74, 351-353. Fucci, D. and Petrosino, L. Lingual vibrotactile sensation magnitudes: Comparison of suprathreshold responses for three different age ranges. Perceptual and Motor Skills, 1983c, 57, 31-38. Fucci, D., Petrosino, L., Wallace, D., and Small, L.H. Modification of instrumentation for research on lingual vibrotactile sensitivity: Elimination of the
75
tongue clamping procedure.
Review
of ScientijTc
Instruments,
1982, 53, 1294-
1296.
Hutchinson, stuttering
J.M. and Ringel, R.L. The effect of oral sensory deprivation on behavior. Journal of Communication Disorders, 1975, 8, 249-258.
Jensen, P.J., Sheehan, J.G., Williams, W.N., and LaPointe, L.L. Oral sensory perceptual integrity of stutterers. Folia Phoniatrica, 1975, 17, 38-45. Martin, R.R., Lawrence, B.A., Haroldson, S.K., and Gunderson, D. Stuttering and oral stereognosis. Perceptual and Motor Skills, 1981, 53, 155-162. Ringel, R.L., Burk, K.W., and Scott, C.M. Tactile perception: Form discrimination in the mouth. British Journal of Disorders of Communication, 1968, 3, 150-155.
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