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Age and task complexity variables in motor performance of stuttering and nonstuttering children
J. FLUENCY DISORD. 16 (1991), 207-217
AGE AND TASK COMPLEXITY VARIABLES IN MOTOR PERFORMANCE OF STUTTERING AND NONSTUTTERING CHILDREN JUDITH HIDDING BISHOP, HARRIET G. WILLIAMS, WILLIAM
and
A. COOPER
University of SON~II Curdim.
Colrrmbicr
This paper is the first in a series of studies that explores the performance of young stutterers and nonstutterers on vocal and manual tasks of three levels of complexity in a simple reaction-time paradigm. Special attention was given to the selection of 40 subjects. Severity ratings were cited for stuttering subjects; they were matched with control subjects for gender. age, race, and school placement. An examiner screening sought to eliminate subjects with other known speech or language disorders. Stutterers had significantly slower reaction times (RTs) than nonstutterers. Changes in vocal and manual RTs followed a parallel course of improvement with age for both groups. Differences between performances of stutterers and nonstutterers increased with task complexity. Variability of performance of stutterers on manual tasks was not affected by task complexity; in contrast, variability of performance was significantly greater for stutterers under six on the most complex vocal tasks.
INTRODUCTION Psychology, physiology, and motor control have an extensive body of literature on reaction time dating back to the 1930s. Speech-language pathology, with special reference to the exploration of the disorder of stuttering, has had a surge of vocal onset studies followed by a surge of vocal reaction-time studies beginning in the early 1970s. (Adams et al., 1984). The majority of these studies have recorded slower reaction times for stutterers versus nonstutterers. Cross and Luper (1979, 1983) studied both vocal reaction times (VRTs) and manual reaction times (MRTs) of Syear-old, 9-year-old, and adult stutterers and nonstutterers. The VRTs (production of “uh” in response to a lOOO-Hz tone) for stutterers and nonstutterers decreased as an inverse function of age; the largest decrease in reaction time occurred between those age 5 and 9. VRTs of stutterers, however, were significantly slower than those of nonstutterers at each of the three ages studied. Cross and Luper (1983) also reported comparisons of VRTs and MRTs. Address correspondence to Judith H. Bishop. 1601 St. Julian Place, Columbia, SC 29204. Q 1991 by Elsevier Science Publishing Co., Inc. 655 Avenue of the Americas,
New York. NY 10010
Ph.D.,
USC Speech
and Hearing
Center, 207
0094-730x/91/$3.50
208
J. H. BISHOP ET AL.
Stutterers of all ages exhibited mean MR7’s on a forefinger-pressing task that were significantly longer and more variable than those of nonstutterers. High correlations were also found between MRTs and VRTs for both stutterers and nonstutterers. In contrast, Reich and colleagues (1981) and Till et al. (1983) concluded that forefinger reaction times of adult stutterers and stuttering children (8-12 years of age) were comparable to those of nonstutterers. Laryngeal reaction times (throat clearing and the word “upper”), however, were longer in stutterers than in normals. Till et al. (1983) suggested that stuttering in children was not necessarily related to an “organically based overall slowness” in movement production. Starkweather et al. (1984) proposed that a combination of two factors, one constitutional and the other developmental, may be involved in stuttering and introduced the statistic “VMD”: the difference between vocal and manual reaction times. They stated that stutterers’ vocal reaction times might be slowed even more than controls by secondary by-products of the disorder such as “acquired chronic laryngeal and supralaryngeal muscle tension’ (p. 194). Cullinan and Springer (1980) studied 20 stutterers (aged 5-11); I I were children who had other speech/language problems in addition to stuttering. Although “stutterers only” did not differ significantly from normal controls, the “stuttering-plus” group had significantly slower vocal initiation (VIT) and vocal termination (VTT) times. These authors reported that whereas older stuttering children had longer phonation times than did nonstuttering children, younger stuttering children did not. Several studies have investigated vocal/speech reaction times on tasks that were presumed to represent different levels of complexity (McKnight and Cullinan, 1987; Peters et al., 1989: Reich et al., 1981; Starkweather et al., 1976: Till et al., 1983). Results of these studies suggested that the motoric complexity of a task influenced response time. Although there is general agreement that vocal reaction time of various stuttering populations is slower than that of control subjects, age differences in VRT performance are not as clear cut. Findings on differences and/or similarities between stutterers and nonstutterers on performance of manual and vocal tasks have been equivocal. The purpose of the present study was twofold: (1) to investigate trends in vocal and manual control in young stutterers as a function of age and (2) to examine the effects of task complexity on vocal and manual motor control in stutterers and nonstutterers. We reasoned that if stuttering is primarily a reflection of an overall slowness or inefficiency of the motor-control system, then both vocal and manual RTs and manual/vocal ratios should follow a parallel course of development with increasing age. If stutterers’ vocal RTs do not improve parallel to manual RTs over age and nonstutterers RTs do,
AGE AND TASK COMPLEXITY
VARIABLES
this would point to either speech/specific slow VRT at older ages. If stuttering is a manifestation of general system, increasing task complexity should in a similar manner for both stutterers and
IN CHILDREN
or developmental
209
factors
that
slowness of the motor-control affect vocal and manual RTs nonstutterers.
METHOD
Subjects Subjects were five stutterers and five nonstutterers in each of four age groups (3.0-5.9; 6.7-7.4; 8.0-g. II; 9. I-10. II). Pairs of subjects (stutterer and control) were matched to within 3 months of age. Children were recruited from local school districts, clinics, and private practices within a 40-mile radius of Columbia, SC. With four exceptions, individual pairs were in the same classroom. All subjects were making satisfactory academic progress and were NOT receiving special services for academic, or speech/language difficulties other than stuttering. To control for potential confounding of gender and ethnic differences, only Caucasian boys were included in the sample. Prior to the experiment proper, each of the stuttering children was evaluated by the experimenter and received a minimum classification of “mild” severity on the Stuttering Severity Instrument for Children and Adults (Riley, 1980) or, in the case of preschoolers, The Stuttering Prediction Instrument (Riley, 1981). All were identified as stuttering by one of twelve practicing speech-language pathologists and were currently in therapy. With one exception, all parents of school-age stutterers reported preschool onset. The instrument was administered in the home or school setting. Severity was distributed across age as reported in Table I. Experience with stuttering therapy was not systematically controlled. The stuttering subjects had been in therapy for varying lengths of time with different clinicians presumably using different techniques.
Table 1. Age Distribution
of Severity Ratings of Stuttering Subjects Based on Performance on the Stuttering Prediction Instrument” or the Stuttering Severity Instrumen?’ (Most S’s were tested on the SSI.) Frequency Severity
3.0-5.9
distribution
6.7-7.4
(per age group) 8.0-8.1
I
9.1-10.11
Mild
3
4
2
3
Moderate
2
1
3
I 1
Severe U Riley, 1981. b Riley, 1980.
210
J. H. BISHOP
ET AL.
All subjects were screened and passed tests for age-appropriate articulation and language skills. Children 5 years of age and under were screened with the Coston-Reidenbach Articulation Quick Screening/Language Quick Screening Test (Coston and Reidenbach, 1978). Children 6 years and over were tested with the screening sections of the FisherLogemann Test of Articulation (Fisher and Logemann, 1971) and The Clinical Evaluation of Language Functions (CELF) Elementary Level (Semel and Wiig. 1980). A minimum CELF Total Score Performance at the 30th percentile was required for inclusion in the study.
Tasks Three manual tasks of increasing complexity were performed by all subjects: simple finger-life response (Level I), finger lift followed by a finger press (Level 2) and finger lift followed by a touch and a press (Level 3). The three vocal tasks of increasing complexity were the production of the isolated vowel “a” (Level 1); the words “a cow” (Level 2) and the words “a cowboy” (Level 3).
Procedures All data were collected at The University of South Carolina Motor Development/Motor Control Laboratory. Reaction times for all manual and vocal tasks were cued and recorded on an adaptation of the Lafayette Reaction/Movement Time Apparatus (model #63017, Lafayette Instrument Co., Lafayette, Indiana). The stimulus for all tasks was a green light of fixed intensity. A small white “ready” signal was presented prior to random prestimulus intervals (PSI) of l-2 set duration. Intertrial intervals were approximately 30 sec. The digital clock was activated by the onset of the stimulus light and stopped by release of a telegraph key (finger-lift response) or the initiation of the vowel “a,” which appeared at the beginning of each vocal response. Reaction time for initiation of vocal or manual responses was recorded in milliseconds. The child’s vocal response was detected by a throat microphone sewn to a bow tie worn by the child and positioned against the lamina of the thyroid cartilage. Output was low pass filtered and amplified to achieve maximum sensitivity to phonation rather than neck noise. The equipmental setting was designed to be nonthreatening. A black screen (60.96 cm by 35.56 cm) blocked the child’s view of the recording instrument. The child was seated on a high chair facing a table with two telegraph keys (located 46.99 cm apart) and a black box (31.75 cm by 22.86 cm) that served as a stand for the stimulus light box. Toy replicas of a cow and a cowboy were used to prompt responses for vocal tasks and the black box was turned to reveal a running deer for the “lift-touchpress” response.
AGE AND TASK COMPLEXITY
VARIABLES
IN CHILDREN
211
Subjects were instructed to respond as quickly as possible to the visual stimulus. Order of task complexity was randomized for each subject. All vocal tasks were presented together and all manual tasks were presented together; the order of vocal or manual presentation was by predetermined random order. The order of task complexity was preserved within task. The experimenter gave instructions specific to each task immediately preceding the task. Practice sessions were carried out until the experimenter was satistied that the child understood what he was to do and was responding without obvious hesitancy. No child exceeded a limit of ten practice trials per response condition. Subjects performed 10 trials under each experimental condition (60 trials in all). Some 3 and 4-year-old subjects only completed a minimum of five trials. If a subject lost attention or responded prematurely the trial was repeated. With the exception of the 3-year-old pair, retrials for any one condition were limited to four. A short break was provided if attention waned. Research Design and Analysis To control for unequal variances and unequal correlations among repeated measures (Finn, 1974), data were analyzed using multivariate (as opposed to univariate) repeated measures technique. The 20 matched pairs were treated as single subjects with 24 variables representing all possible combinations of task, group, and performance measure (mean, SD). Dependent variables were: mean reaction time (vocal and manual); standard deviation or variability of RT (vocal and manual); and manual/vocal ratio. The model for this study was a 4 (Age) x 2 (Group) x 2 (Task) x 3 (Complexity) mixed design with one between-subjects factor (Age) and 3 within-subjects factors (Group, Task, Complexity). Tests of sphericity confirmed the need for the use of the multivariate model. RESULTS Reaction Time Mean reaction times are shown in Table 2. Overall, reaction time decreased with age (p = 0.013). However, post hoc analysis indicated that only subjects in the 3.0-5.9 age group were significantly slower than all other age groups (p = 0.002). None of the other age group contrasts were significant. Stutterers were slower than nonstutterers (p = 0.013); VRTs were longer than MRTs (p = 0.000); and reaction time increased with increased task complexity (p = 0.003). The Group x Complexity (across modality) interaction was significant
212
J. H. BISHOP
Table 2. Grand Means over Groups,
Age, Task,
ET AL.
and Task Complexity
Mean Performance Group (Stutterers set)
vs. Nonstutterers)
Mean Performance
on All Tasks over All Ages (in
Stutterers Mean SD
Nonstutterers
0.471 0.104
Vocal vs. Manual Mean Performance Complexity
Mean SD
0.412 0.070
by All Groups over All Ages at All Levels of Vocal
Manual
0.501 0.100
0.383 0.074
Mean Performance of Four Age Groups on All Tasks at All Levels of Complexity
Mean SD Mean Performance
Age I
Age 2
Age 3
Age 4
0.609 0.162
0.409 0.078
0.379 0.050
0.370 0.056
of All Groups on All Tasks at Each Level of Complexity
Mean SD
Level I
Level 2
Level 3
0.421 0.077
0.448 0.086
0.457 0.098
Mean Manual/vocal Ratio of Stutterers vs. Nonstutterers Stutterers 0.748
on All Tasks at All Ages Nonstutterers 0.784
(p = 0.041) as is shown in Figure 1. Nonstutterers always had faster RTs than stutterers; this difference increased with task complexity. No other interactions were significant. It is important to note that interactions involving type of task (vocal versus manual) or age were not significant. Both members of two pairs of subjects demonstrated extremely poor performance on at least one task and/or required considerable deviation in procedure (fewer than ten trials per task). Therefore, a second data analysis was performed with the scores of these two pairs omitted. With one exception, results of this analysis were identical to the previous analyses (there were significant main effects for Age, Group, Task, and Complexity). However, the two-way interaction between Group x Complexity was not significant (p = 0.109).
AGE AND TASK COMPLEXITY
VARIABLES
213
IN CHILDREN
I-
CC
5 4oo 2 300
200
3
1
TASK
COMPLEXITY
Figure 1. Mean reaction times of stutterers of task complexity.
versus nonstutterers
at three levels
Figure 2. Consistency of performance of stutterers versus nonstutterers on vocal versus manual tasks as a function of complexity. (Solid line indicates nonstutterers, broken line indicates stutterers.) zoo-
MANUAL
VOCAL
z
z 8 > iti c” 52 loo-. 2
0 0
0.
,/ __-,_-__--
,’/
,’ ,’
,/’
/’
____----
*
1
2
3
I
.I
1
TASK COMPLEXITY
____-------_________
2
3
1
214
J. H. BISHOP ET AL.
Variability of RT Results of the multivariate repeated measures analysis for the standard deviation of RT indicated that main effects of age (p = 0.004), group (p = 0.009), and task (p = 0.039) were significant. Variability of performance decreased with increased age; RTs of stutterers were signifrcantly more variable than RTs of nonstutterers; and performances on vocal tasks were more variable than manual tasks. The three-way interaction among Group x Task x Complexity was significant (p = 0.052) and is plotted in Figure 2. The significant (p = 0.041) four-way interaction of Group x Age x Task x Complexity is shown in Figure 3. Reaction times were most variable in young stutterers (under the age of six) on the most complex vocal task (level 3). As before, a second analysis was carried out that excluded scores of two deviant pairs. Results of this analysis indicated that there was a significant main effect for age (p = 0.003), group (p = 0.034), and task complexity (p = 0.037). The two-way interaction for Task x complexity (p = 0.015) and the three-way interaction for Age x Group x Complexity were also significant.
Figure 3. Consistency of response of stutterers (S) versus nonstutteres (NS) on vocal (VOC) tasks versus manual (MAN) tasks as a function of age: Group 1 3.0-
5.9, Group 2 6.7-7.4,
Group 3 8.0-8.11,
Group 4 9.1-10.11.
400
AGE 2
5300 z n v) >
200
100
9 Y v)
0
ix
5 4oo 0 E
300
0”
fJj 200 iii 100
0
1
2
3
TASK
1
COMPLEXITY
2
3
AGE AND TASK COMPLEXITY
VARIABLES
IN CHILDREN
21.5
Manual/Vocal Ratio Mean RT scores were converted to manual vocal ratios and analyzed. Manual vocal ratios did not differ as a function of age. group, or task complexity.
DISCUSSION Significant improvements in RT with age were observed for stutterers and nonstutterers on both vocal and manual tasks. Although stutterers always had slower RTs than nonstutterers, changes in vocal and manual RTs followed a parallel course of improvement/development for both groups of children. These data suggest that speech and manual processes are not independent, unrelated functions of the motor-control system at least as far as development is concerned. Also, one of the characteristics of the motor-control system of the stutterer may be a decreased or diminished capacity for speed in initiating manual and vocal responses. The manual/vocal ratios of stutterers and nonstutterers were not significantly different and essentially did not change with age. These data also point to a parallel course of development for vocal and manual reaction times for both stutterers and nonstutterers. This finding is not in keeping with increased VRT relative to MRT at older ages as suggested by Cullinan and Springer (1980), and Starkweather et al. (1984). The authors acknowledge that as this was not a longitudinal study, our age groups may represent different populations. We also acknowledge that therapy techniques that might have improved reaction time were not controlled. The effect of task complexity was different depending on whether the two “deviant” pairs of children were included. Regardless of whether the task was manual or vocal, RTs of nonstutterers were not affected by increases in task complexity whereas those of stutterers were. Because both vocal and manual RTs were similarly affected in stuttering children this points to a more generalized effect of task complexity on sensorymotor and motor-control processes in stutterers. With regard to variability or consistency of RTs, it has been proposed that if the information-processing demands of a given task are within the capacity of the system, it is likely that the system will be more consistent in repeatedly producing that same or a similar response. Data from the present study suggest that consistency of response programming was similar for older stutterers and nonstutterers on both vocal and manual tasks and that it was independent of task complexity. In contrast, variability of RTs of young stutterers on vocal tasks increased with complexity, whereas variability of performance of young nonstutterers increased with task complexity only for manual tasks. These data suggest that programming demands of all vocal and manual tasks were within the capacity of
J. H.
BISHOP ET AL.
the motor-control system of older children but were not for younger children. There appears to be support for the idea that, at least for white male stutterers, there is a predisposition toward slower sensorimotor performance that is common to both vocal and manual systems and that the differences in performance between stutterers and nonstutterers is more apparent at an early age. Reaction time is assumed to be composed of several components: stimulus recognition (time to respond to the environmental stimulus, in this case a green light); central planning or preparation for response (which includes both response selection and response programming); and motor time (a small peripheral component defined as the time from the first change in EMG to movement or response initiation). If, on the average, stutterers tend to have slower RTs than nonstutterers, one has to ask where the delay occurs and if it occurs consistently in the same component of the response production or RT process. The present study did not fractionate RT into its sensory, central (premotor), and peripheral (motor) components. No definitive statement can be made on the proportion of time devoted to sensory, central, and/or peripheral processes. Although it might be expected that older stutterers, because of increased length of stuttering experience, would be more likely to react to speech production with excess tension and thereby perform more poorly on vocal tasks than on manual tasks, current data do not support this position. Actually younger stutterers demonstrated a greater vocal/manual RT difference than older stutterers. This may indicate that the less mature system of the young stutterer reacts more to the stuttering/ speech experience than the older, more mature system. Such information encourages the trend to intervene early in the stuttering process. It implies that early reactions or constitutional predispositions put the young stutterer at a real disadvantage. The authors thank the subjects, their parents, and the referring speech-language pathologists. The authors appreciate the efforts of Susan Nickles in the preparation of the manuscript.
REFERENCES Adams, M., Freeman, F., & Conture,
G. (1984) Laryngeal dynamics of stutterers. In: Nature and Treatment of Stuttering: New Directions (W. Perkins and R. Curlee, eds.). San Diego: College-Hill Press.
Coston, G.N., and Reidenbach, E. (1978) Coston-Reidenbach Articulation Quick Screening/Language Quick Screening. Columbia, SC: Columbia Educational Resources. Cross, D.E., and Luper, H.L. (1979) Voice reaction time of stuttering and nonstuttering children and adults. Journal of Fluency Disorders, 4 59-77.
AGE AND TASK COMPLEXITY
VARIABLES
IN CHILDREN
217
Cross, D.E., and Luper, H.L. (1983) Relation between finger reaction time and voice reaction time in stuttering and nonstuttering children and adults. Journal of Speech and Hearing Research,
26, 356-361.
Cullinan, W.L., and Springer, M.T. (1980) Voice initiation and termination times in stuttering and nonstuttering children. Journal of Speech and Hearing Research, 23, 344-360.
Finn, J.D. (1974) A General Model for Multivariate Analysis. New York: Holt, Rhinehart, Winston. Fisher, H., and Logemann, J. (1971) The Fisher Logemann Competence. Iowa City: Houghton Mifflin. McKnight, R., and Cullinan, of Fluency Disorders,
Test of Articulation
W. (1987) Subgroups of stuttering children. Journal
12, 217-233.
Murphy, M., and Baumgartner, J. (1981) Voice initiation and termination time in stuttering and nonstuttering children. Journal of Fluency Disorders, 6, 257264.
Peters, H.F.M., Hulstijn, W., and Starkweather, C.W. (1989) Acoustic and physiological reaction times of stutterers and nonstutterers. Journal of Speech and Hearing Research,
32, 668-680.
Reich A, Till, J., and Goldsmith, H. (1981). Laryngeal and manual reaction times of stuttering and nonstuttering adults. Journal of Speech and Hearing Research, 24, 192-196.
Riley, G. (1980) Stuttering Severity Index. Tigard, OR: C.C. Publications. Riley, G. (1981) Stuttering Prediction Instrument. Tigard, OR: C.C. Publications. Semel, E.M., and Wiig, E.H. (1980) Clinical Evaluation of Language Functions. Columbus, OH: Charles E. Merrill. Starkweather, C.W., Hirshman, P., and Tannenbaum (1976) Latency of vocalization onset: Stutterers versus nonstutterers. Journal of Speech and Hearing Research,
19, 481-492.
Starkweather, C.W., Franklin, S., and Smigo, T., (1984) Vocal and finger reaction times in stutterers and nonstutterers; differences and correlations. Journal of Speech and Hearing Research,
27, 193-196.
Till, J., Reich, A., Dickey, S., and Seiber, J. (1983) Phonatory and manual reaction times of stuttering and nonstuttering children. Journal of Speech and Hearing Research,
27, 171-180.
Manuscript received July 1991; revised December 1991; accepted January 1992.
AGE AND TASK COMPLEXITY VARIABLES IN MOTOR PERFORMANCE OF STUTTERING AND NONSTUTTERING CHILDREN JUDITH HIDDING BISHOP, HARRIET G. WILLIAMS, WILLIAM
and
A. COOPER
University of SON~II Curdim.
Colrrmbicr
This paper is the first in a series of studies that explores the performance of young stutterers and nonstutterers on vocal and manual tasks of three levels of complexity in a simple reaction-time paradigm. Special attention was given to the selection of 40 subjects. Severity ratings were cited for stuttering subjects; they were matched with control subjects for gender. age, race, and school placement. An examiner screening sought to eliminate subjects with other known speech or language disorders. Stutterers had significantly slower reaction times (RTs) than nonstutterers. Changes in vocal and manual RTs followed a parallel course of improvement with age for both groups. Differences between performances of stutterers and nonstutterers increased with task complexity. Variability of performance of stutterers on manual tasks was not affected by task complexity; in contrast, variability of performance was significantly greater for stutterers under six on the most complex vocal tasks.
INTRODUCTION Psychology, physiology, and motor control have an extensive body of literature on reaction time dating back to the 1930s. Speech-language pathology, with special reference to the exploration of the disorder of stuttering, has had a surge of vocal onset studies followed by a surge of vocal reaction-time studies beginning in the early 1970s. (Adams et al., 1984). The majority of these studies have recorded slower reaction times for stutterers versus nonstutterers. Cross and Luper (1979, 1983) studied both vocal reaction times (VRTs) and manual reaction times (MRTs) of Syear-old, 9-year-old, and adult stutterers and nonstutterers. The VRTs (production of “uh” in response to a lOOO-Hz tone) for stutterers and nonstutterers decreased as an inverse function of age; the largest decrease in reaction time occurred between those age 5 and 9. VRTs of stutterers, however, were significantly slower than those of nonstutterers at each of the three ages studied. Cross and Luper (1983) also reported comparisons of VRTs and MRTs. Address correspondence to Judith H. Bishop. 1601 St. Julian Place, Columbia, SC 29204. Q 1991 by Elsevier Science Publishing Co., Inc. 655 Avenue of the Americas,
New York. NY 10010
Ph.D.,
USC Speech
and Hearing
Center, 207
0094-730x/91/$3.50
208
J. H. BISHOP ET AL.
Stutterers of all ages exhibited mean MR7’s on a forefinger-pressing task that were significantly longer and more variable than those of nonstutterers. High correlations were also found between MRTs and VRTs for both stutterers and nonstutterers. In contrast, Reich and colleagues (1981) and Till et al. (1983) concluded that forefinger reaction times of adult stutterers and stuttering children (8-12 years of age) were comparable to those of nonstutterers. Laryngeal reaction times (throat clearing and the word “upper”), however, were longer in stutterers than in normals. Till et al. (1983) suggested that stuttering in children was not necessarily related to an “organically based overall slowness” in movement production. Starkweather et al. (1984) proposed that a combination of two factors, one constitutional and the other developmental, may be involved in stuttering and introduced the statistic “VMD”: the difference between vocal and manual reaction times. They stated that stutterers’ vocal reaction times might be slowed even more than controls by secondary by-products of the disorder such as “acquired chronic laryngeal and supralaryngeal muscle tension’ (p. 194). Cullinan and Springer (1980) studied 20 stutterers (aged 5-11); I I were children who had other speech/language problems in addition to stuttering. Although “stutterers only” did not differ significantly from normal controls, the “stuttering-plus” group had significantly slower vocal initiation (VIT) and vocal termination (VTT) times. These authors reported that whereas older stuttering children had longer phonation times than did nonstuttering children, younger stuttering children did not. Several studies have investigated vocal/speech reaction times on tasks that were presumed to represent different levels of complexity (McKnight and Cullinan, 1987; Peters et al., 1989: Reich et al., 1981; Starkweather et al., 1976: Till et al., 1983). Results of these studies suggested that the motoric complexity of a task influenced response time. Although there is general agreement that vocal reaction time of various stuttering populations is slower than that of control subjects, age differences in VRT performance are not as clear cut. Findings on differences and/or similarities between stutterers and nonstutterers on performance of manual and vocal tasks have been equivocal. The purpose of the present study was twofold: (1) to investigate trends in vocal and manual control in young stutterers as a function of age and (2) to examine the effects of task complexity on vocal and manual motor control in stutterers and nonstutterers. We reasoned that if stuttering is primarily a reflection of an overall slowness or inefficiency of the motor-control system, then both vocal and manual RTs and manual/vocal ratios should follow a parallel course of development with increasing age. If stutterers’ vocal RTs do not improve parallel to manual RTs over age and nonstutterers RTs do,
AGE AND TASK COMPLEXITY
VARIABLES
this would point to either speech/specific slow VRT at older ages. If stuttering is a manifestation of general system, increasing task complexity should in a similar manner for both stutterers and
IN CHILDREN
or developmental
209
factors
that
slowness of the motor-control affect vocal and manual RTs nonstutterers.
METHOD
Subjects Subjects were five stutterers and five nonstutterers in each of four age groups (3.0-5.9; 6.7-7.4; 8.0-g. II; 9. I-10. II). Pairs of subjects (stutterer and control) were matched to within 3 months of age. Children were recruited from local school districts, clinics, and private practices within a 40-mile radius of Columbia, SC. With four exceptions, individual pairs were in the same classroom. All subjects were making satisfactory academic progress and were NOT receiving special services for academic, or speech/language difficulties other than stuttering. To control for potential confounding of gender and ethnic differences, only Caucasian boys were included in the sample. Prior to the experiment proper, each of the stuttering children was evaluated by the experimenter and received a minimum classification of “mild” severity on the Stuttering Severity Instrument for Children and Adults (Riley, 1980) or, in the case of preschoolers, The Stuttering Prediction Instrument (Riley, 1981). All were identified as stuttering by one of twelve practicing speech-language pathologists and were currently in therapy. With one exception, all parents of school-age stutterers reported preschool onset. The instrument was administered in the home or school setting. Severity was distributed across age as reported in Table I. Experience with stuttering therapy was not systematically controlled. The stuttering subjects had been in therapy for varying lengths of time with different clinicians presumably using different techniques.
Table 1. Age Distribution
of Severity Ratings of Stuttering Subjects Based on Performance on the Stuttering Prediction Instrument” or the Stuttering Severity Instrumen?’ (Most S’s were tested on the SSI.) Frequency Severity
3.0-5.9
distribution
6.7-7.4
(per age group) 8.0-8.1
I
9.1-10.11
Mild
3
4
2
3
Moderate
2
1
3
I 1
Severe U Riley, 1981. b Riley, 1980.
210
J. H. BISHOP
ET AL.
All subjects were screened and passed tests for age-appropriate articulation and language skills. Children 5 years of age and under were screened with the Coston-Reidenbach Articulation Quick Screening/Language Quick Screening Test (Coston and Reidenbach, 1978). Children 6 years and over were tested with the screening sections of the FisherLogemann Test of Articulation (Fisher and Logemann, 1971) and The Clinical Evaluation of Language Functions (CELF) Elementary Level (Semel and Wiig. 1980). A minimum CELF Total Score Performance at the 30th percentile was required for inclusion in the study.
Tasks Three manual tasks of increasing complexity were performed by all subjects: simple finger-life response (Level I), finger lift followed by a finger press (Level 2) and finger lift followed by a touch and a press (Level 3). The three vocal tasks of increasing complexity were the production of the isolated vowel “a” (Level 1); the words “a cow” (Level 2) and the words “a cowboy” (Level 3).
Procedures All data were collected at The University of South Carolina Motor Development/Motor Control Laboratory. Reaction times for all manual and vocal tasks were cued and recorded on an adaptation of the Lafayette Reaction/Movement Time Apparatus (model #63017, Lafayette Instrument Co., Lafayette, Indiana). The stimulus for all tasks was a green light of fixed intensity. A small white “ready” signal was presented prior to random prestimulus intervals (PSI) of l-2 set duration. Intertrial intervals were approximately 30 sec. The digital clock was activated by the onset of the stimulus light and stopped by release of a telegraph key (finger-lift response) or the initiation of the vowel “a,” which appeared at the beginning of each vocal response. Reaction time for initiation of vocal or manual responses was recorded in milliseconds. The child’s vocal response was detected by a throat microphone sewn to a bow tie worn by the child and positioned against the lamina of the thyroid cartilage. Output was low pass filtered and amplified to achieve maximum sensitivity to phonation rather than neck noise. The equipmental setting was designed to be nonthreatening. A black screen (60.96 cm by 35.56 cm) blocked the child’s view of the recording instrument. The child was seated on a high chair facing a table with two telegraph keys (located 46.99 cm apart) and a black box (31.75 cm by 22.86 cm) that served as a stand for the stimulus light box. Toy replicas of a cow and a cowboy were used to prompt responses for vocal tasks and the black box was turned to reveal a running deer for the “lift-touchpress” response.
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Subjects were instructed to respond as quickly as possible to the visual stimulus. Order of task complexity was randomized for each subject. All vocal tasks were presented together and all manual tasks were presented together; the order of vocal or manual presentation was by predetermined random order. The order of task complexity was preserved within task. The experimenter gave instructions specific to each task immediately preceding the task. Practice sessions were carried out until the experimenter was satistied that the child understood what he was to do and was responding without obvious hesitancy. No child exceeded a limit of ten practice trials per response condition. Subjects performed 10 trials under each experimental condition (60 trials in all). Some 3 and 4-year-old subjects only completed a minimum of five trials. If a subject lost attention or responded prematurely the trial was repeated. With the exception of the 3-year-old pair, retrials for any one condition were limited to four. A short break was provided if attention waned. Research Design and Analysis To control for unequal variances and unequal correlations among repeated measures (Finn, 1974), data were analyzed using multivariate (as opposed to univariate) repeated measures technique. The 20 matched pairs were treated as single subjects with 24 variables representing all possible combinations of task, group, and performance measure (mean, SD). Dependent variables were: mean reaction time (vocal and manual); standard deviation or variability of RT (vocal and manual); and manual/vocal ratio. The model for this study was a 4 (Age) x 2 (Group) x 2 (Task) x 3 (Complexity) mixed design with one between-subjects factor (Age) and 3 within-subjects factors (Group, Task, Complexity). Tests of sphericity confirmed the need for the use of the multivariate model. RESULTS Reaction Time Mean reaction times are shown in Table 2. Overall, reaction time decreased with age (p = 0.013). However, post hoc analysis indicated that only subjects in the 3.0-5.9 age group were significantly slower than all other age groups (p = 0.002). None of the other age group contrasts were significant. Stutterers were slower than nonstutterers (p = 0.013); VRTs were longer than MRTs (p = 0.000); and reaction time increased with increased task complexity (p = 0.003). The Group x Complexity (across modality) interaction was significant
212
J. H. BISHOP
Table 2. Grand Means over Groups,
Age, Task,
ET AL.
and Task Complexity
Mean Performance Group (Stutterers set)
vs. Nonstutterers)
Mean Performance
on All Tasks over All Ages (in
Stutterers Mean SD
Nonstutterers
0.471 0.104
Vocal vs. Manual Mean Performance Complexity
Mean SD
0.412 0.070
by All Groups over All Ages at All Levels of Vocal
Manual
0.501 0.100
0.383 0.074
Mean Performance of Four Age Groups on All Tasks at All Levels of Complexity
Mean SD Mean Performance
Age I
Age 2
Age 3
Age 4
0.609 0.162
0.409 0.078
0.379 0.050
0.370 0.056
of All Groups on All Tasks at Each Level of Complexity
Mean SD
Level I
Level 2
Level 3
0.421 0.077
0.448 0.086
0.457 0.098
Mean Manual/vocal Ratio of Stutterers vs. Nonstutterers Stutterers 0.748
on All Tasks at All Ages Nonstutterers 0.784
(p = 0.041) as is shown in Figure 1. Nonstutterers always had faster RTs than stutterers; this difference increased with task complexity. No other interactions were significant. It is important to note that interactions involving type of task (vocal versus manual) or age were not significant. Both members of two pairs of subjects demonstrated extremely poor performance on at least one task and/or required considerable deviation in procedure (fewer than ten trials per task). Therefore, a second data analysis was performed with the scores of these two pairs omitted. With one exception, results of this analysis were identical to the previous analyses (there were significant main effects for Age, Group, Task, and Complexity). However, the two-way interaction between Group x Complexity was not significant (p = 0.109).
AGE AND TASK COMPLEXITY
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213
IN CHILDREN
I-
CC
5 4oo 2 300
200
3
1
TASK
COMPLEXITY
Figure 1. Mean reaction times of stutterers of task complexity.
versus nonstutterers
at three levels
Figure 2. Consistency of performance of stutterers versus nonstutterers on vocal versus manual tasks as a function of complexity. (Solid line indicates nonstutterers, broken line indicates stutterers.) zoo-
MANUAL
VOCAL
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z 8 > iti c” 52 loo-. 2
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J. H. BISHOP ET AL.
Variability of RT Results of the multivariate repeated measures analysis for the standard deviation of RT indicated that main effects of age (p = 0.004), group (p = 0.009), and task (p = 0.039) were significant. Variability of performance decreased with increased age; RTs of stutterers were signifrcantly more variable than RTs of nonstutterers; and performances on vocal tasks were more variable than manual tasks. The three-way interaction among Group x Task x Complexity was significant (p = 0.052) and is plotted in Figure 2. The significant (p = 0.041) four-way interaction of Group x Age x Task x Complexity is shown in Figure 3. Reaction times were most variable in young stutterers (under the age of six) on the most complex vocal task (level 3). As before, a second analysis was carried out that excluded scores of two deviant pairs. Results of this analysis indicated that there was a significant main effect for age (p = 0.003), group (p = 0.034), and task complexity (p = 0.037). The two-way interaction for Task x complexity (p = 0.015) and the three-way interaction for Age x Group x Complexity were also significant.
Figure 3. Consistency of response of stutterers (S) versus nonstutteres (NS) on vocal (VOC) tasks versus manual (MAN) tasks as a function of age: Group 1 3.0-
5.9, Group 2 6.7-7.4,
Group 3 8.0-8.11,
Group 4 9.1-10.11.
400
AGE 2
5300 z n v) >
200
100
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0
ix
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300
0”
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0
1
2
3
TASK
1
COMPLEXITY
2
3
AGE AND TASK COMPLEXITY
VARIABLES
IN CHILDREN
21.5
Manual/Vocal Ratio Mean RT scores were converted to manual vocal ratios and analyzed. Manual vocal ratios did not differ as a function of age. group, or task complexity.
DISCUSSION Significant improvements in RT with age were observed for stutterers and nonstutterers on both vocal and manual tasks. Although stutterers always had slower RTs than nonstutterers, changes in vocal and manual RTs followed a parallel course of improvement/development for both groups of children. These data suggest that speech and manual processes are not independent, unrelated functions of the motor-control system at least as far as development is concerned. Also, one of the characteristics of the motor-control system of the stutterer may be a decreased or diminished capacity for speed in initiating manual and vocal responses. The manual/vocal ratios of stutterers and nonstutterers were not significantly different and essentially did not change with age. These data also point to a parallel course of development for vocal and manual reaction times for both stutterers and nonstutterers. This finding is not in keeping with increased VRT relative to MRT at older ages as suggested by Cullinan and Springer (1980), and Starkweather et al. (1984). The authors acknowledge that as this was not a longitudinal study, our age groups may represent different populations. We also acknowledge that therapy techniques that might have improved reaction time were not controlled. The effect of task complexity was different depending on whether the two “deviant” pairs of children were included. Regardless of whether the task was manual or vocal, RTs of nonstutterers were not affected by increases in task complexity whereas those of stutterers were. Because both vocal and manual RTs were similarly affected in stuttering children this points to a more generalized effect of task complexity on sensorymotor and motor-control processes in stutterers. With regard to variability or consistency of RTs, it has been proposed that if the information-processing demands of a given task are within the capacity of the system, it is likely that the system will be more consistent in repeatedly producing that same or a similar response. Data from the present study suggest that consistency of response programming was similar for older stutterers and nonstutterers on both vocal and manual tasks and that it was independent of task complexity. In contrast, variability of RTs of young stutterers on vocal tasks increased with complexity, whereas variability of performance of young nonstutterers increased with task complexity only for manual tasks. These data suggest that programming demands of all vocal and manual tasks were within the capacity of
J. H.
BISHOP ET AL.
the motor-control system of older children but were not for younger children. There appears to be support for the idea that, at least for white male stutterers, there is a predisposition toward slower sensorimotor performance that is common to both vocal and manual systems and that the differences in performance between stutterers and nonstutterers is more apparent at an early age. Reaction time is assumed to be composed of several components: stimulus recognition (time to respond to the environmental stimulus, in this case a green light); central planning or preparation for response (which includes both response selection and response programming); and motor time (a small peripheral component defined as the time from the first change in EMG to movement or response initiation). If, on the average, stutterers tend to have slower RTs than nonstutterers, one has to ask where the delay occurs and if it occurs consistently in the same component of the response production or RT process. The present study did not fractionate RT into its sensory, central (premotor), and peripheral (motor) components. No definitive statement can be made on the proportion of time devoted to sensory, central, and/or peripheral processes. Although it might be expected that older stutterers, because of increased length of stuttering experience, would be more likely to react to speech production with excess tension and thereby perform more poorly on vocal tasks than on manual tasks, current data do not support this position. Actually younger stutterers demonstrated a greater vocal/manual RT difference than older stutterers. This may indicate that the less mature system of the young stutterer reacts more to the stuttering/ speech experience than the older, more mature system. Such information encourages the trend to intervene early in the stuttering process. It implies that early reactions or constitutional predispositions put the young stutterer at a real disadvantage. The authors thank the subjects, their parents, and the referring speech-language pathologists. The authors appreciate the efforts of Susan Nickles in the preparation of the manuscript.
REFERENCES Adams, M., Freeman, F., & Conture,
G. (1984) Laryngeal dynamics of stutterers. In: Nature and Treatment of Stuttering: New Directions (W. Perkins and R. Curlee, eds.). San Diego: College-Hill Press.
Coston, G.N., and Reidenbach, E. (1978) Coston-Reidenbach Articulation Quick Screening/Language Quick Screening. Columbia, SC: Columbia Educational Resources. Cross, D.E., and Luper, H.L. (1979) Voice reaction time of stuttering and nonstuttering children and adults. Journal of Fluency Disorders, 4 59-77.
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Cross, D.E., and Luper, H.L. (1983) Relation between finger reaction time and voice reaction time in stuttering and nonstuttering children and adults. Journal of Speech and Hearing Research,
26, 356-361.
Cullinan, W.L., and Springer, M.T. (1980) Voice initiation and termination times in stuttering and nonstuttering children. Journal of Speech and Hearing Research, 23, 344-360.
Finn, J.D. (1974) A General Model for Multivariate Analysis. New York: Holt, Rhinehart, Winston. Fisher, H., and Logemann, J. (1971) The Fisher Logemann Competence. Iowa City: Houghton Mifflin. McKnight, R., and Cullinan, of Fluency Disorders,
Test of Articulation
W. (1987) Subgroups of stuttering children. Journal
12, 217-233.
Murphy, M., and Baumgartner, J. (1981) Voice initiation and termination time in stuttering and nonstuttering children. Journal of Fluency Disorders, 6, 257264.
Peters, H.F.M., Hulstijn, W., and Starkweather, C.W. (1989) Acoustic and physiological reaction times of stutterers and nonstutterers. Journal of Speech and Hearing Research,
32, 668-680.
Reich A, Till, J., and Goldsmith, H. (1981). Laryngeal and manual reaction times of stuttering and nonstuttering adults. Journal of Speech and Hearing Research, 24, 192-196.
Riley, G. (1980) Stuttering Severity Index. Tigard, OR: C.C. Publications. Riley, G. (1981) Stuttering Prediction Instrument. Tigard, OR: C.C. Publications. Semel, E.M., and Wiig, E.H. (1980) Clinical Evaluation of Language Functions. Columbus, OH: Charles E. Merrill. Starkweather, C.W., Hirshman, P., and Tannenbaum (1976) Latency of vocalization onset: Stutterers versus nonstutterers. Journal of Speech and Hearing Research,
19, 481-492.
Starkweather, C.W., Franklin, S., and Smigo, T., (1984) Vocal and finger reaction times in stutterers and nonstutterers; differences and correlations. Journal of Speech and Hearing Research,
27, 193-196.
Till, J., Reich, A., Dickey, S., and Seiber, J. (1983) Phonatory and manual reaction times of stuttering and nonstuttering children. Journal of Speech and Hearing Research,
27, 171-180.
Manuscript received July 1991; revised December 1991; accepted January 1992.