Voice reaction time of stuttering and nonstuttering children and adults

The voice reaction time (VRT) of 5-yr old, 9-yr old, and adult stutterers and nonstutterers was investigated. Subjects initiated the sound / Λ / in response to fifty-five 1000-Hz tones of 1 sec duration. The tones were presented in five equal sets of 11 tones each with the silent intervals between the tones randomly selected to be 3, 4, 5, or 6 sec. Data analysis was based on responses 2–11 for each set. The VRTs for both the stutterers and the nonstutterers decreased significantly as an inverse function of age, with the largest decrease in reaction time occuring between 5 and 9 yr. The VRTs for the stutterers, however, were significantly slower than those of the nonstutterers at each of the three age levels. The results suggest that observed disruption in the laryngeal behavior for at least some stutterers may not result from the development of stuttering with age, but may contribute to early difficulty in the child's ability to produce fluent speech. Consideration of central factors are discussed.     

Dichotic speech perception: A comparison between stuttering and nonstuttering children

A stop consonant-vowel dichotic listening task was administered to 90 right- handed boys, 30 in each age group of 5, 7, and 9 yr. Half in each group were stutterers, half nonstutterers. Two and a half times as many stutterers as nonstutterers were found to display either a left-ear advantage (LEA) or no ear advantage (NEA). This finding suggested a greater tendency on the part of stutterers, as opposed to nonstutterers, for reversed or bilateral representation of the auditory speech areas of the brain. In addition, both stutterers and nonstutterers displayed significant developmental increases in the number of times they were able to identify both dichotic speech stimuli, thereby supporting the hypothesis of an age-related increase in children's total information processing capacity. The results are discussed in terms of the differences between stutterers and nonstutterers with respect to the issues of motor representation, cognitive modes, and higher-order linguistic processes.     

Performance differences between stuttering and nonstuttering subjects on a sound fusion task

This study investigated the possibility that there are central auditory level processing differences between stutterers and nonstutterers. The experimental subjects were eight male and three female stutterers ranging in age from 20–45 yr, with a mean age of 31.2 yr. The control group consisted of the same number of males and females, ranging in age from 20–45 yr, with a mean age of 30.1 yr. Each subject participated in a sound fusion task under three variable conditions: 1) group performance (nonstutterers vs. stutterers); 2) ears (right vs. left); and 3) lead-time presentation (0–100 msec). Statistically significant differences were found for lead-time presentation.     

Cerebral lateralization of visual stimulus recognition in stutterers and fluent speakers

Cerebral lateralization of stutterers and nonstutterers was assessed in terms of choice reaction times to stimuli presented to either the left or right visual hemifield on letter recognition and figure recognition tasks. Reaction times on both tasks were determined before and after a behavioral speech therapy program. Stutterers demonstrated a significant reduction in mean reaction times in the letter recognition task over the course of the therapy program. This change differed significantly from that obtained from stutterers in the figure recognition task. The stutterers' responses were in contrast to the responses of the nonstutterers, who showed no reduction in mean reaction times for the letter or figure recognition tasks. The results were discussed in terms of alterations in aspects of central nervous system processing as a result of participation in the behavioral speech therapy.     

Brain stem electrical responses of stutterers and normals by sex,ears, and recovery

Auditory brainstem electrical responses (BSER) of right and left ears of active stutterers, recovered stutterers, and nonstutterers, both male and female adults, were obtained at click rates of 11.1 and 71.1/sec. Latency intervals of waves I, III, and V were measured. The auditory systems of subjects were stressed using a rapid rate of 71.1 clicks/sec. The latency of wave V was used as the measure of the stress condition.Analysis of variance was used to determine statistical significances of main effects and interactions of mean BSER (waves I, III, V, and wave V in stress condition) of left and right ears of male stutterers (active and recovered), female stutterers (active and recovered), and male and female nonstutterers.With one exception, all main effects and all higher order interactions were nonsignificant. The one main effect that was significant was gender. Females have significantly faster rates of neural transmission than do males. The question was raised, does this finding contribute toward an explanation of the sex ratio in stuttering?     

Variability in the initiation of articulatory movements in the speech of stutterers and normal speakers

This study was designed to investigate the differences between stutterers and normal speakers in phonatory and articulatory timing during the initiation of fluent utterances of monosyllabic words. Electromyographic recordings of four articulatory muscles and recordings of glottal vibrations were made of repetitive utterances of a series of monosyllabic words by 15 stutterers and 17 nonstutterers. These data were analyzed in terms of average interval times between voice onset and onset of EMG activity and between onset of EMG activity in each articulator and in terms of the intrasubject variability of these durational measures. Results showed that there were no significant differences between stutterers and nonstutterers in average interval times and that stutterers, in general, were significantly more variable in their speech onset timing. Findings are discussed in terms of recent hypotheses concerning the role of timing disturbances as the main source of speech disruption in stutterers.     

Lateral stimulus-response compatibility effects in the oculomotor system.

Eye movement reaction time (RT) was measured in simple and choice RT situations in which monaural tones were presented to the left or right ear. In the choice RT conditions, tones of one frequency signaled a left looking response and tones of another frequency signaled a right looking response. In the simple RT condition, tones were presented in 2 blocks signaling right or left looking responses. RTs were measured by electro-oculogram (EOG), with electrodes placed over the outer canthus of each eye. In the choice RT condition, oculomotor RTs were faster when the tones signaling right or left looking were presented in the ears corresponding to the direction of looking than when they occured in the opposite ear. No such correspondence was present in the simple RT condition. Ss also performed a manual choice RT task. The lateral stimulus- response (S-R) compatibility effects obtained confirmed previous findings and were of the same magnitude as those obtained in the oculomotor response modality. Asymmetry in correlations between oculomotor and manual compatibility effects suggests differential hemispheric mediation.     

Reaction time for voiced and whispered /a/ in stutterers and nonstutterers

Recent research reviewed in this article suggests that stutterers' inability to initiate phonation promptly could be a significant factor in the occurence of stuttering. Since stuttering is either completely absent or markedly reduced in frequency during whisper, the present study tested the hypothesis that stutterers do not significantly differ from nonstutterers in reaction time (RT) for the initiation of whispered/a/, whereas the two groups differ significantly in RT for the initiation of voiced /a/. Ten adult stutterers and an equal number of comparable nonstutterers produced prolonged versions of the vowel /a/ using voice and whisper in response to tone stimuli. The results showed that stutteres and nonstutterers did not differ in RT for either voiced or whispered /a/. The stutterers, however, exhibited significantly longer RT to produce voiced /a/ than whispered /a/.     

Sequence initiation performance by stutterers under conditions of response competition

Male stutterers and nonstutterers were compared on their performance of a task that required tapping keys as rapidly and accurately as possible to reproduce different sequences of finger movements as soon as they had been demonstrated on a visual display panel. Testing using the right hand alone confirmed previous findings that stutterers are significantly slower than nonstutterers in initiating new movement sequences and make significantly more errors on initial sequences. Subjects were also tested on this sequence reproduction task while they performed concurrently a manual task with the left hand that required turning a knob in response to signal tones. The hypothesis underlying the study was that associated with stuttering is a dysfunction in the mechanisms regulating interhemispheric communication, and it was predicted that the concurrent task would interfere more with the sequence reproduction task performance of stutterers than with that of nonstutterers. A joint analysis of the speed and accuracy aspects of performance of the two tasks confirmed the prediction. Additional research required to clarify whether the effects are in fact due to the hypothesized interhemispheric mechanisms or to a generally greater susceptibility of stutterers to interference from any concurrent motor or cognitive activity is discussed.     

Reaction-time measures of stutterers and nonstutterers

Ten adult male stutterers and ten adult male nonstutterers participated in six reaction-time tasks designed to measure manual, acoustic, and laryngeal-region response latencies. The analysis revealed statistically significant differences between the groups for the acoustic data only. The results indicated that acoustic reaction-time differences are not accounted for by the speed of the general laryngeal response.     

Feature processing during high-rate auditory selective attention

Auditory event-related brain potentials (ERPs) and reaction times were, analyzed in a selective attention task in which subjects attended to tone pips presented at high rates-Xinterstimulua intervals [ISIs] of 40-200 msec). Subjects responded to infrequent target tones of a specified frequency (250 or 4000 Hz) and location (left or right ear) that were louder than otherwise identical tones presented randomly to the left and right ears. Negative difference (Nd) waves were isolated by subtracting ERPs to tones with no target features from ERPs to the same tones when they shared target location, frequency, or both frequency and location cues. Nd waves began 60-70 msec after tone onset and lasted until 252–350 msec after tone onset, even for tones with single attended cues. The duration of Nd waves exceeded the ISIs between successive tones, implying that several stimuli underwent concurrent analysis. Nd waves associated with frequency processing had scalp distributions different from those associated with location processing, implying that the features were analyzed in distinct cortical areas. Nd waves specific to auditory feature conjunction were isolated. These began at latencies of 110–120 msec, some 30-40 msec after the Nds to single features. The relative timing of the different Nd waves suggests that auditory feaure conjunction begins after a brief parallel analysis of individual features but before feature analysis is complete.     

Reading rates of stutterers and nonstutterers during silent and oral reading

The purpose of this study was to investigate the differences between the reading rates of stutterers and nonstutterers during both silent and oral reading of fluently spoken words. Ten adult stutterers and 14 nonstutterers were instructed to read two lists of words over four trials each. The first trial of either the first or the second list was a silent reading trial. All the other trials were oral reading trials. The word lists consisted of nouns with word lengths from two to five syllables. The dependent variables were the silent and oral reading times per word and per syllable. The major findings were that stutterers, as compared to nonstutterers, required longer reading times per word and per syllable during both silent and oral reading. These results indicate that stutterers differ from nonstutterers in the basic processing time for verbal material.     

Speech and bimanual hand organization in adult stutterers and nonstutterers

A multivariate approach was used to investigate the relationship between speech fluency and bimanual handwriting in right-handed male stutterers and nonstutterers. Handedness was determined by the Harris Test of Lateral Dominance. Subjects were required to write the numbers 1 through 12 simultaneously, as quickly as possible. Speech measures were derived from the Stuttering Severity Instrument and from a reading passage. Stutterers performed more poorly than nonstutterers on all speech measures. There were no differences in bimanual handwriting performance for the dominant hand. However, stutterers performed more poorly than nonstutterers in nondominant handwriting. There were no relationships between speech measures and bimanual handwriting for stutterers or nonstutterers. Some stutterers performed better on the handwriting task than did some nonstutterers. It is suggested that disorganization in interhemispheric integration functions may be a more fundamental problem in stuttering than is incomplete cerebral dominance.     

Effects of redundant auditory stimuli on reaction time

Auditory redundancy gains were assessed in two experiments in which a simple reaction time task was used. In each trial, an auditory stimulus was presented to the left ear, to the right ear, or simultaneously to both ears. The physical difference between auditory stimuli presented to the two ears was systematically increased across experiments. No redundancy gains were observed when the stimuli were identical pure tones or pure tones of different frequencies (Experiment 1). A clear redundancy gain and evidence of coactivation were obtained, however, when one stimulus was a pure tone and the other was white noise (Experiment 2). Experiment 3 employed a two-alternative forced choice localization task and provided evidence that dichotically presented pure tones of different frequencies are apparently integrated into a single percept, whereas a pure tone and white noise are not fused. The results extend previous findings of redundancy gains and coactivation with visual and bimodal stimuli to the auditory modality. Furthermore, at least within this modality, the results indicate that redundancy gains do not emerge when redundant stimuli are integrated into a single percept.     

Bimanual handedness in adults who stutter

25 adult stutterers and 29 nonstutterers who were right-handed as defined by a positive Laterality Quotient on the Edinburgh Handedness Inventory were compared with respect to their pattern of hand use in performing seven common tasks that involve bimanual cooperation. Among the stutterers was a higher proportion of participants who showed anomalies in how they carried out the two tasks that required synchronous manipulation by the two hands. On two other tasks that required speeded performance, the groups were similar in dealing playing cards with the right or left hands, but the stutterers were slower than nonstutterers and did not show a right-hand advantage on a task requiring removal of a nut from a bolt. The results were interpreted as indicating difficulty by stutterers in carrying out synchronously different response elements of motoric tasks.     

Temporal ordering deficits following anterior temporal lobectomy

Subjects were required to report the pitch sequence of two 10-msec tones of different frequency presented monaurally while the stimulus onset asynchrony (SOA) between the two tones was varied. The value of the SOA at which the subjects achieved an 80% correct sequence report was determined by an adaptive procedure without feedback. This measure was compared in the right and left ears, on subjects with a right or left anterior temporal lobectomy and on a normal control group. The results reveal an elevated threshold for performing temporal order judgments in the ear contralateral to the surgical lesion.     

Articulatory-laryngeal interaction in stutterers and normal speakers: Effects of a bite-block on rapid voice initiation

The purpose of this study was to investigate the effects of restricting jaw movement with a bite-block on the voice reaction times (VRT) of adult stutterers and normal speakers. Ten stutterers and ten normal speakers initiated the sound // as rapidly as possible in response to 1 KHz cues in a nonbite-block and bite-block condition. In the nonbite-block condition all responses were initiated from a mandibular “closed” position. In the bite-block condition the jaw was fixed in a position approximating average jaw displacement for production of // in a VRT task. Results showed the group mean VRTs for the stutterers were significantly longer than for the normal speakers in both experimental conditions. Group mean VRTs were also significantly faster in the bite-block than the nonbite-block condition for both groups. Investigation of individual subject data, however, revealed that unlike the normal speakers, a subgroup of stutterers exhibited atypically long reaction times and an increase in VRTs with the jaw fixed. The possible role of neurophysiological interactions between articulatory and laryngeal behavior in stuttering is discussed.     

Brainstem auditory electrical response characteristics of stutterers and nonstutterers: A preliminary report

In the present study, eight adult male stutterers and nonstutterers showed no significant latency or amplitude differences in BSERs recorded in response to monaural and binaural clicks. However, significantly greater variance was found in the stutterers' group under the monaural stimulation condition at click rates of 12/sec and 5/sec. Left and right monaural waveforms were subtracted individually from the binaural waveform. The resultant binaural interaction difference traces were examined to determine auditory tract preference for binaural stimulation. While some subjects from both groups showed no auditory tract preference, it was found that the significant variance between groups for wave V latency was attributable to the subset of stutterers without auditory tract preference. This finding is interpreted as evidence of neurological differences in stutterers' auditory processing at the brainstem level.     

Manual reaction time to linguistic stimuli in child stutterers and nonstutterers

Ten stuttering and ten nonstuttering children, ages 4–8 yr, served as subjects for a motor reaction task to simple and complex linguistic stimuli. The subjects reacted by pressing one of four panels on a touch-sensitive board that depicted the appropriate semantic relationship in response to 30 simple and complex linguistic stimuli. There was a significant increase in the reaction time of both groups with increasing linguistic complexity. No significant differences were found in the reaction time between the two groups, nor in the interaction between group and complexity. Implications regarding linguistic processing are discussed, and an “overload” hypothesis of stuttering is dispelled. It is concluded that stutterers and nonstutterers in this study did not differ in their reaction time nor in their processing time of linguistic material.     

A dual-task investigation of young stutterers and nonstutterers

Twenty right-handed grade-school stutterers and nonstutterers matched for sex, handedness, and age were the subjects of this neuromotor investigation. They were required to tap a button as rapidly as possible in a single-task control condition, in three increasingly demanding dual-task conditions in which finger-tapping and speech occured concurrently, and in a dual-task condition in which the subjects finger-tapped and vocalized the sound of a siren. The conditions were randomized, and hand order was counterbalanced. The overall tapping rate of the nonstutterers was statistically faster than that of the stutterers for both the right and left hand. Relative to the single-task silent control condition, the tapping rates of both groups decreased as the dual-task speech conditions became more demanding. However, the tapping rate of the nonstutterers was significantly faster across the speech conditions. Neither the group by hand, group by condition, or group by hand by condition interaction was statistically significant. The stutterers responded like the nonstutterers, though more slowly, providing support for the current contentions that the neuromotor system of stutterers is less robust than that of nonstutterers and more affected by the demands of speech production.