Foreperiod and stuttering severity effects on acoustic laryngeal reaction time

An earlier paper presented a model of the laryngeal reaction time (LRT) paradigm that included several factors that appeared to affect LRT values. The present study assesses the effects of two of these factors: foreperiod and stuttering severity. The former was assessed by the use of 13 foreperiod durations. The latter was assessed by classifying experimental subjects as either mild or severe stutterers. Both factors significantly affected LRT values. More importantly, these factors demonstrated a composite effect on group LRT differences. Specifically, mild stutterers' LRT values approached normal values as foreperiod increased, whereas severe stutterers' LRT values remained significantly greater than normal values at all foreperiods. Results are discussed in terms of differential posturing and/or vibration initiation deficits underlying stutterers' delayed LRT values. We caution that acoustic measurements alone are insufficient to specify fully the nature of the underlying deficits.     

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.     

Speech timing skills of normally fluent and stuttering children and adults

This study was designed to explore the speech timing skills of normally fluent and stuttering children and adults producing two sentences, ten consecutive times at basal and modified speaking rates. Spectrographic displays of subjects' utterances in both conditions were made in order to obtain consonant, vowel, pause, and utterance duration measures. Results showed that (1) the two groups of children produced speech durational values similar to those of the two adult groups and (3) there were no consistent between- and within-group differences in the basal and modified rate conditions. Findings are discussed in terms of methodological and sampling differences that exist between the present study and past research on stutterers' speech production abilities.     

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/.     

Response force is sensitive to the temporal uncertainty of response stimuli

Three experiments examined whether temporal uncertainty about the delivery of a response stimulus affects response force in a simple reaction time (RT) situation. All experiments manipulated the foreperiod; that is, the interval between a warning signal and the response stimulus. In the constant condition, foreperiod length was kept constant over a block of trials but changed from block to block. In the variable condition, foreperiod length varied randomly from trial to trial. A visual warning and response stimulus were used in Experiment 1; response force decreased with foreperiod length in the variable condition, but increased in the constant condition. This result is consistent with the hypothesis that responses are less forceful when the temporal occurrence of the response stimulus is predictable. In a second experiment with an auditory warning signal and a response stimulus, response force was less sensitive to foreperiod manipulations. The third experiment manipulated both the modality and the intensity of the response signal and employed a tactile warning signal. This experiment indicated that neither the modality nor the intensity of the response signal affects the relation between response force and foreperiod length. An extension of Näätänen’s (1971) motor-readiness model accounts for the main results.     

Voice onset time in aphasia: Thai. I. Perception

This study investigated left brain-damaged aphasic and right brain-damaged non-aphasic patients' ability to label synthetic speech continua differing in voice onset time (VOT) at three places of articulation. The language chosen for investigation was Thai, which exhibits 3 contrasting labial and apical stop categories (voiced, voiceless unaspirated, voiceless aspirated) and 2 contrasting velar stop categories (voiceless unaspirated, voiceless aspirated). Results of the labelling task indicated an impairment in VOT perception at all three places of articulation across clinical types of aphasia. Normal performance by the right brain-damaged patient indicated that deficits in VOT perception can be attributed to pathology specific to the language-dominant hemisphere. No relation was found between the aphasic patient's level of auditory language comprehension and his performance on the VOT perception task. It is suggested that the aphasics' impairment reflects a deficit in phonological processing at the linguistic level.     

An evaluation of the effects of supplemental “fluency” training during maintenance

The voice onset time (VOT) of two groups of treated stutterers and a normal-speaking group was assessed by spectrographic analysis. Both groups of stutterers had significantly slower VOT than the normal speakers. The experimental group of stutterers was given 8 wk of “fluency” training designed to remediate characteristics of speech identified as related to “tenuous” fluency. The control group of stutterers received ongoing maintenance therapy. Posttreatment VOT was assessed. The experimental stuttering group had significantly decreased their VOT in the direction of the normal-speaking group, whereas the control group of stutterers had a greater VOT between pre- and posttreatment. The implication of these results for the maintenance of fluency are discussed.     

A correlational study of stutterers' adaptation and voice initiation times

The purpose of this study was to determine the strength of the relationship, if any, between stutterers' amount of improvement in controlling phonation (voice initiation time) and their amount of improvement in stuttering during adaptation.Thirteen adult stutterers were required to participate in an adaptation task and a voice initiation time (VIT) task. The major finding was a weak, positive correlation between subjects' adaptation and their VIT difference scores. The correlation obtained, though weak, was interpreted to be informative; namely that while there is quite probably a laryngeal component in stuttering, it does not stand alone. It seems likely that the complexities of stuttering will not be fully understood until experiments include a number of potential or known dimensions of the disorder.     

Electromyographic indications of laryngeal-area activity during stuttering expectancy

Using surface electrodes, mean microvolt values of laryngeal-area muscle activity were determined for 13 male and 6 female stutterers during 10-sec periods in which single words were silently read and stuttering expectancy was indicated. No significant differences in levels of laryngeal-area muscle activity were found between periods of fluency expectancy and stuttering expectancy preceding both fluent and stuttered speech. The results were interpreted as being nonsupportive of the hypothesis that a breakdown in stutterers' laryngeal-area muscle activity occurs during moments of stuttering expectancy. In addition, the results suggest that the most common rationale for the utilization of laryngeal biofeedback procedures to enhance fluency should be questioned.     

Cortico-spinal inhibition reflects time but not event preparation: neural mechanisms of preparation dissociated by transcranial magnetic stimulation.

Changes in cortico-spinal excitability related to time and event preparation were investigated by transcranial magnetic stimulation (TMS) of the motor cortex during the foreperiod of a movement-precuing task. Subjects performed a four alternative choice reaction time (RT) task involving a button-press with the index or middle finger (FI) of the left or right hand. Advance information about the to-be-signaled response was provided by a precue, which preceded the response signal by a 1 s foreperiod. The precue either indicated the hand (right or left) or FI (index or middle) with which the response would be executed or was uninformative. TMS was delivered to the left or right cortical hand area at one of five possible times during the foreperiod: -1000, -500, -333, -166 or 0 ms prior to the response signal. Surface EMG activity from a prime mover involved in flexion of the response FIs (Flexor digitorum superficialis) was used to measure the magnitude of the motor evoked potential (MEP) elicited by TMS. Cortico-spinal excitability--as assessed by the magnitude of the MEP evoked in the target muscle contralateral to the stimulated hemisphere--progressively decreased during the foreperiod. The identity of the precued responses, however, had no effect on MEP magnitude. These results suggest that preparation to respond at a particular time inhibited excitability of the cortico-spinal tract, while advance preparation to perform specific responses affected more central structures only.     

Stutterers' voice initiation times during conditions of novel stimulation

The present experiment examined stutterers' voice initiation times (VITs) during conditions of novel stimulation. The experimenters were interested in determining how VITs varied as a function of pacing and masking. Stutterers were examined in control, pacing, and masking conditions. The results indicated that: (1) stutterers significantly improved their VITs in the pacing condition as compared with the control condition (p = 0.005), (2) stutterers had significantly faster VITs in the pacing condition as compared with the masking condition (p = 0.005), and (3) stutterers improved VITs in the masking condition as compared with the control condition (p = 0.075). These results are discussed in terms of the facilatory nature of novel stimulation in modifying speech-system functioning.     

The foreperiod effect revisited

This paper explores four factors which could be important in accounting for the discrepant results which have previously been obtained with respect to the effect of foreperiod duration on reaction time (RT). In some studies a clear effect of foreperiod duration on auditory RT has been found, in contrast to a recent finding that foreperiod duration affected visual RT but not auditory RT. By means of two experiments, the effects of practice, time-on-task, reaction task (a-reaction versus selective reaction) and signal intensity were studied. The latter variable appears to be the principal determinant of the discrepant results in that there is an interaction between signal intensity, foreperiod duration and modality. The results fit the hypothesis that signals beyond a given intensity exert an immediate arousing effect which counteracts the foreperiod effect.     

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.     

Visual signal detection and the locus of foreperiod effects

The effect of alertness on S's sensitivity to external signals was determined by varying the foreperiod in a visual signal detection task. Discriminability increased with increasing foreperiods up to an optimal foreperiod, beyond which it decreased slightly. This pattern of results parallels closely that of many foreperiod studies in which reaction time was the dependent variable. Because no speeded response was required in this signal detection task, it was concluded that alertness must be affecting an information processing stage prior to those associated with responding. Other evidence indicates that alertness does not affect sensory stages either. Alertness, by elimination, must be affecting the operation of a central stage, Posner's view of alertness which implicates the central stages is discussed.     

Stability of performances of individual stutterers on oral reading adaptation tasks

This study aimed to determine whether individual oral reading adaptation task performances are sufficiently reliable to be used as predictive indicators of improvement in stuttering behavior by testing the stability of individual stutterers' adaptation scores. Results demonstrated that all stutterers are not stable in their individual adaptation scores and therefore individual adaptation scores may be insufficiently reliable for predicting and classifying. Theoretical and clinical implications are discussed.     

Behavioral definition of minimal reaction time in monkeys

Two monkeys (Macaca mulatta) were trained to press a key after onset of a tone and to release it after a 1-sec fixed foreperiod terminated by a light. The effects of imposing temporal contingencies on key release reaction times were determined by reinforcing only those releases whose latencies from the light fell within a “payoff band”, two time limits 50 msec apart located at some delay following the light. Over several days this delay was first gradually decreased, shortening the interval between light and payoff band, and then gradually increased again. For each delay, the median reaction time and a measure of variability were obtained from the latency distribution. For both animals, median latency could be decreased to 180 msec with the variability remaining small. Moving the payoff band still closer to the light resulted in further decrease in median latency but an abrupt increase in variability. This is in agreement with a model for simple reaction time derived from human research which suggests that this increased variability results from the inclusion of high-variability foreperiod time estimations in the latency distribution. These results indicate that interpretation of monkey response latencies as “minimal reaction times” requires examination of temporal reinforcement contingencies and variability of latencies.     

Retrieval processes in recall

A reaction time (RT) paradigm was developed to study retrieval processes in paired associate (PA) recall. Prior to the experimental session, subjects learned lists of PAs (varying in length from three to 24 pairs); during the experimental session, subjects' RT to say the response word from the onset of a visually presented stimulus word was measured. The implications of several classes of retrieval models were discussed in the context of this paradigm. The shape of the RT-list length function, practice, and sequential effects were all of interest in distinguishing among models. Four experiments were reported which were designed to (1) establish the baseline effects in this paradigm, (2) determine which of these effects should be attributed to the retrieval stage of processing, and (3) investigate the effect of semantic memory in this task. Results suggest that simple serial scanning models are inadequate to handle the data from this task. Strength, direct-access, or parallel processing models, on the other hand, seem to capture the qualitative effects present in our experiments. When a strength model was formalized and fit to the data from Experiment I, it was found that a two-trace version gave good quantitative fits while a one-trace version did not, suggesting that both short- and long-term memory independently contribute in this task.     

The effective time course of preparation

In reaction time (RT) research on nonspecific preparation, the preparation period is often identified with the foreperiod (FP), the interval between the offset of a neutral warning stimulus (S1) and the onset of the reaction stimulus (S2). However, the “effective preparation period” may be longer than FP: nonspecific preparation may start prior to FP (e.g., at the onset of S1) and/or continue after it (i.e., in parallel with the reaction process). In four experiments, we factorially varied FP and an additional factor (S1-duration; S2-luminance; stimulus–response compatibility) that probed the effective preparation period outside the bounds of FP. By examining how equivalent RT–FP functions obtain at the different levels of the additional factor, we showed that nonspecific preparation (1) starts at the onset of S1 for brief FPs but at its offset for longer FPs and (2) continues in parallel with S2-encoding but stops prior to response selection.     

VOT discrimination by four to six and a half month old infants from Spanish environments.

Thirty 4–6.5 mo-old-infants from monolingual Spanish speaking homes were tested for discrimination of bilabial stop consonants differing in VOT. Discrimination was determined by the habituation and dishabituation of the orienting reflex as indexed by cardiac deceleration. Subjects were placed in one of three groups of ten subjects each. The three groups were used to determine whether bilabial stops with VOT values of ?60 and ?20 msec, ?20 and +20 msec or +20 and +60 msec could be discriminated. Subjects were presented eight trial blocks of ten repetitions of a CV syllable; these eight trial blocks were followed by two trial blocks of ten repetitions of a different CV syllable. The only difference between the CV syllables presented during the first eight and the last two trial blocks was the VOT value of the bilabial stop consonants. Subjects in the ?20 and +20 msec group showed no signs of being able to discriminate these stimuli while the subjects in the ?60 and ?20 msec group and the +20 and +60 msec group did. These results correspond to those reported for infants from English speaking families but do not correspond to those reported for Spanish speaking adults. Thus, the failure to find evidence of discrimination in the ?20 and +20 msec group suggests that experience has little effect in determining bilabial stop phonetic categories in 4–6.5 mo-old infants.     

Dissociative patterns of foreperiod effects in temporal discrimination and reaction time tasks

This study examined whether the process of temporal preparation for a target stimulus is the same regardless of the task required by the target stimulus. To this end, the same variable-foreperiod design was used in a temporal discrimination task (Experiment 1) and a reaction time task (Experiment 2). In Experiment 1, both temporal sensitivity and perceived duration increased as a function of foreperiod, whereas in Experiment 2, foreperiod did not influence reaction time. Furthermore, both temporal sensitivity and perceived duration revealed an asymmetric sequential effect of foreperiod, but the pattern of this effect was opposite to the pattern observed in the reaction time task. Together these dissociative patterns of foreperiod effects suggest that the mechanism of temporal preparation depends on the task required by the target stimulus.