Vocal changes in stutterers and nonstutterers during high- and low-pitched speech

This study was conducted to provide an indirect test of Wingate's “modified vocalization” hypothesis. In this formulation, the improved fluency that stutterers experience in various novel conditions is attributed to changes in the key correlates of stress, namely, fundamental frequency, vocal SPL, and rate.Normal speakers and stutterers read aloud in an habitual condition following instructions to read at higher- and lower-than-normal pitches. Objective measures were taken of subjects' fundamental frequency, fundamental frequency deviation, vocal SPL, and fluent reading rate. Disfluences were also counted. Findings showed that both stutterers and normals altered several features of voicing from the habitual to the two experimental conditions. Significant condition main effects emerged for fundamental frequency deviation, vocal SPL, fluent reading rate, and disfluency. The only meaningful between-group difference noted showed that the stutterers were more disfluent than the normals across all conditions. Results were interpreted as supporting Wingate's “modified vocalization” position and were discussed relative to how the vocal changes observed might act to promote fluency.     

Fluency breaks in older speakers: Implications for a model of stuttering throughout the life cycle

In order to test a model describing the occurence of fluency breaks throughout the life cycle, spontaneous speech samples of 40 nonstutterers and 4 stutterers above the age of 50 were perceptually analyzed. Fluency breaks were classified into categories of formulative or motoric breaks. The results supported research, noting an increase in formulative fluency breaks (especially fillers and interjections) for older speakers. There was, however, a significant decrease in the occurence of formulative fluency breaks during the final years of late adulthood. No change was found in the occurence of motoric fluency breaks in the nonstuttering speakers. Stuttering speakers had significantly less formulative breaks and significantly more motoric breaks than nonstuttering speakers.     

Auditory processing and perceptual abilities of “organic” and “functional” stutterers

The present investigation was undertaken to determine whether significant differences in auditory processing and perceptual abilities exist between (1) stutterers as a supposedly homogeneous group when compared with controls, (2) two differentiated subgroups of stutterers, and (3) either of the stuttering subgroups when separately compared with controls. Dichotic listening and masking level difference (MLD) tasks were administered to the two groups of school-age stutterers and an age-matched nonstuttering control group. Stuttering subjects were differentiated into “organic” and “functional” subgroups on the basis of neuropsychological test performances. Organic stutterers performed significantly poorer than did controls on one MLD experimental condition. Functional stutterers performed more like control subjects than like organic stutterers.     

Voice initiation and termination time in stuttering and nonstuttering children

Voice initiation time (VIT) and voice termination time (VTT) was measured in seven stuttering and eight nonstuttering children ranging in age from 4 yr, 6 mo to 6 yr, 10 mo. The experimental task was the production of /a/ in response to a 1000-Hz pure tone. Voice initiation time was defined as the period of time elapsing between the onset of the auditory stimulus and the onset of the subject's response of /a/, as displayed on an oscilloscope. Voice termination time was defined as the latency between termination of the stimulus tone and the point at which the oscilloscopic signal decreased by 90%. No statistically significant differences were found between the two groups with respect to either VIT or VTT. In addition, no apparent relationships were present among VIT, VTT, or stuttering severity.     

Equivalence relations between visual stimuli: the functional role of naming

The functionality of verbal behavior in equivalence class formation was demonstrated by training 30 verbally able adults using different combinations of the same easily nameable, yet formally unrelated, pictorial stimuli. Match-to-sample baselines for four four-member classes were established sequentially (i.e., AB-BC-CD), with participants in the rhyme condition trained to select comparisons whose normative names rhymed with those of the samples. For the orthogonal condition, class rearrangement was such that on every trial all available comparisons' names rhymed with each other, but not with the name of the sample. In the diagonal condition, stimuli were allocated pseudorandomly as samples and comparisons. Although all participants maintained baseline discriminations prior to emergent testing, equivalence was confined almost exclusively to the rhyme condition, in which it was ubiquitous. These participants also required less training than those in the control conditions, among whom effects of nodal distance were observed most strongly. Subsequent testing presented participants with no-reinforcement trials involving novel pictorial stimuli, in which one of the available comparisons' names always rhymed with that of the sample. All rhyme participants consistently selected these comparisons. Results indicate that visual stimuli are named, that the phonological properties of those names can influence equivalence class formation, and that the emergence of untrained discriminations may, under certain circumstances, be rule governed.     

Stimuli, reinforcers, and behavior: an integration

We propose that a fundamental unit of behavior is the concurrent discriminated operant, and we discuss in detail a quantitative model of the concurrent three-term contingency that is based on the notion that an animal's behavior is controlled to differing extents by both stimulus—behavior and behavior—reinforcer relations. We show how this model can describe performance in a variety of experimental procedures: conditional discrimination and matching to sample, both with and without reinforcement for responses that are traditionally identified as errors; conditional discrimination with more than two stimuli and choice alternatives; delayed matching to sample and delayed reinforcement in matching to sample; second-order and complex conditional discrimination; and multiple and concurrent schedules. Although the model is incomplete in its coverage, and may be incorrect, we believe that this conceptual approach will bear fruit in the development of behavior theory.     

Discrimination of multidimensional geometrical figures by chickens: categorization and pattern-learning

Japanese bantam hens were trained to discriminate between geometrical figures varying along four integral dimensions. Only one dimension predicted food: selections of sharp-cornered figures were reinforced, while selections of rounded figures were not. In experiment 1, hens were subsequently trained to discriminate between nine figure pairs in a simultaneous discrimination task. Because single pairs contained multiple redundant cues, whereas the relevant dimension was obvious only across stimulus pairs, the results revealed effects of both generalization and reversal learning. Accordingly, learning speed was enhanced for later discriminations. Experiment 2 tested the hens’ transfer performance to unknown pairs, following experience of 9 or 18 figure pairs. Four of seven hens showed reliable transfer after experience with 9 figures, but only three showed transfer after experience with 18 figures, indicating lower transfer with higher number of stimulus pairs learned. In experiment 3, hens were trained to discriminate 27 figure pairs. Discrimination ratios further decreased and the groups of pairs differed significantly in their ratios of discrimination. Individual hens’ pecking behaviour was analysed in relation to each dimension of single figures and in relation to relative differences in the levels of dimensions between paired figures. Hens were shown to be oriented towards irrelevant information and more towards relational and configurational than elemental and dimensional aspects. The results are discussed in the biological context of individual recognition in chickens’ dominance hierarchies, in which we suppose that chickens identify individual flock mates by representation of their visual pattern rather than by single characteristics. Received: 18 September 1998 / Accepted after revision: 23 December 1998     

Reduction of stimulus overselectivity with nonverbal differential observing responses

Three individuals with mental retardation exhibited stimulus overselectivity in a delayed matching-to-sample task in which two sample stimuli were displayed on each trial. Intermediate accuracy scores indicated that participants could match one of the samples but not both of them. Accuracy in a baseline condition was compared to accuracy with a differential observing response procedure. This procedure prompted participants to make simultaneous identity-matching responses that required observation and discrimination of both sample stimuli. These observing responses were never followed by differential consequences. When observing responses were prompted, participants' accuracy scores improved. In a return to the baseline condition, when differential observing responses were no longer prompted, accuracy returned to intermediate levels. The results show that stimulus overselectivity can be greatly reduced by a behavioral intervention that controls observing behavior and verifies discrimination, but that exposure to such procedures alone may be insufficient for lasting benefits.     

Quantitative and methodological aspects of stimulus equivalence

The number of different ways of linking stimuli in the training phase of a conditional discrimination procedure designed to teach equivalence relations has hitherto been underestimated. An algorithm from graph theory that produces the correct number of such different ways is given. The establishment of equivalence relations requires transitive stimulus control. A misconception in a previous analysis of the conditions necessary for demonstrating transitive stimulus control is indicated. This misconception concerns responding in an unreinforced test trial to a negative rather than a positive comparison stimulus. Such behavior cannot be attributed to discriminative control by degree of association with reinforcement if the negative comparison stimulus has been less associated with reinforcement than the positive comparison stimulus in an antecedent training phase.     

Protocol analysis of the correspondence of verbal behavior and equivalence class formation.

In two equivalence experiments, a "think aloud" procedure modeled after Ericsson and Simon's (1980) protocol analysis was implemented to examine subjects' covert verbal responses during matching to sample. The purpose was to identify variables that might explain individual differences in equivalence class formation. The results from Experiment 1 suggested that subjects who formed equivalence classes described the relations among stimuli, whereas those not showing equivalence described sample and comparison stimuli as unitary compounds. Because Experiment 1 only demonstrated a correlation between describing stimulus compounds and the absence of equivalence classes, a second study was conducted. In Experiment 2, equivalence class formation was brought under experimental control through pretraining manipulations that facilitated responding either to stimulus compounds or to relations among stimuli. The results demonstrated that a history of describing stimulus compounds, when compared with describing the relations among the stimuli, interfered with the emergence of stimulus equivalence. These findings clarify individual differences in stimulus equivalence. They also demonstrate the utility of analyzing verbal reports to identify possible variables that can be manipulated experimentally.