Functional neuroimaging of cerebellar activation during single word reading and verb generation in stuttering and nonstuttering adults.

Articulatory discoordinations typically observed in fluent and disfluent speech of stuttering adults suggest an underlying deficiency in the precise timing needed for speech production. Positron emission tomography scans of stuttering adults showed generally higher cerebellar activations pre-treatment compared to nonstuttering control subjects. Intensive fluency treatment resulted in increased cerebellar activation during reading immediately post-treatment and a decrease to near normal levels at the 1 year follow scan. In contrast, verb generation resulted in a gradual but consistent decrease over the three scans. The results suggest that automaticity in motor and cognitive processes during speech production may need to be considered as an important factor in future investigations of stuttering.

A positron emission tomography study of silent and oral single word reading in stuttering and nonstuttering adults.

Over the last decade positron emission tomography (PET) has been used extensively for the study of language and other cognitive and sensorimotor processes in healthy and diseased individuals. In the present study, [15O]H2O PET scanning was used to investigate the lateralization and functional distribution of cortical and subcortical activity involved in single word reading in stuttering and nonstuttering individuals. Ten right-handed male stuttering adults and matched nonstuttering individuals were instructed to read individually presented single words either silently or out loud. Subtraction of functional brain images obtained during each of the two reading tasks, and during a non-linguistic baseline task, was used to calculate within-group and between-group differences in regional cerebral blood flow by means of statistical parametric mapping. Increased activation in the left anterior cingulate cortex (ACC) was observed during silent reading in the stuttering speakers but not in the nonstuttering group. Because of the hypothesized role of the ACC in selective attention and covert articulatory practice, it is suggested that the observed increased ACC activation in the stuttering individuals reflects the presence of cognitive anticipatory reactions related to stuttering. During the oral reading task, within-group comparisons showed bilateral cortical and subcortical activation in both the stuttering and the nonstuttering speakers. Between-group comparisons showed a proportionally greater left hemisphere activation in the nonstuttering speakers, and a proportionally greater right hemisphere activation in the stuttering individuals. The results of the present study provide qualified support for the hypothesis that stuttering adults show atypical lateralization of language processes.

Kinematic analysis of lip closure in stutterers' fluent speech.

An analysis of lip and jaw motion was carried out in order to evaluate previous observations on the fluent speech of stutterers and to describe possible effects of speech therapy. A strain gauge system was used to transduce lip and jaw movements during fluent repetitions of "sapapple" in adult stutterers and nonstutterers. Fifteen movement parameters were measured on lip closure for the initial /p/ sound in a group of 10 normal speakers, 10 stutterers who had no recent speech therapy, and 8 stutterers who had been through an intensive speech therapy program involving modification of speech timing. The no-therapy group and nonstutterers did not differ significantly in terms of any movement parameter. Stutterers who had been through speech therapy showed significant increases in jaw movement duration and time to peak velocity of the upper lip, lower lip, and jaw. The expected timing pattern for lip and jaw velocity peaks on lip closure (UL-LL-J) was the most frequently occurring pattern, but deviations from this pattern were observed in both stutterers and nonstutterers. The occurrence of reversals was most prevalent in the therapy group, and it was associated with increases in jaw movement duration across subjects. It is suggested that for the type of movement studied here, anomalies in stutterers' fluent speech are likely to be the result of acquired adjustments rather than properties of the speech neuromotor system that underly dysfluency.

The influence of task presentation and information load on the adaptation effect in stutterers and normal speakers.

Fourteen stutterers and 14 normal speakers read two passages differing in information value under two different conditions. Condition I provided subjects with a priori knowledge regarding the experimental limits and requirements. Condition II withheld such knowledge. Results indicate that adaptation curves for both stutterers and normal speakers were influenced by the information value of the reading passage. Less adaptation was observed with the high information than with the low information passage. The task presentation variable differentiated stutterers from normal speakers. When a priori instructions were provided to stutterers, the adaptation curve assumed a smooth, decelerating course. When a priori instructions were withheld, the curve deviated from the expected course. For normal speakers, identical adaptation trends were observed whether or not a priori instructions were provided. Stuttering adaptation is a function of both linguistic and situational variables; normal nonfluency adaptation is primarily a function of linguistic variables. Theoretical, experimental, and clinical implications are offered.

Communication disorders: a power analytic assessment of recent research.

This study assessed the relative statistical power of contemporary research in communication disorders. Results of the analysis, based upon an evaluation of two major journals, revealed overall mean power figures of 0.16, 0.44, and 0.73 for small, medium, and large effect sizes, respectively. Interdisciplinary comparisons indicated that low statistical power is not unique to research in communication disorders, but is apparent in other behavioral science areas as well. Several alternatives are offered to the researcher who will want to ensure sufficient power for his investigation on an a priori basis. The implications of this study are discussed in reference to the experimenter/clinician model.