Differential contribution of working memory to auditory rhythm discrimination in stuttering and nonstuttering adults.

Stuttering is a neurodevelopmental condition characterized by involuntary disruptions in the rhythmic flow of speech. Notably, stuttering is associated with aberrant structure and function of the basal ganglia thalamocortical network. Separately, the BGTC network has been implicated in non-speech beat and rhythm perception. Supporting a link between the two sets of findings, children who stutter exhibit poorer auditory rhythm discrimination compared to non-stutterers, especially for complex rhythms without a consistently marked beat. For adults who stutter (AWS), data showing a link between stuttering and poorer auditory rhythm discrimination has been mixed. One possible reason may be that AWS have developed strategies for rhythm discrimination that leverage an alternative non-BGTC network dependent timing mechanism. One candidate from the timing literature is the use of an interval-based mechanism that involves the cerebellum. From this perspective, rhythm discrimination judgments for AWS would involve interval-by-interval duration comparisons, which should be expected to place a greater burden on working memory compared to the more automatic beat-based timing processes implemented by the BGTC network. To investigate this hypothesis, we combined data from three studies where AWS and age-matched controls performed the same rhythm discrimination and working memory tasks. Across studies, AWS, as hypothesized, showed a significantly stronger positive correlation between working memory and rhythm discrimination than controls where there were no (or very weak) correlations. Moreover, separate group comparison of rhythm discrimination performance for AWS with high and low working memory scores reveals no difference between controls and AWS with high working memory scores, but much poorer performance by AWS with low working memory scores compared to controls. These results support the view that AWS may mask difficulties in rhythm perception and an underlying impairment in beat-based timing by leveraging a distinct working memory dependent interval timing mechanism to discriminate rhythms.