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. Children who stutter also exhibit poorer auditory rhythm discrimination compared to peers who do not stutter, especially for complex rhythms without a consistently marked beat, suggesting a potential link between stuttering and non-speech rhythm perception. For adults who stutter (AWS), however, data supporting a link between stuttering and poorer auditory rhythm discrimination has been less conclusive. One possible reason may be that AWS have developed strategies for rhythm discrimination that leverage a distinct timing mechanism compared to non-stuttering adults. Consistent with this possibility, there is a well-established theoretical distinction in the timing literature between an automatic beat-based timing mechanism and a more controlled interval-based timing mechanism where a key element of the latter is a working memory component. From this perspective, one hypothesis is if AWS have a deficit in beat-based timing they may leverage the controlled interval-based timing mechanism to make rhythm discrimination judgments. If so, then interval-by-interval comparisons associated with interval-based timing would be expected to place a greater burden on working memory compared to automatic beat-based timing, which in contrast does not have a working memory component. 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 capacity, but much poorer performance by AWS with low working memory capacity. These results support the view that AWS may mask difficulties in rhythm perception associated with an underlying impairment in beat-based timing by engaging a distinct working memory dependent interval timing mechanism to discriminate rhythms.