The cadence of social communication: Unraveling speech rhythm and underlying neural, motor, and genetic mechanisms. - Project Summary/Abstract Successful communication is dependent on a multitude of intricately coordinated skills that facilitate connections between interlocutors, including prosody, or the rhythm, rate, and intonation of speech. Speech rhythm, specifically, is critical for communicating intent and enhancing speech comprehension through predictable, regularly-timed beats. Without rhythm, speech lacks the temporal guideposts that instruct the listener what to listen for and when, leading to miscommunications (i.e., “let’s eat, mom!” vs. “let’s eat mom!”). Amongst autistic individuals and their first-degree relatives, prosody, and speech rhythm specifically, has been identified as a salient contributor to social communication differences. Parallel findings have been reported in fragile X syndrome (FXS; the leading monogenetic cause of autism) and in FMR1 premutation (PM) carriers, who show similar but less striking rhythmic variability. Together, these findings suggest a shared, heritable, neurobiological mechanism underpinning speech and higher-order language skills impacted in autism, and linked to a known autism risk gene. Importantly, recent acoustic research has revealed links between rhythmic variability, speech rate, and FMR1-mediated molecular-genetic variation in females with FXS, who are largely understudied in FXS research and tend to show less cognitive impairment than males. Notably, recent work in autism has pointed to differences in cortical processing of continuous speech, whereas studies in FXS and the PM have identified articulatory abnormalities, as potential perceptual and speech-motor mediators of speech-rhythm differences, but their associations with speech rhythm remain largely unexplored. As such, evaluating the perception and production of continuous speech in relation to speech rhythmicity in FMR1-mediated conditions is a critical next step towards understanding the role of FMR1 in autism-related phenotypes. Further, exploring speech rhythm in females with FXS and the PM will allow for greater characterization of the neural and speech-motor mechanisms contributing to a broad spectrum of FMR1-mediated speech and language profiles, from clinically to sub-clinically affected, without the confounding impact of intellectual impairment. Given mounting evidence of impacted cortical speech processing and speech-motor differences in autism, as well as speech-motor incoordination in FMR1 conditions, we hypothesize that speech rhythmicity may be disrupted across in females with FXS and the PM and contribute to pragmatic language differences. Moreover, we hypothesize that differences in speech rhythm are differentially mediated by domain-general rhythmicity, speech-motor coordination, cortical speech perception, and rooted in underlying variation in FMR1-mediated molecular-genetic correlates. If completed, the proposed study has potential to provide key insights into the role of a known genetic mutation in the autism language phenotype with relevance to future behavioral interventions.
