Differential contributions of domain-general cerebellar timing mechanisms to temporal deficits in ataxic dysarthria

点击翻译按钮获取中文摘要

Project Summary/Abstract Spoken language uses precise sub-second timing to mark phonemic contrasts, lexical stress differences, and phrasal boundaries, among other distinctions. Ataxic dysarthria is a speech motor disease caused by damage to or degeneration of the cerebellum and is linked to a variety of temporal deficits, including reduced contrast between temporal categories in speech and irregular speech rate and rhythm. These symptoms result in decreased speech naturalness and intelligibility, significantly impacting quality of life. While the temporal symptoms of ataxic dysarthria are well established, their underlying causes are poorly understood and there are currently no evidence-based treatments to improve speech intelligibility and naturalness in this population. The experiments in this proposal test how impairments to two domain-general functions of the cerebellum lead to specific subsets of temporal deficits in the speech of individuals with ataxic dysarthria. In the first aim, we test how damage to the domain-general timing function contributes to deficits in producing categorical temporal contrasts. The cerebellum is involved in the control of event timing, which deals with the duration of single even or multiple irregular events, but not in relative timing, which deals with the timing of multiple regular events. This leads to differential impairments in the perception and production of different types of timing tasks. We use a suite of perceptual and production tasks in both speech and non-speech domains to establish which aspects of speech timing are controlled by event timing. To test the hypothesis that the control of event timing largely affects categories but not prosodic characteristics, we also compare performance on these tasks with evaluations of rhythmic deficits in speech. In the second aim, we test how damage to the maintenance of forward models and consequent increased reliance on feedback lead to altered speech rhythm and overly variable segment durations. Speakers continuously monitor their own speech to ensure that they are accurately producing speech targets; individuals with cerebellar damage show increased dependence on temporally delayed feedback to correct ongoing movements, rather than relying on accurate forward models of production. We use two altered auditory feedback studies to test the temporal effects of perceived errors in vowel target attainment. We determine the extent to which reliance on feedback for spatial accuracy disturbs temporal accuracy. We also establish the relationship between the magnitude of temporal disturbances in these experiments and overall spatial and temporal inaccuracy in speech. The proposed studies will establish the respective contributions of domain-general timing impairments and changes in feedback use to temporal deficits in ataxic dysarthria. This is a critical first step towards the development of therapies that target the specific impairments that result in reduced naturalness and intelligibility in this population.