Communication is dependent as much on what one says (segmental speech) as on how one says it (prosody). Dysarthria is the most prevalent neurologic communication disorder and has congenital and acquired etiologies. Since both segmental and prosodic aspects of speech production are often compromised in dysarthria, it can profoundly hinder spoken communication. Historically, dysarthria research has primarily focused on segmental errors observed in speakers with acquired impairments, which has led to the current taxonomy and therapeutic interventions. Recent work has begun to investigate the nature of prosodic impairments in dysarthria and has revealed that prosodic deficits in congenital populations do not conform to conventional descriptions of dysprosody in acquired dysarthria. Specifically, speakers with congenital dysarthria tend to yield exaggerated, or otherwise atypical prosody while those with acquired dysarthria exhibit dampened or restricted modulation of typical contrasts. These differences in prosody production have not been reconciled since acquired and congenital groups are often studied separately using different stimuli and tasks, and the underlying cause of production differences is unknown. However, typical speech development, including prosody, is a partially closed-loop system in which learning is influenced by sensorimotor feedback. Given a motor disorder beginning in childhood, and known effects of production on perception, it is plausible that prosody is improperly learned during development for those with congenital dysarthria, but not for those with acquired (post-developmental onset) dysarthria. Understanding the origin of prosodic production differences between these groups is critical for delivering tailored interventions. The proposed work is the first to investigate the effect of impaired sensorimotor feedback during development on learning and producing prosody. Major innovations include 1) the study of perception-production interactions in congenital and acquired subgroups using the same stimuli and tasks for objective comparison and 2) the use of a novel non-vocal task to dissociate vocal motor execution deficits from prosodic knowledge differences. Experiment 1 investigates prosodic perception by examining the ability to classify utterances varying in prosodic contrast magnitude. Experiment 2 examines perception-production interactions by comparing vocal imitations to productions via a non-vocal, visuo-spatial interface (Prosodic Marionette). These interconnected experiments will provide a more complete understanding of prosody in dysarthria. Resulting advances have the potential to fuel new diagnostic and intervention practices that account for the impact of developmental experience on perceiving and producing prosody and may spark new lines of inquiry into whether similar factors are at play in segmental impairments in dysarthria.
Variations in timing and intonation of speech (i.e., prosody) are disrupted in dysarthria, a prevalent speech disorder resulting from congenital or acquired neurological conditions, in ways that impede communication. The proposed work challenges existing clinical practice which assumes that prosodic impairments in dysarthria result from motor deficits alone, to account for the impact of development on speech motor learning. Findings will inform new treatments that target differential deficits in speakers with congenital and acquired dysarthria, enabling more effective communication and thereby improving access to fuller educational, employment and social opportunities.
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