Speech Impairment in Cerebellar Ataxia Affects Naturalness More Than Intelligibility

The purpose of this analysis was to document intelligibility and naturalness in ataxia, a neurological condition that results from cerebellar damage. The cerebellum is important for normal speech production to scale and coordinate articulatory and laryngeal movements. The disruption of these cerebellar mechanisms has unique implications for how intelligibility and naturalness are affected in ataxia. The results of research on speech in ataxia have important clinical implications for assessment and treatment of individuals with ataxic dysarthria. Speech samples from 27 participants with ataxia and 28 age- and sex-matched control participants were assessed by nine speech-language pathology graduate students for intelligibility and naturalness. Intelligibility was measured as the percentage of words transcribed correctly, and naturalness was assessed as a subjective rating on a seven-point interval scale. Both intra- and inter-rater reliability were moderate to high for both intelligibility and naturalness. Speech intelligibility and naturalness were robustly decreased in the ataxia group compared to the control group; however, the difference was greater for measures of speech naturalness. There were robust relationships among dysarthria severity, length of diagnosis, and speech naturalness in speakers with ataxia, but there were no other robust effects for age, sex, or impact on quality of life for intelligibility or naturalness. Speech naturalness was more impaired than intelligibility in speakers with ataxia. Impaired naturalness can have debilitating consequences for communicative participation, effectiveness, and quality of life. Assessment and treatment for ataxic dysarthria should include aspects of prosodic control for speech naturalness.