Ben Parrell, PhD – Slide of the Week

Ben Parrell, PhD – Slide of the Week

Title: Correction for self-produced errors is intact in individuals with cerebellar ataxia but is not reduced when auditory feedback is unavailable.

Legend: Our previous work has shown that when individuals with degenerative cerebellar ataxia are presented with perturbations to the auditory feedback they hear while speaking, they produce larger compensatory responses for these perturbations than age-matched controls. This suggests these individuals may rely more on auditory feedback control during normal speech than neurobiologically typical individuals. Here, we test this using unaltered feedback by measuring vowel centering (A), the change in vowel variability from vowel onset (teal) to vowel midpoint (orange). This reduction has been hypothesized to be driven at least partially by auditory feedback-based control. To test this, we additionally included a masking condition where auditory  feedback was eliminated through playing loud (~85 dB) speech-shaped noise to the participants over headphones. Results show that individuals with ataxia produce vowels that are longer (B) and more variable (C) than controls, consistent with typical descriptions of this disorder. We found no evidence for increased centering in individuals with ataxia (D), even when controlling for the fact that these individuals were more variable overall (E and F).

Citation: Parrell B, Ivry R, Nagarajan S, Houde J (in press). Intact correction for self-produced vowel formant variability in individuals with cerebellar ataxia regardless of auditory feedback availability. Journal of Speech, Language, and Hearing Research.

Abstract: Purpose – Individuals with cerebellar ataxia (CA) caused by cerebellar degeneration exhibit larger reactive compensatory responses to unexpected auditory feedback perturbations than neurobiologically typical speakers, suggesting they may rely more on feedback control during speech. We test this hypothesis by examining variability in unaltered speech. Previous studies of typical speakers have demonstrated a reduction in formant variability (centering) observed during the initial phase of vowel production from vowel onset to vowel midpoint. Centering is hypothesized to reflect feedback-based corrections for self-produced variability, and thus may provide a behavioral assay of feedback control in unperturbed speech in the same manner as the compensatory response does for feedback perturbations. Method – To comprehensively compare centering in individuals with CA and controls, we examine centering in two vowels (/i/ and /ɛ/), under two contexts (isolated words and connected speech). As a control, we examine speech produced both with and without noise to mask auditory feedback. Results – Individuals with CA do not show increased centering compared to age-matched controls, regardless of vowel, context, or masking. Contrary to previous results in neurobiologically typical speakers, centering was not affected by the presence of masking noise in either group. Conclusions – The similar magnitude of centering seen with and without masking noise questions whether centering is driven by auditory feedback. However, if centering is at least partially driven by 2 auditory/somatosensory feedback, these results indicate that the larger compensatory response to altered auditory feedback observed in individuals with CA may not reflect typical motor control processes during normal, unaltered speech production.

About the Lab: The Speech Motor Action + Control Lab investigates the human capacity to produce speech using behavioral, computation, and neurological methods. Our current projects focus on the role of the cerebellum in speech motor control and speech disorders associated with cerebellar damage by using computational models to understand the architecture of the speech motor system and investigating how speech motor control is updated and altered through various types of learning.

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