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Hearing and Donuts (Brain and Bagels) Seminar
September 16, 2022 @ 8:30 am - 9:30 am
Parrell (SMAC) and Niziolek (BLAB) Labs
Communication Sciences and Disorders & Waisman Center
University of Wisconsin
Topic: Speech Variability is Mediated by Auditory Error Sensitivity
Although movement variability is often attributed to unwanted noise in the motor system, recent work in reaching has demonstrated that variability may be actively controlled. Our recent work examined how variability may be regulated during speech production. To do so, we assessed the effects of auditory feedback manipulations that modulate perceived speech variability, shifting every production either towards (inward-pushing) or away from (outward-pushing) the center of the distribution for each vowel. Results showed that speakers adjusted their produced vowel formant variability when exposed to real-time auditory perturbations that increase (outward-pushing) or decrease (inward-pushing) their perceived variability, suggesting that speech variability is actively regulated (Tang et al., 2021). Simulations using a state-space model of motor behavior identified two distinct mechanisms that could lead to the observed increase in variability: a direct increase in controlled variability (equivalent to relaxing requirements for precision) or an increase in the sensitivity to auditory errors, which would amplify the corrective changes from one trial to the next.
We then aimed to distinguish these mechanisms by examining how these perturbations affect neural responsiveness to errors as measured by magnetoencephalography (MEG). Based on the model simulation, we hypothesize that exposure to the outward-pushing perturbation (but not the inward-pushing perturbation) will result in an increased sensitivity to auditory error. In each of three MEG sessions (control, inward-pushing and outward-pushing perturbation, order counterbalanced), participants produced and listened to playback of the stimulus words. As a neural measure of auditory error sensitivity, we use the magnitude of speaking-induced suppression (SIS). SIS is a measure of the reduction in the auditory evoked response (M100) to subjects’ own speech as compared to the response to playback of the same acoustic stimuli, and is thought to arise from the cancellation of incoming auditory feedback during speaking by a prediction of that feedback. Preliminary results suggest that auditory cortical responses to self-produced speech are less suppressed after perturbations that increase perceived variability (outward-pushing), supporting our hypothesis that the increase in produced variability induced by this perturbation is mediated by a change in auditory error sensitivity.
Tang, D-L., Parrell, B; Niziolek, C. A., (under revision). Variability is actively regulated in speech. bioRxiv DOI: https://doi.org/10.1101/2021.10.08.462639.