The motor system’s [modest] contribution to speech perception

Abstract

Recent evidence suggests that the motor system may have a facilitatory role in speech perception during noisy listening conditions. Studies clearly show an association between activity in auditory and motor speech systems, but also hint at a causal role for the motor system in noisy speech perception. However, in the most compelling "causal" studies performance was only measured at a single signal-to-noise ratio (SNR). If listening conditions must be noisy to invoke causal motor involvement, then effects will be contingent on the SNR at which they are tested. We used articulatory suppression to disrupt motor-speech areas while measuring phonemic identification across a range of SNRs. As controls, we also measured phoneme identification during passive listening, mandible gesturing, and foot-tapping conditions. Two-parameter (threshold, slope) psychometric functions were fit to the data in each condition. Our findings indicate: (1) no effect of experimental task on psychometric function slopes; (2) a small effect of articulatory suppression, in particular, on psychometric function thresholds. The size of the latter effect was 1 dB (~5% correct) on average, suggesting, at best, a minor modulatory role of the speech motor system in perception.

Speech-Driven Spectrotemporal Receptive Fields Beyond the Auditory Cortex

“…Overall, this more recent research has coalesced around analysis-by-synthesis (Bever, 2010;Skipper, Nusbaum, & Small, 2005) and Bayesian inference (Moulin-Frier, Diard, Schwartz, & Bessière, 2015) frameworks in which heard (or seen) speech is, at some level, re-encoded in articulatory terms to generate perceptual hypotheses that constrain the analysis and interpretation of incoming speech sounds. While several researchers have dismissed the notion that such mechanisms are a core component of speech perception Holt & Lotto, 2008;Rogalsky et al, 2020;Scott, McGettigan, & Eisner, 2009;Venezia & Hickok, 2009), it has been acknowledged that motor speech circuits likely play a small, modulatory role in certain listening situations (Stokes, Venezia, & Hickok, 2019).…”

Effect of Bilateral Opercular Syndrome on Speech Perception

“…(Recall that these tasks are known to dissociate, as mentioned above.) Motor stimulation significantly increased errors only for the sublexical task, resulting in between 5-10% change in accuracy under noisy conditions, which approximates a 1 dB size effect (Stokes et al, 2019). The effects of motor stimulation during word comprehension affected only reaction times but not accuracy.…”

“…Accordingly, the research questions are becoming more nuanced as well, with an aim toward quantifying the magnitude of motor influence and specifying the condition(s) under which it holds (Skipper et al, 2017). For example, Stokes et al (2019) used a behavioral psychometric approach to estimate the effect size of motor interference (articulatory suppression) on minimal pair perception in noise. They reported that motor interference reduced speech perception under noisy conditions by an average of approximately 1 dB, which is to say that increasing the stimulus volume by just 1 dB was enough to overcome the perceptual decrement of motor suppression.…”

Rapid cortical plasticity induced by active associative learning of novel words in human adults

“…These routes are thought to participate in acoustic/phonological transcoding (Catani et al, 2005). The recurrent motor-perceptual interaction is known to facilitate speech perception of unfamiliar speech stimuli, e.g., distorted speech and novel or low-frequency words (Wu et al, 2014;Stokes et al, 2019). Therefore, greater involvement of the entire perisylvian network into the APW compared to the NPW response in our experiment may indicate that newly learned semantic association boosted perceptual processing of incoming novel linguistic stimuli.…”