Response Bias Modulates the Speech Motor System during Syllable Discrimination

Area of Science:

• Neuroscience
• Cognitive Science
• Psychology

Background:

• Emerging evidence implicates the speech motor system in speech perception.
• Previous studies using repetitive transcranial magnetic stimulation (TMS) showed motor cortex involvement but did not account for response bias.

Purpose of the Study:

• To investigate how response bias influences brain activity during speech perception.
• To determine if motor cortex activation during speech perception is modulated by response bias.

Main Methods:

• Functional magnetic resonance imaging (fMRI) was used to measure brain activity.
• Participants performed a speech perception task (same-different discrimination) with minimal consonant-vowel stimuli.
• Response bias was manipulated by altering the ratio of same-to-different trials and measured using criterion (C).

Main Results:

• Brain activity in a fronto-parietal network, including pre- and post-central regions, significantly covaried with changes in response bias.
• These motor and sensory-motor regions showed bias-related activation even when the auditory stimuli remained constant.
• Temporal brain regions did not show this bias-related modulation.

Conclusions:

• Motor cortex activity is sensitive to response bias in speech perception tasks.
• The findings question the direct role of the speech motor cortex in the perceptual analysis of speech, suggesting bias effects may explain previous observations.