How Prior Motor States Can Shape Perceptual Decision Bias: Insights from Sensorimotor Beta Oscillations
Emerging evidence suggests that decision making is not a purely cognitive process preceding motor output but rather an embodied phenomenon in which the sensorimotor system actively shapes choice selection. Beta oscillations (13-30 Hz) over left and right sensorimotor cortex have been shown to encode motor action and exert inhibitory influence through lateralization of the post-movement rebound, biasing subsequent decisions toward responses with the other hand. This study investigated whether sensorimotor beta oscillations elicited by an isolated choice-unrelated motor action could influence a subsequent perceptual decision. Twenty-nine healthy adults (25 right-handed) completed a two-stage task while 64-channel EEG was recorded. In each trial, participants executed an initial button press with either the left or right thumb to a letter cue ("L" or "R") followed by, after a variable delay (0.5, 1.2 or 3 s), a briefly presented visual grating requiring a decision response on the orientation of the grating via a second button press. We computed the degree of beta power lateralization between left and right (pre-) motor cortical sources that was present during presentation of the grating stimulus and quantified choice bias as the threshold difference between psychometric curves fitted to left- versus right-initial response trials. Participants with stronger beta lateralization during stimulus presentation showed a greater tendency to alternate their decision response from the hand used for the initial button press and exhibited slower decision speeds. However, we failed to detect a significant group-level decision bias induced by the initial motor action, nor were there consistent within-subject correlations between decision bias and beta lateralization across delays. Following the perspective of embodied-decision making, our results partially support the influence of motor cortex activity on the choice process, while also suggesting that beta activity may serve as a trait-like index of individual susceptibility to decision bias.