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 sensorimotor cortex are known to encode movement-related activity and have recently been shown to influence behaviour in perceptual decision-making tasks through lateralization of the post-movement rebound following response execution, biasing subsequent decisions toward the alternative response hand. This study investigated whether sensorimotor beta oscillations elicited by an isolated choice-unrelated motor action influence a subsequent perceptual decision. Twenty-nine healthy adults completed a two-stage task while 64-channel EEG was recorded. Each trial began with a left or right thumb button press, followed after a variable delay (.5, 1.2, or 3 sec) by a briefly presented visual grating requiring a decision response on its orientation via a second button press. Beta activity following the initial movement was related to subsequent decision bias at both the between-subject and the within-subject single-trial level: participants with stronger beta power lateralization during decision stimulus presentation exhibited stronger alternation bias, and stronger lateralized beta power in individual trials was associated with higher alternation probability, independent of the delay between the initial movement and the decision stimulus. These results suggest that beta activity may index individual susceptibility to decision bias, while also acting as a momentary neural signal influencing alternation behaviour. Within the framework of embodied decision-making, these findings support the influence of sensorimotor beta oscillations on the choice process.