Goal-Directed Action Planning Modulates Surround Suppression in the Visual System.

Action planning has been traditionally viewed through the lens of motor command specification. However, converging evidence indicates planning also modulates early cortical sensory systems. While previous studies mainly focused on the modulation to a single target object, it remains unclear how action planning modulates the spatial interaction between target and flankers in a cluttered scene. Here we directly tested this using EEG with frequency tagging to measure visual surround suppression-a key cortical mechanism for object segregation-while participants (22 females, 14 males) planned to grasp a target among flankers. We hypothesized that surround suppression, essential for distinguishing the target from distractors, would be enhanced when planning to grasp the target compared with planning a nontarget-directed action where segregation is less critical. Further, based on evidence suggesting that surround suppression when "executing" a grasping movement is greater for dominant than nondominant hand, we predict that this specificity should likewise exist during "planning". Confirming our predictions, EEG results demonstrated that planning a grasp significantly amplified surround suppression relative to planning a simple key release. This enhancement was additively modulated by target relevance and hand dominance, being strongest when planning a dominant-hand grasp. Crucially, a control task (planning a perceptual judgment) elicited no such suppression, supporting the action specificity of this sensory tuning. These results provide neural evidence at the level of visual mechanisms that action preparation actively and selectively refines early sensory processing for efficient goal-directed action.