Rapid Motor Inhibition as a Mechanism to Prevent Outdated Movements.

Sudden environmental changes can render planned hand movements suboptimal or even counterproductive. To prevent the execution of outdated motor plans, the motor system may transiently inhibit actions following salient changes, allowing time to evaluate alternatives. While such a mechanism is well established for eye movements, its applicability to hand movements remains unclear. Here, we present findings from three online behavioral experiments and two lab-based replications designed to probe key features of this mechanism in manual responses: reflexive inhibition, temporal precedence, complete movement updating, and sensitivity to saliency. Participants of either sex performed rapid sequential tapping movements toward onscreen targets. At an unpredictable time, either a relevant change (a target displacement) or an irrelevant change (a brief luminance flash) occurred. We measured movement initiation rates following these changes and compared them with a no-change baseline. A significant transient inhibition of movement initiation followed both relevant and irrelevant changes. This inhibition preceded observable updates to the movement plan. At the time of inhibition release, the update to a movement plan was complete. Across experiments, we observed stronger inhibitory effects for more salient changes. The lab-based replication confirmed that the latency of this inhibitory response aligns with visuomotor reaction times. These results support the existence of a general-purpose, rapid inhibitory mechanism in hand movements analogous to inhibition in the oculomotor system. We propose that such inhibition provides a reflexive, domain-general safeguard against obsolete actions following unexpected changes.