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 To prevent the execution of outdated motor plans, the motor system may transiently inhibit actions following salient changes, allowing time to evaluate alternatives.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 to 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. Significance Statement As we act within dynamic environments, sudden changes can invalidate our planned movements. In such cases, rather than relying on continuous sensorimotor integration, the brain may employ a different mechanism: the rapid inhibition of potentially outdated actions. Our studies show that the human motor system exhibits abrupt, non-selective inhibition in response to unexpected changes. This response occurs before the selection of a new action, suggesting a central, preemptive control process. These findings highlight an automatic, stimulus-driven mechanism that interrupts ongoing motor activity. This work advances our understanding of how the brain prioritizes error prevention over movement execution in action planning, with implications for models of sensorimotor control.
Kuper et al. (Tue,) studied this question.