An inhibitory mechanism prevents outdated actions of eye and hand movements

Sequences of saccadic eye movements are inhibited after salient changes, even when they are task-irrelevant [Reingold & Stampe, 2002]. This phenomenon of saccadic inhibition is considered an adaptive mechanism, preventing outdated movements while the change is evaluated [Stanford & Salinas, 2018]. Here, we show that inhibition extends to sequences of hand movements, implying that a global signal inhibits action execution across motor systems until the evaluation of changes is complete and new movement plans have been established. In two experiments executed online on participants’ smartphone touchscreens, we evaluated hand movement rates after task-relevant and task-irrelevant changes. Participants collected a series of six randomly jittered movement targets by tapping on them. The task-relevant change (shown in 50% of all trials) was a displacement of the movement targets. The task-irrelevant change (shown in an independently chosen 50% of all trials) was a brief flash. The location and contrast of the flash varied between the experiments. Movement rates dropped below baseline after both task-relevant and irrelevant changes. Actions after the inhibition reflected a complete movement update, never an average of two responses. This suggests that the evaluation of the change continued throughout the inhibition. In a lab-based replication of the key results, we assessed the reliability of the timing of the online measurements and collected eye movement behavior. The combined data confirms that trials in which eye movements were likely to be inhibited were also more likely to show inhibited hand movements. We suggest that upon detection of a salient change, any overt motor output is suppressed – regardless of the motor system – to prevent the execution of outdated actions. This mechanism could reduce the number of incorrect motor actions without disrupting the cognitive processes evaluating the state of the world.