Covert inhibition potentiates online control in a double-step task.

A planned action awaiting execution requires withholding a prepared response. We asked whether such a form of inhibition would interact with online decision processes that require changes in planned responses when new goals are unexpectedly specified. To investigate this issue with respect to oculomotor control, subjects performed, in separate sessions, standard visually-guided (SV) saccades, or memory-guided (MG) and delayed visually-guided (DV) saccades, both of which required withholding a planned saccade. To probe control, a second target (target-step) was presented in some trials after a variable delay that instructed subjects to redirect their gaze to the newly specified target. The time taken to cancel or inhibit the saccade directed at the initial target, the target step reaction time, was calculated using a race model that hypothesizes a covert inhibitory process, and was found to be significantly smaller for memory-guided redirect task (MGR; 94 ms) and delayed visually-guided redirect task (DVR; 96 ms) compared to standard visually-guided redirect task (SVR; 117 ms), suggesting facilitation of online inhibition in MGR and DVR. These results suggest that a tonic level of inhibition interacts with online decision processes to potentiate inhibitory control during double-step tasks.