Erroneous saccade co-execution during manual action control is independent of oculomotor stimulus-response translation ease.

Recent multiple action control studies have demonstrated difficulties with single-action (vs. dual-action) execution when accompanied by the requirement to inhibit a prepotent additional response (e.g., a highly automatic eye movement). Such a dual-action performance benefit is typically characterized by frequent false-positive executions of the currently unwarranted response. Here, we investigated whether the frequency of false-positive saccades is affected by the ease of translating a stimulus into a spatial oculomotor response (S-R translation ease): Is it harder to inhibit a saccade that is more automatically triggered via the stimulus? Participants switched on a trial-by-trial basis between executing a single saccade, a single manual button press, and a saccadic-manual dual action in response to a single visual stimulus. Importantly, we employed three different stimulus modes that varied in oculomotor S-R translation ease (peripheral square > central arrow > central shape). The hierarchy of S-R translation ease was reflected by increasing saccade and manual reaction times. Critically, however, the frequency of false-positive saccades in single manual trials was not substantially affected by the stimulus mode. Our results rule out explanations related to limited capacity sharing (between inhibitory control and S-R translation demands) as well as accounts related to the time available for the completion of saccade inhibition. Instead, the findings suggest that the erroneous co-activation of the oculomotor system was elicited by the mere execution of a (frequently associated) manual response (action-based co-activation).