Saccadic eye movements in dual tasking: No impairment of spatial planning, but delayed execution of saccades.

In the target-distractor saccade task, a target and an irrelevant distractor are simultaneously presented and the task itself consists of a target-directed saccade. Findings usually show that as saccade latency increases, saccade trajectory deviation towards the distractor decreases. We presented this saccade task in two dual-task experiments to address the open question of whether performance of an auditory-manual task simply delays the temporal execution of a saccade, or whether it also interferes with the spatial planning of the saccade trajectory. We measured saccade latency, as a measure of a delay in execution, and saccade trajectory deviation, as a measure of the spatial planning. In Experiment 1, the auditory-manual task was a two-choice reaction time (two-CRT) task, and in Experiment 2, it was a go-no-go task. Performing the two tasks in close temporal succession shortly delayed the temporal execution of the saccade, but did not influence the spatial planning of the saccade trajectory. This result pattern was more pronounced when the auditory-manual task required the selection and execution of one of two possible manual responses (Experiment 1), less pronounced when the auditory-manual task required the decision to execute a button press (go condition, Experiment 2), and absent when the auditory-manual task required the decision to inhibit a button press (no-go condition, Experiment 2). Taken together, the manual response rather than the response selection process of the auditory-manual task led to a delay of saccade execution, but not to an impairment of the spatial planning of the saccade trajectory.