Switching between simple response-sets: Inferences from the lateralized readiness potential

Behavioral studies have documented that task switching incurs a longer reaction time than task repetition, and that advance cueing information about the forthcoming task reduces mean reaction time. The present study used P₃₀₀ peak latency and two lateralized readiness potential (LRP) intervals - stimulus-locked and response-locked - to infer the loci of task switch and task-cueing effects and how they may interact in the basic task processing chain. Participants performed two tasks in a random order, so that on each trial they either repeated the task from the previous trial or switched to another task. In one condition, each stimulus was preceded by a cue informing participants which of the two tasks to perform; and in the other condition, each stimulus was preceded by a non-informative cue. Results indicated that both mean reaction times and the stimulus-locked LRP intervals were longer for switch than repeated trials, whereas P₃₀₀ peak latencies and response-locked LRP intervals were identical for both trials. Similarly, both reaction times and the stimulus-locked LRP intervals were longer for no task-cueing than for task-cueing conditions, and P₃₀₀ peak latencies and the response-locked LRP intervals were identical for both conditions. Finally, task switch and task-cueing effects appeared to be approximately additive, indicating the two factors influence distinct stage processes. We suggest that task switching resulted in prolongation of the response selection process by carry-over priming effects from the previous task, whereas task-cueing shortened the duration of the earlier process before response selection on both switch and repeated trials.