Irrelevant Stimulus Processing When Switching Between Tasks

Frequent switching between two tasks afforded by the same stimuli is associated with between-task congruency effects, that is, relatively impaired performance when a stimulus affords different responses as compared to the same responses in both tasks. These congruency effects indicate some form of application of the stimulus-response (S-R) rules of the currently irrelevant task. Between-task congruency effects are usually enhanced on task switch trials compared with task repetition trials. Here we investigate whether this interaction reflects stronger proactive interference from the irrelevant task on switch trials or whether performance on switch trials is characterized by generally enhanced susceptibility to task-irrelevant information processing. To this end, we contrasted between-task congruency effects with interference exerted from flanker stimuli taken from the current task (Experiment 1) and from spatial-numerical association of response codes (SNARC; Experiment 2). In both experiments, between-task congruency effects were larger on switch trials than on repetition trials, whereas interference from the other source remained constant, thus demonstrating that switch trials are not characterized by generally increased distractibility.