Abstract
Stroop interference is among the most extensively used markers of cognitive and neural function ever used. The fundamental intrusion of conflicting sensory information provides a sensitive marker of interference that has been used to study the nature of attentional selectivity, cognitive control, and automatic versus controlled psychological processes, to name a few. Here we exploit the high temporal resolution of EEG to study automaticity and information integration in the human brain using variants of the Stroop (color naming) and Reverse Stroop (word naming) tasks in which the task-relevant and task-irrelevant features were presented with varying temporal separations. Whole-head event-related potentials (ERPs) and behavioral performance were measured while participants reported in separate experimental session, either the bar color or the color-word, as quickly as possible while ignoring the other dimension. The task-irrelevant component could appear at one of five stimulus onset asynchronies (SOAs) relative to the presentation of the task-relevant component: −200 or −100 ms before, +100 or +200 ms after, or simultaneously. ERP and behavioral markers of stimulus conflict (congruent vs. incongruent) and of target selection (word vs. color) were analyzed for main effects and interactions with SOA.
We observed for both tasks that incongruent relative to congruent presentations elicited slower reaction times, higher error rates, and ERP difference waves. Responses for the two tasks both contained early, negative-polarity, central-parietal deflections, and later positive components, though the distribution and latencies differed slightly with task. These congruency-related differences interacted with SOA, showing the greatest behavioral (RT and error rates) and electrophysiological effects when irrelevant stimulus information preceded task-relevant target occurrence and reduced effects when the irrelevant information followed the relevant target. We interpret these data as reflecting two separate processes: (1) a priming mechanism for the more efficient processing of a task-relevant target stimulus when preceded by a congruent, but irrelevant distractor; and (2) the diminishing effects of Stroop-related interference when irrelevant distractor information follows the task-relevant target. The high-degree of symmetry in the effects for these two tasks suggests that stimulus (in)congruency affects the strength, rather than the speed, of processing in the activated brain network.