Hemispheric Interactions and Event-Related Potentials in Lateralized Stroop and Stroop Analog Tasks

Abstract

Classical Stroop stimuli and newly developed face/word Stroop analog stimuli were used to investigate hemispheric interactions in Stroop interference effects (SEs) and corresponding event-related potentials (ERPs). Lateralized stimuli were presented unilaterally and bilaterally as congruent or incongruent color strip-word or face-word pairs (to invoke right hemisphere (RH) and left hemisphere (LH) specialization, respectively, in the latter case). The common finding for such tasks is that responses for the congruent condition are faster and more accurate than for the incongruent condition (i.e., the SE). A primary prediction is that the SE will be maximized when both the distractor and target components, or distractor alone, are presented to the specialized hemisphere (i.e., LH for words and RH for faces). A total of 88 right-handed University of North Texas students participated in one of four experiments. Participants manually responded to one component of the stimuli (i.e., color, face, or word), while ignoring the other. Behaviorally, participants showed a robust SE across all experiments, especially for the face/word task with word targets. Findings from the face/word Stroop analog tasks also indicated that SEs were produced by selective attention to either faces or words, implicating a role for top-down (controlled) processes. Hemispheric asymmetries were observed only for bilateral presentations of the face/word Stroop analog stimuli and did not differ for word versus face targets. The results suggest that the LH is less susceptible to interference from the RH than vice versa. Electrophysiologically, anterior N1 and P1, posterior P1 and N1, N2, and P3 components were identified. A SE was found for P3 amplitudes, but not latencies, across all four experiments such that the congruent condition generated greater amplitudes than the incongruent condition, suggesting that the P3 is an index of task difficulty. Surprisingly, SEs were also observed for the early ERP components, albeit embedded in higher order interactions. Taken together, the ERP evidence suggests that there is no single locus of the SE, and instead, the SE appears to be distributed over several stages of information processing