Neural correlates of stimulus and response interference in a 2-1 mapping stroop task.

Two sources of interference (i.e., stimulus and response) are believed to contribute to the Stroop interference effect. Some neurophysiological evidence reveals that different neuro-cognitive processes are related to stimulus and response interference in the Stroop and related tasks. However, other evidence indicates that similar patterns of neural recruitment may be associated with these two types interference. Given these discrepant findings, the current study used a 2-1 mapping Stroop task in combination with event-related brain potentials (ERPs) to examine the neural correlates of stimulus and response interference. The response time data revealed that stimulus interference was constant across the response time distribution. In contrast, response interference increased in magnitude across the response time distribution for all but the slowest trials. The stimulus-locked ERP data revealed that early and later modulations of the medial frontal negativity may be sensitive to response interference, but not stimulus interference. These data also revealed that the conflict slow potential (SP) over the parietal and right lateral frontal regions was sensitive to both stimulus and response interference; in contrast, the conflict SP over the left lateral frontal region was only sensitive to response interference. Together the stimulus- and response-locked data lead to the conclusion that the parietal region is primarily involved in response selection in the Stroop task, and that the lateral frontal regions may participate in response monitoring and conflict adaption.