THE COUNTING STROOP - AN INTERFERENCE TASK SPECIALIZED FOR FUNCTIONALNEUROIMAGING - VALIDATION-STUDY WITH FUNCTIONAL MRI

The anterior cingulate cortex has been activated by color Stroop tasks , supporting the hypothesis that it is recruited to mediate response s election or allocate attentional resources when confronted with compet ing information-processing streams. The current study used the newly d eveloped ''Counting Stroop'' to identify the mediating neural substrat e of cognitive interference. The Counting Stroop, a Stroop variant all owing on-line response time measurements while obviating speech, was c reated because speaking produces head movements that can exceed those tolerated by functional magnetic resonance imaging (fMRI), preventing the collection of vital performance data. During this task, subjects r eport by button-press the number of words (1-4) on the screen, regardl ess of word meaning. Interference trials contain number words that are incongruent with the correct response (e.g., ''two'' written three ti mes), while neutral trials contain single semantic category common ani mals (e.g., ''bird''). Nine normal right-handed adult volunteers under went fMRI while performing the Counting Stroop. Group fMRI data reveal ed significant (P less than or equal to 10(-4)) activity in the cognit ive division of anterior cingulate cortex when contrasting the interfe rence vs. neutral conditions. On-line performance data showed 1) longe r reaction times for interference blocks than for neutral ones, and 2) decreasing reaction times with practice during interference trials (d iminished interference effects), indicating that learning occurred. Th e performance data proved to be a useful guide in analyzing the image data. The relative difference in anterior cingulate activity between t he interference and neutral conditions decreased as subjects learned t he task. These findings have ramifications for attentional, cognitive interference, learning, and motor control mechanism theories. Hum. Bra in Mapping 6:270-282, 1998. a 1998 Wiley-Liss, Inc.