Journal of Cognitive Neuroscience
Event-related brain potentials (ERPs) from 26 scalp sites were used to investigate whether or not and, if so, the extent to which the brain processes subserving the understanding of imageable written words and line drawings are identical. Sentences were presented one word at a time to 28 undergraduates for comprehension. Each sentence ended with either a written word (regular sentences) or with a line drawing (rebus sentences) that rendered it semantically congruous or semantically incongruous. For half of the subjects regular and rebus sentences were randomly intermixed whereas for the remaining half the regular and rebus sentences were presented in separate blocks (affording within-subject comparisons in both cases). In both presentation formats, words and line drawings generated greater negativity between 325 and 475 msec post-stimulus in ERPs to incongruous relative to congruous sentence endings (i.e., an N400-like effect). While the time course of this negativity was remarkably similar for words and pictures, there were notable differences in their scalp distributions; specifically, the classic N400 effect for words was larger posteriorly than it was for pictures. The congruity effect for pictures but not for words was also associated with a longer duration (lower frequency) negativity over frontal sites. In addition, under the mixed presentation mode, the N400 effect peaked about 30 msec earlier for pictures than for words. All in all, the data suggest that written words and pictures when they terminate sentences are processed similarly, but by at least partially nonoverlapping brain areas.