Event-related brain potentials as a function of evaluative and nonevaluative judgment processes: A late positive brain potential that varies as a function of categorization rather than response operations

The foundation for the scientific study of attitudes was established by Thurstone (1928) when he outlined a self-report technique for assessing attitudes that was based on the theory and methods of psychophysics. The application of ideas from psychophysics helped to characterize attitudinal processes as involving (1) an evaluative percept (categorization) of a stimulus and (2) a bivalent action disposition toward the stimulus. Because the evaluative percepts that underlie attitudes can be obscured during the behavioral expression of attitudes, however, the reliance on self-report measures has restricted the study of attitudinal processes by (1) limiting research to attitudes that are unlikely to be influenced by nonattitudinal response selection and execution processes and (2) making it difficult to examine the unique aspects of evaluative as opposed to nonevaluative judgment processes. In the present studies, a late positive potential (LPP) of the ERP that is sensitive to evaluative categorizations is used to address these limitations. As has been found previously, the amplitude of the LPP was found to vary as a function of the evaluative inconsistency of the eliciting stimulus. In addition, results suggest that the LPP is particularly sensitive to variations in evaluative categorization rather than response processes as instructions to misreport the valence of stimuli led to the instructed changes in attitude report but did not significantly change the LPP evoked by these stimuli. The evaluative/nonevaluative nature of the experimental tasks that are used to elicit the LPP was also varied; results are consistent with the notion that there are common information processing operations underlying evaluative and nonevaluative semantic categorizations but that the sets of psychological operations are not completely overlapping. Specifically, the LPP elicited by evaluative categorizations was found to be asymmetrically distributed over the left and right scalp regions, with a larger amplitude over the right than the left scalp regions, relative to the LPP elicited by nonevaluative categorizations. Thus, these results suggest that evaluative and nonevaluative semantic categorizations have at least partially distinct information processing operations.