Neurophysiological correlates of human concept formation

Human event-related potentials were evaluated during the trial-and-error learning of a sorting criterion for complex visual stimuli. Prior to the discovery of the correct criterion a sustained positivity was observed in frontal-mastoid recordings during the visual stimuli. A parieto-occipital negativity preceded auditory feedback. Two late positive waves following feedback—P₃ (355 msec) and P₄ (647 msec)—were both of greater amplitude in the trials before the subject finally confirmed the correct criterion. Their scalp distributions were, however, distinctly different, the P₄ wave being of relatively greater amplitude in the parieto-occipital regions. A general negative baseline shift occurred with a change in criterion.