Averaged evoked potential (AEP) is an event-related brain response obtained by averaging the scalp electrical potentials elicited by repeated presentations of the same event. It has proven to be an accurate measure of the activity of the mature human brain when involved in a wide variety of psychological tasks. Distinct psychological processes appear to be associated with changes in the averaged evoked potential at different points in time with respect to the stimulus event. When an infrequent or unexpected stimulus is presented to the adult, a characteristic enhancement of the late positive component (LPC) of the averaged evoked cortical potential is observed. To test whether this effect obtains near birth, in two studies, low and high-probability visual stimuli were presented to twenty-nine 3-month-old infants. Electrical potentials were recorded from occipital and parietal scalp sites. A clear LPC effect was observed at both sites between 300-600 msec following the onset of the infrequent stimulus. This is the first demonstration of an LPC effect in infants, reflecting cognitive processing involving memory. A method for analyzing single trials is incorporated, demonstrating individual differences in early cognitive functioning. (Author/RH)