Young infants' event-related potentials (ERPs) to familiar and unfamiliar visual and auditory events in a recognition...

Three studies were conducted to test whether 3-month-old infants demonstrate differential brain activity to familiar and unfamiliar characteristics in compound visual-auditory stimuli. Infrequent changes in the stimuli occurred in: (1) visual characteristics alone (VC study); (2) auditory characteristics alone (AC study); or (3) both visual and auditory characteristics (VAC study). Single trial and average event-related potentials (ERPs) were computed at Oz, Pz, and Cz. In the VC and VAC studies a strong LPC effect was found mainly at Oz and Pz for the average ERPs to the unfamiliar stimuli during the interval 150-600 msec after stimulus onset. In the AC study no evidence for an LPC effect was found in the average ERPs at any location. Linear discriminant functions were used to assess LPC effects for single trial ERPs. A local probability index (LPI) was calculated to examine the effects of prior presentations of familiar events on the infants' responses to specific occurrences of unfamiliar events. In the VC study the LPC was present more often at Pz for infrequently occurring trials preceded by a sequence of three or more familiar stimuli than by only one or two. The same effect was present at Cz in the AC study. Concordance among the discriminants' assessment at each scalp site for individual trials was calculated. The discriminant concordances among the combinations of scalp sites were different for each study resulting in a unique spatial representation of the infants' brain responses in different experimental conditions. These studies provide a paradigm to assess LPC effects during recognition memory tasks using both averaged and single trial evoked potential data in young infants.