YOUNG INFANTS' EVENT-RELATED POTENTIALS (ERPS) TO HIGH PROBABILITY AND LOW PROBABILITY VISUAL AND AUDITORY EVENTS IN A RECOGNITION MEMORY TASK

Three studies were designed to test whether three-month-old infants demonstrate differential brain activity to familiar and unfamiliar characteristics of 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). When an unfamiliar or infrequent stimulus is presented to the adult and older child, a characteristic enhancement of the late positive component (LPC) of the event-related potential (ERP) is observed.;Single-trial and averaged event related potentials were computed at visual (Oz), parietal (Pz), and auditory (Cz) scalp sites during three conditions: (1) 100% condition--ERPs to repeated presentations of a familiarized compound stimulus, (2) 80% condition--ERPs to presentations of the familiarized compound stimulus during the test phases, and (3) 20% condition--ERPs to presentations of the unfamiliar compound stimulus during the test phases.;In the VC and VAC Studies a strong LPC effect was found mainly at Oz and Pz for the average ERPs in the 20% condition during the 150-600 msec interval after stimulus onset. In the AC Study no evidence for an LPC effect was found in the average ERPs at any location.;Analysis using linear discriminant functions assessed LPC effects on 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 seqeunce 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' assessments at each scalp site for individual trials was calculated. The discriminant concordance among the combinations of scalp sites was different for each study, resulting in a unique spatial representation of the infants' brain responses in different tasks.;These studies provide a paradigm to assess LPC effects during recognition memory tasks in young infants using both average and single trial evoked potential data.