The effect of repetition of infrequent familiar and unfamiliar visual patterns on components of the event-related brain potential.

Examined changes in the waveforms of the event-related brain potential (ERP) during repeated presentations of infrequent-familiar and infrequent-unfamiliar visual patterns; Ss were 12 male university students. The EEG waveforms were averaged separately for each presentation of the 2 types of stimuli across different stimulus blocks. Principal components analysis and baseline-to-peak measurement identified 3 ERP components (a P3, P4, and a slow wave of diminishing positivity at anterior, central, and posterior scalp sites). Unfamiliar stimuli evoked components of greater positivity and P3 waves of longer latencies than familiar stimuli. Repetition of these stimuli was associated with a progressive diminution of the amplitude of the 3 components and a shortening of P3 latency. For the slow wave the decline in amplitude was more pronounced during repetition of unfamiliar than familiar stimuli. These effects are interpreted as signs of alterations in cognitive processes that play a role during orienting and perceptual learning.