Repetition and emotion during an explicit categorization task

The late positive potential (LPP) is a well-known component of the event-related potentials that reflects motivational significance. Previous studies have found that, despite a decrease in overall amplitude of the LPP with repeated presentation of the same picture, emotional stimuli continued to elicit a larger LPP than neutral pictures. These data seem to support the hypothesis that the categorization of emotional stimuli reflected in the LPP modulation is an obligatory process that does not depend on attention. On the other hand, in these studies participants were only asked to look at the pictures (passive viewing), making picture emotionality the most salient aspect to process, despite repetition. Following this reasoning, we might expect a competing task will enhance the impact of picture repetition on the LPP affective modulation. In the present study, picture repetition occurred either in a passive viewing context or during a categorization task (within subject design), with pictures depicting any mean of transportation as targets, and repeated stimuli (both emotional and neutral) as non target stimuli. Replicating previous findings, emotional pictures continued to prompt a larger LPP compared to neutral pictures, after multiple repetitions, and even during the categorization task. These results suggest that the affective modulation of the LPP reflects an automatic engagement of cortico-limbic appetitive and defensive systems, which continues to occur after multiple repetitions, regardless of the task-relevance of the stimuli.