Transient tasks and enduring emotions: the impacts of affective content, task relevance, and picture duration on the sustained late positive potential.

The present experiments were designed to examine the influences of picture duration, task relevance, and affective content on neural measures of sustained engagement, as indexed by the late positive potential (LPP). Much prior work has shown that the event-related potential in and around the P3-here referred to as the early LPP-is modulated by affective content, nonaffective task relevance, and stimulus duration. However, later portions of the LPP (>1,000 ms) may represent either a return to baseline or a continued physiological process related to motivational engagement. In the present experiments, we tested whether modulation of the later LPP depends on varying motivational engagement using stimulus duration, affective content, and task relevance. The results of Experiment 1 revealed that stimulus duration modulates the sustained LPP (i.e., 1,000-2,000 ms) in response to affective, but not task-relevant, stimuli from a modified counting oddball task. The results of Experiment 2 revealed that the sustained increase in the LPP is sensitive to both emotional content and task relevance when the task requires sustained engagement with target stimuli (e.g., determining the duration of stimulus presentation). The impacts of emotional content and task relevance had additive effects on the later portion of the LPP. In sum, both emotional content and task relevance can result in a protracted increase in the later LPP. These data suggest that affective content automatically sustains engagement, whereas task relevance only prolongs engagement when it is necessary for task completion.