Performance-dependent reward hurts performance: The non-monotonic attentional load modulation on task-irrelevant distractor processing

Selective attention is essential when we face sensory inputs with distractions. In the past decades, Lavie's load theory of selective attention delineates a complete picture of distractor suppression under different attentional control load. The present study was originally designed to explore how reward modulates the load effect of attentional selection. Unexpectedly, it revealed new findings under extended attentional load that was not involved in previous work. Participants were asked to complete a rewarded attentive visual tracking task while presented with irrelevant auditory odd-ball stimuli, with their behavioral performance, event-related potentials and pupillary responses recorded. We found that although the behavioral performance and pupil sizes varied unidirectionally with the attentional load, the processing of distractors as reflected by the mismatch negativity (MMN) increased first and then decreased. In contrast to the prediction of Lavie's theory that attentional control fails to effectively suppress distractor processing under high attentional control load, our finding suggests that extremely high attentional control load may instead require suppression of distractor processing at a stage as early as possible. Besides, P3a, a positive-polarity response sometimes following the MMN, was not affected by the attentional load, but both N1 (a negative-polarity component peaking similar to 100 ms from sound onset) and P3a were weakened at higher reward, indicating that reward leads to attenuated early processing of distractor and thus suppresses the attentional orienting towards distractors. These findings altogether complement Lavie's load theory of selective attention, presenting a more complex picture of how attentional load and reward affects selective attention.