Novelty detection is enhanced when attention is otherwise engaged: an event-related potential study

Novel stimuli are detected and evaluated quickly, suggesting that processing them is a priority for the brain. In the present study, the effects of attention on this early visual novelty processing were investigated in two experiments using the event-related potential (ERP) technique. In the first experiment, participants performed two tasks that varied in the amount of attention available for novel stimuli. In the Visual Oddball task, participants responded to an infrequent target presented among standard and novel stimuli. In the Working Memory task, participants saw the same stimuli, but they could ignore them. Instead, participants had to keep six letters in working memory and report one of these letters at the end of the trial; attention was thus maximally allocated away from the visual oddball stimuli. In line with attention being fully occupied in the Working Memory task, the P3a to the visual oddball stimuli was smaller in the Working Memory than in the Visual Oddball task. In contrast, the anterior N2 component to task-irrelevant stimuli was enhanced in the Working Memory task. These findings suggest that the initial detection of novel stimuli is enhanced (large anterior N2) when few attentional resources are available, which is inconsistent with earlier findings that if anything, the N2 is enhanced by attention. In a second experiment, a condition was added in which working memory load was low, but visual oddball stimuli were task-irrelevant. Results from this experiment showed that while the reduction in P3a amplitude was due to task irrelevance, the enhanced anterior N2 was linked to a high working memory load. This suggests that novelty detection is enhanced when attention is otherwise engaged.