Top-down directed attention to stimulus features and attentional allocation to bottom-up deviations.

One highly controversial issue with respect to visual selective attention concerns the degree to which the top-down attentional mechanism modulates attentional allocation to bottom-up deviation. We investigated whether top-down directed attention to a stimulus feature modulates attentional allocation to task-irrelevant, bottom-up deviation. The P3 event-related potential was measured as an electrophysiological marker of attentional allocation. Target and non-target objects were serially presented in random order. Bottom-up deviations occurred as a change in task-irrelevant features of target or non-target objects, or as the appearance of task-irrelevant distractor objects around target or non-target objects. When task-irrelevant features were changed, the P3 deviant effect was greater in target than in non-target trials. In contrast, when distractor objects appeared, the P3 deviant effect was smaller in target than in non-target trials. These findings suggest that top-down directed attention to a stimulus feature modulates attentional allocation to bottom-up deviation such that attentional allocation is enhanced when bottom-up deviation and an attended feature share the same object but is inhibited when bottom-up deviation occurs outside an object with an attended feature. Thus, the top-down attentional mechanism has a strong influence even for deviant processing and provides a competitive advantage for objects with an attended feature.