Task-irrelevant optic flow guides attention in visual search.

Motion is an important factor in visual information processing. Studies have shown that global optic flow guides attention, but it remains unclear whether this attentional guidance occurs regardless of top-down attentional control settings for another endogenous cue. To address this issue, we developed a visual search paradigm in which a task-irrelevant optic flow starts and stops prior to a visual search task itself. Participants first observed an initial optic flow motion pattern for a brief period; next, they searched a static display for a target amongst multiple distractors. Results showed faster target detection when a target's locus coincided with the implied focus of expansion (FOE) from the preceding optic flow (vs. other loci). Eye-movement analyses revealed that initial saccades were drawn to the FOE during optic flow exposures and that relatively few saccades were needed to find targets contingent to the preceding FOE. The advantage of FOE for finding target occurred even when a salient feature singleton captured attention or when a task-relevant feature singleton was prioritized. Results of six experiments suggest that attentional control settings for a feature singleton do not over-ride a sustained influence of optic flow on attentional guidance.