Searching for Life Motion Signals: Visual Search Asymmetry in Local but not Global Biological-motion Processing

The visual search paradigm has been widely used to study the mechanisms underlying visual attention, and search asymmetry provides a source of insight into preattentive visual features. In the current study, we tested visual search with biological-motion stimuli that were spatially scrambled or that represented feet only and found that observers were more efficient in searching for an upright target among inverted distractors than in searching for an inverted target among upright distractors. This suggests that local biological-motion signals can act as a basic preattentive feature for the human visual system. The search asymmetry disappeared when the global configuration in biological motion was kept intact, which indicates that the attentional effects arising from biological features (e.g., local motion signals) and global novelty (e.g., inverted human figure) can interact and modulate visual search. Our findings provide strong evidence that local biological motion can be processed independently of global configuration and shed new light on the mechanisms of visual search asymmetry.