The feet have it: Local biological motion cues trigger reflexive attentional orienting in the brain

Most vertebrates, humans included, have a primitive visual system extremely sensitive to the motion of biological entities. Most previous studies have examined the global aspects of biological motion perception, but local motion processing has received much less attention. Here we provide direct psychophysical and electrophysiological evidence that human observers are intrinsically tuned to the characteristics of local biological motion cues independent of global configuration. Using a modified central cueing paradigm, we show that observers involuntarily orient their attention towards the walking direction of feet motion sequences, which triggers an early directing attention negativity (EDAN) in the occipito-parietal region 100-160ms after the stimulus onset. Notably, such effects are sensitive to the orientation of the local cues and are independent of whether the observers are aware of the biological nature of the motion. Our findings unambiguously demonstrate the automatic processing of local biological motion without explicit recognition. More importantly, with the discovery that local biological motion signals modulate attention, we highlight the functional importance of such processing in the brain.