Human observers infer the attended direction of others based on head and gaze orientation, which results in covert and unintended shifts of attention. Known as social reflexive orienting, peripheral targets preceded by directed gaze speed detection of cued targets, even when subjects are aware that the cues are not predictive (Friesen & Kingstone, 1998). Recently, researchers demonstrated improved peripheral target discrimination following a point-light biological motion sequence when the target location was cued by the facing direction of the walker (Shi et al., 2010). Here we explore two aspects of biological motion social reflexive orienting: the evolution of covert orienting over time, and the interaction between symbolic (i.e. arrows) and social orienting cues. Methods. Subjects viewed a stationary array of oriented arrows or a point-light profile view walker (4x1.5deg visual angle). Subjects reported the position (left or right) of a 93ms target that appeared after a stimulus onset asynchrony (SOA) of 70-850ms. The subjects were informed that the facing or pointing direction of central cue was not predictive of the target location. In a second set of experiments, the subjects performed the same task with biological motion animations constructed from small arrows (instead of point-lights). Results. Trials with targets validly cued by the stationary arrows and biological motion resulted in RTs approximately 20ms faster than invalid trials. The arrow-driven reflexive orienting effect was apparent at nearly all SOAs, while orienting from biological motion was evident at early (93-350ms) and late (650ms) intervals. Both stimuli induced an inhibition of return (longer RT for validly cued trials) at 500ms SOA. Walkers constructed with oriented arrows effectively cancelled any reflexive orienting. Conclusions. The timecourse of reflexive orienting in biological motion differs from that generated by arrows. This social orienting cue, however, is fragile and relatively weak in comparison to symbolic orienting cues.
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