Abstract
Previous research has suggested a close link between apparent motion perception and attentive tracking (Cavanagh, 1992; Lu & Sperling, 1995). A strong version of this account predicts that shifts of spatial attention solve the correspondence problem. Consistent with this account, we show that spatial selection closely tracks objects during apparent motion, and that manipulating spatial attention can have a causal effect on apparent motion percept. In Experiment 1, participants were presented with a 6-frame ambiguous apparent motion display that could be perceived as either a yellow circle moving left and right, or two circles moving up and down separately on the left and right sides. By monitoring spatial attention with an electrophysiological correlate (N2pc, CDA/SPCN), we observed spatial selection synchronously tracking a single object in the direction of its apparent motion. In Experiment 2, participants viewed a 4-frame ambiguous apparent motion display that could be seen as two circles rotating clockwise or counter-clockwise. Eye movements revealed that participants spontaneously selected the top object and shifted selection in tandem with the perceived motion trajectory. In Experiment 3, we directed exogenous spatial attention by presenting a brief flash cue in the middle of a 2-frame ambiguous apparent motion display. The location of the cue systematically biased the perceived direction of rotation, and participants again tended to spontaneously track the top object. In Experiment 4, we required participants to endogenously attend to the top or the bottom object initially. Motion was perceived in the direction of selection shift driven by the exogenous cue, relative to the initial selection. We have thus demonstrated that spatial selection tracks an object during apparent motion and that spatial selection shifts determine the direction of apparent motion, providing compelling evidence that spatial selection can be an important agent in guiding the object correspondence in ambiguous apparent motion.
Meeting abstract presented at VSS 2013