Visual Perception of Apparent Motion Follows Minimization Principles of Geometry, not Physics Open Access

Liu, Yaxin (Summer 2021)

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Apparent motion is a robust perceptual phenomenon in which observers perceive a stimulus traversing the vacant visual space between two flashed stimuli. It is known that the "filling-in" of apparent motion perception tends to favor the simplest and most economical paths of motion (Wagemans et al., 2012). However, the principles that underlie such computations remain largely unknown. Here, we tested whether the path of apparent motion is favored by the principle of kinematic geometry or Newtonian mechanics. In Experiment 1, a Pacman-shaped object was presented in succession across two positions differing by 0° to 120° in increments of 30°. Participants adjusted the position of a gap to indicate their perception of apparent motion. We found that adjusted gap position increased linearly with angular disparity, consistent with a curved path of motion defined by the unique center of rotation, as predicted by kinematic geometry, rather than a straight path constrained by objects’ centroids, as predicted by Newtonian mechanics. To test this conclusion more directly, we gave participants a target detection task in conjunction with concurrent apparent motion in Experiment 2. Similar to Experiment 1, a Pacman-shaped object was briefly presented in alternation (90° differences). Participants were instructed to respond as soon as they detected the target. We found that participants' RTs were significantly longer when a target appeared on a curved path, compared to a straight path, suggesting that apparent motion, as predicted by geometry, disrupted target detection, even after controlling for attentional biases and Pacman position. Taken together, our findings suggest that the "filling-in" perception of apparent motion is guided by kinematic geometry, not physics.

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