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Yujia Peng, Steven Thurman, Hongjing Lu; Phenomenal Causality in Biological Motion Perception. Journal of Vision 2016;16(12):395. doi: https://doi.org/10.1167/16.12.395.
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The "moonwalk", a renowned dance move, has fascinated people for decades. We hypothesize that the movement's impact is due to the surprise triggered by its violation of a fundamental expectation. Humans naturally assign the role of cause to relative limb movements, and the role of effect to body motion (i.e., limb movements cause changes of body position in the environment). The present study examined causal movements based on the ubiquitous expectation of causal asymmetry: an effect does not precede its cause. Action sequences were generated by shifting the temporal sequence of body positions relative to limb movements either ahead of time (i.e., effect precedes) or behind (i.e., cause precedes). Experiment 1 showed that actions with preceding limb movements were rated as more natural than actions with preceding body motion, suggesting the causal binding of two movement cues impacts perceived naturalness of actions. Experiment 2a explicitly separated the causal movements from the effect motion. A movie presented an actor walking on a treadmill conveyed relative limb movements (cause), while a moving dot signaled body position change over time (effect). We again found that participants were more likely to judge the two movements as matched when limb movements (cause) preceded body motion (effect) rather than vice versa. Experiment 2b used identical stimuli, except that participants were informed of the reversed cause-effect relation as a person aimed to track a moving laser spot. Observers now judged displays to be more natural when the dot movements preceded the limb movements, establishing that the temporal asymmetry effect is based on the understanding of the causal relation. Finally, we developed an observer model solely based on visual statistics of action stimuli. This model failed to account for the empirical findings, due to its lack of knowledge about the critical causal relations between the two movement cues.
Meeting abstract presented at VSS 2016
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