Perception of Continuous Movements from Causal Actions

AbstractWe see the world as continuous with smooth movements of objects and people, even though visual inputs can consist of stationary frames. The perceptual construction of smooth movements depends not only on low-level spatiotemporal features but also high-level knowledge. Here, we examined the role of causality in guiding perceptual interpolation of motion in the observation of human actions. We recorded videos of natural human-object interactions. Frame rate was manipulated to yield short and long stimulus-onset-asynchrony (SOA) displays for a short clip in which a catcher prepared to receive a ball. The facing direction of the catcher was either maintained intact to generate a meaningful interaction consistent with causality, or was transformed by a mirror reflection to create a non-causal situation lacking a meaningful interaction. Across three experiments, participants were asked to judge whether the catcher’s action showed smooth movements or sudden changes. Participants were more likely to judge the catcher’s actions to be continuous in the causal condition than in the non-causal condition, even with long SOA displays. This causal interpolation effect was robust to manipulations of body orientation (i.e. upright versus inverted). These findings indicate that causality in human actions guides interpolation of body movements, thereby completing the history of an observed action despite gaps in the sensory information. Hence, causal knowledge not only makes us see the future, but also fills in information about recent history.

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