A Pushing Stick or a Pulled Rubber Band: Material Perception Reverses the Causal Arrow in Agent-Patient Dynamics

Abstract

People effortlessly recognize objects of various materials and predict their behavior from visual information. However, research on causal perception has largely underexplored dynamic interactions involving nonrigid objects, often treating spatiotemporal causality as independent of object properties. To address this gap, we introduce a novel causal perception phenomenon in which speed profiles alone evoke the perception of elastic, nonrigid motion in interactions between simple geometric figures, ultimately shaping causal perception. Using an ambiguous-motion stimulus involving a separation event, we show that a line segment elongating with a disc at its end before separating can be interpreted in two distinct ways-as a rigid stick pushing a disc or as a disc pulling an elastic band. Across four experiments, deceleration before separation followed by rapid postseparation motion consistently biased perception toward the elastic band interpretation, demonstrating the critical role of kinematic regularities in shaping both causal and material perception. Four follow-up experiments using a pause-detection task revealed sensitivity to motion dynamics inconsistent with a stretched elastic band, even when causal and material perception was entirely task-irrelevant, further indicating the perceptual nature of this phenomenon. These findings illustrate how subtle kinematic patterns can simultaneously reverse perceived force dynamics and causal roles, accompanied by corresponding shifts in material perception, contributing to a unified framework for material and causal perception. Ultimately, this work provides new insights into how the visual system uses kinematic information to assign causal agents and patients in dynamic interactions. Public Significance Statement When observing two objects moving in contact, how do we determine whether A pushes B, B pulls A, or whether A and B move as a unit? Our study demonstrates that acceleration or deceleration patterns play a critical role for inferring force direction, which does not always align with motion direction. This inference further shapes perceptions of object materials and their transformations (e.g., rigid translation vs. elastic stretching) and even extends to the type of event (e.g., pushing vs. pulling) and causal direction-determining who acts on whom and how. By bridging causal perception, material perception, intuitive physics, and event cognition, our findings highlight how the visual system integrates motion and material information to construct coherent interpretations of dynamic interactions in the physical world.