The psychophysics of bouncing: Perceptual constraints, physical constraints, animacy, and phenomenal causality

PLOS ONE RESEARCH ARTICLE The psychophysics of bouncing: Perceptual constraints, physical constraints, animacy, and phenomenal causality Michele Vicovaro ID1, Loris Brunello1, Giulia Parovel ID2* 1 Department of General Psychology, University of Padova, Padova, Italy, 2 Department of Social, Political and Cognitive Sciences, University of Siena, Siena, Italy * a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 OPEN ACCESS Citation: Vicovaro M, Brunello L, Parovel G (2023) The psychophysics of bouncing: Perceptual constraints, physical constraints, animacy, and phenomenal causality. PLoS ONE 18(8): e0285448. https://doi.org/10.1371/journal. pone.0285448 Editor: Robin Baurès, Universite Toulouse III - Paul Sabatier, FRANCE Received: December 2, 2022 Accepted: April 23, 2023 Published: August 18, 2023 Peer Review History: PLOS recognizes the benefits of transparency in the peer review process; therefore, we enable the publication of all of the content of peer review and author responses alongside final, published articles. The editorial history of this article is available here: https://doi.org/10.1371/journal.pone.0285448 Copyright: © 2023 Vicovaro et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: Data and research material are available on OSF at the following link: osf.io/xz8t3. Abstract In the present study we broadly explored the perception of physical and animated motion in bouncing-like scenarios through four experiments. In the first experiment, participants were asked to categorize bouncing-like displays as physical bounce, animated motion, or other. Several parameters of the animations were manipulated, that is, the simulated coefficient of restitution, the value of simulated gravitational acceleration, the motion pattern (uniform acceleration/deceleration or constant speed) and the number of bouncing cycles. In the second experiment, a variable delay at the moment of the collision between the bouncing object and the bouncing surface was introduced. Main results show that, although observers appear to have realistic representations of physical constraints like energy conservation and gravitational acceleration/deceleration, the amount of visual information available in the scene has a strong modulation effect on the extent to which they rely on these representations. A coefficient of restitution >1 was a crucial cue to animacy in displays showing three bouncing cycles, but not in displays showing one bouncing cycle. Additionally, bouncing impressions appear to be driven by perceptual constraints that are unrelated to the physical realism of the scene, like preference for simulated gravitational attraction smaller than g and perceived temporal contiguity between the different phases of bouncing. In the third experiment, the visible opaque bouncing surface was removed from the scene, and the results showed that this did not have any substantial effect on the resulting impressions of physical bounce or animated motion, suggesting that the visual system can fill-in the scene with the missing element. The fourth experiment explored visual impressions of causality in bouncing scenarios. At odds with claims of current causal perception theories, results indicate that a passive object can be perceived as the direct cause of the motion behavior of an active object. Introduction Then he squatted down, held the ball about a half-inch from the floor, dropped it. PLOS ONE | https://doi.org/10.1371/journal.pone.0285448 August 18, 2023 1 / 38 PLOS ONE The psychophysics of bouncing Funding: This publication was made possible thanks to the specific contribution of the University of Siena (Italy) for Open Access support and the PSR funding of the Department of Social, Political and Cognitive Sciences (DISPOC), University of Siena (Italy). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. It bounced, naturally enough. Then it bounced again. And again. Only this was not natural, for on Competing interests: The authors have declared that no competing interests exist. air and going higher each time. the second bounce the ball went higher in the air than on the first, and on the third bounce higher still. After a half minute, my eyes were bugging out and the little ball was bouncing four feet in the I grabbed my glass. “What the hell!” I said. (W. Tevis, The Big Bounce, 1958) If we are asked to represent the typical behavior of a bouncing ball, we would probably imagine a ball falling down, bouncing against a surface, and then moving back off repeatedly with a decreasing speed and a lower peak height after each bounce, until stillness. Instead, we would be really surprised, or even amused, if we saw a ball increasing its speed and peak height after each bounce, as if it were jumping (see the incipit, and see this video at: https://youtu.be/ oQs5WJLUFEM). Apparently, we do not need knowledge of energy conservation principles to perceive a bounce or a jump, like we do not need knowledge of the physics of light to perceive colors. From a perceptual standpoint, bouncing can be defined as an event, that is, as a sequence of motions with a definite, meaningful perceptual structure. A prominent feature of visually perceived events is phenomenal causality, that is, the impression that the motions of the objects in the scene are causally related [1]. For instance, in Michotte’s [2] launching effect, observers are presented with two horizontally aligned squares, and at a point in time one square (A) starts moving towards the other (B). When A touches B, B starts moving with the same velocity as A, whilst A came to a stop. This simple configuration leads to the vivid visual impression that A launches or kicks B, that is, that the motion of B is caused by the collision with A. The phenomenon is impervious to observers’ explicit knowledge and expectations, which provides support to its perceptual (rather than post-perceptual) origins [3–6]. As another example of visual event, White and Milne [7] presented the participants with simple 2D animations showing an object (A) moving towards a set of initially stationary elements that, upon contact with A, started moving in different directions. Under appropriate conditions, this stimulus configuration led to the vivid impressions of enforced disintegration or bursting. Other examples of visually perceived events include triggering, entraining, expulsion [2], braking [8], penetration [9], pulling [10], generative transmission [11], intentional reaction [12], and shattering [13]. According to Gestalt-theoretic accounts, visual perception of events depends on specific perceptual principles that are unrelated to physical laws, such as moti (...truncated)