Perceived object stability depends on shape and material properties

Abstract

Humans can detect whether an unstable object will fall or right itself, suggesting that the visual system can extract an object's center of mass (COM) and relate this to its base of support. While the COM can be approximated by its shape, this assumes uniform density. We created images of computer-generated goblets made of different materials to assess whether the visual system estimates an object's COM from both shape and material properties. The images were either uniformly dense (e.g., glass, gold, etc.) or made of composite materials (e.g., glass and gold) and positioned upright or upside-down near a table ledge. We compared each goblet's critical angle (CA), the angle at which each goblet is equally likely to fall or right itself, to the perceived CA in a two-alternative-forced-choice paradigm. Participants also rank-ordered 20 materials by density on a questionnaire. The results show that observers accurately estimate the CA for all goblets and are sensitive to subtle changes of an object's COM with change in shape and composite material properties. Importantly, rated density - as measured from the questionnaire - and true material density were positively correlated, suggesting that humans might maintain a representation of relative material density with which to assess object stability. We conclude that the brain is able to assess an object's behavior in a gravitational environment by forming a reliable assessment of an object's COM from both its geometric shape and material properties.

Intuitive understanding of the relationship between the elasticity of objects and kinematic patterns of collisions

“…Moreover, the results of Experiment 3 showed that the rated bounciness of the colliding spheres consistently depended on the implicit coefficient C in the collisions. These findings are in line with the results of recent studies (Lupo & Barnett-Cowan, 2015; showing that people properly take account of material properties when asked to judge the physical behavior of objects.…”

“…The results of that study showed that people have a good qualitative understanding of the relationship between the relative masses of the colliding objects and the kinematic patterns of collisions. Recently, manipulations of simulated materials have also been used for varying the implied masses of virtual objects in research on the visual perception of objects' stability (Lupo & Barnett-Cowan, 2015).…”

Inferring mass in complex scenes by mental simulation

“…There is ample evidence that people have strong expectations about physical properties based on their size and perceived material. Expectations about material densities are generally correct and lead to accurate predictions about the stability of objects (Lupo & Barnett-Cowan, 2015). Thus, we would expect people to be biased in their inferences if visual cues provide evidence for different sizes or materials.…”

May the force be against you: Better visual sensitivity to speed changes opposite to gravity.

“…In addition to demonstrations of implicit knowledge of physics in perception and memory, there have also been several studies BETTER VISUAL SENSITIVITY TO SPEED CHANGES 1027 exploring how subjects explicitly reason about physical structures and events. When asked whether a structure will remain balanced or fall over, observers make judgments that are approximately accurate (Barnett-Cowan et al, 2011;Battaglia et al, 2013;Lupo & Barnett-Cowan, 2015). Moreover, when viewing pointlight animations, observers are able to correctly estimate the weight of a lifted object based on dynamic cues (Runeson & Frykholm, 1981;Valenti & Costall, 1997).…”