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Steven A. Cholewiak, Manish Singh, Roland Fleming; Perception of Physical Stability of Asymmetrical Three-Dimensional Objects. Journal of Vision 2011;11(11):44. doi: 10.1167/11.11.44.
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© ARVO (1962-2015); The Authors (2016-present)
Visual estimation of object stability is an ecologically important judgment that allows observers to predict an object's physical behavior. One way to measure perceived stability is by estimating the ‘critical angle’ (relative to upright) at which an object is perceived to be equally likely to fall over versus return to its upright position. However, for asymmetrical objects, the critical angle varies with the direction in which the object is tilted. Here we ask: (1) Can observers reliably track the change in critical angle as a function of tilt direction? (2) How do observers visually estimate the overall stability of an object, given the different critical angles in various directions? Observers stereoscopically viewed a rendered scene containing a slanted conical frustum, with variable aspect ratio, sitting on a table. In Exp. 1, the object was placed near the edge of the table, and rotated through one of six angles relative to this edge. Observers adjusted its tilt angle (constrained to move directly toward the edge) in order to set the critical angle. We found that their settings tracked the variation in critical angle with tilt direction remarkably well. In Exp. 2, observers viewed on each trial one of the slanted frustums from Exp. 1, along with a cylindrical object of variable aspect ratio. They adjusted the aspect ratio of the cylinder in order to match the perceived stability of the slanted frustum. The results showed that on average observers' estimates of overall stability are well predicted by the minimum critical angle across all tilt directions, but not by the mean critical angle. Observers thus reasonably appear to use the critical angle in the least stable direction in order to estimate the overall stability of an asymmetrical object.
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