Abstract
Physical stability is an ecologically important judgment about objects that allows observers to predict object behavior and appropriately guide motor actions to interact with them. Moreover, it is an attribute that observers can estimate from vision alone, based on an object's shape. In previous work, we have used different tasks to investigate perceived object stability, including estimation of critical angle of tilt and matching stability across objects with different shapes (VSS 2010, 2011). The ability to perform these tasks, however, does not necessarily indicate that object stability is a natural perceptual dimension. We asked whether it is possible to obtain adaptation aftereffects with perceived object stability. Does being exposed to a sequence of highly stable (bottom-heavy) objects make a test object appear less stable (and vice versa)? Our test objects were vertically elongated shapes, with a flat base and a vertical axis of symmetry. Its axis could be curved to different degrees, while keep its base horizontal. The Psi adaptive procedure (Kontsevich & Tyler, 1999) was used to estimate the "critical curvature" - the minimum axis curvature for which the test object is judged to fall over. This was estimated in three conditions: baseline (no adaptation), post-adaptation with high-stability shapes (mean critical angle: 63.5 degrees), and post-adaptation with low-stability shapes (mean critical angle: 16.7 degrees). In the adaptation conditions, observers viewed a sequence of 40 distinct adapting shapes. Following this, a test shape was shown, and observers indicated whether the object would stay upright or fall over. Adaptation was "topped up" after every test shape. Most observers exhibited an adaptation to object stability: the estimated critical curvature was lower following adaptation to high-stability shapes, and higher following adaptation to low-stability shapes. The results suggest that object stability may indeed be a natural perceptual variable.
Meeting abstract presented at VSS 2012