A computational mechanism for seeing dynamic deformation

Abstract

Human observers perceptually discriminate the dynamic deformation of materials in the real world. However, the psychophysical and neural mechanisms responsible for the perception of dynamic deformation have not been fully elucidated. By using a deforming bar as the stimulus, we showed that the spatial frequency of deformation was a critical determinant of deformation perception. Simulating the response of direction-selective units (i.e., MT pattern motion cells) to stimuli, we found that the perception of dynamic deformation was well explained by assuming a higher-order mechanism monitoring the spatial pattern of direction responses. Our model with the higher-order mechanism also successfully explained the appearance of a visual illusion wherein a static bar apparently deforms against a tilted drifting grating. In particular, it was the lower spatial frequencies in this pattern that strongly contributed to the deformation perception. Finally, by manipulating the luminance of the static bar, we observed that the mechanism for the illusory deformation was more sensitive to luminance than contrast cues. Significance StatementFrom the psychophysical and computational points of view, the present study tried to answer the question, "how do human observers see deformation?". In the psychophysical experiment, we used a clip wherein a bar dynamically deformed. We also tested the illusory deformation of a bar, which was caused by tilted drifting grating, because it was unclear whether the illusory deformation could be described by our model. In the computational analysis, in order to explain psychophysical data for deformation perception, it was necessary to assume an additional unit monitoring the spatial pattern of direction responses of MT cells that were sensitive to local image motion.