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Vincent J. Chen, Jose F. Barraza, Laurent Itti; Perception of contours defined by integrative motion mechanisms. Journal of Vision 2003;3(12):48. doi: 10.1167/3.12.48.
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We studied the performance of human subjects for velocity discrimination in six varieties of motion stimuli. Motion was defined by dynamic modulation of luminance, contrast, or color of randomly placed, sparse small dots on a homogeneous background. Importantly, in each and every display used in this study, no dots ever moved relative to the background. For each of the modulation scheme, two varieties of displays are generated: one with static dots and the other with dynamic dots(popping up and disappearing at different locations in each frame of the movie, but never translated), resulting in six varieties of displays. Average luminance stayed constant across regions in the contrast and color modulation displays. Two classes of velocity discrimination thresholds were found. The higher threshold was approximately ten times that of the lower one. Interestingly, the higher threshold was consistently associated with the absence of the perception of well-defined contours in the motion stimuli. Moreover, keeping the average luminance constant throughout the stimuli did not necessarily produce high discrimination thresholds. Contours, real or subjective, appeared to be critical for the estimate of motion parameters such as velocity. To further investigate the link between the perception of contour and the perception of motion, vernier acuity tests were performed on each of the six varieties of displays. Results further supported the existence of motion-based mechanisms that integrate spatio-temporally coherent, but dispersed local changes over large regions that ultimately produce the perception of contours and surfaces.
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