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Kazushi Maruya, Takao Sato; A dichotomy in representation for locations of moving objects.. Journal of Vision 2004;4(8):578. doi: 10.1167/4.8.578.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: The existence of multiple motion detectors has been heavily discussed, but representations for location of moving objects have received little attention. We report here results of a study on a perceptual offset phenomenon (POP, Maruya & Sato, VSS ′03) that suggest the existence of at least two types of location representations for moving objects. The POP is an illusory offset perceived between two motion stimuli defined by different attributes, despite that they are physically in phase and moving at a same speed. Methods: Stimuli were motion- and luminance-defined square wave gratings same as those in our previous study (VSS′03). Motions were generated by shifting the gratings by 30 deg phase angle once every 120 ms. The ISI was 0 ms for luminance-defined stimuli and either 0 ms (expt.1) or 80 ms (expt.2) for motion-defined stimuli. The spatial frequencies of patterns were varied in 4 steps between 0.1 and 0.4 c/d, and that of the two gratings were always equal. Subjects' task was to detect the direction of the spatial offset between the two gratings with a 2-AFC method. We systematically varied the spatial offset between two gratings and estimated the physical offset that cancelled the peceived offset. This point is an index for the amount of POP. Results and discussions: Estimated offsets, when expressed by phase angle of the spatial pattern, were almost constant in expt.1 with no ISI. However, this constancy collapsed in expt.2 with larger ISI. The perceptual offset increased as spatial frequency of patterns increased. These indicate that two separate mechanisms are involved in this phenomenon, one that depends on phase angles, and the other that operates over absolute distances.
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