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David Nguyen-Tri, Jocelyn Faubert; Possible mechanisms for pedestal effects on speed perception. Journal of Vision 2008;8(6):603. doi: 10.1167/8.6.603.
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© ARVO (1962-2015); The Authors (2016-present)
Previous research has demonstrated that the superimposition of a static pattern on a moving one produces an increase in the apparent speed of motion. The purpose of the current experiments was to investigate the mechanism underlying this increase in perceived speed. In Experiment 1, we investigated the effects of static grating (pedestal) and drifting grating (target grating) spatial frequency on the perceived speed of the target grating. The results show that both target and pedestal grating spatial frequency have an influence on the increase in perceived speed. The results suggest a spatial frequency tuning of the speed effect where the optimal pedestal spatial frequency changes as a function of target grating spatial frequency. In Experiment 2, we measured the effects of the pedestal grating in monoptic (pedestal and target gratings presented to the same eye) and dichoptic (pedestal and target gratings presented to different eyes) viewing conditions and when the pedestal was coextensive with the target grating or presented adjacently to it. Adjacent presentation of the pedestal was not found to produce systematic increases in perceived speed. Further, whereas monoptic presentation of the pedestal and target gratings produced an increase in perceived speed similar to that observed in Experiment 1, no increase in perceived speed was observed in dichoptic viewing conditions. In Experiment 3, we studied the effect of temporal frequency on the increase in perceived speed. No change in the relative increase in perceived speed occurred with changing temporal frequency. We conclude that the effects of a static pedestal on the perceived speed of a target grating are mediated early in motion processing, at a stage sensitive to spatial frequency and prior to binocular integration.
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