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Peter Thompson, Steve Hammett; Perceived speed in peripheral vision: it can go up as well as down. Journal of Vision 2004;4(8):83. doi: 10.1167/4.8.83.
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It is well-known that moving stimuli can appear to move slower when presented in peripheral vision (Lichtenstein 1963 J.O.S.A. 53 302–306). Recently we (Thompson et al 2003 Perception 32 105) reported that these effects might be accounted for by the reduction in perceived contrast of peripheral stimuli as reduced contrast itself can lead to perceptual slowing (Thompson 1982 Vis Res 22 377–380). However in those experiments we only investigated eccentricities up to 8 degrees. We now report on data collected at far greater eccentricities. Pairs of (2 degree diameter circular) patches of horizontal grating stimuli (all 2 cycles/degree with a standard rate of movement of 2 cycles/sec) were presented simultaneously, one foveally the other horizontally displaced by 8, 16, 24 or 32 degrees. Subjects reported which grating appeared to move faster. A staircase procedure determined the point of subjective equality of the two stimuli. According to condition, either the speed of the foveal or the peripheral stimulus was staircased. Equal contrast stimuli (both 0.1 or 0.7 contrast) & unequal contrast stimuli (0.1 foveal, 0.7 peripheral & 0.7 foveal, 0.1 peripheral) were investigated. 4 subjects completed all conditions at least 4 times. The results show that at low contrast (0.1) perceived speed drops (as much as 50%) as the stimuli move into the periphery. However high contrast (0.7) stimuli appear to move faster (up to 30%) in the periphery. Even larger effects can occur if unequal contrasts are used: a low contrast grating in the fovea can look up to 40% slower than a high contrast in the periphery & a low contrast peripheral stimulus can be matched by a high foveal contrast of only 40% the speed. To explain these results we shall invoke both the usual dependence of speed on contrast and also a ratio model of speed perception that predicts increases in speed with increasing eccentricity.
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