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Craig Aaen-Stockdale, Ben Thompson, Pi-Chun Huang, Robert Hess; A low-level explanation of paradoxical motion percepts. Journal of Vision 2008;8(17):40. doi: 10.1167/8.17.40.
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A recent series of experiments have demonstrated a deterioration of motion perception with increasing stimulus size for stimuli of high contrast (Tadin et al., 2003). This counterintuitive finding has been explained as a result of surround-suppression in visual area V5. Equally paradoxical was the finding that older observers appeared to show better motion perception than younger observers using the same technique (Betts et al., 2005). This second curious result was explained as a consequence of a reduction in V5 surround-suppression due to age-related changes in GABA-mediated inhibition. Using an opponent-motion stimulus, similar to that of previous studies but of constant duration, we have replicated the paradoxical effect of contrast on motion discrimination and also replicated the finding that this effect is much reduced or non-existent in older subjects. Our results can, however, be explained by low-level mechanisms: a proportional increase in the motion energy required to discriminate stimuli of progressively higher suprathreshold contrasts and spatial summation of motion in stimuli of progressively larger sizes. In previous studies, suprathreshold contrast co-varies with size, which may be responsible for the unusual results.
TadinD.LappinJ. S.GilroyL. A.BlakeR. (2003). Perceptual consequences of centre-surround antagonism in visual motion processing. Nature, 424(6946), 312–315.
Betts L. R. TaylorC. P.SekulerA. B.BennettP. J. (2005). Aging reduces center-surround antagonism in visual motion processing. Neuron, 45(3), 361–366.
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