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Sergei Gepshtein, Luis Lesmes, Thomas Albright; Motion adaptation as a redistribution of visual sensitivity. Journal of Vision 2009;9(8):683. doi: 10.1167/9.8.683.
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Motion adaptation is a robust perceptual phenomenon known from antiquity, yet understanding its principles has been elusive. Recent theories proposed that adaptation optimizes visual sensitivity to properties of the variable environment, thus improving the ability to perceive motion at the adapting conditions (Sakitt and Barlow, 1982; Wainwright, 1999; Stocker and Simoncelli, 2005). Previous efforts to support this premise produced controversial results. In speed adaptation, for example, sensitivity to adapting speeds either increased or decreased; it also changed for speeds very different from the adapting speed (Krekelberg, van Wezel, and Albright, 2006).
According to a new normative-economic theory of motion perception (Gepshtein, Tyukin, and Kubovy, 2007) spatiotemporal sensitivity manifests an optimal allocation of scarce computational resources in the visual system, driven by two factors: Gabor's uncertainty principle of measurement and statistics of stimulation. The theory predicts that speed adaptation should induce a characteristic pattern of sensitivity changes, forming foci of increased and decreased sensitivity across the spatiotemporal sensitivity function (Gepshtein, Tyukin, and Albright, 2008, www.journalofvision.org/8/6/1037).
We measured human contrast sensitivity over a large range of spatial and temporal frequencies (0.25–8 c/deg and 0.5–32 Hz). The observers viewed drifting luminance gratings of variable contrast and discriminated the direction of motion. We varied the statistics of motion speed: In some blocks of trials low speeds were more common than high speeds, and in other blocks high speeds were more common than low speeds. We compared the spatiotemporal contrast sensitivity functions obtained in the different statistical contexts and found changes of sensitivity that formed foci of increased and decreased sensitivity similar to our predictions. These findings support the normative-economic theory and the view that motion adaptation amounts to reallocation of computational resources in the visual system.
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