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Paul McGraw, Neil Roach; Centrifugal propagation of motion adaptation effects across visual space. Journal of Vision 2007;7(9):737. doi: 10.1167/7.9.737.
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© ARVO (1962-2015); The Authors (2016-present)
Prolonged inspection of a visual pattern has the potential to profoundly alter subsequent perception - via a process known as visual adaptation. These perceptual distortions, or after-effects, are greatest when the visual characteristics defining the adapting and test patterns are similar and both are presented in the same region of visual space. Adaptation effects are a ubiquitous feature of visual processing and are thought to arise through the selective stimulation of discrete subpopulations of neurons that respond to similar image features. Adapting to unidirectional motion results in an inveterate phenomenon known as the motion after-effect (MAE), whereby subsequently viewed objects appear to drift in a direction opposite to that of the adapting stimulus. In addition, motion adaptation induces a perceived shift in the spatial location of the stimulus as a whole. In the present study we examine the spatial specificity of motion-induced positional shifts as a function of adapting location. We demonstrate that when translational motion adaptation occurs close to fixation (0.5 deg. eccentricity), significant positional offsets result (∼10 arcmin) and the after-effects propagate centrifugally across visual space, resulting in broad spatial tuning. In marked contrast, when motion adaptation occurs more peripherally (5 deg. eccentricity) greater positional shifts are observed (∼15 arcmin), but more importantly, the effects are largely restricted to the adapted spatial region. This marked difference in tuning between adapted locations cannot be explained by changes in positional sensitivity - a factor that was equated across the range of eccentricities tested. We also show that this eccentricity dependant change in spatial tuning of the after-effect is unique to motion. Using almost identical stimuli and procedures, other classical after-effects (spatial frequency and orientation) show the opposite pattern, with narrow spatial tuning centrally and slightly broader tuning with increasing adaptor eccentricity.
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