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Hoko Nakada, Mizuki Kiyonaga, Ikuya Murakami; Adaptation to an illusory aspect ratio distorted by motion induced position shift. Journal of Vision 2019;19(10):287c. doi: https://doi.org/10.1167/19.10.287c.
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It is widely known that a stationary contour of a stimulus that contains visual motion inside is perceptually shifted in the direction of the motion (motion-induced position shift). Although a lot of studies have examined various kinds of motion that can induce illusory position shifts and explored relationship between position perception and motion processing, how these motion induced position shifts have effects on other visual attributes have been rarely studied. Thus, we focused on perception of aspect ratio, which is one kind of shape perception producing a negative aftereffect, and investigated whether perceived aspect ratio was affected after adaptation to a shape comprised of patches yielding illusory position shifts caused by motion, namely Gabor patches with drifting sinusoidal carriers. The static contrast envelope of each Gabor patch appears to be shifted in the direction of motion, thus perceptually deforming the global shape defined by these patches. In this experiment, a number of drifting Gabor patches were geometrically arranged to comprise a diamond with a physical aspect ratio of 1:1, and its perceptual aspect ratio was distorted vertically or horizontally by motion-induced position shift. Participants were adapted to these diamonds that appeared to have a distorted aspect ratio, and were immediately tested for the aftereffect by indicating whether a diamond consisting of stationary Gaussian luminance blobs was elongated vertically or horizontally. We found that the perceptually distorted aspect ratio did not cause the negative shape aftereffect, whereas a physically distorted aspect ratio did. These results were at odds with some previous researches claiming that the aspect ratio aftereffects seemingly arise from a perceived difference between the adapting and test stimuli, rather than a difference in physical aspect ratio. We will discuss the relationship between perceived position distorted by motion and dedicated visual mechanisms for aspect ratio.
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