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Jason Bell, Elena Gheorghiu, Fredrick Kingdom; Orientation tuned curvature detectors revealed by the shape-amplitude after-effect. Journal of Vision 2009;9(8):887. doi: 10.1167/9.8.887.
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© ARVO (1962-2015); The Authors (2016-present)
Aim: Contour shape after-effects have been used to reveal the mechanisms that process and represent curvature-defined shape. Here we use the shape-amplitude after-effect, or SAAE, to explore whether curvature detectors are tuned for the overall orientation of a curve. Methods: We measured the perceived amplitude of curved contours in the upper and lower visual fields as a function of the orientation of adapting contours, which were respectively higher and lower in amplitude than the test. Results: SAAEs (i) are greatest when the adaptor and test are the same orientation, (ii) decrease rapidly as the orientation of the adapting contours is rotated away from the test, the data being well fit by a Gaussian function with a standard deviation of 15°, (iii) increase again when the adapting contours are rotated 180° relative to the test contours. The increase at 180° is not consistent with curvature opponency. Control experiments show that the shape of the tuning function cannot be explained by local orientation adaptation. Conclusions: Curvature encoding mechanisms are tuned for orientation. The slight increase in SAAEs when adaptor and test differ by 180° could be explained by the combined operation of polarity-selective and polarity-non-selective curvature mechanisms. The results are discussed in relation to recent psychophysical and physiological models of form processing.
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