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Elena Gheorghiu, Frederick A. A. Kingdom; Spatial properties of curvature encoding revealed by the shape-frequency and shape-amplitude after-effects. Journal of Vision 2007;7(9):272. doi: 10.1167/7.9.272.
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Aim: The shape-frequency and shape-amplitude after-effects, or SFAE and SAAE, are the phenomena in which adaptation to a sine-wave-shaped contour causes a shift in respectively the apparent shape-frequency and shape-amplitude of a test contour in a direction away from that of the adapting stimulus. We have examined whether the SFAE and SAAE manifest selectivity to (a) local curvature, (b) curvature polarity (or sign), and (c) whether the contours were selective to local orientation. We also investigated (d) whether curvature encoders are arranged in a curvature-opponent manner and (e) whether the high- and low-shape-frequency shape components of complex shapes are processed independently or not. Methods: These included measuring SFAEs/SAAEs for adapting and test contours that were either the same or different in a given spatial property (e.g. same-polarity or opposite-polarity half-wave rectified sinusoidal curves to test for curvature-polarity specificity) the rationale being that if the after-effects were smaller when adaptor and test differed along a particular spatial property then curvature encoders must be selective for that property. Results: SFAEs and SAAEs (i) are mediated by mechanisms sensitive to contour fragments that have a constant sign of curvature (i.e. half-a-cycle of the test contour in ± cosine phase); (ii) show a degree of selectivity to curvature polarity (or sign); (iii) show a degree of selectivity to local orientation; (iv) reveal some evidence for curvature-opponency, and (v) reveal that the high and low shape-frequency shape components of a complex shape are separately adaptable. Conclusion: Curvature is encoded by mechanisms that are selective to a variety of spatial properties.
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