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Elena Gheorghiu, Frederick A. A. Kingdom; Luminance-contrast properties of contour-shape processing revealed through adaptation. Journal of Vision 2006;6(6):338. doi: 10.1167/6.6.338.
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Aim: We investigated the nature of 1st-order inputs to contour-shape mechanism using the shape-frequency after-effect (SFAE), in which adaptation to a sinusoidally-modulated contour causes a shift in the apparent shape-frequency of a test contour away from that of the adapting stimulus. We measured SFAEs for adapting and test contours that differed in the phase, scale (or blur) and magnitude of luminance contrast. Methods: Adapting and test stimuli were pairs of 2D sinusoidal-shaped contours and edges. The adapting pair were presented above and below fixation and differed in shape frequency by a factor of three. During the test period, subjects indicated whether the upper or lower test contour had the higher perceived shape-frequency, and a staircase procedure estimated the ratio of test shape-frequencies at the point of subjective equality. Results: SFAEs revealed (i) selectivity to luminance contrast polarity for both even-symmetric (contours only) and odd-symmetric (both contours and edges) luminance profiles; (ii) a degree of selectivity to luminance scale (or blur); (iii) higher selectivity to fine-scale (thin) compared to coarse-scale (thick) contours/edges and (iv) a small preference for equal-in-contrast adaptors and tests. Conclusion: Contour/edge shape encoding mechanisms are tuned to many luminance-contrast properties. This implies that contour shape mechanisms make use of a ’feature-rich’ representation, and do not represent contour shapes as super-sparse cartoon-like sketches as might be presumed by local energy, i.e. non-phase-selective models.
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