Gheorghiu Elena, Kingdom Frederick A A, Sull Manpreet, Wells Samantha
McGill Vision Research, Department of Ophthalmology, McGill University, Montreal, Quebec, Canada H3A 1A1.
Vision Res. 2009 Oct;49(20):2518-30. doi: 10.1016/j.visres.2009.08.009. Epub 2009 Aug 12.
We have employed the shape frequency and shape-amplitude after-effects (SFAE and SAAE) to investigate: (i) whether the shapes of illusory and real curves are processed by the same or different mechanisms, and (ii) the carrier-tuning properties of illusory curvature mechanisms. The SFAE and SAAE are the phenomena in which adaptation to a sinusoidal-shaped contour results in a shift in, respectively, the perceived shape-frequency and perceived shape-amplitude of a test contour in a direction away from that of the adapting stimulus. Both after-effects are believed to be mediated by mechanisms sensitive to curvature (Gheorghiu & Kingdom, 2007a, 2009; see also Hancock & Peirce, 2008). We observed both shape after-effects in sinusoidally-shaped illusory contours defined by phase-shifted line-grating carriers. We tested whether illusory and real contours were mediated by the same or different mechanisms by comparing same adaptor-and-test with different adaptor-and-test combinations of real and illusory contours. Real contour adaptors produced after-effects in illusory contour tests that were as great as, or even greater than those produced by illusory contour adaptors. However, illusory contour adaptors produced much weaker after-effects in real contour tests than did real contour adaptors. This asymmetry suggests that illusory contour curves are encoded by a sub-set of mechanisms sensitive to real contour curves. We also examined the carrier-tuning properties of illusory-contour curvature processing using adaptor and test illusory contours that differed in the luminance contrast-polarity, luminance scale and orientation of the carriers. We found no selectivity to any of these dimensions for either even-symmetric or odd-symmetric line-gratings carriers, even though selectivity to these dimensions was found for real contours.
我们运用形状频率和形状幅度后效（SFAE和SAAE）来研究：（i）虚幻曲线和真实曲线的形状是通过相同还是不同的机制进行处理的，以及（ii）虚幻曲率机制的载波调谐特性。SFAE和SAAE是这样的现象，即适应正弦形状的轮廓会分别导致测试轮廓的感知形状频率和感知形状幅度在远离适应刺激的方向上发生偏移。这两种后效都被认为是由对曲率敏感的机制介导的（Gheorghiu & Kingdom，2007a，2009；另见Hancock & Peirce，2008）。我们在由相移线光栅载波定义的正弦形状的虚幻轮廓中观察到了这两种形状后效。我们通过比较真实和虚幻轮廓的相同适配器 - 测试与不同适配器 - 测试组合，来测试虚幻轮廓和真实轮廓是否由相同或不同的机制介导。真实轮廓适配器在虚幻轮廓测试中产生的后效与虚幻轮廓适配器产生的后效一样大，甚至更大。然而，虚幻轮廓适配器在真实轮廓测试中产生的后效比真实轮廓适配器产生的后效要弱得多。这种不对称性表明，虚幻轮廓曲线是由对真实轮廓曲线敏感的一部分机制编码的。我们还使用在载波的亮度对比极性、亮度比例和方向上不同的适配器和测试虚幻轮廓，研究了虚幻轮廓曲率处理的载波调谐特性。我们发现，对于偶对称或奇对称线光栅载波，对这些维度中的任何一个都没有选择性，尽管在真实轮廓中发现了对这些维度的选择性。
