Gheorghiu Elena, Kingdom Frederick A A
McGill Vision Research, Department of Ophthalmology, McGill University, 687 Pine Avenue West, Montreal, Quebec, Canada H3A 1A1.
Vision Res. 2007 Mar;47(6):834-44. doi: 10.1016/j.visres.2006.11.023. Epub 2007 Feb 9.
The shape-frequency and shape-amplitude after-effects, or SFAE and SAAE, refer respectively to the shifts observed in the perceived shape-frequency and shape-amplitude of a sinusoidal test contour following adaptation to a similar-shaped contour. As with other shape after-effects the shifts are in a direction away from that of the adapting stimulus. Using a variety of procedures we tested whether the spatial feature that was adapted in the SFAE and SAAE was (a) local orientation, (b) average unsigned curvature, (c) periodicity/density, (d) shape-amplitude and (e) local curvature. Our results suggest that the last of these, local curvature, underlies both the SFAE and SAAE. The evidence in favour of local curvature was that the after-effect reached its maximum value when just half-a-cycle of the test contour, in +/-cosine phase, was present. We suggest that the SFAE and SAAE are mediated by intermediate-level mechanisms that encode the shapes of contour fragments with constant sign of curvature. Given the neurophysiological evidence that neurons in area V4 encode parts of shapes with constant sign of curvature, we suggest V4 is the likely neural substrate for both the SFAE and SAAE.
形状频率和形状幅度后效，即SFAE和SAAE，分别指的是在适应了形状相似的轮廓后，在正弦测试轮廓的感知形状频率和形状幅度中观察到的偏移。与其他形状后效一样，这些偏移的方向与适应刺激的方向相反。我们采用了多种方法来测试在SFAE和SAAE中被适应的空间特征是（a）局部方向、（b）平均无符号曲率、（c）周期性/密度、（d）形状幅度还是（e）局部曲率。我们的结果表明，其中最后一项，即局部曲率，是SFAE和SAAE的基础。支持局部曲率的证据是，当测试轮廓仅存在半周期（处于正负余弦相位）时，后效达到最大值。我们认为，SFAE和SAAE是由中间水平机制介导的，这些机制对具有恒定曲率符号的轮廓片段的形状进行编码。鉴于有神经生理学证据表明V4区域的神经元对具有恒定曲率符号的形状部分进行编码，我们认为V4是SFAE和SAAE可能的神经基础。
