Gwinn O Scott, Brooks Kevin R
Department of Psychology, Macquarie University, Sydney, New South Wales, Australia.
J Vis. 2013 Aug 22;13(10):13. doi: 10.1167/13.11.13.
Opposing aftereffects can be simultaneously induced by adapting to faces of different races distorted in opposite directions, allowing researchers to infer that faces are encoded against race-specific prototypes. This effect also suggests the existence of dissociable pools of neurons sensitive to race, each of which has been differently adapted to cause an opposite aftereffect. More recent studies have suggested that changes in the strength of race-contingent aftereffects reveal evidence of categorical perception, as they are larger when the adapting faces straddle the racial category boundary. We examined whether changes in these effects more closely correspond to a dichotomous categorical judgment, reflecting highly race-selective neural mechanisms, or more continuous perceptions of racial typicality, reflecting visual channels that are more broadly tuned. In Experiment 1, faces with a range of "morph levels" (i.e., relative contributions of Asian/Caucasian faces) were either rated on a continuous scale for Asian/Caucasian typicality, or simply categorized as Asian/Caucasian. As expected, typicality ratings showed a shallow slope (observers were sensitive to morph level over a broad range), while dichotomous racial categorization showed a steep slope (a rapid switch from categorization as Asian-Caucasian). In Experiment 2, race-contingent adaptation was assessed using test faces with various morph levels. Aftereffect size showed a shallow slope, closely resembling the racial typicality ratings, but showing a significant difference to the categorization data. This suggests that although the visual channels processing these faces do show some selectivity to race, they are sensitive to perceptions of racial typicality, showing a gradual transition of activity across a broad range of faces along the racial continuum.
通过适应向相反方向扭曲的不同种族面孔，可以同时诱发相反的后效应，这使研究人员能够推断出面孔是根据特定种族原型进行编码的。这种效应还表明存在对种族敏感的可分离神经元池，每个神经元池因不同的适应而产生相反的后效应。最近的研究表明，种族相关后效应强度的变化揭示了类别知觉的证据，因为当适应面孔跨越种族类别边界时，这种变化会更大。我们研究了这些效应的变化是更紧密地对应于二分法的类别判断（反映高度种族选择性的神经机制），还是更连续的种族典型性知觉（反映更广泛调谐的视觉通道）。在实验1中，对一系列具有不同“形态水平”（即亚洲/白种人面孔的相对贡献）的面孔，要么以连续量表对亚洲/白种人典型性进行评分，要么简单地归类为亚洲人/白种人。正如预期的那样，典型性评分显示出较浅的斜率（观察者在很宽的范围内对面孔形态水平敏感），而二分法的种族分类显示出较陡的斜率（从亚洲人到白种人的分类快速转换）。在实验2中，使用具有不同形态水平的测试面孔评估种族相关适应。后效应大小显示出较浅的斜率，与种族典型性评分非常相似，但与分类数据有显著差异。这表明，尽管处理这些面孔的视觉通道确实显示出对种族的一些选择性，但它们对种族典型性知觉敏感，沿着种族连续统在广泛的面孔范围内显示出活动的逐渐转变。
