Radonjic Ana, Ding Xiaomao, Krieger Avery, Aston Stacey, Hurlbert Anya C, Brainard David H
Department of Psychology, University of Pennsylvania, Philadelphia, PA, USA.
Department of Psychology & Neuroscience Graduate Group, University of Pennsylvania, Philadelphia, PA, USA.
J Vis. 2018 May 1;18(5):11. doi: 10.1167/18.5.11.
Previous studies have shown that humans can discriminate spectral changes in illumination and that this sensitivity depends both on the chromatic direction of the illumination change and on the ensemble of surfaces in the scene. These studies, however, always used stimulus scenes with a fixed surface-reflectance layout. Here we compared illumination discrimination for scenes in which the surface reflectance layout remains fixed (fixed-surfaces condition) to those in which surface reflectances were shuffled randomly across scenes, but with the mean scene reflectance held approximately constant (shuffled-surfaces condition). Illumination discrimination thresholds in the fixed-surfaces condition were commensurate with previous reports. Thresholds in the shuffled-surfaces condition, however, were considerably elevated. Nonetheless, performance in the shuffled-surfaces condition exceeded that attainable through random guessing. Analysis of eye fixations revealed that in the fixed-surfaces condition, low illumination discrimination thresholds (across observers) were predicted by low overall fixation spread and high consistency of fixation location and fixated surface reflectances across trial intervals. Performance in the shuffled-surfaces condition was not systematically related to any of the eye-fixation characteristics we examined for that condition, but was correlated with performance in the fixed-surfaces condition.
先前的研究表明，人类能够辨别光照中的光谱变化，而且这种敏感性既取决于光照变化的色彩方向，也取决于场景中表面的总体情况。然而，这些研究总是使用表面反射率布局固定的刺激场景。在这里，我们将表面反射率布局保持固定的场景（固定表面条件）下的光照辨别能力，与表面反射率在不同场景中随机排列但场景平均反射率大致保持恒定的场景（随机表面条件）下的光照辨别能力进行了比较。固定表面条件下的光照辨别阈值与先前的报告一致。然而，随机表面条件下的阈值则大幅提高。尽管如此，随机表面条件下的表现仍超过了随机猜测所能达到的水平。对眼动注视的分析表明，在固定表面条件下，（不同观察者的）低光照辨别阈值可通过较低的总体注视分散度以及跨试验间隔的注视位置和注视表面反射率的高一致性来预测。随机表面条件下的表现与我们针对该条件所考察的任何眼动注视特征均无系统关联，但与固定表面条件下的表现相关。
