Chung Susana T L, Levi Dennis M, Li Roger W
College of Optometry and Center for Neuro-Engineering and Cognitive Science, University of Houston, Houston, TX, USA.
Vision Res. 2006 Mar;46(6-7):1038-47. doi: 10.1016/j.visres.2005.10.013. Epub 2005 Dec 6.
Performance for identifying luminance-defined letters in peripheral vision improves with training. The purpose of the present study was to examine whether performance for identifying contrast-defined letters also improves with training in peripheral vision, and whether any improvement transfers to luminance-defined letters. Eight observers were trained to identify contrast-defined letters presented singly at 10 degrees eccentricity in the inferior visual field. Before and after training, we measured observers' thresholds for identifying luminance-defined and contrast-defined letters, embedded within a field of white luminance noise (maximum luminance contrast=0, 0.25, and 0.5), at the same eccentric location. Each training session consisted of 10 blocks (100 trials per block) of identifying contrast-defined letters at a background noise contrast of 0.5. Letters (x-height=4.2 degrees) were the 26 lowercase letters of the Times-Roman alphabet. Luminance-defined letters were generated by introducing a luminance difference between the stimulus letter and its mid-gray background. The background noise covered both the letter and its background. Contrast-defined letters were generated by introducing a differential noise contrast between the group of pixels that made up the stimulus letter and the group of pixels that made up the background. Following training, observers showed a significant reduction in threshold for identifying contrast-defined letters (p<0.0001). Averaged across observers and background noise contrasts, the reduction was 25.8%, with the greatest reduction (32%) occurring at the trained background noise contrast. There was virtually no transfer of improvement to luminance-defined letters, or to an untrained letter size (2 x original), or an untrained retinal location (10 degrees superior field). In contrast, learning transferred completely to the untrained contralateral eye. Our results show that training improves performance for identifying contrast-defined letters in peripheral vision. This perceptual learning effect seems to be stimulus-specific, as it shows no transfer to the identification of luminance-defined letters. The complete interocular transfer, and the retinotopic (retinal location) and size specificity of the learning effect are consistent with the properties of neurons in early visual area V2.
通过训练，在周边视觉中识别亮度定义字母的表现会得到改善。本研究的目的是检验在周边视觉中，识别对比度定义字母的表现是否也会通过训练得到改善，以及这种改善是否会迁移到亮度定义字母上。八名观察者接受训练，以识别在下视野中单独呈现于10度偏心度处的对比度定义字母。在训练前后，我们测量了观察者在相同偏心位置识别嵌入白色亮度噪声场（最大亮度对比度=0、0.25和0.5）中的亮度定义和对比度定义字母的阈值。每次训练 session 由10个 block（每个 block 100次试验）组成，在背景噪声对比度为0.5的情况下识别对比度定义字母。字母（x高度=4.2度）为 Times-Roman 字母表中的26个小写字母。亮度定义字母是通过在刺激字母与其中灰色背景之间引入亮度差异而生成的。背景噪声覆盖了字母及其背景。对比度定义字母是通过在构成刺激字母的像素组和构成背景的像素组之间引入差分噪声对比度而生成的。训练后，观察者在识别对比度定义字母的阈值上有显著降低（p<0.0001）。在观察者和背景噪声对比度之间进行平均，降低幅度为25.8%，在训练的背景噪声对比度下降低幅度最大（32%）。几乎没有改善迁移到亮度定义字母、未训练的字母大小（原始大小的2倍）或未训练的视网膜位置（上视野10度）。相比之下，学习完全迁移到了未训练的对侧眼睛。我们的结果表明，训练提高了在周边视觉中识别对比度定义字母的表现。这种知觉学习效应似乎是刺激特异性的，因为它没有迁移到亮度定义字母的识别上。完全的眼间迁移以及学习效应的视网膜定位（视网膜位置）和大小特异性与早期视觉区域V2中神经元的特性一致。
