Department of Psychology, University of Chicago, Chicago, IL, USA.
Institute for Mind and Biology, University of Chicago, Chicago, IL, USA.
Psychophysiology. 2021 Apr;58(4):e13779. doi: 10.1111/psyp.13779. Epub 2021 Feb 7.
A long-standing question in the field of vision research is whether scalp-recorded EEG activity contains sufficient information to identify stimulus chromaticity. Recent multivariate work suggests that it is possible to decode which chromaticity an observer is viewing from the multielectrode pattern of EEG activity. There is debate, however, about whether the claimed effects of stimulus chromaticity on visual evoked potentials (VEPs) are instead caused by unequal stimulus luminances, which are achromatic differences. Here, we tested whether stimulus chromaticity could be decoded when potential confounds with luminance were minimized by (1) equating chromatic stimuli in luminance using heterochromatic flicker photometry for each observer and (2) independently varying the chromaticity and luminance of target stimuli, enabling us to test whether the pattern for a given chromaticity generalized across wide variations in luminance. We also tested whether luminance variations can be decoded from the topography of voltage across the scalp. In Experiment 1, we presented two chromaticities (appearing red and green) at three luminance levels during separate trials. In Experiment 2, we presented four chromaticities (appearing red, orange, yellow, and green) at two luminance levels. Using a pattern classifier and the multielectrode pattern of EEG activity, we were able to accurately decode the chromaticity and luminance level of each stimulus. Furthermore, we were able to decode stimulus chromaticity when we trained the classifier on chromaticities presented at one luminance level and tested at a different luminance level. Thus, EEG topography contains robust information regarding stimulus chromaticity, despite large variations in stimulus luminance.
一个长期存在于视觉研究领域的问题是头皮记录的 EEG 活动是否包含足够的信息来识别刺激的色度。最近的多元工作表明，从 EEG 活动的多电极模式中解码观察者正在观看的色度是可能的。然而，关于视觉诱发电位 (VEP) 的刺激色度的声称效应是否是由非彩色差异的刺激亮度引起的存在争议。在这里，我们通过以下两种方法测试了在最小化与亮度相关的潜在混淆时，刺激色度是否可以被解码：（1）使用每个观察者的异谱闪烁光度计使色度刺激在亮度上相等，（2）独立地改变目标刺激的色度和亮度，使我们能够测试给定色度的模式是否在亮度的广泛变化中普遍存在。我们还测试了从头皮上的电压分布中是否可以解码亮度变化。在实验 1 中，我们在单独的试验中呈现了三种亮度水平下的两种色度（呈现红色和绿色）。在实验 2 中，我们在两种亮度水平下呈现了四种色度（呈现红色、橙色、黄色和绿色）。使用模式分类器和 EEG 活动的多电极模式，我们能够准确地解码每个刺激的色度和亮度水平。此外，当我们在一个亮度水平上训练分类器并在不同的亮度水平上进行测试时，我们能够解码刺激的色度。因此，尽管刺激亮度有很大变化，但 EEG 地形图包含有关刺激色度的可靠信息。
