Low pre-stimulus EEG alpha power amplifies visual awareness but not visual sensitivity
Low pre-stimulus EEG alpha power amplifies visual awareness but not visual sensitivity
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DOI：
10.1111/ejn.15166
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发表时间：
2021-03-24
影响因子：
3.4
通讯作者：
Thut, Gregor
中科院分区：
文献类型：
--
作者：
Benwell, Christopher S. Y.;Coldea, Andra;Thut, Gregor
刺激前的神经振荡活动与对感觉刺激的觉察程度有关。更具体地说，刺激开始前的低频振荡(主要是在阿尔法频段，即8-14赫兹)的功率与视觉任务中的主观表现指标(如自信心和视觉觉知)呈负相关。有趣的是，相同的脑电信号似乎并不影响任务绩效的客观衡量标准(即准确性)。我们在这里研究了当使用严格的精确度测量时，这种解离是否成立。以前的脑电研究已经采用了2-替代强迫选择(2-AFC)辨别任务，将刺激前振荡活动与正确/不正确的反应联系起来，作为单次试验水平的准确性/客观表现的指标。然而，2-AFC任务不能很好地估计单次试验的准确性，因为许多被归类为正确的回答将被猜测所污染(正确应答率的机会为50%)。取而代之的是，我们采用了19个AFC字母识别任务来衡量每个试验的准确性和主观报告的知觉水平。由于正确的猜测率可以忽略不计(-5%)，这项任务提供了一种更纯粹的准确性度量。我们的结果复制了刺激前α/β频段功率和知觉知觉评级之间的反向关系，而不存在与识别准确性的联系。刺激前的振荡阶段并不能预测主观意识或准确性。因此，我们的结果证实了前刺激脑电功率-任务性能链接在主观和客观性能测量中的分离，并进一步证实了前刺激阿尔法功率作为视觉意识的神经预测因子。
Pre-stimulus oscillatory neural activity has been linked to the level of awareness of sensory stimuli. More specifically, the power of low-frequency oscillations (primarily in the alpha-band, i.e., 8-14 Hz) prior to stimulus onset is inversely related to measures of subjective performance in visual tasks, such as confidence and visual awareness. Intriguingly, the same EEG signature does not seem to influence objective measures of task performance (i.e., accuracy). We here examined whether this dissociation holds when stringent accuracy measures are used. Previous EEG-studies have employed 2-alternative forced choice (2-AFC) discrimination tasks to link prestimulus oscillatory activity to correct/incorrect responses as an index of accuracy/objective performance at the single-trial level. However, 2-AFC tasks do not provide a good estimate of single-trial accuracy, as many of the responses classified as correct will be contaminated by guesses (with the chance correct response rate being 50%). Here instead, we employed a 19-AFC letter identification task to measure accuracy and the subjectively reported level of perceptual awareness on each trial. As the correct guess rate is negligible (-5%), this task provides a purer measure of accuracy. Our results replicate the inverse relationship between pre-stimulus alpha/ beta-band power and perceptual awareness ratings in the absence of a link to discrimination accuracy. Pre-stimulus oscillatory phase did not predict either subjective awareness or accuracy. Our results hence confirm a dissociation of the pre-stimulus EEG power-task performance link for subjective versus objective measures of performance, and further substantiate pre-stimulus alpha power as a neural predictor of visual awareness.