Perceptual decisions depend both on the features of the incoming stimulus and on the ongoing brain activity at the moment the stimulus is received. Specifically, trial-to-trial fluctuations in cortical excitability have been linked to fluctuations in the amplitude of prestimulus α oscillations (~8-13 Hz), which are in turn are associated with fluctuations in subjects' tendency to report the detection of a stimulus. It is currently unknown whether α oscillations bias postperceptual decision-making, or even bias subjective perception itself. To answer this question, we used a contrast discrimination task in which both male and female human subjects reported which of two gratings (one in each hemifield) was perceived as having a stronger contrast. Our EEG analysis showed that subjective contrast was reduced for the stimulus in the hemifield represented in the hemisphere with relatively stronger prestimulus α amplitude, reflecting reduced cortical excitability. Furthermore, the strength of this spontaneous hemispheric lateralization was strongly correlated with the magnitude of individual subjects' biases, suggesting that the spontaneous patterns of α lateralization play a role in explaining the intersubject variability in contrast perception. These results indicate that spontaneous fluctuations in cortical excitability, indicated by patterns of prestimulus α amplitude, affect perceptual decisions by altering the phenomenological perception of the visual world.

SIGNIFICANCE STATEMENT Our moment-to-moment perception of the world is shaped by the features of the environment surrounding us, as much as by the constantly evolving states that characterize our brain activity. Previous research showed how the ongoing electrical activity of the brain can influence whether a stimulus has accessed conscious perception. However, evidence is currently missing on whether these electrical brain states can be associated to the subjective experience of a sensory input. Here we show that local changes in patterns of electrical brain activity preceding visual stimulation can bias our phenomenological perception. Importantly, we show that the strength of these variations can help explain the great interindividual variability in how we perceive the visual environment surrounding us.

感知决策既取决于传入刺激的特征，也取决于收到刺激时正在进行的大脑活动。具体来说，皮层兴奋性的试验间波动与刺激前 α 振荡（~8-13 Hz）振幅的波动有关，而后者又与受试者报告检测到刺激的倾向的波动相关。 。目前尚不清楚α振荡是否会影响知觉后的决策，甚至会影响主观知觉本身。为了回答这个问题，我们使用了对比度辨别任务，其中男性和女性受试者都报告了两个光栅（每个半场一个）中哪一个被认为具有更强的对比度。我们的脑电图分析表明，刺激前 α 幅度相对较强的半球代表的半视野刺激的主观对比度降低，反映了皮质兴奋性降低。此外，这种自发半球偏侧化的强度与个体受试者偏差的大小密切相关，这表明α偏侧化的自发模式在解释对比感知的受试者间变异性方面发挥着重要作用。这些结果表明，刺激前 α 振幅模式所表明的皮层兴奋性的自发波动，通过改变视觉世界的现象学感知来影响感知决策。

意义陈述我们对世界的每时每刻的感知是由我们周围环境的特征以及我们大脑活动的不断变化的状态决定的。先前的研究表明，大脑持续的电活动如何影响刺激是否进入有意识的感知。然而，目前还没有证据表明这些脑电状态是否与感觉输入的主观体验相关。在这里，我们表明视觉刺激之前脑电活动模式的局部变化可能会导致我们的现象学感知产生偏差。重要的是，我们证明这些差异的强度可以帮助解释我们如何感知周围视觉环境的巨大个体差异。