Neurocomputation and Neuroimaging Unit, Freie Universität Berlin, 14195 Berlin, Germany
Neurocomputation and Neuroimaging Unit, Freie Universität Berlin, 14195 Berlin, Germany.
J Neurosci. 2021 May 26;41(21):4686-4696. doi: 10.1523/JNEUROSCI.2950-20.2021. Epub 2021 Apr 13.
A central challenge in the study of conscious perception lies in dissociating the neural correlates of perceptual awareness from those reflecting its precursors and consequences. No-report paradigms have been instrumental in this endeavor, demonstrating that the event-related potential P300, recorded from the human scalp, reflects reports rather than awareness. However, these paradigms cannot probe the degree to which stimuli are consciously processed from trial to trial and, thus, leave open the possibility that the P300 is a genuine correlate of conscious access enabling reports. Here, instead of removing report requirements, we took the opposite approach and equated postperceptual task demands across conscious and unconscious trials by orthogonalizing target detection and overt reports in a somatosensory detection task. We used Bayesian model selection to track the transformation from physical to perceptual processing stages in the EEG data of 24 male and female participants and show that the early P50 component scaled with physical stimulus intensity, whereas the N140 component was the first correlate of target detection. The late P300 component was elicited for both perceived and unperceived stimuli and was not substantially modulated by target detection. This was in stark contrast to a control experiment using a classical direct report task, which replicated the P50 and N140 effects but additionally showed a strong effect of target detection in the P300 time range. Our results demonstrate the task dependence of the P300 in the somatosensory modality and show that late cortical potentials dissociate from perceptual awareness even when stimuli are always reported. The time it takes for sensory information to enter our conscious experience can be an indicator of the neural processing stages that lead to perceptual awareness. However, because many cognitive processes routinely correlate with perception, isolating those signals that uniquely reflect perceptual awareness is not a trivial task. Here, we show that late electroencephalography signals cease to correlate with somatosensory awareness when common task confounds are controlled. Importantly, by balancing report requirements instead of abolishing them, we show that the lack of late effects cannot be explained by a lack of conscious access. Instead, we propose that conscious access occurs earlier, at ∼150 ms, supporting the view that early activity in sensory cortices is a neural correlate of conscious perception.
意识知觉研究的一个核心挑战在于将知觉意识的神经相关物与反映其前体和结果的神经相关物区分开来。无报告范式在这方面发挥了重要作用，证明了从人类头皮记录的事件相关电位 P300 反映了报告而不是意识。然而，这些范式不能探测刺激在每次试验中被意识处理的程度，因此，仍然存在 P300 是意识进入并允许报告的真正相关物的可能性。在这里，我们没有取消报告要求，而是采取了相反的方法，通过在体感检测任务中正交化目标检测和显性报告，使有意识和无意识试验之间的后知觉任务需求相等。我们使用贝叶斯模型选择来跟踪 24 名男性和女性参与者的脑电图数据中从物理处理阶段到知觉处理阶段的转换，并表明早期 P50 成分与物理刺激强度成正比，而 N140 成分是目标检测的第一个相关物。晚期 P300 成分被感知和未感知的刺激引发，并且不受目标检测的显著调制。这与使用经典直接报告任务的对照实验形成鲜明对比，该实验复制了 P50 和 N140 效应，但另外在 P300 时间范围内显示出目标检测的强烈影响。我们的结果表明，在体感模式中 P300 具有任务依赖性，并且表明即使始终报告刺激，晚期皮质电位也与知觉意识分离。感觉信息进入我们意识经验所需的时间可以作为导致知觉意识的神经处理阶段的指标。然而，由于许多认知过程通常与知觉相关联，因此分离那些唯一反映知觉意识的信号并不是一项简单的任务。在这里，我们表明，当控制常见任务混淆时，晚期脑电图信号不再与体感意识相关。重要的是，通过平衡报告要求而不是取消它们，我们表明缺乏晚期效应不能用缺乏意识进入来解释。相反，我们提出意识进入发生得更早，约为 150 毫秒，支持了早期活动在感觉皮层中是意识知觉的神经相关物的观点。
