关键词: 非注意视盲, 情绪面孔, 视觉失匹配负波, 视觉意识负波, 晚期正成分

Abstract:

The neural correlates of consciousness are debatable due to the confounding effects of subjective reports. In addition, although previous studies have suggested that vMMN is relatively insensitive to the manipulation of visual attention, the relationship between vMMN and visual consciousness remains unclear. The inattentional blindness paradigm can not only effectively manipulate visual consciousness, but also explore the conscious process without relying on subjective reports. Therefore, we used this paradigm to manipulate visual consciousness. Moreover, we introduced emotional (happy and fearful) faces, which are biologically and socially significant visual stimuli, to explore the neural correlates of consciousness and the relationship between automatic detection of changes and visual consciousness.
Fifty-six Chinese participants took part in the present study. We recorded electroencephalography (EEG) in three phases. In phase A, the participants needed to detect changes of the red dots. However, because they were not informed of the existence of emotional faces, some participants were unconscious of the task-irrelevant emotional faces. In phase B and C, all participants were informed about the emotional faces. Thus, they were conscious of the emotional faces. Specifically, in phase B, the participants still needed to detect changes of the red dots, and the emotional faces are task-irrelevant. However, in phase C, the participants were asked to detect changes of emotional faces, and thus they were task-relevant in phase C. To check the conscious state of emotional faces, subjects were required to fill out an awareness questionnaire after completing phases A and B. Then the participants were divided into unconscious group and conscious group according to their conscious state of emotional faces in phase A.
Results can be summarized as following. (1) Two primary contrasts were made: conscious versus unconscious (equally task irrelevant) to reveal the neural correlates of consciousness and task-relevant versus task-irrelevant (equally aware) to reveal the effect of task relevance. In the early stage, the results showed that the standard emotional faces in phase B evoked significantly stronger negativity than in phase A for the unconscious group, suggesting that the conscious process of emotional faces evoked visual awareness negativity (VAN) (200~300 ms). By contrast, compared with the task-irrelevant condition (phase B), the standard emotional faces under the task-relevant condition (phase C) evoked significantly stronger negativity, suggesting that task relevance evoked selection negativity (SN) (180~250 ms). This provides evidence that VAN is a neural correlate of consciousness by separating the neural activity of visual awareness and selective attention of emotional faces. Moreover, in the late stage, the results showed that the standard emotional faces in phase B evoked significantly stronger positivity than in phase A for the unconscious group, suggesting that the conscious process of emotional faces evoked late positivity (LP) (300~400 ms) and late occipital positivity (LOP) (400~600 ms). By contrast, compared with the task-irrelevant condition (phase B), the standard emotional faces under the task-relevant condition (phase C) evoked significantly stronger positivity, suggesting that task relevance evoked LP (300~400 ms) and LOP (400~500 ms) that may reflect the post-perceptual processing of target stimuli. Therefore, this study also provides evidence that LP and LOP are neural correlates of consciousness without the confounding effects of task relevance. In short, VAN may reflect the early perceptual process of emotional faces, LP and LOP may reflect the further process of classifying and recognizing the stimulus representations of emotional faces, such as assessing the emotional valence of faces.
(2) The ERP results showed that a vMMN effect was found in all three phases: compared to standard emotional faces, deviant evoked significantly stronger negativity at the 250~350 ms latency in three phases. Importantly, a vMMN effect was observed for the unconscious group in the phase A. Furthermore, no amplitude difference of vMMN was observed between the aware (phase B) and the unaware (phase A) conditions among unconscious group, suggesting that the deviance processing of emotional faces is independent of visual consciousness. Compared with Chen (2020), this study provides evidence that the deviance processing of emotional faces is independent of visual consciousness under the condition that the unconsciousness level is manipulated more effectively.
(3) Compared with the task-irrelevant condition (phase B), the vMMN amplitude under the task-relevant condition (phase C) was larger, suggesting that task relevance modulates the amplitude of vMMN and the attentional effect of task relevance promotes the deviance processing of emotional faces.
The conclusions of this study can be summarized as following. (1) VAN is the neural correlate of consciousness under the condition of avoiding confounding effects of visual attention, and LP and LOP are the neural correlates of consciousness under the condition of avoiding confounding effects of task relevance. (2) The visual awareness of emotional faces has different ERP indicators at different time stages. Specifically, VAN reflects the early perceptual experience, LP and LOP reflect the late conscious experience of non-perceptual information. (3) The deviance processing of emotional faces is independent of visual consciousness. (4) The attentional effect of task relevance modulates the deviance processing of emotional faces.

Key words: inattentional blindness, emotional faces, visual mismatch negativity, visual awareness negativity, late positivity