Abstract
It remains controversial whether visual awareness is correlated with early activation indicated by VAN (visual awareness negativity), as the recurrent process hypothesis theory proposes, or with later activation indicated by P3 or LP (late positive), as suggested by global workspace theories. To address this issue, a backward masking task was adopted, in which participants were first asked to categorize natural scenes of color photographs and line-drawings and then to rate the clarity of their visual experience on a Perceptual Awareness Scale (PAS). The interstimulus interval between the scene and the mask was manipulated. The behavioral results showed that categorization accuracy increased with PAS ratings for both color photographs and line-drawings, with no difference in accuracy between the two types of images for each rating, indicating that the experience rating reflected visibility. Importantly, the event-related potential (ERP) results revealed that for correct trials, the early posterior N1 and anterior P2 components changed with the PAS ratings for color photographs, but did not vary with the PAS ratings for line-drawings, indicating that the N1 and P2 do not always correlate with subjective visual awareness. Moreover, for both types of images, the anterior N2 and posterior VAN changed with the PAS ratings in a linear way, while the LP changed with the PAS ratings in a non-linear way, suggesting that these components relate to different types of subjective awareness. The results reconcile the apparently contradictory predictions of different theories and help to resolve the current debate on neural correlates of visual awareness.
Highlights
An increasing amount of attention has been given to neural correlates of visual awareness, i.e., the subjective experience of seeing
There was no difference for accuracy between color photographs and line-drawings for each experience rating and the accuracy for both types of image gradually increased with rating, consistent with the experience ratings reflecting visibility
The event-related potential (ERP) results showed that the posterior P1 amplitude did not change with the Perceptual Awareness Scale (PAS) ratings, confirming previous findings that the early P1 component is not related to visual awareness (Del Cul et al, 2007; Koivisto et al, 2008; Melloni et al, 2011)
Summary
An increasing amount of attention has been given to neural correlates of visual awareness, i.e., the subjective experience of seeing. Neural imaging studies have revealed that a distributed system, including the primary visual cortex (V1), V2, temporal, parietal, and frontal areas, plays a crucial role in the generation of visual awareness (see Koch et al, 2016 for a review; Rees, 2001; Vuilleumier et al, 2002; Salminen-Vaparanta et al, 2012). There is no agreement on what the identity of the neural indicator is for the emergence of visual awareness. The identity of the neural indicator for the emergence of visual awareness is still unclear
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