Subjective visual awareness emerges prior to P3

Abstract

Studies on the neural basis of visual awareness, the subjective experience of seeing, have found several potential neural correlates of visual awareness. Some of them may not directly correlate with awareness but with post-perceptual processes, such as reporting one's awareness of the stimulus. We dissociated potential electrophysiological correlates of visual awareness from those occurring during response selection and thus co-occurring with post-perceptual processing. The participants performed two GO-NOGO conditions. In the aware-GO condition they responded with a key press when they were aware of the stimulus and withheld responding when they were unaware of it. In the unaware-GO condition they withheld responding when they were aware and responded when they were not aware of the stimulus. Thus, event-related potentials could be measured to aware and unaware trials when responding was required and when not required. The results revealed that the N200 amplitude (180-280 ms) over the occipital and posterior temporal cortex was enhanced in aware trials as compared with trials without awareness. This effect (visual awareness negativity, VAN) did not depend on responding. The amplitude of P3 (350-450 ms) also was enhanced in aware trials as compared with unaware trials. In addition, the amplitudes in the P3 time window depended on responding: they were greater when awareness was mapped to GO-response than when not, suggesting that P3 reflects post-perceptual processing, that is, it occurs after awareness has emerged. These findings support theories of visual awareness that assume a relatively early onset of visual awareness before P3.

Subjective perceptual experience tracks the neural signature of sensory evidence accumulation during decision formation

“…Moreover, our data show that the CPP was also present in catch trials, when no visual evidence was physically displayed. The signal recorded during catch trials resembles the shallow evidence accumulation signal observed in monkey parietal areas when no evidence was displayed [37], and replicates previous findings in humans showing a low amplitude late potential in catch trials or when clearly subliminal stimuli were presented [38,39]. However, it is unclear what this late potential in the absence of sensory evidence reflects, besides that it corroborates that the CPP aligns with an internal quantity.…”

“…Moreover, and in further analogy to Kang et al [21], our study suggests a remarkable degree of reliance that can be placed on observers' subjective impressions to gain access to core internal decision quantities. Intriguingly, a parallel line of research on the neural correlates of consciousness [22] has also identified a late potential of similar topography and latency that tracks conscious reports [23,24,25,26,27,28], further substantiating a link between the CPP and conscious perception.…”

Lights from the Dark: Neural Responses from a Blind Visual Hemifield

“…Both components were present irrespective of whether the stimuli were static or moving and therefore cannot be considered as related to the behavioral evidence of a static-motion discrimination but rather to the “feeling that something appeared in the blind field”. The time window of the N1-P2a components is roughly compatible with that of the Visual Awareness Negativity (VAN) that is, a ERP component resulting from the difference between conscious and unconscious stimulus processing (Koivisto and Grassini, 2016; Koivisto et al, 2016). Notably, the electrode location where the N1 was clearly detectable was widespread in the ipsilesional hemisphere, see Figure 6.…”

Conscious Perception: Time for an Update?

“…An Activation Likelihood Estimation (ALE) meta-analysis performed recently Bisenius and colleagues (Bisenius, Trapp, Neumann, & Schroeter, 2015) yielded diffused activity that included clusters of activation in inferior and middle occipital gyrus; fusiform gyrus; inferior temporal gyrus; caudate nucleus; insula; inferior, middle, and superior frontal gyri; precuneus; as well as in inferior and superior parietal lobules. In the temporal domain, as the explored space is more restricted, the P3b component (~350 ms after stimulus onset) and a negative early component, usually referred to as Visual Awareness Negativity (VAN, ~200 ms after stimulus onset) stand-out as potential NCCs (Koivisto & Revonsuo, 2003;Koivisto, Salminen-Vaparanta, Grassini, Revonsuo, & Foxe, 2016). According to the taxonomy put forward by Aru (Aru, Bachmann, Singer, & Melloni, 2012) and colleagues , the genuine NCC should be distinguished from (i) events of that precede and support consciousness "NCC-pr", and (ii) events that follow consciousness and are the consequence of it "NCCco".…”