Physiological Correlates of Sensory Consciousness: Evidence for a Perceptual Awareness Negativity

Abstract

We critically review the recent literature on six EEG and MEG markers of the neural correlates of consciousness (NCC) for visual, auditory and tactile stimuli in neurotypical volunteers and neurological patients. After ruling out four of these as candidate NCC, we focus on two prominent evoked signals: an early, modality-specific negativity, termed the visual or auditory awareness negativity (VAN and AAN, respectively) and a late, modality-independent positivity termed the P3b. More than twelve diverse experimental studies found that the P3b is absent despite consciously seeing, hearing, or feeling stimuli, ruling out the P3b as a true NCC. In contrast, no convincing evidence for a dissociation between the awareness negativities and consciousness has been reported thus far. Furthermore, there is evidence for an equivalent signal in the tactile domain, which we term the somatosensory awareness negativity (SAN). These three neural signals are usually maximal on the side of the scalp contralateral to the evoking stimulus, above the associated sensory cortices. We conclude that the data from these three modalities is consistent with a generalized awareness negativity (GAN) correlated with perceptual consciousness that arises 120-200 ms following stimulus onset and originates from the underlying sensory cortices. The identification of this GAN points towards new, promising avenues for future research and raises an array of concrete questions that can be empirically investigated.

More than a feeling: scalp EEG and eye correlates of conscious tactile perception

“…for not perceived trials but not for perceived, our data is inconsistent with the attribution of the P100 as simply a marker of positive perceptual status. Dembski, Koch, and Pitts (2021) suggest that the N140 negativity is the somatosensory equivalent to the visual and the auditory awareness negativity (VAN and AAN respectively), and that these negativities, collectively, should be considered a main marker of consciousness. However, there is some variability about the interpretation and localization of a negativity occurring at ~140 ms post-stimulus across studies.…”