Absence of Face-specific Cortical Activity in the Complete Absence of Awareness: Converging Evidence from Functional Magnetic Resonance Imaging and Event-related Potentials

Abstract

Abstract■ In this study, we explored the neural correlates of perceptual awareness during a masked face detection task. To assess awareness more precisely than in previous studies, participants employed a 4-point scale to rate subjective visibility. An eventrelated fMRI and a high-density ERP study were carried out. Imaging data showed that conscious face detection was linked to activation of fusiform and occipital face areas. Frontal and parietal regions, including the pre-SMA, inferior frontal sulcus, anterior insula/frontal operculum, and intraparietal sulcus, also responded strongly when faces were consciously perceived. In contrast, no brain area showed face-selective activity when participants reported no impression of a face. ERP results showed that conscious face detection was associated with enhanced N170 and also with the presence of a second negativity around 300 msec and a slow positivity around 415 msec. Again, face-related activity was absent when faces were not consciously perceived. We suggest that, under conditions of backward masking, ventral stream and fronto-parietal regions show similar, strong links of face-related activity to conscious perception and stress the importance of a detailed assessment of awareness to examine activity related to unseen stimulus events. ■

Neural processing stages during object-substitution masking and their relationship to perceptual awareness

“…First, activity reflecting the attentional shifting to the lateralized target was markedly reduced for unaware trials, as reflected by a reduced N2pc component beginning at 180 ms. Concurrently, a lateralized negativity with a distribution similar to the previously characterized visual awareness negativity (VAN, present for images that were seen and not those unseen) (Rodriguez et al, 2012) was reduced here in cases of unawareness. However, as noted above, this response is likely a convolution of the VAN and face-specific negativity, both of which are reduced in cases of unawareness (Figure S1).…”

Prioritized Detection of Personally Familiar Faces

“…An alternative route that bypasses the visual ventral temporal pathway has been proposed for fast processing of this type of stimuli [21]. The existence of such a pathway in processing affective stimuli in humans has been questioned by others who suggest that the visual pathway may be sufficient for fast processing of these stimuli – even with reduced attentional resources and awareness – and, further, propose a role for top-down biasing of visual cortex involving frontal-parietal regions [22]–[24]. An alternative direct frontal-occipital pathway has been proposed to explain unconscious face processing in normal cognition and covert recognition in prosopagnosics [25].…”

Emotional Processing of Personally Familiar Faces in the Vegetative State

“…Evidence that unseen stimuli undergo some unconscious processing in the primary and selective visual areas [21] as well as the amygdala [22] has previously been taken to imply that activity per se in these areas is not sufficient for conscious access. However, a recent study has shown that FFA activation to faces may in itself be a correlate of aware perception [23]. In the case of the amygdala as well, support for the notion that its activation is related to aware perception is growing [17].…”