Eye contact facilitates awareness of faces during interocular suppression

Eye contact captures attention and receives prioritized visual processing. Here we asked whether eye contact might be processed outside conscious awareness. Faces with direct and averted gaze were rendered invisible using interocular suppression. In two experiments we found that faces with direct gaze overcame such suppression more rapidly than faces with averted gaze. Control experiments ruled out the influence of low-level stimulus differences and differential response criteria. These results indicate an enhanced unconscious representation of direct gaze, enabling the automatic and rapid detection of other individuals making eye contact with the observer

Sustained invisibility through crowding and continuous flash suppression: a comparative review

The study of non-conscious vision benefits from several alternative methods that allow the suppression of an image from awareness. Here, we present and compare two of them that are particularly well-suited for creating sustained periods of invisibility, namely visual crowding and continuous flash suppression (CFS). In visual crowding, a peripheral image surrounded by similar flankers becomes impossible to discriminate. In CFS, an image presented to one eye becomes impossible to detect when rapidly changing patterns are presented to the other eye. After discussing the experimental specificities of each method, we give a comparative overview of the main empirical results derived from them, from the mere analysis of low-level features to the extraction of semantic contents. We conclude by proposing practical guidelines and future directions to obtain more quantitative and systematic measures of non-conscious processes under prolonged stimulation

Adults' Awareness of Faces Follows Newborns' Looking Preferences

From the first days of life, humans preferentially orient towards upright faces, likely reflecting innate subcortical mechanisms. Here, we show that binocular rivalry can reveal face detection mechanisms in adults that are surprisingly similar to inborn face detection mechanism. We used continuous flash suppression (CFS), a variant of binocular rivalry, to render stimuli invisible at the beginning of each trial and measured the time upright and inverted stimuli needed to overcome such interocular suppression. Critically, specific stimulus properties previously shown to modulate looking preferences in neonates similarly modulated adults' awareness of faces presented during CFS. First, the advantage of upright faces in overcoming CFS was strongly modulated by contrast polarity and direction of illumination. Second, schematic patterns consisting of three dark blobs were suppressed for shorter durations when the arrangement of these blobs respected the face-like configuration of the eyes and the mouth, and this effect was modulated by contrast polarity. No such effects were obtained in a binocular control experiment not involving CFS, suggesting a crucial role for face-sensitive mechanisms operating outside of conscious awareness. These findings indicate that visual awareness of faces in adults is governed by perceptual mechanisms that are sensitive to similar stimulus properties as those modulating newborns' face preferences

Size Aftereffects Are Eliminated When Adaptor Stimuli Are Prevented from Reaching Awareness by Continuous Flash Suppression

Size aftereffects are a compelling perceptual phenomenon in which we perceive the size of a stimulus as being different than it actually is following a period of visual stimulation of an adapter stimulus with a different size. Here, we used continuous flash suppression (CFS) to determine if size aftereffects require a high-level appraisal of the adapter stimulus. The strength of size aftereffects was quantified following a 3-s exposure to perceptually visible and invisible adapters. Participants judged the size of a target that followed the adapter in comparison to a subsequent reference. Our experiments demonstrate that the adapter no longer influenced the perceived size of the subsequent target stimulus under CFS. We conclude that the perception of size aftereffects is prevented when CFS is used to suppress the conscious awarness of the adapting stimulus

Privileged access to awareness for faces and objects of expertise

Access to visual awareness for human faces is strongly influenced by spatial orientation: Under continuous flash suppression (CFS), upright faces break into awareness more quickly than inverted faces. This effect of inversion for faces is larger than for a wide range of other animate and inanimate objects. Here we asked whether this apparently specific sensitivity to upright faces reflects face-specific detection mechanisms or whether it reflects perceptual expertise more generally. We tested car experts who varied in their degree of car and face expertise and measured the time upright and inverted faces, cars, and chairs needed to overcome CFS and break into awareness. Results showed that greater car expertise was correlated with larger car inversion effects under CFS. A similar relation between better discrimination performance and larger CFS inversion effects was found for faces. CFS inversion effects are thus modulated by perceptual expertise for both faces and cars. These results demonstrate that inversion effects in conscious access are not unique to faces but similarly exist for other objects of expertise. More generally, we interpret these findings as suggesting that access to awareness and exemplar-level discrimination rely on partially shared perceptual mechanisms. (PsycINFO Database Recor

Own-race and own-age biases facilitate visual awareness of faces under interocular suppression

The detection of a face in a visual scene is the first stage in the face processing hierarchy. Although all subsequent, more elaborate face processing depends on the initial detection of a face, surprisingly little is known about the perceptual mechanisms underlying face detection. Recent evidence suggests that relatively hard-wired face detection mechanisms are broadly tuned to all face-like visual patterns as long as they respect the typical spatial configuration of the eyes above the mouth. Here, we qualify this notion by showing that face detection mechanisms are also sensitive to face shape and facial surface reflectance properties. We used continuous flash suppression (CFS) to render faces invisible at the beginning of a trial and measured the time upright and inverted faces needed to break into awareness. Young Caucasian adult observers were presented with faces from their own race or from another race (race experiment) and with faces from their own age group or from another age group (age experiment). Faces matching the observers’ own race and age group were detected more quickly. Moreover, the advantage of upright over inverted faces in overcoming CFS, i.e., the face inversion effect (FIE), was larger for own-race and own-age faces. These results demonstrate that differences in face shape and surface reflectance influence access to awareness and configural face processing at the initial detection stage. Although we did not collect data from observers of another race or age group, these findings are a first indication that face detection mechanisms are shaped by visual experience with faces from one’s own social group. Such experience-based fine-tuning of face detection mechanisms may equip in-group faces with a competitive advantage for access to conscious awareness

Early cross-modal interactions and adult human visual cortical plasticity revealed by binocular rivalry

In this research binocular rivalry is used as a tool to investigate different aspects of visual and multisensory perception. Several experiments presented here demonstrated that touch specifically interacts with vision during binocular rivalry and that the interaction likely occurs at early stages of visual processing, probably V1 or V2. Another line of research also presented here demonstrated that human adult visual cortex retains an unexpected high degree of experience-dependent plasticity by showing that a brief period of monocular deprivation produced important perceptual consequences on the dynamics of binocular rivalry, reflecting a homeostatic plasticity. In summary, this work shows that binocular rivalry is a powerful tool to investigate different aspects of visual perception and can be used to reveal unexpected properties of early visual cortex

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

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 event-related 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