In "The Quest for Consciousness," Caltech neuroscientist Christof Koch explores the biological basis of consciousness.

Conscious experience is one of the most difficult and thorny problems in psychological science. Its study has been neglected for many years, either because it was thought to be too difficult, or because the relevant evidence was thought to be poor. Bernard Baars suggests a way to specify empirical constraints on a theory of consciousness by contrasting well-established conscious phenomena - such as stimulus representations known to be attended, perceptual, and informative - with closely comparable unconscious ones - such as (...) stimulus representations known to be preperceptual, unattended, or habituated. Adducing data to show that consciousness is associated with a kind of global workplace in the nervous system, and that several brain structures are known to behave in accordance with his theory, Baars helps to clarify many difficult problems. (shrink)

This study examines whether human gaze lacking the confounding factor of eye whites can be processed unconsciously and explores the critical aspects for such process. Utilizing the continuous flash suppression paradigm, a schematic face—with direct or averted gaze, and with neutral, fearful or happy expressions—was presented to one eye while dynamic masks rendered it invisible to the other eye. Schematic faces were used to avoid unwanted influence from salient eye whites. Participants’ detection time of anything other than the masks was (...) used as an index of unconscious processing time. Faster detection was found for faces with direct gaze than those with averted gaze. However, there was no difference between detection times for different facial expressions and upright-face, inverted-face, and eyes-only conditions . These results confirm that, with schematic faces, gaze can be processed unconsciously regardless of facial expression, and eyes alone are sufficient for such process. (shrink)

There is currently no consensus regarding what measures are most valid to demonstrate perceptual processing without awareness. Likewise, whether conscious perception and unconscious processing rely on independent mechanisms or lie on a continuum remains a matter of debate. Here, we addressed these issues by comparing the time courses of subjective reports, objective discrimination performance and response priming during meta-contrast masking, under similar attentional demands. We found these to be strikingly similar, suggesting that conscious perception and unconscious processing cannot be dissociated (...) by their time course. Our results also demonstrate that unconscious processing, indexed by response priming, occurs, and that objective discrimination performance indexes the same conscious processes as subjective visibility reports. Finally, our results underscore the role of attention by showing that how much attention the stimulus receives relative to the mask, rather than whether processing is measured by conscious discrimination or by priming, determines the time course of meta-contrast masking. (shrink)

Face perception, perhaps the most highly developed visual skill in humans, is mediated by a distributed neural system in humans that is comprised of multiple, bilateral regions. We propose a model for the organization of this system that emphasizes a distinction between the representation of invariant and changeable aspects of faces. The representation of invariant aspects of faces underlies the recognition of individuals, whereas the representation of changeable aspects of faces, such as eye gaze, expression, and lip movement, underlies the (...) perception of information that facilitates social communication. The model is also hierarchical insofar as it is divided into a core system and an extended system. The core system is comprised of occipitotemporal regions in extrastriate visual cortex that mediate the visual analysis of faces. In the core system, the representation of invariant aspects is mediated more by the face-responsive region in the fusiform gyrus, whereas the representation of changeable aspects is mediated more by the face-responsive region in the superior temporal sulcus. The extended system is comprised of regions from neural systems for other cognitive functions that can be recruited to act in concert with the regions in the core system to extract meaning from faces. (shrink)

This paper reviews the history of psychological investigations of unconscious perception and summarizes the current status of experimental research in this area of investigation. The research findings described in the paper illustrate how it is possible to distinguish experimentally between conscious and unconscious perception. The most successful experimental strategy has been to show that a stimulus can have qualitatively different consequences on cognitive and affective reactions depending on whether it was consciously or unconsciously perceived. In addition, recent studies of patients (...) undergoing general anaesthesia have shown that the effects of stimuli perceived unconsciously during surgery can last for approximately 24 hours. Taken together, the results of these recent psychological investigations provide empirical support for the importance of unconsciously perceived information in determining cognitive and affective reactions. (shrink)

The study aims to help characterize the sort of structures about which people can acquire unconscious knowledge. It is already well established that people can implicitly learn n-grams and also repetition patterns. We explore the acquisition of unconscious structural knowledge of symmetry. Chinese Tang poetry uses a specific sort of mirror symmetry, an inversion rule with respect to the tones of characters in successive lines of verse. We show, using artificial poetry to control both n-gram structure and repetition patterns, that (...) people can implicitly learn to discriminate inversions from non-inversions, presenting a challenge to existing models of implicit learning. (shrink)

Previous studies suggested that emotions can be correctly interpreted from facial expressions in the absence of conscious awareness of the face. Our goal was to explore whether subordinate information about a face’s gender and race could also become available without awareness of the face. Participants classified the race or the gender of unfamiliar faces that were ambiguous with regard to these dimensions. The ambiguous faces were preceded by face-images that unequivocally represented gender and race, rendered consciously invisible by simultaneous continuous-flash-suppression. (...) The classification of ambiguous faces was biased away from the category of the adaptor only when it was consciously visible. The duration of subjective visibility correlated with the aftereffect strength. Moreover, face identity was consequential only if consciously perceived. These results suggest that while conscious awareness is not needed for basic level categorization, it is needed for subordinate categorization. Emotional information might be unique in this respect. (shrink)

The nonconscious orientation of attention to famous faces was investigated using masked 17 ms stimulus exposure. Each trial presented a simultaneous pair of one famous and one unfamiliar face, matched on physical characteristics, one each in left visual field (LVF) and right visual field (RVF). These were followed by a dot probe in either LVF or RVF to which participants made a speeded two-alternative forced-choice discrimination response. Participants subsequently evaluated the affective valence (good/evil) of the famous persons on a 7-point (...) scale. Higher accuracy of dot probe discrimination in the same visual field (VF) as the famous face suggested that attention was oriented towards faces of persons evaluated “good”, but a reverse orientation effect was observed for those evaluated “evil”. The awareness check presented the same face pairs under the same conditions, and participants were at chance in a task of selecting the famous face in each pair. The results suggest that famous faces can be identified without awareness, and that attention is attracted by the faces of famous persons not regarded as “evil”. (shrink)

Illusions that produce perceptual suppression despite constant retinal input are used to manipulate visual consciousness. Here we report on a powerful variant of existing techniques, Continuous Flash Suppression. Distinct images flashed successively around 10 Hz into one eye reliably suppress an image presented to the other eye. Compared to binocular rivalry, the duration of perceptual suppression increased more than 10-fold. Using this tool we show that the strength of the negative afterimage of an adaptor was reduced by half when it (...) was perceptually suppressed by input from the other eye. The more likely the adaptor was completely suppressed, the larger the reduction of the afterimage intensity. Paradoxically, trial-to-trial visibility of the adaptor did not correlate with the degree of suppression. Our results imply that formation of afterimages involves neuronal structures that access input from both eyes, but that do not correspond directly to the neuronal correlates of perceptual awareness. (shrink)

How internal categories influence how we perceive the world is a fundamental question in cognitive sciences. Yet, the relation between perceptual awareness and perceptual categorization has remained largely uncovered so far. Here, we addressed this question by focusing on face perception during subliminal and conscious perception. We used morphed continua between two face identities and we assessed, through a masked priming paradigm, the perceptual processing of these morphed faces under subliminal and supraliminal conditions. We found that priming from subliminal faces (...) followed linearly the information present in the primes, while priming from visible faces revealed a non-linear profile, indicating a categorical processing of face identities. Our results thus point to a special relation between perceptual awareness and categorical processing of faces, and support the dissociation between two modes of information processing: a subliminal mode involving analog treatment of stimuli information, and a supraliminal mode relying on discrete representation. (shrink)