The early but not the late neural correlate of auditory awareness is contralateral to auditory stimulation

Theories disagree as to whether it is the early or the late neural correlate of awareness plays a critical role in phenomenal awareness. According to recurrent processing theory, early activity in primary sensory areas should correspond closely to phenomenal awareness. In support, research with electroencephalography found that in the visual and somatosensory modality, an early neural correlate of awareness is contralateral to stimulation, whereas a late neural correlate of awareness does not appear to be lateralized. Thus, early activity is sensitive to the perceived location of visual and somatosensory stimulation. Critically, it is unresolved whether this is true also for hearing. In the present study (N = 26 students), we found that the early neural correlate of awareness (auditory awareness negativity, AAN) was contralateral to auditory stimulation, whereas the late (late positivity, LP) was not. Because these findings match those in the visual and somatosensory modalities, they suggest that recurrent processing theory is valid across modalities.

Visual processing: conscious until proven otherwise

Unconscious perception, or perception without awareness, describes a situation where an observer's behaviour is influenced by a stimulus of which they have no phenomenal awareness. Perception without awareness is often claimed on the basis of a difference in thresholds for tasks that do and do not require awareness, for example, detecting the stimulus (requiring awareness) and making accurate judgements about the stimulus (based on unconscious processing). Although a difference in thresholds would be expected if perceptual evidence were processed without awareness, such a difference does not necessitate that this is actually occurring: a difference in thresholds can also arise from response bias, or through task differences. Here we ask instead whether the pattern of performance could be obtained if the observer were aware of the evidence used in making their decisions. A backwards masking paradigm was designed using digits as target stimuli, with difficulty controlled by the time between target and mask. Performance was measured over three tasks: detection, graphic discrimination and semantic discrimination. Despite finding significant differences in thresholds measured using proportion correct, and in observer sensitivity, modelling suggests that these differences were not the result of perception without awareness. That is, the observer was not relying solely on unconscious information to make decisions.

Large scale temporal coordination of cortical activity as prerequisite for conscious experience

Phenomenal awareness, the ability to be aware of one’s sensations and feelings, emerges from the capacity of evolved brains to represent their own cognitive processes by iterating and self-reapplying the cortical operations that generate representations of the outer world. Search for the neuronal substrate of awareness therefore converges with the search for the neuronal code through which brains represent their environment. The hypothesis is put forward that the mammalian brain uses two complementary representational strategies. One consists of the generation of neurons responding selectively to particular constellations of features, and is based on selective recombination of inputs in hierarchically structured feed-forward architectures. The other relies on the dynamic association of large numbers of distributed neurons into functionally coherent cell assemblies which as a whole represent a content of cognition. Arguments and data are presented in favor of the second strategy as the one according to which meta-representations that support awareness are established. My hypothesis is that such distributed representations self-organize through transient synchronization of the oscillatory activity. Evidence showing that similar brain states are required both for the occurrence of these synchronization phenomena and for awareness is provided.

Localisation of “unseen” visual stimuli: Blindsight in normal observers?

We developed two experiments on normal subjects to simulate “blindsight”, i.e., above chance localization performance of visual stimuli without phenomenal awareness. In both experiments, visual targets were presented on a computer screen at one of six possible locations, followed by a metacontrast mask. Subjects (1) indicated whether they had seen the target stimulus or not, and (2) guessed at which location the stimulus had been presented. Fifty percent were blank trials. We found that even when subjects did not acknowledge the presence of a stimulus, they nevertheless guessed its location with above chance accuracy. Apparent motion improved both detection and localization performance. Subjective confidence was related to stimulus presence and localisation performance. Thus, simulated blindsight appeared to be based on residual conscious awareness.