Exploring different stages of consciousness using a temporal analysis of EEG signals

The concepts of consciousness and unconsciousness, and their respective stages, are of particular interest in the domain of neuroscience, philosophy and psychology. This study aims to investigate the brain's response to visual stimuli, with a specific focus on differentiating between conscious perception and the subliminal and preconscious stages of unconscious perception. The study used two experimental paradigms to test three hypotheses, evaluating the predictions of the Global Neural Workspace Theory (GNWT) regarding the spread of cerebral activation during information processing. The research aimed to analyse the VAN and P300 waves as indicators of visual stimulus perception and neural correlates of consciousness, as well as exploring additional non-conventional EEG parameters as potential consciousness indicators. A total of 66 subjects participated in the experiment, which comprised three blocks of an inattentional blindness paradigm and two blocks of a visual masking paradigm. Electroencephalographic (EEG) signals were recorded during these experiments using a 32-electrode system. Their responses to the stimulus were recorded through the administration questionnaires and keyboard feedback. All signals were then processed and the epochs and all parameters were extracted using the MATLAB extension "EEGLAB". The parameters of the various conditions were consequently compared to detect any differences in the stages of consciousness using non-parametric statistical analysis. The results obtained lend support to the predictions of the Global Neural Workspace Theory. As postulated by the hypothesis of global information diffusion, conscious stimuli have been shown to induce a progressive activation that originates in the occipital zone and subsequently extends to the parietal-frontal areas. The findings indicate that preconscious stimuli elicit a more restrained occipital activation response, while subliminal stimuli evoke only minimal responses. In the inattentional blindness experiment, the neural correlates VAN and P300 were found to be capable of distinguishing between the preconscious and conscious stages, with the amplitude of these responses being proportional to the difference between them. The results obtained by the visual masking paradigms were less clear, due to some challenging issues of the experimental environment. With regard to the final hypothesis, the parameter termed 'Φ' has been identified as a potential indicator of the extent to which information is processed by the brain, effectively discriminating across the stages of consciousness. These findings contribute to a deeper understanding of how hypotheses concerning such a significant topic of interest in the neuroscientific field can be explored only using basic and portable instrumentation.