Beyond Awareness: Neural Dynamics of Conscious and Unconscious Visual Processing of Object Size

The relationship between the visual system and conscious vision has long been at the center of a theoretical debate with wide-ranging conceptual and practical implications. This thesis addresses how the brain processes a fundamental visual feature—object size—under different levels of awareness. Convinced of the importance of jointly examining behavioural and neural indices, we investigated this topic through a series of experiments combining EEG and behavioural measures. Our primary goal was to investigate the dynamic interplay between neural activity and behaviour that enables us to interact efficiently with our surroundings. We first examined the neural integration of retinal and distance cues during the perception of real 3D objects, revealing that the use of naturalistic stimuli facilitates earlier visuomotor integration, thereby enhancing the brain’s ability to build a coherent representation of the external environment. To extend this investigation to conditions of reduced awareness, we employed the Continuous Flash Suppression (CFS) paradigm, which allows the prolonged suppression of visual stimuli from consciousness. The analysis of suppression dynamics indicated that visual processing is consistently modulated by a temporal frequency of 6 Hz. Finally, the exploration of size perception under CFS revealed that conscious awareness may be essential for accurate size discrimination, yet unconscious stimuli still undergo partial neural processing. Taken together, these findings contribute to a better characterization of the temporal and neural mechanisms underlying conscious and suppressed visual processing, thereby establishing a framework for future investigations that integrate behavioural and electrophysiological approaches, realistic visual stimulation, and controlled manipulations of temporal dynamics to further refine current models of conscious and unconscious vision.