Conscious access to information, e.g. visual information, is accompanied by increased activity both in sensory areas and in a distributed fronto-parietal network, with increased coupling between the two.
However, the neural events leading to these changes in brain activity are relatively unexplored. It is well established that events occurring after the presentation of a visual stimulus can, surprisingly, still determine whether it will enter consciousness, but the neural mechanisms are unknown. I will study two classic and complementary examples of this situation: partial report and object substitution masking. Because, in each case, the events giving rise to a stimulus entering or being denied entry to consciousness occur after stimulus presentation, I will be able to dissociate neural mechanisms associated with stimulus presentation and conscious access. I will use these paradigms to probe the spatial and temporal limits of non-conscious processing, and to assess which neural processes can occur long after stimulus offset to allow conscious report.
To achieve this goal, I will combine the high spatial resolution of high field functional Magnetic Resonance Imaging (fMRI) with the high temporal resolution of Magneto-Encephalography (MEG). In the partial report paradigm, I will investigate whether activity in early sensory areas (outlined very finely with retinotopic mapping) is enhanced by the cue long after stimulus offset, and whether this increase is linked to enhanced long distance connectivity. With MEG, I will study the detailed timecourse of these neural mechanisms. Finally, analogous studies of object substitution masking with fMRI and MEG will allow me to probe the depth, the strength and the temporal limits of non-conscious sensory processing of an un degraded stimulus. This project, beside its scientific relevance, will give me a unique opportunity to reinforce my existing skills (fMRI) and acquire excellence in a new complementary technique (MEG).
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