What is a possible physical substrate of the qualitative aspects of consciousness (qualia)? Answering this question is a central goal of consciousness research. Due to their subjective and ineffable nature, finding a quantitative way to characterise qualia from verbal description has thus far proven elusive. To overcome the challenge of expressing subjective experience, recent structural and relational approaches have been proposed from mathematics. Yet, as far as we know, no attempts have been made to evaluate the relationship between a certain structure of qualia and a structure of its possible underlying physical substrate. Towards this ambitious goal of linking qualia and the physical, we set out to make an empirical first step by focusing on qualia of visual motion in human participants and their possible neural substrate recorded in mouse primary visual cortex. From human participants (N=171), we obtained dissimilarity ratings of visual motion experiences induced by 48 stimuli, spanning across 8 directions and 6 spatial frequencies. Analysis revealed similarity structures of visual motion qualia that were disassociated from similarity structures purely expected from physical parameters or their combinations. From nine individual mice, we recorded single-neuron activity (n=751) with optical imaging in both awake and lightly anaesthetised conditions (isoflurane 0.6-0.8%, which retains neural responses and renders mice unresponsive to sensory stimulation). From neuron population responses to a similar set of motion stimuli, we computed a distance matrix that is comparable to our human dissimilarity matrix. Quantitative analyses show structural commonalities between human qualia structure and mouse neural structure, where a categorical organisation of stimulus direction best explains human qualia structure and mice neural activity. Interestingly, these commonalities held true for both awake and lightly anaesthetised conditions, leaving a possibility that mice may have been unresponsive but conscious of visual motion under light anaesthesia. Finally, we list several empirical factors that can be improved to promote our qualia structure approach in the future.
Robinson et al. (Thu,) studied this question.