Common Phenomenal and Neural Substrate Geometry in Visual Motion Perception

Summary

The qualitative aspects of consciousness (qualia) are difficult to study because they are subjective. This work takes a first step toward linking the structure of qualia to brain activity by comparing human dissimilarity ratings of visual motion experiences with neural population responses in mouse primary visual cortex. Human participants (N=171) rated dissimilarity of 48 visual motion stimuli. Mouse neural activity (n=751 neurons) was recorded from nine mice using optical imaging. Both human and mouse data showed structural commonalities: a categorical organization of stimulus direction best explained both structures. These commonalities were similar in awake and anaesthetized mice, suggesting coarse V1 geometry is relatively insensitive to this anesthesia. The authors note that future work combining behavior with causal intervention is needed to relate such neural structures to conscious experience.

Study at a glance

Abstract

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 the structure of a candidate underlying physical substrate. Towards this ambitious goal of linking the structures of qualia and physical, we set out to make an empirical first step by focusing on experienced dissimilarity of visual motion in human participants and stimulus-evoked neural population response geometry recorded from 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 a human dissimilarity structure that was not well captured by a simple monotonic function of physical motion-direction difference alone nor by a pure orientation-symmetry account. 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%). 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 a human dissimilarity structure and mouse neural structure, where a categorical organisation of stimulus direction best explained both. These commonalities were similar in awake and anaesthetised recordings, suggesting that this coarse V1 geometry is relatively insensitive to this type of anaesthesia; future work combining behaviour with causal intervention is required to relate such neural structures to conscious experience. Finally, we list several empirical factors that can be improved to promote our qualia structure approach in the future.