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To what extent are sensory experiences equivalent between individuals? One promising approach to this fundamental question about consciousness is to intersubjectively compare the similarity relationships of sensory experiences, named "qualia structures". Conventional methods for comparing the similarity relationships largely sidestep the issue by assuming experiences evoked by the same stimuli are matched across individuals, precluding the possibility that my "red" might be your "blue". Here, we present an unsupervised optimal transport method for assessing the similarity of qualia structures without assuming correspondence between individuals. As proof of concept, we analyzed two massive datasets: dissimilarity judgments for 93 colors and 1854 natural objects. In both cases, we found that qualia structures can be "correctly" aligned across participants based solely on similarity relationships, providing quantitative evidence for the structural equivalence of qualia of color and natural objects across individuals. This method is applicable to any modality of experience, enabling general structural exploration of subjective experiences.
Kawakita et al. (Sat,) studied this question.