A new method based on optimal transport can align the similarity structures of color experiences between people without assuming which colors correspond. After collecting subjective similarity judgments for 93 colors, the method correctly aligned the color qualia structures of color-neurotypical participants at the group level, but could not align the structures of color-blind participants with those of color-neurotypical participants. This provides quantitative evidence that color-neurotypical people's experience of "red" is relationally equivalent to other color-neurotypical people's "red", but not to color-blind people's "red". The method can be applied across sensory modalities.
Top-down attention affects not just whether we see something, but how we see it—the quality of conscious experience, or qualia. Using a dual-task paradigm, participants rated similarity of stimulus pairs in the periphery for rotated letters, bisected disks, and greyscale faces. Similarity ratings served as a proxy for qualia structures, analyzed with dimension reduction and optimal transport alignment. Attention withdrawal collapsed qualia structures for letters and disks, but alignment accuracy remained high for face qualia structures under both full and poor attention. This relational judgment approach extends previous binary categorization methods and offers a novel way to study qualia structures.