“Do we see colors the same way?” is a fundamentally human question and one of great importance in research into the human mind. While impossible to answer at present, researchers from the University of Tokyo and from Monash University in Australia take steps to answering it using a method that can map the experiences of colors between individuals, including those with colorblindness.

A research team including Associate Professor Masafumi Oizumi’s lab at the University of Tokyo and Professor Naotsugu Tsuchiya’s lab at Monash University explore ways to quantify various aspects of consciousness. Their most recent study looks at a fundamental question we all ask ourselves at some point about our subjective experiences, or qualia: “Is my red your red?”; or if two people’s subjective experiences might differ: “Is my red your green?” It’s traditionally difficult to analyze because both subjects can agree on what is red or green in terms of verbal reports, even if what they see in their minds’ eyes is different.

“To begin to unpick this, we need to separate the experience of colors that people have from their labels, the color terms like ‘red’ and ‘green,’ that people use when they refer to them,” said Oizumi. “Although it is notoriously difficult to explain our internal experience of ‘red’ by referring only to ‘red’ itself, we can relatively easily describe the relations between our experiences. For example, the experience of red is closer to pink than to green. Our strategy is to accumulate as many such relations between our experiences, or qualia, as possible.”

The research introduces a novel experimental and computational paradigm called the qualia structure paradigm. This paradigm focuses on relational structures of our experiences, called qualia structures, and then compares qualia structures across individuals on a structural basis, as opposed to comparing colors one on one. In this framework, the specific color labels are removed and the optimal mapping between individuals’ subjective experiences can be made using only internal relations, which have been experimentally quantified.

“Using massive online experimental data from both color-neurotypical and colorblind participants, we empirically found that color similarity judgment data derived from color-neurotypical participants can be correctly aligned at the group level, such that red correctly mapped to the same red or similar reddish colors,” said Oizumi. “In contrast, those of colorblind participants could not be aligned with those of color-neurotypical participants, implying that color-neurotypical red is relationally equivalent to other color-neurotypical’s red, but not to colorblind people’s red.” Oizumi also noted an important limitation of this study: “We however did not perform any unsupervised alignment at the individual level. Therefore, we could not say anything about individual differences. To answer these questions, we need to perform an individual-basis alignment. So, stay tuned for our follow-up studies.”

The team are keen to explore other senses beyond sight, but also continue to explore how color experiences can differ between specific individuals and not just at a group level. Although it is a more complicated and time-consuming challenge, they will continue to work enthusiastically on this line of research based on the key idea of qualia as structure.