Does everyone experience colour in the same way? A new investigation into this long-standing philosophical question has provided the strongest evidence yet that people with typical colour vision do indeed share the same subjective experiences of colour.
Putting our subjective conscious experiences into words is notoriously challenging, making it hard to directly compare how our reality lines up to someone else’s, but researchers have previously tried various tricks to get around this.
One technique, known as the , is to ask people to consider the relationship between concepts – for example, most people consider red to be the opposite of green. “Our experience of red is somewhat characterised by the relationship between the other experiences,” says at the University of Tokyo in Japan.
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using this approach asked people to rate the likeness of pairs of colours and then mapped these colour relationships, labelling the position of each colour. Comparing these positions – under the assumption that one person’s red will align with someone else’s – provides some information about how we perceive colour, but, crucially, it cannot fully rule out the possibility that one person’s red could be another person’s green, says Oizumi.
In an attempt to do so, Oizumi and his colleagues asked 683 people to rate the similarity of pairs of colours drawn from 93 unique shades, varying slightly in hue, lightness and saturation, using an eight-point scale. Around a third of the participants were colour-blind, mostly red-green, allowing the team to compare their experience to that of people with typical colour vision.
The team then created a map of the similarity ratings from each participant but, in a new step, they did not label the colours on this map. Using a computer model, the researchers randomly combined the maps from different participants, teasing out relational structures that weren’t explicitly linked to colour.
Despite this, the team found that, at the group level, people with typical colour vision share the same relative colour structure as one another. Oizumi says that this means other mappings, including an inverted colour experience, are implausible. More studies are needed to decisively disprove the idea of inverted colour experiences, says team member at Monash University in Melbourne, Australia, “but we know we are going in that direction”.
The same was also true for the colour-blind participants, despite them having differing degrees of red-green colour-blindness. The colour structures were also broadly similar across all of the participants, although the experiences of red and green were much closer together for the colour-blind individuals, suggesting – as we might expect – that they see these colours as more similar than people with typical colour vision.
Because the team’s model works by matching based on similarity structure alone and not by trying to align predefined labels, the findings are much more robust, says , an independent researcher who was previously at Massey University in New Zealand. “It’s a positive result that hasn’t been built into things on the sly,” he says.
iScience
