The colour of words: how dichromats construct a colour space

ABSTRACT

People with strong protanopia and deuteranopia – colloquially termed “red-green colour blindness” – are dichromatic and are unable to visually discriminate between colours corresponding to the long-wavelength end of the visible light spectrum. We used nonmetric multidimensional scaling to create colour spaces for a sample of protanopes and deuteranopes, and compared them to spaces derived from trichromats with normal colour vision. Colour spaces based on dissimilarity judgements between actual colours (hue-only condition) revealed the anticipated collapse of a dimension distinguishing long-wavelength colours. Judgements based on basic or descriptive colour terms (term-only conditions) produced two-dimensional configurations resembling those of trichromats. When hues and terms were presented together (hue + term condition), the dichromatic colour space was intermediate between the spaces derived from the hue-only and term-only conditions. The findings reveal that language can effectively substitute for an impoverished colour experience, and indicate a surprising element of “visual capture” in dichromatic observers.

KEYWORDS:

• Dichromacy
• multidimensional scaling
• colour space
• colour perception
• colour conception
• language

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes

1 We also performed this task with completely blind participants, which required verbal presentation of colour names. We retained this here to allow direct comparison with the blind participants (see Saysani et al., 2018).

2 We were primarily concerned with presenting colour stimuli that best represented canonical colours, rather than controlling for luminance differences between colours. Had we controlled for luminance, the colours corresponding to the middle-and long-wavelength regions of the visible light spectrum (green, yellow, orange, red, and brown) would have appeared even more similar to to dichromats. Accordingly their configuration (for the hue-only task) would likely have appeared even more unidimensional.

3 Note that there are also some trichromatic observers who weigh heavily on one dimension. This observation implies that even people of normal colour vision approach the “dissimilarity” task with in a variety of ways, one of which appears to be relying on a single dimension. Nevertheless, most trichromats appear to rely on a more “two-dimensional” comparison strategy.