Elementary Colour Perception in Hue Judgment

The ratios of psychological elementary colours perceived in chromatic colour papers with a variety of hues were measured by a paired comparison method. Stimulus sets were composed of two colour papers with hues between two of four elementary colours, but on either side of one elementary colour. Five students observed stimulus sets comprising two colour papers under approximately 1000 lux D₆₅ illumination, and they chose the one which caused the stronger elementary colour percept. The results showed that the sum of the ratios of two elementary colours in a colour whose hue is located between them was less than 100%. This result was the same for every hue condition.

This shows that observers underestimated psychological elementary colours, consistent with previous studies (Sakata, 1996 Perception 25 Supplement, 100) which showed that the sum of black and white was less than 100% in the perception of greys. If elementary colours are processed simultaneously from the whole colour percept, their sum would be 100%. The result of these experiments strongly shows that psychological elementary colours are processed independently from the inputs of the three cone systems and the rod system, and they are integrated to form the whole colour percept after each process.