Experimental study of the individual differences in chromatic perception through blue‐yellow metameric matches of a white‐light continuum

A metameric colour matching test was designed to study inter‐observer variability. Blue‐yellow metameric matching to a white‐light continuum was used to define the optimal wavelengths at which each of eight non‐colour‐defective observers achieved a match. The tests involved chromatic stimuli on a 2° bipartite field, with a white‐light continuum presented on the left half, and a mixture of two monochromatic stimuli on the right half. The luminance of these chromatic stimuli was adjusted by the researcher using a staircase method, with the observer providing feedback about the similarity in luminance and chromaticity between the two halves of the field. Two series were performed for each observer, using different fixed yellow wavelengths. Since for each fixed yellow wavelength the match with the target white can be achieved by only one corresponding blue wavelength which is particular for each observer, the initial blue wavelengths were approximations based on the 2° CIE 1931 standard observer. Once the observers had attained an achromatic match, they modified the blue wavelength to achieve a perfect match of both halves. Generally, the observers found this modification of the blue wavelength necessary to achieve the metameric match. Each observer had a particular optimal blue wavelength which differed between the two series. The differences between the deviations from the standard observer for the two series were constant in value among the observers.