Optimization of stimuli for trit-anomaloscopy.

Free-choice colour matches were made by 50 young normal trichromats on an anomaloscope. Six equations, of the kind 'blue' + 'green' = 'cyan' + 'yellow', were used in which the stimuli were defined by narrow-band well blocked interference filters. The stimuli were selected so that the instrument controls, which varied the quantities (blue/green), (cyan/yellow) and (cyan + yellow), were nearly independent controls for hue, saturation and brightness respectively. 'Yellow', 'green' and 'cyan' were fixed at 589, 499 and 480 nm, respectively, and the least interindividual variation in blue/green was found for 'blue' in the region 430-439 nm. This and a similar finding in the pilot study of Moreland and Young agree with expectations based on the density spectrum for macular pigment measured by Ruddock. Matches made by a few selected subjects, when the saturation control was locked at a position for the population mean, in the presence of large but typical saturation differences, were the same as when all three controls were used.