The minimum motion technique applied to determine isoluminance in psychophysical experiments with monkeys

Isoluminance ratios for red/green, red/blue and blue/green sinusoidal gratings were determined in macaque monkeys using the minimum motion heterochromatic photometry technique (Anstis & Cavanagh, 1983), in which the motion of specially constructed test grating reverses at the point of isoluminance. The point of luminance equality between the two colors was determined using (1) overt responses of monkeys trained to discriminate motion direction and (2) reversals in the direction of the nystagmic eye movements. Both measures yielded essentially identical isoluminance points. Both the spatial and the temporal frequency of the grating patterns were found to influence the isoluminance settings in all animals tested. The amount of blue equating a preset red or green value was found to increase consistently with increased spatial frequency and with increasing eccentricity. These results show the necessity of spatial and temporal frequency dependent adjustment of visual patterns used in psychophysical and physiological experiments dealing with the processing of color. Furthermore, eye movement measurements appear to be sufficiently in order to determine isoluminance in foveally presented moving patterns with nonhuman primates.