Visual evoked cortical potentials and psychophysical determination of color contrast thresholds along different chromatic axes.

Color vision can be assessed by examining the color contrast threshold along various color axes. We investigated the possibility of determining these thresholds objectively by means of visual evoked cortical potentials. A color-calibrated flicker-free (112-Hz) monitor and a 14-bit-per-gun board allowed visualization of colors with specified xyY CIE 1931 coordinates. Horizontal grating, 1 c/deg were sinusoidally alternated at 8 Hz for both visual evoked cortical potential recordings and psychophysical determinations. Two healthy emmetropic 35 year-old subjects performed color brightness matching along each color axis, before any recording and reduction in color contrast. For each color axis, extrapolation to zero voltage of the visual evoked cortical potential amplitude versus log color contrast response allowed determination of the color contrast threshold. The visual evoked cortical potential-derived threshold changed considerably with the color axis, with evident intersubject differences. These differences were similar to those observed in the psychophysically determined thresholds. Visual evoked cortical potential responses to suitable chromatic stimuli allow determination of color contrast thresholds that correspond well to those determined psychophysically. Hence, with the visual evoked cortical potential, accurate objective assessment of color vision is feasible and may be useful in both research and clinical settings.