Red-green flicker resolution as a function of heterochromatic luminous modulation.

Critical fusion frequencies have been evaluated in heterochromatic red-green flicker as a function of red-green luminous modulation defined by mL = (R-G)/(R+G)%, at five different mean luminance levels, two test sizes (2 degrees and 5 degrees) and square wave stimuli. The extreme values mL = +/- 100 correspond to ordinary light-dark flicker (red or green); mL = 0 corresponds to pure chromatic flicker, and any other values correspond to simultaneous luminous and chromatic flicker. To implement the stimuli we have developed a new stimuli generator (AVICO, colour vision analyser) using bicolour LEDs as the light source and electronic control of the luminances and frequencies. The results for any luminance level and both test sizes show a minimum critical fusion frequency in the case of pure chromatic flicker (photometric match condition) and a critical fusion frequency which is slightly higher in the green extreme (mL = -100) than in the red (mL = +100). The shape of the variation between the minimum and the extremes is consistent with the results recently reported by Swanson and the theoretical models for the luminance channel response to heterochromatic flicker.