Wavelength effect on visual latency

Chromatic stimuli were matched in luminance to a homogeneous white background field. The relative visual latency, as measured by subjective simultaneity, of 621-nanometer (red) light was 20 to 25 milliseconds less than that for 549-nanometer (green) light. When the chromatic stimuli were different in luminance fronm the background field, no differences in visual latency related to the wavelength of light were observed. The procedure of matching the luminance of test fields to that of a background field appears to be crucial for observing a visual latency difference related to wavelength.