Modification of the human visual evoked potential by monochromatic backgrounds.

Abstract Monochromatic flicker stimuli (17.5 Hz) were delivered to the human eye in the presence of steady monochromatic backgrounds of equal photopic luminance. The average visual evoked potential was recorded from the scalp. Under most conditions involving a large difference in wavelengths of stimulus and background, the responses were found to be from 1 -5 to 3 times larger than those evoked by superimposing the same stimulus on a background of identical wavelength. The responses evoked by heterochromatic stimulus-background combinations were often larger than the responses elicited by the same stimulus when no background was present. The presence of a background of the same wavelength as the stimulus usually reduced the size of response. Wavelength-dependent temporal effects were also found. Backgrounds of equal photopic luminance caused shifts as large as 0.5 cycle in the phase relationship of the response wave to the stimulus flash when the test stimulus was kept constant and the background wavelength varied. It is concluded that there are components of the evoked potential which differ in spectral sensitivity and that some of these components also differ in the time domain.