Adaptation of a color-opponent mechanism increases parafoveal sensitivity to luminance flicker

Sensitivity to 25 Hz luminance flicker is enhanced as the intensity of a background is increased. This effect is due, in part, to light adaptation of cones. Preliminary studies suggested that, in the parafovea, the enhancement of flicker sensitivity is due to the adaptation of a color-opponent mechanism rather than a single cone mechanism or achromatic mechanism. In the present study, action spectra and field additivity experiments demonstrated that the enhancing effect was opponent in nature. The field sensitivity function had a notch at 570 nm; fields on either side of the notch acted subadditively. This suggests that, in the parafovea, the sensitivity of an achromatic flicker mechanism is influenced by the adaptation of a chromatic mechanism.