Opponent and Non Opponent Contributions to Detection of Small, Brief Flashes

Spectral sensitivities for small, brief lights presented on a neutral adapting field resemble the photopic luminosity function. The lights often appear achromatic near threshold. These findings are consistent with a hypothesis linking sensitivity to an independent class of nonopponent cells. To test this hypothesis, a variation of the Stiles two-color threshold procedure was used. Field sensitivities were measured with a small, brief 580 nm target presented on flashed fields of monochromatic light; a 633/541 nm flash mixture was also used. All stimuli were delivered on a 4.0 log td steady neutral adapting field. The field sensitivity and field mixture data refute the hypothesis. They argue instead that red/green opponent cells can substantially influence the detectability of small, brief lights