Abstract
The spectral sensitivity of the eye is determined by the combined contributions of myriad visual pathways, each with different temporal and spatial tuning. Consequently, the shape of the spectral sensitivity function depends greatly on stimulus parameters. Unlike flicker photometry, which produces a single-peaked, “luminosity” function, increment thresholds produce multi-peaked spectral sensitivity functions reflecting chromatic opponent mechanisms. We recently reported a comparison of decrement and increment sensitivities and concluded that like increments, decrement sensitivities were similar and determined largely by chromatic mechanisms. However, the data suggested that although the functions were essentially identical regarding L- and M-cone input, the S-cone pathways appeared to contribute more strongly to decrements than to increments. Here we report further investigation of the relative contribution of the S-cone pathways to decrement and increment spectral sensitivities.