Spectral sensitivity of the peripheral retina to large and small stimuli.

Increment-threshold spectral sensitivity functions were taken foveally and at four other retinal locations with different sized test stimuli. For the fovea and parafovea at 4 degrees, a 1 degree, 250 msec stimulus of variable wavelength, flashed on a 1000 td white background yielded spectral sensitivity curves with three distinct maxima located near 455, 530-540 and 600 nm. As eccentricity increased so did the minimum spot size needed to produce spectral curves with three peaks. In particular, the 2 degrees 10' spot at 20 degrees, 4 degrees 10' at 30 degrees and 5.5 degrees at 45 degrees gave this result. Smaller stimuli in the periphery yielded curves with a minor peak at 455 nm, present under some conditions, and a major broad peak at 560 nm that resembled the CIE photopic luminosity function. Two different systems subserve detection: the three-peaked curves indicate mediation by the opponent-color system while the other type of function can be attributed to the non-opponent system.