SPATIAL-FREQUENCY ADAPTATION - EVIDENCE FOR A MULTIPLE-CHANNEL MODEL OF SHORT-WAVELENGTH-SENSITIVE-CONE SPATIAL VISION

The frequency selective effects of spatial adaptation were measured with vertically-oriented, cosine stimuli upon an intense long-wavelength (yellow) field, which isolated the short-wavelength-sensitive (S) cones. Consistent with isolated-S-cone spatial threshold and masking results, the adaptation measurements demonstrate S-cones input to multiple, orientation selective, spatial frequency mechanisms. Moreover, the adaptation measurements show the minimum number of S-cone mechanisms is three. The frequency tuning of each mechanism was derived from the S-cone threshold and masking results. Two of the tuning curves are bandpass with peak sensitivities in a vicinity of 0.7 and 1.4 c/deg, respectively. These two closely resemble tuning curves derived from results with luminance-modulated stimuli. Confined to the range of frequencies examined (0.25-2.83 c/deg), the third tuning curve is lowpass with a high-frequency cutoff of roughly 2.0 c/deg. However, subsequent measurements of orientation selectivity demonstrate the third mechanism to have bandpass frequency tuning as well.