Spatial frequency mechanisms with short-wavelength-sensitive cone inputs.

We have estimated the minimum number and frequency tuning of spatial mechanisms with Short-Wavelength-Sensitive (SWS)-cone inputs. This was accomplished by isolating SWS cones with intense, long-wavelength (yellow) adaptation, and measuring threshold elevation functions for short-wavelength, spatially localized test stimuli masked by obliquely oriented, short-wavelength, cosine gratings. Peak spatial frequency of the cosine gratings and test stimuli varied from 0.25 to 2.83 cpd in 0.5 octave steps. Results derived in this manner demonstrate that SWS cones input to at least two orientation selective mechanisms with peak spatial frequencies of approx. 0.7 and 1.4 cpd, respectively. The frequency tuning of the isolated-SWS-cone, spatial frequency mechanisms resemble closely the lowest two mechanisms measured with luminance modulation (i.e. normal viewing conditions where all cones contribute to the response).