Spectral sensitivity in the far peripheral retina.

Relative spectral sensitivity was measured at different intensity levels 45 degrees temporally during the cone-plateau period and in a dark-adapted state. Both heterochromatic brightness matching, flicker photometry, and threshold measurements were employed. The relative spectral sensitivity obtained during the cone-plateau period was found to coincide closely with the foveal luminosity function in the long and medium regions of the spectrum irrespective of intensity and method employed, suggesting that the relative spectral sensitivities and the weighted contributions of the long- and medium-wavelength cone photopigments do not change appreciably between fovea and 45 degrees. The relative spectral sensitivity obtained in the dark-adapted state, on the other hand, was found to be purely scotopic in form invariant to intensity and method, suggesting that it is dominated almost completely by rod activity even at intensity levels commonly labeled "photopic.