Spectral sensitivity for flicker and acuity criteria.

Different channels in the visual system mediate the detection of flicker and the detection of high spatial frequencies. The magnocellular channel is optimized for flicker detection, whereas the parvocellular channel is optimized for color vision and spatial resolution. The spectral sensitivity of the magnocellular (flicker) channel is obtained by combining cone inputs in the ratio R/G = 5/3; the spectral sensitivity of the parvocellular channel is obtained with the ratio R/G = 2/3. However, when the parvocellular channel is used for resolution, the sensitivity changes from R/G = 2/3 to R/G = 5/3. By hypothesis, this occurs because only parvocellular centers resolve high spatial frequencies and because parvocellular centers are distributed in the same ratio as cones feeding magnocellular cells.