The spatial tuning of color and luminance peripheral vision measured with notch filtered noise masking

We have measured the spatial bandwidths of the bandpass red-green chromatic and luminance mechanisms at four locations in the nasal visual field (0, 10, 20 and 30 degrees) using a method of notch filtered noise masking which effectively removes the artifact of off-frequency looking for our stimuli. Detection thresholds were measured for luminance or isoluminant red-green Gaussian enveloped test gratings of 0.5 cpd embedded in 1/f noise. Firstly, thresholds were obtained as a function of increasing noise spectral density and were fitted using a standard noise masking model. These results support the existence across the visual field of independent, red-green chromatic and luminance mechanisms with similar sampling efficiencies. Secondly, we measured thresholds in notch filtered noise as a function of notch width and derived the spatial bandwidth of the detection mechanism. We find both color and luminance mechanisms have similar bandwidths which remain virtually constant across eccentricity. These results indicate strong overall similarities between the early processing of color and luminance vision, and lend support to the role of color as an 'intrinsic image' in spatial vision. The results are discussed in the light of the anchored channel and shifting channel models of peripheral contrast sensitivity and pattern detection.