Masking of grating detection in the isoluminant plane of DKL color space.
A novel noise-masking technique was used to test D'Zmura and Knoblauch's (1998) idea that subjects employ off-channel looking in detecting chromatic test stimuli embedded in spatiotemporal chromatic noise. Detection thresholds were obtained for stationary, isoluminant, Gaussian-windowed (sigma(x) = sigma(y) = 2.25 deg; sigma(t) = 0.25 s), 135 deg (yellow/blue) or 160 deg (orange/blue-green), sinusoidal test gratings (11 deg x 11 deg; 0.75 cycle/deg) superimposed on each of a series of dynamic, random-check chromatic noise masks varying in azimuth in DKL space. Thresholds for detecting the test in the presence of these variable masks were again measured in the presence of an additional (auxiliary) noise mask created from colors falling on azimuths of 0 deg or 90 deg (135-deg test) or 0 deg or 135 deg (160-deg test). The effectiveness, k(var), of the variable noise masks in elevating grating detection thresholds was determined by fitting the detection data to the Pelli-Legge equation relating test detection energy to variable noise-mask energy: E(t) = K + k(var)N(var). Differences in the calculated values of k(var) for detection data obtained with and without the auxiliary masks were consistent with off-channel looking and were well accounted for by a simple model based on the idea that subjects possess a multichannel array of linear chromatic detectors spanning the isoluminant plane of DKL space, and they can choose the channel that has the highest signal-to-noise ratio.