Channel selection with non-white-noise masks.

It is frequently assumed that the accuracy with which luminance gratings can be detected depends solely on the signal-to-noise ratio at the output of a single linear channel. Proportionality between threshold elevation and power spectral density is implicit in this assumption. I demonstrate that this proportionality does not hold for 1-cycle/degree gratings masked by low-pass noise with a 0.5-cycle/degree cutoff frequency. This implies that different channels can mediate detection, depending on the contrast of masking stimuli.