Contrast detection and detection of contrast modulation for noise gratings

Threshold contrast was measured for noise gratings of various spatial frequency bandwidths and central frequencies. The results indicate that the contrast reaches threshold whenever the spatial power of the stimulus, filtered according to the contrast sensitivity function, exceeds a fixed level, irrespective of the width of the spatial frequency range over which the power is distributed. No "critical band effect" is found. For suprathreshold noise gratings of various bandwidths we measured thresholds for the detection of sinusoidal (amplitude) modulation of the contrast. The results indicate that the visual system uses the spatial power always with about the same efficiency, irrespective of the bandwidth over which it is distributed. The thresholds depend on the spatial frequency of the modulation: the visual system appears to be unable to use information from more than one cycle of the modulation frequency.