LOW-FREQUENCY ATTENUATION IN DETECTION OF GRATINGS - SORTING OUT ARTIFACTS

Human visual sensitivity was measured with sinusoidal gratings in which a constant number of periods were presented either (1) within a homogeneous surround, the luminance of which was the average luminance of the grating or, (2) within narrow dark borders or dark surrounds. In condition (1), sensitivity decreased steadily as spatial frequency was reduced from 8 cycles/degree and was only affected slightly by the number of grating periods that were presented. Condition (2), which caused illusory luminance gradients across the stimulus, resulted in a substantial loss of sensitivity to intermediate spatial frequencies, which flattens the sensitivity vs. frequency function. This effect should not be misinterpreted as an absence of low-frequency attenuation.