Abstract

Contrast-detection thresholds were measured for vertical and circular cosine gratings with and without two-dimensional static noise by means of a two-alternative forced-choice method. The stimuli were produced on a high-resolution computer monitor with computer graphics. The increase in the contrast energy thresholds produced by noise was equal for circular and vertical gratings for all spatial frequencies and grating areas studied. The increase in energy threshold was a single function of relative grating area and was independent of spatial frequency. The relative grating area is described by the number of square-cycles which is given by Af2 where A is the grating area and f is the spatial frequency. Noise produced the same increase in energy threshold between 1 and 64 square-cycles. Above 64 square-cycles the increase in energy threshold became progressively larger. The results show that stimuli with highly different spectral properties are equally detectable: A change in stimulus orientation bandwidth (from vertical to circular gratings) does not affect the detection performance of vision. Moreover, the detection performance of vision is independent of relative spatial-frequency bandwidth (inversely proportional to relative stimulus size) over a broad range. These results support the view that in vision signals are not detected by detectors with fixed filtering properties but that the visual system adaptively uses knowledge about the properties of the stimulus.

© 1990 Optical Society of America