Contrast detection and its dependence on the presence of edges and lines in the stimulus field.
The influence of sharp luminance discontinuities (dark lines and edges) in the stimulus field on the contrast sensitivity has been measured using sinusoidal gratings. Merely by changing the position of edges or lines in the stimulus field, it is possible to alter the contrast sensitivity by a factor of 3 or more. The distance from which such a discontinuity can affect the contrast sensitivity depends on the spatial frequency of the grating itself, and can be up to several degrees for gratings of low spatial frequency. No difference could be found between the effect of edges and the effect of very thin (5 min of arc) dark lines on the contrast sensitivity. The apparently conflicting experimental results in the literature concerning the relationship between the number of periods in a grafting and the contrast sensitivity, and especially concerning the influence that the surround of the grating has on this relationship, can be ascribed to the effect of these luminance discontinuities. In all cases where the number of periods was reported to have a large effect on the contrast sensitivity (up to a factor 10), the position of edges or lines in the stimulus field was also varied when the number of periods was changed. The change in the contrast sensitivity is no more than a factor 2 to 3 when there are no lines or edges in the grating surround.
D005556:Form Perception / Q000502:physiology*; D006801:Humans; D010775:Photic Stimulation; D012684:Sensory Thresholds