APA Dictionary of Psychology

a measure of spatial resolution based on an individual’s ability to detect subtle differences in light and dark coloring or shading in an object of a fixed size. Detection is affected by the size of contrasting elements and is usually tested using a grating of alternating light and dark bars, being defined by the minimum contrast required to distinguish that there is a bar pattern rather than a uniform screen. Contrast sensitivity is less for both coarse and fine gratings than it is for gratings of intermediate frequency. Humans have peak contrast sensitivity for gratings with 4 to 8 cpd (cycles per degree) and can detect contrast over a range from about 0.5 cpd to 50 to 60 cpd. Contrast sensitivity can be reduced after injury to the peripheral or central visual system: Patients complain of visual blurring, although visual acuity may be only moderately affected. Also called spatial contrast sensitivity. See also spatial frequency.