HUMAN VISUAL ACUITY MEASURED WITH COLORED STIMULI
Final rept. 1 Sep 1964-31 Aug 1965
HUMAN SCIENCES RESEARCH INC MCLEAN VA
Pagination or Media Count:
Previous studies of visual acuity have dealt almost exclusively with achromatic brightness differences. The present study measures acuity under conditions in which the target and surround are equated in brightness but differ in wavelength. It has been suggested that acuity should always be less under these conditions, such monochromatic stimuli may stimulate fewer foveal color sensitive receptors than white stimuli. Light from two monochromators illuminated alternate bars of a grating target. The resulting stimuli were presented in modified Maxwellian view and appeared to the observer as a 1 degree grating of colored lines in a neutral surround. A zoom system varied the angular subtense of the lines. When the grating consisted of alternate colored and black lines acuity was fairly constant about 1.30 from 430 nm to 670 nm. Equally good acuity could be obtained when alternate lines were matched for brightness, provided that the wavelength separation between adjacent lines was adequate. This separation is minimum in the blue and increases toward the red it does not appear to be simply related to wavelength discrimination. When maximum acuity has been reached by wavelength separation no further improvement can be made by introducing a brightness difference. It is concluded that wavelength difference can be a sufficient condition for good visual acuity.