Relationships between luminance and visual acuity in the rhesus monkey.

1. The ability of rhesus monkeys to detect the gap in Landolt ring test-objects that were presented against background luminances between 5 x 10(-5) cd/m(2) and 5 x 10(3) cd/m(2) was compared with similar human data.2. At high luminance-levels the acuity of human observers is slightly better than that of rhesus, but rhesus have better acuity at scotopic luminance-levels. Both species have distinct photopic and scotopic acuity functions that cross at 6 x 10(-3) cd/m(2).3. The threshold for light detection is estimated to be the same for both species when specified in quanta incident on the retina.4. It is concluded that the receptor and neural mechanisms that mediate visual-acuity function similarly in rhesus and man, and that the differences in acuity that were measured in the two species may be attributed to optical rather than to physiological factors.