Visual capacities of the owl monkey (Aotus trivirgatus)--II. Spatial contrast sensitivity.

Spatial contrast sensitivity functions were measured for the owl monkey (Aotus trivirgatus) in a forced-choice discrimination task in which the animals discriminated sinusoidal luminance gratings variant in contrast from homogeneous fields of the same average luminance. At photopic light levels theAotus monkey is maximally sensitive to gratings having a spatial frequency of 1.5–2.0 c/deg. As target luminance was decreased, both the peak location and the form of the function changed. From a consideration of these functions, and from measurements of square-wave grating acuity, it was con cluded that the maximal resolution for theAotus monkey is about 10 c/deg. In comparison to the human observer, this monkey shows poorer spatial resolution at moderate light levels but better resolution when the target is very dim.