Suprathreshold contrast sensitivity in experimentally strabismic monkeys

Human strabismic amblyopes show deficits in spatial vision that can be revealed in a variety of visual tasks. In particular, they show a reduced sensitivity to contrast for a wide range of spatial frequencies. The ability of strabismic amblyopes to process contrast information at levels well above detection threshold is less well understood and somewhat controversial. In the course of investigating the neural basis of strabismic amblyopia we studied contrast processing both at and above detection threshold in experimentally strabismic monkeys (Macaca nemestrina). First we trained them to perform a contrast detection task and measured their contrast sensitivity for a wide range of spatial frequencies. Then we trained them to discriminate between two gratings that were identical except for their contrast. We show that these monkeys exhibit deficits in both tasks. The deficits in the contrast discrimination task cannot be solely attributed to their deficit at threshold.