The role of local contrast in the visual deficits of humans with naturally occurring amblyopia.

We measured the positional acuity of amblyopic observers and their sensitivity to the local contrast information which provides the cue for the position judgement. Our results suggest that there exist fundamental differences in the neural losses in humans with strabismic and anisometropic amblyopia. The losses in positional acuity of anisometropic amblyopes may be accounted for on the basis of the reduced contrast sensitivity and increased neural pooling of the underlying visual filters; whereas strabismic amblyopes, like the normal periphery, show an extra loss, which may be accounted for on the basis of scrambling, or jitter in the topographic mapping of information from retina to cortex. Since neurons in the striate cortex of monkeys show precise positional coding, it would be of particular interest to examine the positional acuity and local contrast sensitivity in cortical neurons of monkeys with experimental amblyopia using the same stimuli to measure both.