Variations in the monocular components of fixation disparity.

Measurements of the monocular components of fixation disparity through small amounts of lateral prism show changes in the proportional contribution of each eye with changing vergence stimuli. Prism does not usually alter the independence of the activity of each eye during binocular viewing. This independence allows the monocular shares to fluctuate from moment to moment. Responses to prism include fixating with one eye or the other, shifting both eyes laterally in the same direction, and distributing the deviations between the two eyes. Some of these strategies reduce the deviation and are therefore adaptive. Others appear to maintain a fairly stable state which frequently involves resorting to the equivalence of a monocular form of localization. Prism adaptation follows decidedly different time courses and occurs to differing extents for the different subjects and for the different conditions tested. It is not uncommon for many of these changes to occur unilaterally. Voluntary activity seems to be an important factor in the processes associated with adaptation to prism.