Some Critical Factors in Prism-Adaptation

This is the authors' abstract. We don't add key points for this paper.

There is general agreement as to the kind of systematic errors in reaching which are induced by wearing prisms displacing the visual field. There is disagreement, however, as to the relative importance of some of the factors which may, alone or in combination with others, determine such displacements. A visuo-motor mechanism has been postulated with strong emphasis on the importance of reafferent stimulation from the musculature. An even stronger emphasis on proprioceptive and motor adjustments, with a corresponding neglect of possible visual factors, was made by Harris.2 As yet, the visual components, though tacitly assumed in the current explanatory schema, have not been specifically studied. This is surprising, since KohlerO reported an early experiment in which prisms were worn which displaced half of the visual field. When the prisms were removed, after-effects were confined to the exposed portion of the visual field. Since this effect varied as S moved his eyes, as well as his head, it was assumed to be not primarily visual in nature. The possibility remains that there may be some specific visual component which may be uncovered if investigated under appropriate conditions. The experiments described below explore the relative importance of visual mechanisms in prism-adaptation. Experiment I will study adaptation to induced displacement in a limb seen through the prism, but not moved by S, hence, providing little reafferent information. Experiments II and II will examine the effects of exposure of a limited retinal area to the prism. A purely proprioceptive-motor hypothesis would be excluded if it were found that under certain conditions of exposure the after-effects were confined to a specific portion of the visual field.