Components of displacement adaptation in acquisition and decay as a function of hand and hall exposure

Tests of proprioceptive shift (PS), visual shift (VS), and negative aftereffect (NA) were made during 25-min exposure to 20-D displacement and during a subsequent 30-min dark decay period in two separate experiments. Different groups of subjects explored hallways or viewed their active hand during exposure. VS was greatest in hall exposure, while PS was greatest in hand exposure. Larger VS occurred in the second experiment, where test procedures were modified to minimize a tendency to center the target within the momentary or remembered field of view. Substantial and possibly complete VS decay occurred when the initial level of adaptation was high, but although PS decay was substantial, it was not complete. In all conditions, the sum of VS and PS numerically exceeded the NA, and this difference tended to be largest and significant in the hall exposure. Implications of this effect for the two-component additivity hypothesis are discussed.