Stratton and Helmholtz’s findings catalyzed a research tradition on ORD adaptation that experienced its heyday in the 1960s and 1970s. Two questions dominated studies conducted during this period. First, what are the necessary and sufficient conditions for adaptation to occur? In particular, which sources of information do subjects use when adapting to the various perceptual and sensorimotor discrepancies caused by ORDs? Second, just what happens when subjects adapt to perceptual rearrangement? What is the “end product” of the relevant form of perceptual learning?