The term “perceptual learning” means different things to different psychologists. The problem of the role of learning in perception has to do with perception and the effect of past experience or practice on it. The most popular theory over the years has been that the supplement to the sensations is the result of learning, and that it comes from past experience. Perceptual learning, thus conceived, necessarily consists of experience becoming more imaginary, more assumptive, or more inferential. The dependence of perception on learning seems to be contradictory to the principle of the dependence of perception on stimulation. The learning process is assumed to have occurred in the past life of the experimental subject; it is seldom controlled by the experimenter. The main difficulty in the way of the traditional enrichment theory is its implication that learning involves a decreasing psychophysical correspondence between perception and stimulation.