 When most people reflect on perceptual learning, the cases that tend to come to mind are cases of differentiation. In differentiation, a person comes to perceive the difference between two properties, where they could not perceive this difference before. It is helpful to think of William James’ case of a person learning to distinguish between the upper and lower half of a particular kind of wine. Prior to learning, one cannot perceive the difference between the upper and lower half. However, through practice one becomes able to distinguish between the upper and lower half. This is a paradigm case of differentiation.