 Another way in which perceptual learning is philosophically significant is because it shows how perception is a product of both the brain and the world. In this respect, there are some similarities between the role of constancy mechanisms and the role of perceptual learning, in that both involve the brain playing a role in structuring perception in a way that goes beyond the perceptual input. Constancy mechanisms, such as those involved in shape, size, and color constancy, are brain mechanisms that allow us to perceive shapes, sizes, and colors more stably across variations in distance or illumination. In cases of constancy, the brain manipulates the input from the world, and this allows the perceiver to track the shape, size, or color more easily. Similarly, in cases of perceptual learning, the brain manipulates the input from the world. In many cases, this may actually make the perception more helpful, as when through learning the perceptual system weights attention in a particular way, say, towards the features relevant for identifying a Cabernet Sauvignon. Perceptual learning might upgrade the epistemic status of perception, putting the perceiver in a better position with respect to knowledge (see Siegel 2017). At the same time, people can learn incorrectly, leading to perceptions that are unhelpful, as when a new golfer with inadequate coaching develops the bad habit of attending to their putter while putting, rather than attending to the golf ball.