Perceptual constancy is the ability of perceptual systems to recognise the same object from widely varying sensory inputs. For example, individual people can be recognised from views, such as frontal and profile, which form very different shapes on the retina. A coin looked at face-on makes a circular image on the retina, but when held at angle it makes an elliptical image. In normal perception these are recognised as a single three-dimensional object. Without this correction process, an animal approaching from the distance would appear to gain in size. One kind of perceptual constancy is color constancy: for example, a white piece of paper can be recognised as such under different colors and intensities of light. Another example is roughness constancy: when a hand is drawn quickly across a surface, the touch nerves are stimulated more intensely. The brain compensates for this, so the speed of contact does not affect the perceived roughness. Other constancies include melody, odor, brightness and words. These constancies are not always total, but the variation in the percept is much less than the variation in the physical stimulus. The perceptual systems of the brain achieve perceptual constancy in a variety of ways, each specialized for the kind of information being processed.