ABSTRACT
In categorical perception, the only properties of sounds that count are those that discriminate between elements of a language. All others are discarded as noise. People who "speak" sign languages use categorical perception too: the visual signals they receive are preprocessed and packed to neutralize the endless variation in gestures caused by differences in the size and build of the signer, and their sloppiness, exuberance, or agitation. Like the language faculty itself, categorical perception is one of those partly hardwired, biological capacities of the brain, and as such it can be impaired at birth or damaged in the course of life. How people behave and survive in the world depends solely on patterns of neurons in different states of agitation inside the brain. There is nothing particularly human about having an inner world. Animals have inner worlds too, with varying levels of complexity. The inner world of Aplysia, is actually larger than its modest capacities for learning suggest.
