Categorical perception

Categorical perception is the experience of percept invariances in sensory phenomena that can be varied along a continuum.

Multiple views of a face, for example, are mapped onto a common identity, visually distinct objects such as cars are mapped into the same category and variable speech sounds are perceived as discrete phonemes. Within a particular part of the continuum, the percepts are perceived as the same, with a sharp change of perception at the position of the continuum where there is identity change. Categorical perception is opposed to continuous perception, the perception of different sensory phenomena as being located on a smooth continuum.

How the neural systems in the brain engages in this many-to-one mapping is a major issue in cognitive neuroscience. Categorical perception (CP) can be inborn or can be induced by learning. Initially it was taken to be peculiar to speech and color perception. However CP turns out to general, and related to how neural networks in our brains detect the features that allow us to sort the things in the world into separate categories by "warping" perceived similarities and differences so that they compress some things into the same category and separate others into different ones.

An area in the left prefrontal cortex has been localized as the place in the brain responsible for phonetic and possibly other types of categorical perception.

A category, or kind, is a set of things. Membership in the category may be (1) all-or-none, as with "bird": Something either is a bird or it isn't a bird; a penguin is 100% bird, a dog is 100% not-bird. In this case we would call the category "categorical." Or membership might be (2) a matter of degree, as with "big": Some things are more big and some things are less big. In this case the category is "continuous" (or rather, degree of membership corresponds to some point along a continuum). There are range or context effects as well: elephants are relatively big in the context of animals, relatively small in the context of bodies in general, if we include planets.

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