All living creatures, even the lowliest, possess the ability to categorize. In order to survive, a creature has to be able, at the very least, to distinguish what is edible from what is not, what is benign from what is harmful. And in order to mate and reproduce, a creature must be able to recognize its own kind.

Strictly speaking, every entity and every situation that we encounter is uniquely different from every other. In order to function in the world, all creatures, including humans, need to be able to group different entities together as instances of the same kind. One of the primary mechanisms through which this is accomplished is categorization.

Definition and Overview

Categorization, often considered a central mechanism of perception and semantic memory, is here defined as the ability (1) to group features together and thereby differentiate objects, events, or qualities; and (2) to see some of these as equivalent, and associate and remember them together in a category.

Different categories are distinguished through the creation of boundaries between categories. The physiological correlate of a category may be a coordination of groups of neurons in different neural maps in the brain (Endelman, 1987).

Human beings are categorizing creatures par excellence. Our ability to function in the complex physical and social world in which we find ourselves depends on elaborate categorizations of things, processes, persons, institutions, and social relations.

We are able to create and operate with literally tens of thousands, perhaps hundreds of thousands of categories, ranging from the extremely fine-grained to the highly general.

Moreover, categorization is flexible, in that we can modify existing categories in order to accommodate new experiences and we can create new categories whenever the need arises.

Categories form the connection between perception Opens in new window and thought Opens in new window, creating a concise form in which experience can be coded and retained. Categories are the primary terms in which many types of memories are stored and recalled.

The consideration of a number of different things as being in some sense the same (in the same category) has the biologically adaptive function of eliciting the same response in similar situations—to quickly provide the appropriate response to a situation without having to consider each new situation in all of its detail.

Our cognitive apparatus does this for us automatically, most of the time. This implies that at least some kinds of categorization involve implicit memory Opens in new window which enable us to form some categories without our conscious knowledge that this is taking place.

Categorization is essential for survival. This ability comes at a cost, however: whereas discrimination and memory between categories is very acute, discrimination and memory for distinction within categories is usually poor.

The ability to generalize allows fast responses and greatly reduces memory load, but at the cost of the ability to remember much of the fine detail of experience. Essentially, the level of detail of an experience that we are able to remember is largely based on the level of detail of our categories.

What we remember often consists of our categories, colored by our experience. Many kinds of “experts” are simply people who through a great deal of practice, have developed fine-grained category structures.

For example, take the way in which we see and remember color categories. Almost anyone can distinguish between the colors red and green (a between-category distinction).

Without special training, however, most of us cannot accurately reidentify a particular shade of red (a within-category distinction) reliably at a later time. Again, from the evolutionary point of view, this allows us to attend to aspects of the world that promote survival, while suppressing unnecessary detail and conserving memory.

Because categories function at several levels of perception and thought, we conclude the literature distinguish between perceptual categories Opens in new window and conceptual categories Opens in new window.

  • First, perceptual categories compute object groups based on their appearance; conceptual categories compute class membership based on an object’s role or function in events.
  • Second, perceptual categories contain detailed information, whereas concepts are relatively crude, abstract, and devoid of specific content.
  • Third, perceptual categories are implicit and incessible to conscious awareness. Concepts are used in conscious thought and recall as exemplified by deferred imitation tasks.
  • Fourth, perceptual categories tend to begin at the basic level and then advance to a more global level, whereas the earliest conceptual categories are global, rather than basic.
  • Finally, perceptual categories are used for purposes of recognition and identification. Concepts provide meaning and are the basis of inductive generalizations.

Certainly perceptual and conceptual categories interact in many ways.

Most conceptual categories must be built up from perceptual categories. Because they involve individual long-term memory, however, the higher-level conceptual categories can have a much more idiosyncratic structure.

Conceptual categories are represented differently in different individuals, and even in a single individual, depending on how they are used (Barsalou, 1993).