Cognitive science asks how organisms sort the objects of the world into categories. An object can be any recurring class of experience, from a concrete entity to an abstract idea. Therefore categorization plays a critical role in perception, thinking and language and is a significant factor in general performance. There are many access points into the problem of categorization. Top-down approaches such as artificial intelligence begin with the symbolic names and descriptions for some categories already given. Cognitive modeling involves the assumption that such symbol-interactions resemble the way our brains categorize. An expectation is that it will eventually join with the bottom-up approach, which tries to model the hardware of the brain. In human performance modeling it is studied by experimentation what and how people categorize. Psychophysical categorization is studied by examining the limits of discrimination and of identification. Psychophysics inquires how small a physical difference we can discern and what classes of stimuli we can reliably label and is also concerned with the relationship between the physical intensity of a stimulus and the psychological intensity of the sensation it causes.
Structural Theories emphasize the relations between features as important information about a pattern. Structural methodology for systems of knowledge acquisition concentrates on extracting implicit pattern-based expertise without requiring experts to generalize beyond the level of specificity encountered in daily practice. In many cases requiring experts to represent their knowledge in another representation introduces error and lowers performance. In his essay "On the Theatre of Marionettes", Heinrich von Kleist talks about the devastating effects of self-consciousness on the natural grace of a human being and the movement of a dancer. A phenomenological critique of representationalism in cognitive science rejects the notion that representational states define and explain the most basic kind of human interaction with the environment. It discards the idea that the relation of a person to the world consists only in the relation of the content of an individual mind to the world of objects, events, and affairs as represented by that content. It argues that the most fundamental variety of human action is the apparently unthinking, skilled action that makes up much of our daily activities, and that some of it is even more successfully accomplished without mental guidance or intervention. Cognitive psychology suggests that to a vast extent people have no conscious experience of what happens in the human mind. Many functions associated with perception, memory, and information processing are conducted prior to and independently of conscious direction and what seemingly appears in consciousness spontaneously is a result of mental processes rather than the process of thinking itself.