The study of the cognitive deficits of neurological patients can provide important information about the organization of the cognitive system in normal subjects. This is the field of cognitive neuropsychology. Contrasting methodologies have been used in order to extrapolate from findings obtained with such patients to models of normal function. This entry primarily considers the methodological problems inherent in single-case studies. It considers four stages in the carrying out of such investigations—(a) patient selection, the carrying out (b) of baseline tests, (c) of theoretically derived tests, and (d) detailed internal analysis of the patients' performance particularly concerning error types. Consideration is then given to the methodologies of (a) series of single cases, (b) neuroanatomically based group studies, and (c) functionally based group studies.
