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Frith, C. D. (1999) Chapter 29: Deficits and pathologies. In A Companion to Cognitive Science, Bechtel, W. & Graham, G. (eds) Blackwell, Malden MA.

Author of the summary: Debajyoti Pati, 2000, gte811q@prism.gatech.edu

Cognitive neuropsychology experienced dramatic changes during the second half of the twentieth century owing to several new developments; new brain imaging techniques, robust experiment designs and standardized tests, and the replacement of behaviorism by cognitive science as the theoretical approach. Thus, unlike the predominant concept of "mass action" in relation to functioning of the brain (despite several pioneering works by Broca, Wernicke, Harlow, among others) prevalent during the early twentieth century, the latter half witnessed a host of research and theories in support of the existence of separate independent cognitive components, within the overall theoretical standpoint of functional segregation.

Study of people with brain abnormalities have gone a long way in support of the latter hypotheses as well as coming up with experimental paradigms. A substantial contribution to the field was made by Broadmann"s work on anatomy during the turn of the century where he showed that the brain could be mapped into 52 discrete areas, the underlying assumption being that the different areas serve different functions. Subsequent works concentrating on recording electrical activity in single cortical cells have provided direct evidence of functional segregation. Several theoretical arguments, based on the theories of evolution (modular brain), economy and level of neural complexity (local specialization with global integration) have also evolved in support of the notion.

Evidence supporting functional segregation are available, among others, in the study of memory, describing & reaching, and neuropsychiatry. Warrington (1970s) provides example of patients with impairment of short-term memory but normal long-term ones, thus suggesting that short-term and long-term memory are stored separately and independently. Further, within short-term memory, storage areas seem to be modality-specific (visual, auditory, etc) which is demonstrated by Baddeley"s dual-task experiments. The study of amnesic patients also demonstrate the segregation with the well documented difference between implicit and explicit learning and remembering, where it has been shown that such patients demonstrate problems in episodic memory, but not in the other memory categories. Similarly, in recognition tasks amnesic patients have been helpful in identifying the separate processes of remembering and familiarity, thus identifying such segregation. Further evidence is available in describing and reaching tasks. There seem to be a clear separation between the processes (one example is Goodale & Milner"s 1992 study) of recognizing an object (conscious) and acting on it (unconscious). Neuropsychiatry too provides examples of functional segregation. A prominent example relates to the Cpagras"s syndrome as well as prosopagnosia which demonstrate a separation between the channels involved with information relating to identity, and familiarity and emotional response. Passivity phenomena is yet another example where a mismatch occur between predicted and observed sensation.

These examples, and many others, have provided a sound initial base for further studies on the psychological basis of consciousness.

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