ABSTRACT
The problem of defining consciousness is an occupational hazard not confined to philosophers and retired neurologists still determined to grapple with the body–mind problem. It emerges at a practical clinical level in an intensive care unit, where estimates of 'level of consciousness' are made that have an important bearing on management and prognosis. The neuropsychologist studies disorders of consciousness for the light they shed on the processes of selective attention and intentional control of behaviour. Some cognitive psychologists have reservations about the extrapolation from pathological data to theories of 'normal' structure and functioning, but it is unreasonable to neglect such 'natural' fractionations of behaviour when designing research on normal populations. The chapter considers some pathological evidence with a bearing on the two approaches to a definition of consciousness: altered levels of activation of the central nervous system, and changes in the contents of conscious experience occurring in some of the cognitive disorders associated with brain damage.
