Dementia is a syndrome characterized by deficits in multiple cognitive domains, including short-and long-term memory and at least one of the following: aphasia, apraxia, agnosia, and impaired executive function (American Psychiatric Association, 1994). The deficits must be sufficiently potent to affect social and occupational functioning and apparent in the absence of delirium. Dementia is associated with many disorders, but most commonly with Alzheimer's disease (AD) and Lewy body disease (LBD). Other common dementia-producing diseases are vascular disease and Parkinson's disease (PD).

Because communicative functioning is a manifestation of cognition, it is necessarily affected when an individual experiences the multiple cognitive deficits that define the syndrome of dementia. However, differences in the nature and distribution of neuropathology in the common dementia-associated diseases produce unique patterns of communication deficits.