Neurolinguistic Approaches to Aphasia

The field of neurolinguistics was born in the 1960s in the context of the growth of multidisciplinary endeavors. It was pre­ ceded by a re-emergence of the idea of the biologic basis of language, the idea that language is an inherent capacity of hu­ mans, like vision or hearing. Neurolinguis­ tics developed from the belief that an adequate understanding of language de­ pends upon correlating information from a variety of fields concerned with the struc­ ture and function of both language and the brain. Underlying this belief is the as­ sumption that speech and language are neural processes that are amenable to analysis, using the techniques of both lin­ guistics and the neurosciences. With this set of assumptions, neurolinguistics took as its primary goal the definition of the relationship between the capacity for language and the functional organization of the human brain. It is assumed that the structure of language reflects the neural organization of the brain. This relationship is most clearly illustrated in the likenesses that exist in very differing language systems— in other words, language universals or constraints on the storage and organiza­ tion of the linguistic system. Undoubtedly, these universals reflect constraints on human perceptual processing systems and on cognitive capacities. Other generaliza­ tions can be made about specific lan­ guages, and these should be based on neurological facts as well. However, given the present state of our knowledge in both linguistics and the neurosciences, attempts to correlate linguistic and neural facts are usually ill conceived, beyond the rather general observation that a lesion in a par­ ticular part of the nervous system typically produces a certain type of language be­ havior. Nevertheless, careful descriptions of aphasic language from populations that have been adequately evaluated neurologically and that are well controlled for var­ iables such as site of lesion and handedness should bring us closer to understanding language in the brain. The last decade has witnessed a dra­ matic extension of the scope of neurolin­ guistics, which was originally restricted to investigations of the oral language of adult aphasic patients. The populations studied now include aphasic children, patients with lesions in the nondominant hemisphere, split-brain patients, hemispherectomized patients, demented patients, and the el­ derly. The communicative behaviors stud­ ied now include modalities other than oral—written language and gestural language—and connected language as well as isolated words and sentences. In addi­ tion, the methodology of testing, based primarily on standardized tests in the 1960s, has been supplemented by a battery of experimental nonstandardized tests and metalinguistic tasks that attempt to tap not only overt language structures but also mechanisms underlying particular linguis­ tic behaviors. This broadening of the scope of neurolinguistics reflects the newer view that aphasia is more properly a distur­ bance of language process than a distur­ bance of language output. As a result, analysis and classification of impaired out-