To this point in this book we have been principally concerned with neurolinguistics – theories of how language is represented and processed in the brain. We now turn to our second topic – linguistic aphasiology. The work we shall consider in Part III deals primarily with the details of the linguistic structures that aphasic patients lose and retain, and with abnormalities in the processing of these structures. The focus of this work is different from that in neurolinguistic studies. Rather than devote their attention principally to how normal and abnormal language is related to the brain, many psychologists and linguists have recently become interested in how aphasic language is related to normal language. In some instances, what we know about normal language structure and processing has helped these investigators understand the nature of aphasic disturbances. In other cases, the direction of theory construction has been reversed, and what has been discovered about aphasic language processing has led to new theories of the processing of normal language. The neural basis for language is a secondary issue, though there are implications of this work for neurolinguistic theory which we shall consider in Part IV.

Linguistic aphasiology developed in a major way well after neurolinguistics had been established. This shift in orientation and focus resulted from the slow growth of knowledge regarding the linguistic and psycholinguistic details of aphasic disorders. There has always been a concern in aphasiology for linguistic and psycholinguistic analyses, as we have seen in the work we reviewed in Part II.