Cross-linguistic research in aphasia: an overview.

Most of us would like to believe that the different patterns of language breakdown observed in aphasic patients reflect the way that the human mind and brain are organized for language. However, because so much modern research on aphasia has been carried out in English, it is difficult to separate universal mechanisms from language-specific content. Crosslinguistic com-parisons permit us to disentangle these confounds, while we address one of the most important issues in cognitive neurobiology, the issue of behavioral and neural plasticity: How many different forms can the language processor take under a range of normal and abnormal conditions? We must have an answer to this question if we want to understand what the neural mechanisms responsible for language really are and really do. The nine papers presented within this special crosslinguistic issue of Brain and Language provide important new information about universal and language-specific patterns of sparing and impairment, in nonfluent "agrammatic" Broca's aphasics and in fluent patients with a diagnosis of Wernicke's aphasia. These crosslinguistic studies fall into two categories: (1) research in which language type is treated as an independent variable, by conducting the same experiment with equivalent materials in two or more different languages, and (2) research in which language type is treated as a natural experiment, using the peculiar characteristics of a single language to answer a question that would be difficult to ask in (for example) English. Studies applying one or both of these cross-linguistic methods have yielded six basic findings, summarized briefly as follows.