Sign Language

It has been nearly forty years since serious investigation of natural sign languages began to show that these languages are bona fide linguistic systems, with structures and rules and the full range of expressive power that characterize spoken languages. Researchers have spent most of that time demonstrating, with increasing rigor and formality, the sometimes surprising similarities between languages in the two modalities, spoken and signed. Concomitantly, scholars in the related disciplines of language acquisition and neurolinguistics have been discovering significant similarities between spoken and signed languages in these domains as well. It is safe to say that the academic world is now convinced that sign languages are real languages in every sense of the term. If this were the whole story, however, there would be no need for a chapter on sign languages in this volume. Each sign language would be seen as a language like any other, English, Hungarian, Central Alaskan Yupik Eskimo, or Mandarin Chinese, each with its own contribution to make toward understanding the general language faculty of humans. But this is not the whole story. Rather, sign languages as a group are of special importance, crucial to our understanding of the essential nature of language, for two reasons. First, the study of natural languages in a different physical modality confirms in a novel way the hypothesis that all natural human languages are characterized by certain nontrivial and identifiable properties. And second, this study raises fundamental questions about the human language capacity, as well as challenges for language theory, that we would never have noticed were it not for the existence of sign languages. Sign language research has already made a significant contribution to our understanding of human language --its structure; its acquisition by children; its representation in the brain; and its extension beyond communication, in poetry --all of which we survey in this chapter. But the survey would be incomplete without considering the potential contribution to be made by the investigation of sign languages in the future. Most importantly, we expect future studies to allow researchers to delve into the second issue we've mentioned above --questions and challenges for the theory of human language that sign languages bring to the fore. For example, it appears that, while the individual structural properties of sign languages are attested in spoken languages, no spoken language has the same clustering of properties that characterizes sign languages. Furthermore, despite the fact that vocabularies differ from sign language to sign language, their grammatical structures seem to be remarkably similar to each other. Recent neurological studies of the language-brain map indicate some differences in brain mediation of spoken and signed languages, posing another challenge. Developing an explanation for these observations will require language theorists to move well beyond the ideas generated by the study of spoken language alone. The sign languages under discussion are the languages used by communities of deaf people all over the world. They are natural languages, in the sense that they are not consciously invented by anyone, but rather develop spontaneously wherever dea