Why Sign Language Research Is Essential for Understanding Language and Language Disorder

Purpose: Sign language research has often been framed as supplementary to spoken language studies. In this article, I argue that sign language research is not only equal in value but also essential to understanding the human language faculty and its disorders. Method: I present three arguments: that sign language reveals phenomena unobservable in speech, enables the testing of otherwise untestable hypotheses, and helps disentangle speech from language. Results: Drawing on research with deaf children with autism and other language disorders, I demonstrate how signed languages can transform both theoretical models and clinical approaches to language impairment. Conclusion: Sign languages provide a unique empirical lens through which to view linguistic and clinical phenomena that would otherwise remain obscured.