American Sign Language (ASL) is a language used by more than 2 million Americans who are deaf. It has the linguistic properties of spoken languages. Through studies of deaf children’s language acquisition, psycholinguists have found that babies can learn ASL from birth and acquire it in almost the same stages and patterns as children acquiring spoken language.

Several researchers have found that this early exposure to language activates the same brain areas regardless of modality—signed or spoken. Importantly, when a language is learned later, different patterns of activation in the brain are seen. An important finding made by Petitto and Marenette is that the plasticity in the brain allows language to be perceived and expressed by the tongue or hands; the brain is not hardwired for ...