ABSTRACT
In 1967, Lenneberg hypothesized that language acquisition may be linked to brain maturation and predicted that the ability to acquire a language would be limited to a period during childhood, before the loss of neural plasticity. In other words, childhood represents an important “window of opportunity” for learning language, and once this developmental period has passed, the ability to acquire language becomes much more difficult. The critical period hypothesis has special import for the Deaf population because if a deaf infant is born to hearing parents who do not sign, then exposure to an accessible natural language will be delayed.1 As discussed in chapter 1, 90% of deaf children are born to hearing parents, and until very recently, there were no programs for early detection of deafness (Yoshinaga-Itano, Sedey, Coulter, & Mehl, 1998) or for early sign language intervention (and more such programs are needed). Thus, some deaf children receive no language input, delayed language input, or inconsistent language input, but unlike other cases of late exposure to language (e.g., the famous case of Genie, who was isolated in her home until age 13; Curtiss, 1977), these deaf children are raised within loving families. The study of such children provide unique insight into the human capacity for language and the limits on language learning imposed by the cognitive and neural maturation that occurs during development.
