The language acquisition device (LAD) was proposed by Noam Chomsky to explain how children, when exposed to any human language, are able to learn it within only a few years following birth. Chomsky argued that all humans are born with the knowledge of what makes a human language. Included in this innate knowledge must be details of important characteristics of all the world’s languages. The term universal grammar has been used to describe the knowledge contained in the LAD. The process of language development is envisioned as one in which the child discovers which grammar rules contained within universal grammar apply to the language that the child is learning.
According to Chomsky, humans are born with the LAD, but other species are not. Nonhuman primates and other species do not spontaneously learn human languages. Furthermore, attempts to teach nonhuman species language have yielded mixed results. Chimpanzees and gorillas have learned to use signed languages, such as American Sign Language (ASL). Washoe the chimpanzee and Koko the gorilla have each learned hundreds of signs and can use them to refer to concrete objects and concepts, such as hungry. However, neither has been able to master the intricacies involved in construction of grammatically correct sentences.
Chomsky’s view of the LAD is consistent with there being specific structures in the brain involved in language learning and language processing. Such brain structures are presumably present in human brains, but absent in nonhuman brains. No specific claim was made regarding the specific location of the LAD in the brain. Although there have been locations in the brain identified as language processing areas, such as Broca’s area and Wernicke’s area, a location corresponding to the LAD has not been found.
Chomsky’s claim that knowledge of language is innate was supported by Eric Lenneberg’s critical period hypothesis. In 1967, Lenneberg published the book Biological Foundations of Language, in which he argued that humans are biologically capable of learning language only until puberty. After puberty, humans are biologically unable to master the intricacies of natural language. For many years, researchers in zoology had recognized the existence of critical periods of development for a range of nonhuman animal species, such as songbirds, ducklings, horses, dogs, and sheep. Evidence for the Lenneberg’s critical period hypothesis for human language was drawn from a variety of sources. Case studies of children raised without sufficient exposure to human language appeared to support the critical period hypothesis. Such individuals, such as Victor, the wild child, and Genie, had not been able to master the grammatical intricacies of sentence construction. Individuals born with severe hearing loss who were not exposed to a signed language until after puberty typically had not been able to achieve nativelike proficiency. Furthermore, there was ample anecdotal evidence that individuals who attempt to learn a second language after puberty rarely achieve a level of proficiency comparable to that of one who learns the language during childhood.
Some researchers have rejected the notion that language acquisition is aided by innate knowledge. In 1957, the behaviorist B. F. Skinner published the book Verbal Behavior, in which he argued that all types of language behavior were learned after birth through the same learning processes that are used for all human learning. Some contemporary cognitive scientists, such as David Rumelhart and James McClelland, as well as others, view language learning as the result of general learning principles, rather than language-specific mechanisms. According to Chomsky, the primary challenge for this alternative approach to language learning is adequately explaining how children produce word forms and sentences that they do not experience in the environment and, thus, have no opportunity to learn.
- Chomsky, (1959). A review of B. F. Skinner’s Verbal behavior. Language, 35, 26–58.
- Chomsky, (1986). Knowledge of language: Its nature, origin, and use. New York: Praeger.
- Lenneberg, (1967). Biological foundations of language. New York: Wiley.
- Noam Chomsky home page, http://web.mit.edu/linguistics/www/chomsky.home.html
- Pinker, S. (1994). The language instinct. New York: W.Morrow.