Lakhasly

We pointed out that language acquisition is central to the demonstration of the biological nature of language. Language acquisition is a natural developmental process.
It is important to be very clear about how we frame the nativist con- ception of language acquisition. The claim is not that humans acquire language without experience – on the contrary. In fact, biologically based systems, for humans and other animals, require environmental input to trigger or stimulate development. For example, the biologi- cally based system for human vision is already well developed at birth, but newborns cannot differentiate the input they receive from their left versus their right eye, so they have no depth perception. During an infant’s first month of life, visual input triggers important changes in how the brain organizes stimuli that enter from the left versus the right eye, and eventually the baby is able to perceive perspective, distances, and depth. If something interferes with the processing of visual stimuli during a critical period of development (the first few months of life), the child will not develop normal vision.
Just as external input is crucial in the development of vision, external input is important indispensable, actually – in language acquisition. Infants who are born deaf, and therefore cannot experience speech, cannot acquire spoken language: they lack the appropriate environ- mental stimulation. Deaf infants can, however, acquire a signed lan- guage with the same facility that hearing infants acquire spoken language, if sign language is present in their environment. The nativist claim is that the developing brain provides the infant with a predis- position to acquire language; but language acquisition will not happen in a vacuum. The child must be exposed to external input to construct a grammar and a lexicon with all the properties associated with human language. Although there are differences of views among psychologists, they agree that language is acquired under the guidance of global grammar rules: innate knowledge of language, and child acquisition strategies imposing an input structure.
The child has been whimsically called – originally by Chomsky (1965) – a LAD, or Language Acquisition Device. The LAD is, of course, not the child but rather a property of the child’s brain that endows it with a predisposition for acquiring language. The child, exposed to language through the environment, processes the input using biologically endowed systems for language acquisition (Universal Grammar and acquisition strategies), and the eventual outcome is a grammar and a lexicon. The medium for the input is not important: the same internal processes will take place if the signal consists of speech or gestures. The specific language of the input is also not important, as long as it is a human language like English , Arabic , or any other language can be acquired by any human child.