when do babies become able to distinguish different speech sounds
Phonological development Infants as young as 1 month perceive some speech sounds as speech categories (they display categorical perception of speech). For example, the sounds /b/ and /p/ differ in the amount of breathiness that follows the opening of the lips. Using a computer generated continuum in breathiness between /b/ and /p/, Eimas et al. (1971) showed that English-learning infants paid more attention to differences near the boundary between /b/ and /p/ than to equal-sized differences within the /b/-category or within the /p/-category.[4] Their measure, monitoring infant sucking-rate, became a major experimental method for studying infant speech perception.
Language development The nativist theory, proposed by Noam Chomsky, argues that language is a unique human accomplishment, and can be attributed to either "millions of years of evolution" or to "principles of neural organization that may be even more deeply grounded in physical law".[3] Chomsky says that all children have what is called an innate language acquisition device (LAD). Theoretically, the LAD is an area of the brain that has a set of universal syntactic rules for all languages. This device provides children with the ability to make sense of knowledge and construct novel sentences with minimal external input and little experience. Chomsky's claim is based upon the view that what children hear—their linguistic input—is insufficient to explain how they come to learn language.[citation needed] He argues that linguistic input from the environment is limited and full of errors. Therefore, nativists assume that it is impossible for children to learn linguistic information solely from their environment.[4] However, because children possess this LAD, they are in fact, able to learn language despite incomplete information from their environment. Their capacity to learn language is also attributed to the theory of universal grammar (UG), which posits that a certain set of structural rules are innate to humans, independent of sensory experience.[5] This view has dominated linguistic theory for over fifty years and remains highly influential, as witnessed by the number of articles in journals and books.[citation needed]