A communication system in which words and their written symbols combine in various, regulated ways to produce an infinite number of messages (pg. Meaning of words & parts of words. Knowledge of how language used to communicate. Infants, like adults, perceive speech sounds categorically. E. g. , although the acoustic difference between /b/ and /p/ falls on a continuum we perceive these consonants as 2 distinct categories. Adults are only able to discriminate phonemes in their native language(s) E. g. , adult native japanese speakers have difficulty hearing difference between /r/ and /l/ Young infants are able to discriminate phonemes from most languages. Tested english learning infants" ability to tell apart non-native speech. 6- to 8-month-old english learners can differentiate the hindi. By 10-12 months they lose this ability. Experimental group exposed to 12 live interaction sessions w/ mandarin speaker (total ~5h) Control group exposed to 12 live interaction sessions w/ Is the problem of dividing spoken language into its component words.