Language DevelopmentLecture Notes: 10/28/14Critical Period: What is it?● Originated in the field of biology● Critical period = time in the early stages of an organism’s life during which it displays a heightened sensitivity to certain environmental stimuli, and develops in particular ways due to experiences at this time. If the organism does not receive the appropriate stimulus during this period, it may be difficult, or even impossible, to develop some functions later in life● First experiments: development of vision in cats○ If impair the function of an eye early in life, neurons in the brain responsible for binocular vision never develop properlyMore experiments: Imprinting● Goslings attach to the parent goose; but, they can also attach to the human, if human was seen first (i.e., within the imprinting window)Critical Period for Birdsong● Birdsong = an evolved, genetic behavior (for reproductive function● If a baby hatchling is not exposed to the song of its species early enough, birdsong never develops properly○ E.g., Zebra finches must be exposed to birdsong in the first year of life● What about human language?Critical Period in Language Acquisiton● Notion that exposure to a stimulus must occur in a specific, and circumscribed period of time in order for learning to occur● Humans must be exposed to language during a specific maturational state in order for language to be fully acquired● “Specific maturational state” = critical period = maturational constraints on language acquisitionWhen does the critical period end?● Gray matter volume increased at earlier ages, followed by sustained loss and thinning starting around puberty● This process reflects greater organization of the brain as it prunes redundant connectionsEvidence for Critical Period: First Language Acquisition● “Feral children”○ Victor and Genie● Lack of early language input → abnormal linguistic competence (mostly notably, morphosyntax)● Difficult to evaluate, because of neglect/abuse issues, and difficulty judging whether intellectual abilities are intact● Eric Lenneberg: “the only safe conclusion to be drawn from the multitude of reports is lifein dark closets, wolves’ dens, forests, or sadistic parents’ backyard is not conducive to good health and normal development”Evidence for Critical Period: First Sign Language Acquisition● No confounding IQ, neglect issues● Same length of exposure to language● Differences in when first exposed to ASL● From birth (native learners of ASL) vs. between 4 and 6 (early learners of ASL) vs. after 12 (late learners of ASL)Critical Period in Second Language Acquisition● Prior to 16: the earlier the age at learning, the better the performance● After age 16: no relationship between age at learning and performance● Native language = Chinese and KoreanBut what about pronunciation?● Zero-to-five: same as native speakers● Five-to-fifteen: the earlier the age at learning, the better the performance● Fifteen-and on: no relationship between age at learning and performance\Why are children better at language learning than adults?● This finding is paradoxical○ I.e., in most otherdomans, the older you are, the better you do (i.e., big kids do better than little kids● So what is different about language?○ Two types of explanations■ Language is special and separate from all other abilities■ Language is not special, and capability to learn it changes with age precisely because big kids are better than little kidsLanguage is Special Explanation● Chomsky’s “innate knowledge of grammar”● This knowledge is intact early in life, and then deteriorates with maturation● Later age of acquisition → less ability to rely on the innate knowledgeBiological/Neurological Explanations● Children who sustain brain damage early in life recover language; children who sustain brain damage later do not● Brain is plastic early on (and other brain regions can take over language functions), but not later, explaining why language learning is made more difficult after a certain age● But…● Time-locked to puberty, but now new evidence suggests that <5 years of age● Studies using neuroimaging show similar regions and processing components for first and second