1 December 1, 2005 Notes Notes on Guasti, M. 2004. LANGUAGE ACQUISITION: The growth of grammar. Cambridge, MA: MIT Press. Prosodic Cues HYPOTHESIS 1: “Babies discriminate languages on the basis of prosodic information at the utterance level” Mehler et al. (1996): Infants extract and build a representation of language based on RHYTHMIC properties (class specific, rather than language specific) that vary across languages—in underspecified units or a covariant unit like a vowel— some type of universal unit that infants first recognize in the initial stages of language development (Bertoncini & Mehler 1981), <This hypothesis gives special status to vowels (reasonable, since vowels are acoustically salient: they carry more energy of the speech signal, are louder than consonants, thereby attracting infants’ attention more than consonants do).> FOUR DAYS OF AGE: infants can discriminate L1 from a foreign language or discriminate between 2 foreign languages. This development serves as the basis for building a more fine-grained representation reflecting phonological properties of L1 FOUR WEEKS OF AGE: infants can discriminate in English between [ba] and [pa]. Eimas et al. (1971): 1 month-olds, like adults, discriminate between consonantal contrasts in a categorical manner. That is, acoustic differences mapped into distinctive linguistic categories are perceived as different by infants; whereas acoustic differences that are not linguistically relevant for adults are not perceived as different by infants. SIX-EIGHT MONTHS OF AGE: infants can detect non-native contrasts as well, while it is clear that adults have (at least partially) lost this skill. Infants extract prosodic boundaries (which allows them to partition sequence of phonemes and syllables into prosodic constituents (pauses, F0 fundamental frequency resetting, syllable lengthening) EIGHT-TEN MONTHS OF AGE: percent of infants able to discern non-native contrasts decreases. “Forgetting as a way of developing a phonological system” HYPOTHESIS (Werker and Pegg 1992, Werker 1995): at least for consonants, there seems to be a functional re-organization of the sound space around 8-10 months. (This does not represent a change in the auditory system, but rather an expression of a postperceptual process, or bias after perception). Vowel quality is already being influenced by ambient language(s). Under this hypothesis, categorical perception may or may not be languagespecific (related to language) or it may be based on general auditory properties. Sequences of word-internal phonemes in a language at about 9 months. 2 TEN-TWELVE MONTHS OF AGE: (Werker and Tees 1994): only about 10-20% of infants tested able to discriminate non-native contrast; this decrease is attributed to increasing experience with the L1. ACQUISITION OF THE LEXICON: separate developmental tasks1) segmenting speech pattern into word-size units (child has a phonological lexicon of word forms)s 2) association of meaning with word forms PHONOLOGICAL BOOTSTRAPPING OF THE LEXICON MODEL (Christophe and Dupoux 1996, Christophe et al. 1997): clues to abstract symbol or linguistic objects (words, categories, syntactic structures) come from perceptual properties associated with that symbol/object readily available in the input. Example: to find candidate words in the input various sources of information are recruited: prosody, phonotactic constraints, etc. ACOUSTIC INPUT (sequence of sounds) Input encoded as phonemes and syllables (perhaps including properties such as stress, etc. (Lang. specific)BOTTOM-UP 6-7 months of age: extract prosodic boundaries (Lang. general) TOP DOWN Obtain a language-specific pre-lexical representation of speech segmented into prosodic units of a certain size, each including a limited number of words (e.g., 23). […] [σ σ σ ] […] / \ / \ / \ l ak t a h o PHONOTACTIC CONSTRAINTS 9 mos. old sequences of word-internal phonemes in a language BOTTOM-UP WORD DISTRIBUTIONAL SHAPE REGULARITIES (rhythmic (statistical information) properties) 8 mos. old-transitional probability 6 mos. old TOP-DOWN, BOTTOM-UP identify streams; 9 mos. old identify individual words BOTTOM-UP 3 (Aslin et al 1996): When new words are presented to infants in the sentences, in sequences of words---isolated words do not occur with significant frequency. LEXICON CONTENT WORDS Once pre-lexical representation is built, infants exploit various sources of information to find word forms or to detect word boundaries, thus building lexicon of content words. These sources all exploit the regularities of a given language (statistical analyses, general purpose mechanisms). PHONOLOGICAL BOOTSTRAPPING INTO SYNTAX Initially prosodically segmented pre-lexical representation can be exploited to find word forms and to bootstrap into syntax, as prosodically segmented units roughly correspond to syntactic units*: 6-9 months: infants sensitive to prosodic coherence of units of different size 7 months: infants can parse ongoing speech stream into clause-sized units 9 months: infants can parse ongoing speech into phrase-sized and word-sized units [ZP [XP the dog ] [YP chases the cat] ] *The phonological bootstrapping hypothesis does not hold that syntactic structure can be read directly from the phonological representation, or that there is a one-to-one mapping between phonological cues and syntactic units. It only states that an initial segmentation and partial bracketing of the acoustic input may get the child started on the process of syntactic structures by limiting the search space. LEXICAL ACQUISITION and BOOTSTRAPPING OF SYNTAX An important generalization emerging from studies about lexical acquisition is that children’s early productive vocabulary consists almost exclusively of nouns, regardless of the ambient language/culture that the child is reared in (Gentner 1982; Caselli et al 1995). Verbs emerge later, and for a while they remain in the minority. Nouns may be prevalent because the meanings of nouns, at least to some extent, are learned differently than verbs. At least for certain (concrete) nouns, children may use the phonological representation discussed above and then map the recovered word forms onto meanings. Fisher et al. (1994) propose that the meaning can be fixed by relying on a word-to-world mapping procedure, such that the word is mapped onto the object to which it refers by observing the external contingencies for its use (and given certain ‘innate’ biases such as whole object bias, mutual exclusivity bias, etc.). Specifically, phonology and word-to-world mapping enable the learner to build a partial sentence representation, including known nouns and an unknown word that the learner takes to be a verb, because learners expect sentences to convey predicate-argument structure. For instance, if the input to the child 4 is: The dog chases the cat, suppose the child knows the nouns dog and cat, but not the word chases. As just outlined, the child assumes that the unknown word chases is a verb, then on the basis of phonological information and word-to-world mapping, the child builds a partial representation scaffolded by nouns, such as: [[…dog] [chases…cat…]] TWENTY-TWENTY-FOUR MONTHS OF AGE: children experience a vocabulary burst, learning between 5-9 new words a day up to the age of 6 years (Carey 1978). When the child can use between 50-200 words, s/he will start putting words together to produce multi-word utterances (Bates, Dale, and Thal 1995). When the child is using about 400 words, a correlation is observed between vocabulary size and sentence complexity (the hypothesis is that the child at that level can tap into a new source of information for learning word meaning—sentence-to-world mapping, or syntactic information). Several experiments have tested the hypothesis that syntax cues verb meaning. The findings show that from age 2, learners do rely on syntax to make hypotheses about the meaning of novel verbs and abstract nouns.