PAPER Two-year-olds compute syntactic structure …

1 Developmental Science 13:1 (2010), pp 69 76 DOI: PAPER . Two-year-olds compute syntactic structure on-line Savita Bernal,1 Ghislaine Dehaene-Lambertz,2,3 Se verine Millotte1,4 and Anne Christophe1,5. 1 . Laboratoire de Sciences Cognitives et Psycholinguistique, EHESS CNRS DEC-ENS, Paris, France 2 . INSERM, Neurospin, Gif Yvette, France 3 . AP-HP, Service de NeuroP diatrie, CHU Bic tre, Paris, France 4 . Laboratoire de Psycholinguistique Exp rimentale, University of Geneva, Switzerland 5 . Maternit Port-Royal, Facult de M decine Paris Descartes, France Abstract Syntax allows human beings to build an infinite number of new sentences from a finite stock of words.

2 Because toddlers typically utter only one or two words at a time, they have been thought to have no syntax. Using event-related potentials (ERPs), we demonstrated that 2- year - olds do compute syntactic structure when listening to spoken sentences. We observed an early left- lateralized brain response when an expected verb was incorrectly replaced by a noun (or vice versa). Thus, toddlers build on-line expectations as to the syntactic category of the next word in a sentence. In addition, the response topography was different for nouns and verbs, suggesting that different neural networks already underlie noun and verb processing in toddlers, as they do in adults.

3 Introduction The main reason why this debate remains unresolved lies in the difficulty of gathering relevant evidence. When Human language is unique because it is generative. children start to produce more than one word at a time, From a finite repertoire of words, humans can build an at around to 2 years of age, their utterances are infinite number of new sentences. The way children come typically incomplete, and often lack grammatical to master the set of syntactic computations that markers such as articles, auxiliaries, or verb endings. underlies spoken language is still being debated.

4 On As a result, it is difficult to decide unambiguously the one hand, these syntactic computations have been whether toddlers simply parrot parts of sentences, or argued to be too complex and too idiosyncratic to be actively exploit syntactic computations to create their acquired by infants on the sole basis of the sentences own novel sentences but are limited by their poor they hear (the poverty of the stimulus' argument, planning and motor control (Fisher, 2002a; Naigles, Chomsky, 1986). In that view, language acquisition 2002; Tomasello & Abbot-Smith, 2002).

5 Comprehension would rely on innate constraints (Fisher, 2002a; Fisher, may thus be a better measure of infants' linguistic Hall, Rakovitz & Gleitman, 1994; Gleitman, 1990; Lidz, competence. At this age, however, behavioural Waxman & Freedman, 2003; Naigles, 1990; Naigles, studies depend on indirect measures of linguistic 2002). The child's early syntactic representations would comprehension, such as looking times to visual scenes, be similar in kind to the adult's, and become functional while children are listening to spoken sentences that are as he she learns words to fill the abstract syntactic either congruent or incongruent with the visual input.

6 Categories. On the other hand, constructivists argue that Even though many of these studies show that children children start without syntax. Their first utterances are between 1 and 3 years of age do extract meaning from limited to specific word strings, produced by rote. spoken sentences (Bernal, Lidz, Millotte & Christophe, Infants construct syntactic categories such as noun' 2007; Fisher, 2002b; Fisher, Klingler & Song, 2006;. and verb', and learn the specific syntactic computations Naigles, 1990), their interpretation in terms of syntactic of their mother tongue, by generalizing on these fixed competence per se remains controversial (Tomasello &.)

7 Utterances, using their general learning capacities and Abbot-Smith, 2002; Tomasello & Akhtar, 2003). Indeed, social skills (Lieven, Behrens, Speares & Tomasello, syntax is not always strictly necessary for meaning 2003; Tomasello, 2000; Tomasello & Abbot-Smith, extraction (for example, telegraphic speech can be 2002). This can only happen once a critical mass of understood). Event-related potentials (ERPs) by-pass exemplars' has been reached, at around 3 years of age. these methodological difficulties, by allowing Address for correspondence: Anne Christophe, Laboratorie de Sciences Cognitives et Psycholinguistique, Ecole Normale Sup rieure, 29, rue d'Ulm, 75005 Paris, France; e-mail: 2009 The Authors.

8 Journal compilation 2009 Blackwell Publishing Ltd, 9600 Garsington Road, Oxford OX4 2DQ, UK and 350 Main Street, Malden, MA 02148, USA. 70 Savita Bernal et al. experimenters to measure cerebral activity while children stopped watching before the end of the test. Before are passively listening to sentences. Here, we investigated beginning the experiment, the experimenter checked with whether 24-month-old toddlers, who are just beginning the parents that the eight target words were known by the to produce multi-word utterances, already show different child.

9 Parents also gave their written informed consent brain responses to grammatical and ungrammatical for the protocol. The study was approved by the regional sentences. ethical committee for biomedical research. High-density ERPs were recorded in 2- year -old French children, who watched short video stories featuring a Stimuli female speaker playing with small toys. Ungrammatical sentences were constructed by inserting a verb in a noun Eight target words were used, four nouns and four verbs, position, or a noun in a verb position (see Table 1). all well known to 24-month-old French infants.

10 Target Crucially, grammatical and ungrammatical sentences words were not noun verb homonyms (nouns: were perfectly matched, in that the critical noun or fraise' strawberry, balle' ball, grenouille' frog, girafe' . verb was always preceded by the same function word, la' giraffe; verbs: mange' eat, donne' give, regarde' look, (meaning the or it depending on the preceding context). finis' finish). For instance, for the verb mange' eat, the word string la Stimuli were audiovisual sequences that were recorded mange' is grammatical in alors je la mange' then I eat it, by a French native speaker who spoke in child-directed but ungrammatical in je prends la mange' I take the eat speech (the last author).