Phrasal prosody constrains word segmentation in French 16-month-olds.

Infants who are in the process of acquiring their mother tongue have to find a way of segmenting the continuous speech stream into word-sized units. We present an experiment showing that French 16-month-olds are able to exploit phonological phrase boundaries in order to constrain lexical access. Using the conditioned head-turning technique, we showed that infants trained to turn their head for a bisyllabic word responded more often to sentences that contained this word, than to sentences that contained both syllables of this word separated by a phonological phrase boundary. We compare these results with similar results obtained with English-speaking infants, and discuss their implication for lexical and syntactic acquisition.

Two-year-olds compute syntactic structure on-line.

Syntax allows human beings to build an infinite number of new sentences from a finite stock of words. 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.

Categorizing words using 'frequent frames': what cross-linguistic analyses reveal about distributional acquisition strategies.

Mintz (2003) described a distributional environment called a frame, defined as the co-occurrence of two context words with one intervening target word. Analyses of English child-directed speech showed that words that fell within any frequently occurring frame consistently belonged to the same grammatical category (e.g. noun, verb, adjective, etc.). In this paper, we first generalize this result to French, a language in which the function word system allows patterns that are potentially detrimental to a frame-based analysis procedure. Second, we show that the discontinuity of the chosen environments (i.e. the fact that target words are framed by the context words) is crucial for the mechanism to be efficient. This property might be relevant for any computational approach to grammatical categorization. Finally, we investigate a recursive application of the procedure and observe that the categorization is paradoxically worse when context elements are categories rather than actual lexical items. Item-specificity is thus also a core computational principle for this type of algorithm. Our analysis, along with results from behavioural studies (Gómez, 2002; Gómez and Maye, 2005; Mintz, 2006), provides strong support for frames as a basis for the acquisition of grammatical categories by infants. Discontinuity and item-specificity appear to be crucial features.

Bootstrapping lexical and syntactic acquisition.

This paper focuses on how phrasal prosody and function words may interact during early language acquisition. Experimental results show that infants have access to intermediate prosodic phrases (phonological phrases) during the first year of life, and use these to constrain lexical segmentation. These same intermediate prosodic phrases are used by adults to constrain on-line syntactic analysis. In addition, by two years of age infants can exploit function words to infer the syntactic category of unknown content words (nouns vs. verbs) and guess their plausible meaning (object vs. action). We speculate on how infants may build a partial syntactic structure by relying on both phonological phrase boundaries and function words, and present adult results that test the plausibility of this hypothesis. These results are tied together within a model of the architecture of the first stages of language processing, and their acquisition.

Effects of chronic stress on dendritic arborization in the central and extended amygdala.

A differential role has been suggested for two important areas in the neural circuitry of stress, central nucleus of the amygdala (CeA) and bed nucleus of stria terminalis (BNST) in the extended amygdala, in regulating fear versus anxiety. Since chronic stress enhances anxiety and consolidation of aversive memories, we examined the effects of chronic immobilization stress (CIS) on neuronal morphology in the CeA and BNST of rats. In contrast to previous reports of stress-induced atrophy in the hippocampus, CIS does not cause dendritic atrophy in CeA and BNST neurons. While dendritic arborization in CeA neurons remains unaffected, it increases in BNST neurons after CIS. These results suggest a role for dendritic remodeling of BNST neurons in stress-induced facilitation of anxiety.