Past research has indicated that English-learning infants begin segmenting words from speech by 7·5 months of age (Jusczyk & Aslin, 1995). More recent work has demonstrated, however, that 7·5-month-olds' segmentation abilities are severely limited. For example, the ability to segment vowel-initial words from speech reportedly does not appear until 13·5 to 16 months of age (Mattys & Jusczyk, 2001; Nazzi, Dilley, Jusczyk, Shattuck-Hufnagel & Jusczyk, 2005). In this paper, we report on three experiments using the Headturn Preference procedure that investigate both phonetic and phonological factors influencing 11-month-olds' segmentation of vowel-initial words from speech. We replicate earlier findings suggesting that infants have difficulty segmenting vowel-initial words from speech. In addition we extend these findings by demonstrating that under certain conditions, infants are capable of segmenting vowel-initial words from speech at a much younger age than earlier studies have reported. Our findings suggest that infants' ability to segment vowel-initial words from speech is tightly constrained by acoustic-phonetic factors such as pitch movement at the onset of vowel-initial words and segmental strengthening. These experiments underscore the complexity of early word segmentation, and highlight the importance of including contextual factors in developmental models of word segmentation.

The aim of this study was to uncover factors accounting for the ability of children with specific language impairment (SLI) to learn agreement morphemes in intervention. Twenty-five children with SLI who participated in a six-month intervention program focused on teaching third person singular -s or auxiliary is/are/was showed a wide range of use of the target morpheme after intervention. Regression analyses showed that age and two factors expected to be related to agreement – the use of noun plural -s and subject/verb constructions prior to intervention – significantly predicted progress in the acquisition of agreement morphemes. In contrast, the pretreatment use of morphemes hypothesized to be unrelated to agreement was not a significant predictor of progress. The results indicate that the ability of children with SLI to learn agreement morphemes relies on their prior ability to use noun plural and subject/verb constructions.

The Agreement/Tense Omission Model (ATOM) predicts that English-speaking children will show similar patterns of provision across different tense-marking morphemes (Rice, Wexler & Hershberger, 1998). The aim of the present study was to test this prediction by examining provision rates for third person singular present tense and first and third person singular forms of copula BE and auxiliary BE in longitudinal data from eleven English-speaking children between the ages of 1 ; 10 and 3 ; 0. The results show, first, that there were systematic differences in the provision rates of the different morphemes; second, that there were systematic differences in the rate at which all of the three morphemes were provided with pronominal and lexical subjects; and, third, that there were systematic differences in the rate at which copula BE and auxiliary BE were provided with the third person singular pronominal subjects It and He and the first person singular subject pronoun I. These results replicate those of Wilson (2003), while controlling for some possible objections to Wilson's analysis. They thus provide further evidence against the generativist view that children's rates of provision of different tense-marking morphemes are determined by a single underlying factor, and are consistent with the constructivist view that children's rates of provision reflect the gradual accumulation of knowledge about tense marking, with much of children's early knowledge being embedded in lexically specific constructions.

Early language comprehension may be one of the most important predictors of developmental risk. The need for performance-based assessment is predicated on limitations identified in the exclusive use of parent report and on the need for a performance measure with which to assess the convergent validity of parent report of comprehension. Child performance data require the development of procedures to facilitate infant attention and compliance. Forty infants (20 at 1 ; 4 and 20 at 1 ; 8) acquiring English completed a standard picture book task and the same task was administered on a touch-sensitive screen. The computerized task significantly improved task attention, compliance and performance. Reliability was high, indicating that infants were not responding randomly. Convergent validity with parent report and 4-month stability was substantial. Preliminary data extending this approach to Mexican-Spanish are presented. Results are discussed in terms of the promise of this technique for clinical and research settings and the potential influences of cultural factors on performance.

Researchers have long noted that children's grammatical morphemes are variably produced, raising questions about when and how grammatical competence is acquired. This study examined the spontaneous production of determiners by two French-speaking children aged 1 ; 5–2 ; 5. It found that determiners were produced earlier with monosyllabic words, and later with disyllabic and trisyllabic words. This suggests that French-speaking children's early determiners are prosodically licensed as part of a binary foot, with determiners appearing more consistently only once prosodic representations become more complex. This study therefore provides support for the notion that grammatical morphemes first appear in prosodically licensed contexts, suggesting that some of the early variability in morphological production is systematic and predictable.

Children pass through a stage in development when they produce utterances that contain auxiliary BE (he's playing) and utterances where auxiliary BE is omitted (he playing). One explanation that has been put forward to explain this phenomenon is the presence of questions in the input that model S-V word order (Theakston, Lieven & Tomasello, 2003). The current paper reports two studies that investigate the role of the input in children's use and non-use of auxiliary BE in declaratives. In Study 1, 96 children aged from 2 ; 5 to 2 ; 10 were exposed to known and novel verbs modelled in questions only or declaratives only. In Study 2, naturalistic data from a dense database from a single child between the ages of 2 ; 8 to 3 ; 2 were examined to investigate the influence of (1) declaratives and questions in the input in prior discourse, and (2) the child's immediately previous use of declaratives where auxiliary BE was produced or omitted, on his subsequent use or non-use of auxiliary BE. The results show that in both the experimental and naturalistic contexts, the presence of questions in the input resulted in lower levels of auxiliary provision in the children's speech than in utterances following declaratives in the input. In addition, the children's prior use or non-use of auxiliary BE influenced subsequent use. The findings are discussed in the context of usage-based theories of language acquisition and the role of the language children hear in their developing linguistic representations.

This study examined information about adjective meanings available in adults' spoken discourse in the original 27 CHILDES corpora of typically developing English-speaking children. In order to increase the probability that adjectives would be novel to children to whom they were addressed, only rare adjectives were examined (those that occurred ⩽5 times in the corpus, N=878). Contexts surrounding adjectives (±3 utterances on either side of the target) were scored for linguistic clues to meaning, including related language, compare/contrast and evaluative information. Linguistic contexts contained more information in adult–child conversations than in adult–adult conversations. There were differences among information categories. For example, explicit definitions were relatively rare compared to other types of information and were far less frequent than reported in structured laboratory situations. Findings highlight the importance of looking at adult input in situations where teaching word meaning is not an explicit goal.

This study sought to determine why American parents from different socioeconomic backgrounds communicate in different ways with their children. Forty-seven parent–child dyads were videotaped engaging in naturalistic interactions in the home for ninety minutes at child age 2 ; 6. Transcripts of these interactions provided measures of child-directed speech. Children's vocabulary comprehension skills were measured using the Peabody Picture Vocabulary Test at 2 ; 6 and one year later at 3 ; 6. Results indicate that: (1) child-directed speech with toddlers aged 2 ; 6 predicts child vocabulary skill one year later, controlling for earlier toddler vocabulary skill; (2) child-directed speech relates to socioeconomic status as measured by income and education; and (3) the relation between socioeconomic status and child-directed speech is mediated by parental knowledge of child development. Potential mechanisms through which parental knowledge influences communicative behavior are discussed.

We found that infant gaze following and pointing predicts subsequent language development. At ages 0 ; 10 or 0 ; 11, infants saw an adult turn to look at an object in an experimental setting. Productive vocabulary was assessed longitudinally through two years of age. Growth curve modeling showed that infants who gaze followed and looked longer at the target object had significantly faster vocabulary growth than infants with shorter looks, even with maternal education controlled; adding infant pointing strengthened the model. We highlight the role of social cognition in word learning and emphasize the communicative-referential functions of early gaze following and pointing.

The present study investigated the roles of pattern detection capacities and understanding of intentions in children's learning of linguistic rules. We taught two-year-olds a Hebrew morphological distinction between noun and verb forms using two different training protocols. The protocols were identical in all parameters except that only in an Intentional, but not in a Control condition, were children introduced to the stimuli in an intentional communicative context. We found that children learned the morphological rule only in the Intentional condition. Thus, besides their pattern detection capacities, children's understanding of intentions substantially boosts their learning of meaningful rules.

Two groups of children were given pictures of animals to name as quickly as they could. The groups comprised 40 nursery aged children (mean age 3 ; 11) and 40 Year 2 children (mean age 6 ; 9) attending primary school in London. The 30 animals were presented one by one, on cards, and any errors made by the children were noted. Consistent with a similar object naming study with adults (Vitkovitch, Kirby & Tyrrell, 1996) and a study with children (Gershkoff-Stowe, 2002), picture naming errors referred to earlier named objects. However, while adults showed below-chance interference from objects that had only just been named (Lag 1), children were most susceptible to interference from very recently named objects (see also Gershkoff-Stowe, 2002). Furthermore, the proportion of younger children making Lag 1 errors was higher than the proportion of older children making Lag 1 errors. The results are discussed in relation to the activation levels of lexical representations.