Our understanding of the relationships between lexical and phonological development has been enhanced in recent years by increased interest in this area from language scientists, psychologists and phonologists. This review article provides a summary of research, highlighting similarities and differences across studies. It is suggested that the research falls into two categories with different goals and different methodological approaches: (1) child-centered studies that examine the influences active in the prelinguistic and early-word period, emphasizing individual developmental patterns and the active role played by the child; and (2) studies inspired by research on word processing in adults; these focus on the effects of the phonological and lexical characteristics of the ambient language on underlying representations and word learning in children. The article concludes with suggestions for integrating the findings from the two approaches and for future research.

We applaud Stoel-Gammon's (this issue) call for a more comprehensive account of the relationship between lexicon and phonology, and we strongly endorse her suggestions for future research. However, we think that it will not be enough simply to integrate findings and methods from the adult-centered and child-centered literatures. Both of these literatures suggest that we need to rethink standard assumptions about what phonological representations are and how they emerge to support the very large vocabularies that speakers develop over the course of a lifetime. Our commentary focuses on three themes relevant to this reconceptualization.

Carol Stoel-Gammon has made a real contribution in bringing together two fields that are not generally jointly addressed. Like Stoel-Gammon, we have long focused on individual differences in phonological development (e.g. Vihman, Ferguson & Elbert, 1986; Vihman, Boysson-Bardies, Durand & Sundberg, 1994; Keren-Portnoy, Majorano & Vihman, 2008). And like her, we have been closely concerned with the relationship between lexical and phonological learning. Accordingly, we will focus our discussion on two areas covered by Stoel-Gammon (this issue) on which our current work may shed some additional light.

When Roger Brown selected Adam, Eve and Sarah to be the first three participants in the modern study of child language, one of the criteria was the intelligibility of their speech (Brown, 1973). According to the prevailing view at the time, accuracy of pronunciation was a peripheral phenomenon that had nothing to do with the development of language qua language. So why not study children who were easy to transcribe? One reason why not, according to Stoel-Gammon (SG; this issue), is that the difficulty of accurately producing sounds influences the words children acquire and the rate at which they acquire them. (It's true that Roger Brown's focus was on the child's acquisition of morphosyntax, but articulation was assumed to be peripheral to everything back then.) This interaction between the articulatory skill of children and phonological properties of words is just one of the mutual influences between phonology and the lexicon SG describes. In her target article, SG brings together data from a wide range of investigations to build an account of how phonology and the lexicon interact in development.

Stoel-Gammon (this issue) states that ‘from birth to age 2 ; 6, the developing phonological system affects lexical acquisition to a greater degree than lexical factors affect phonological development’ (this issue). This conclusion is based on a wealth of data; however, the available data are somewhat limited in scope, focusing on rather holistic measures of the phonological and lexical systems (e.g. production accuracy, number of words known). Stoel-Gammon suggests a number of important avenues to pursue, but does not discuss a critical one that is emerging in the broader literature on word learning. Specifically, recent connectionist models and adult word learning research provide evidence that greater differentiation of the cognitive processes that underlie word learning yields new insights (Leach & Samuel, 2007). This approach may be fruitful for future investigations of the relationship between phonological and lexical development in young children.

Within the subfields of linguistics, traditional approaches tend to examine different phenomena in isolation. As Stoel-Gammon (this issue) correctly states, there is little interaction between the subfields. However, for a more comprehensive understanding of language acquisition in general and, more specifically, lexical and phonological development, we must consider relations between multiple subfields. That is, by examining the interactions between these subfields, a greater understanding of lexical and phonological development can emerge. For instance, the interaction between phonology, syntax and semantics is demonstrated in recent work looking at how phonological patterns can provide a basis for inferring a word's lexical category (such as nouns and verbs) (Christiansen, Onnis & Hockema, 2009; Lany & Saffran, 2010).

In her interesting article, Stoel-Gammon (this issue) reviews studies concerning the interactions between lexical and phonological development. While the focus of the review is on vocabulary production from children acquiring American English, she also suggests that cross-linguistic research be undertaken to examine how universal and language-specific properties affect the interaction between lexical and phonological acquisition. In this regard, Stoel-Gammon referred to the study of Bleses et al. (2008) who found differences in receptive vocabulary development across languages, based on norming studies for the Communicative Development Inventories (Fenson, Marchman, Thal, Dale, Reznick & Bates, 2007). Bleses et al. showed that Danish children were slower in the early comprehension of words (and phrases). It was hypothesized that the phonetic structure of Danish may account for the difference in receptive vocabulary skills in this population (Bleses & Basbøll, 2004).

Stoel-Gammon (this issue) provides a welcome addition to the phonological acquisition literature, bringing together insights from long-standing and more recent research to address the relationship between the developing phonological system and the developing lexicon. A growing literature on children's early use of words across languages and phonological contexts provides additional insight into the nature of the interactions between phonological and lexical development, suggesting that learners' knowledge and connection of the two may develop much earlier than often thought. This commentary highlights some of these exciting results from recent cross-linguistic research on development between the ages of 1 and 3.

Stoel-Gammon (this issue) highlights the close and symbiotic association that exists between the lexical and phonological domains in early linguistic development. Her comprehensive review considers two bodies of literature: (1) child-centred studies; and (2) studies based on adult psycholinguistic research. Within the child-centred studies, both prelinguistic and early meaningful speech is examined. Stoel-Gammon organizes her review of child-centred studies around a series of postulates that capture the associations between lexical and phonological development and here she focuses primarily on normally developing children acquiring American English. My intention is not to question these postulates, which are based on established research findings, but to extend them beyond the limits of her review. In my commentary, I would like to explore the application of some of the stated postulates of the early meaningful speech period in children acquiring two or more languages. In so doing, I add a cross-linguistic dimension to the discussion; a dimension that Stoel-Gammon would like to see pursued in future research on this topic. I also expand our understanding of lexical–phonological relationships by considering the potential for interaction in multiple lexical–phonological relationships.

Although not the focus of her article, phonological development in young children with speech sound disorders of various types is highly germane to Stoel-Gammon's discussion (this issue) for at least two primary reasons. Most obvious is that typical processes and milestones of phonological development are the standards and benchmarks against which we measure disorder and delay. Factors that impact children without disorders may suggest underlying causes or co-occurring symptoms of speech sound deficits, prognostic indicators of improvement, appropriate remediation strategies or some combination of these. Equally important is the fact that studying children with disorders can help us to verify and, in some cases, even unpack relationships among factors that are so closely interwoven in children who develop their phonologies at the typically very rapid rate that their individual influences cannot be discerned. Childhood Apraxia of Speech (CAS) is a particularly interesting case in point because, while it is universally accepted to be a motor speech disorder, symptoms include deficits in speech perception and often in literacy-related skills as well.

Dutch, unlike English, contains two gender-marked forms of the definite article. Does the presence of multiple definite article forms lead Dutch learners to be delayed relative to English learners in the acquisition of their determiner system? Using the Preferential Looking Procedure, we found that Dutch-learning children aged 1 ; 7 to 2 ; 0 use articles during sentence comprehension in a fashion comparable to similarly aged English learners. That is, Dutch learners' sentence processing was impaired when a nonsense (se) as opposed to real article (de, het) preceded target words, much like English learners' sentence processing is disrupted by the use of a nonsense article. At the same time, however, gender cues did not help Dutch learners recognize target nouns more efficiently, indicating that gender has yet to be acquired. Thus, although Dutch-learning children aged 1 ; 7 to 2 ; 0 have not mastered all aspects of their language's article system, they nonetheless use their partial knowledge of articles during speech processing.

The Hebrew Parent Questionnaire for Communication and Early Language (HPQ-CEL) was administered by 154 parents of Hebrew-speaking toddlers aged 1 ; 0 to 1 ; 3 (77 boys, 77 girls). The Questionnaire guided parents in observing and rating their toddlers in six contexts at home. The study aimed to identify inter-correlations between toddlers' non-linguistic behaviors that co-occur during the transition to speech. Seven communicative behaviors were extracted from the questionnaire data: Crying, Vocalizations, Collaboration with Adults, Pointing, Words, Joint Engagement in a Peek-a-Boo Game, and Triadic Interaction in Book Reading. Collaboration with Adults and Triadic Interaction in Book Reading yielded more significant correlations than other prelinguistic behaviors. Participation in social games and book-reading activities was associated with the toddlers' number of words at the period studied.

This paper explores the concurrent and predictive validity of the long and short forms of the Galician version of the MacArthur-Bates CDI (IDHC). Forty-two Galician-speaking children were longitudinally evaluated at age 1 ; 6, 2 ; 0 and 4 ; 0. On the first two occasions, the subjects' vocabulary and grammar skills were assessed through the IDHC. Simultaneously, lexical and grammatical measures were obtained from spontaneous speech samples. Standardized measures of general cognitive abilities (WPPSI-R) and receptive and expressive language (RDLS-III) were obtained at age 4 ; 0. Results showed high and significant levels of concurrent and short-term validity of the IDHC. Strong associations were found between lexical development at age 2 ; 0 and language scores two years later. These results coincide with those obtained with other CDI versions, and suggest that the IDHC is an effective and reliable tool.

In a number of studies, the acquisition of restrictive relative clauses (RCs) shows contrasting findings regarding comprehension and production, with the former usually delayed up to the age of five. As previously claimed in the literature, we suggest that this delay is a task artifact and we present a new procedure for the assessment of restrictive RCs. Data from three- to seven-year-old Italian children were collected and results show that children understand object RCs with preverbal subject in an adult-like manner at four years of age, but some of the three-year-old children were already above chance. Subject relatives show at ceiling performance from three years of age. We consider our results as evidence of continuity between early and adult competence grammars. Children's non-target responses are interpreted as grammatical options exploited by an immature performance system.

In the period between sole use of single words and majority use of multiword utterances, children draw from their existing productive capability and conversational input to facilitate the eventual outcome of majority use of multiword utterances. During this period, children use word combinations that are not yet mature multiword utterances, termed ‘successive single-word utterances’ (SSWUs). The language development of five children, observed in play with their mothers, was studied longitudinally across the transitional period (age 1 ; 3 to 2 ; 0). Results demonstrate a common developmental trajectory from single words to SSWUs, formed with the support of conversation, to more independent SSWUs, and finally to majority use of multiword utterances. The children varied in the extent to which they produced SSWUs and whether they first produced across-turn versus within-turn SSWUs. Possible reasons for variability and why SSWU production may be important to the development of multiword utterances are discussed.

Two studies examined whether preschool children preferred to select a moving object over stationary objects when determining the referent of a novel word. In both studies three- and four-year-olds observed three novel objects, one moving object and two stationary objects. In Study 1, children (n=44) were asked to select the object that best matched a novel word. In Study 2, children (n=45) were asked to select the object that best matched a novel fact. Results across the two studies indicated that three- and four-year-olds showed a preference for selecting the moving object and that this preference was similar for both words and facts. These results suggest that preschool children are able to use movement to determine the referent of a novel word, especially when other cues are unavailable or unhelpful, but that movement may not be uniquely helpful for word learning.

Ten mothers were observed prospectively, interacting with their infants aged 0 ; 10 in two contexts (picture description and noun description). Maternal communicative behaviours were coded for volubility, gestural production and labelling style. Verbal labelling events were categorized into three exclusive categories: label only; label plus deictic gesture; label plus iconic gesture. We evaluated the predictive relations between maternal communicative style and children's subsequent acquisition of ten target nouns. Strong relations were observed between maternal communicative style and children's acquisition of the target nouns. Further, even controlling for maternal volubility and maternal labelling, maternal use of iconic gestures predicted the timing of acquisition of nouns in comprehension. These results support the proposition that maternal gestural input facilitates linguistic development, and suggest that such facilitation may be a function of gesture type.

In this paper we report on a visual world eye-tracking experiment that investigated the differing abilities of adults and children to use referential scene information during reanalysis to overcome lexical biases during sentence processing. The results showed that adults incorporated aspects of the referential scene into their parse as soon as it became apparent that a test sentence was syntactically ambiguous, suggesting they considered the two alternative analyses in parallel. In contrast, the children appeared not to reanalyze their initial analysis, even over shorter distances than have been investigated in prior research. We argue that this reflects the children's over-reliance on bottom-up, lexical cues to interpretation. The implications for the development of parsing routines are discussed.