These findings have potential to affect how nonword repetition tasks are used and interpreted, and suggest several directions for future research.

The present experiments investigated how the process of statistically segmenting words from fluent speech is linked to the process of mapping meanings to words. Seventeen-month-old infants first participated in a statistical word segmentation task, which was immediately followed by an object-label-learning task. Infants presented with labels that were words in the fluent speech used in the segmentation task were able to learn the object labels. However, infants presented with labels consisting of novel syllable sequences (nonwords; Experiment 1) or familiar sequences with low internal probabilities (part-words; Experiment 2) did not learn the labels. Thus, prior segmentation opportunities, but not mere frequency of exposure, facilitated infants' learning of object labels. This work provides the first demonstration that exposure to word forms in a statistical word segmentation task facilitates subsequent word learning.

Infants must develop both flexibility and constraint in their interpretation of acceptable word forms. The current experiments examined the development of infants’ lexical interpretation of non-native variations in pitch contour. Fourteen, 17-, and 19-month-olds (Experiments 1 and 2, N = 72) heard labels for two novel objects; labels contained the same syllable produced with distinct pitch contours (Mandarin lexical tones). The youngest infants learned the label-object mappings, but the older groups did not, despite being able to discriminate pitch differences in an object-free task (Experiment 3, N = 14). Results indicate that 14-month-olds remain flexible regarding what sounds make meaningful distinctions between words. By 17–19 months, experience with a non-tonal native language constrains infants’ interpretation of lexical tone.

The processes of infant word segmentation and infant word learning have largely been studied separately. However, the ease with which potential word forms are segmented from fluent speech seems likely to influence subsequent mappings between words and their referents. To explore this process, we tested the link between the statistical coherence of sequences presented in fluent speech and infants’ subsequent use of those sequences as labels for novel objects. Notably, the materials were drawn from a natural language unfamiliar to the infants (Italian). The results of three experiments suggest that there is a close relationship between the statistics of the speech stream and subsequent mapping of labels to referents. Mapping was facilitated when the labels contained high transitional probabilities in the forward and/or backward direction (Experiment 1). When no transitional probability information was available (Experiment 2), or when the internal transitional probabilities of the labels were low in both directions (Experiment 3), infants failed to link the labels to their referents. Word learning appears to be strongly influenced by infants’ prior experience with the distribution of sounds that make up words in natural languages.

How do infants use their knowledge of native language sound patterns when learning words? There is ample evidence of infants' precocious acquisition of native language sound structure during the first years of life, but much less evidence concerning how they apply this knowledge to the task of associating sounds with meanings in word learning. To address this question, 18-month-olds were presented with two phonotactically legal object labels (containing sound sequences that occur frequently in English) or two phonotactically illegal object labels (containing sound sequences that never occur in English), paired with novel objects. Infants were then tested using a looking-while-listening measure. The results revealed that infants looked at the correct objects after hearing the legal labels, but not the illegal labels. Furthermore, vocabulary size was related to performance. Infants with larger receptive vocabularies displayed greater differences between learning of legal and illegal labels than infants with smaller vocabularies. These findings provide evidence that infants' knowledge of native language sound patterns influences their word learning.Keywords language acquisition; speech perception; word learning At its foundation, word learning requires mapping between sounds and meanings. To acquire a new lexical item, learners must associate a sound sequence representation with a meaning representation. Studies conducted over the past four decades have revealed that young infants possess remarkable speech perception skills, and become attuned to the sound structure of their native language very early in life (for a review, see Saffran, Werker, & Werner, 2006). A separate body of work investigating children's learning of word meaning has demonstrated that children possess a wide range of strategies and biases that allow them to access the appropriate meanings of new words (for a review, see Waxman & Lidz, 2006). However, the relationship between these two key aspects of language acquisition has only recently received attention (e.g., Fennell, Byers-Heinlein, & Werker, 2007;Mani & Plunkett, 2008;Stager & Werker, 1997; see also Saffran & Graf Estes, 2006 for a review).Before infants produce their first words, they gather a great deal of information about the sound system of the ambient language. At 6 to 8 months of age, infants discriminate many native and non-native language phoneme distinctions, but by 12 months, infants' discrimination is focused on contrasts that are relevant in their native language (e.g., Werker & Tees, 1984). Infants also learn about distributional patterns in the sound combinations of their native language. By 9 months of age, infants discriminate sound sequences that occur in their native language from sequences that do not occur; they prefer to listen to phoneme combinations present in the language Jusczyk, Friederici, Wessels, Svenkerud, & Jusczyk, 1993). Nine-month-olds also distinguish between words containing frequently occurring native language sound sequences from words contai...