Adults' performance on a variety of tasks suggests that phonological processing of nonwords is grounded in generalizations about sublexical patterns over all known words. A small body of research suggests that children's phonological acquisition is similarly based on generalizations over the lexicon. To test this account, production accuracy and fluency were examined in nonword repetitions by 104 children and 22 adults. Stimuli were 22 pairs of nonwords, in which one nonword contained a low-frequency or unattested two-phoneme sequence and the other contained a high-frequency sequence. For a subset of these nonword pairs, segment durations were measured. The same sound was produced with a longer duration (less fluently) when it appeared in a low-frequency sequence, as compared to a high-frequency sequence. Low-frequency sequences were also repeated with lower accuracy than high-frequency sequences. Moreover, children with smaller vocabularies showed a larger influence of frequency on accuracy than children with larger vocabularies. Taken together, these results provide support for a model of phonological acquisition in which knowledge of sublexical units emerges from generalizations made over lexical items.

Research has shown that children repeat high-probability phoneme sequences more accurately than low-probability ones. This effect attenuates with age, and its decrease is predicted by developmental changes in the size of the lexicon (J. Edwards, M. E. Beckman, & B. Munson, 2004; B. Munson, 2001; B. Munson, J. Edwards, & M. Beckman, 2005). This study expands on these findings by examining relationships between vocabulary size and repetition accuracy of nonwords varying in phonotactic probability by 16 children with specific language impairment (SLI), 16 chronological-age-matched (CA) peers with typical speech and language development, and 16 younger children matched with the children with SLI on vocabulary size (VS). As in previous research, children with SLI repeated nonwords less accurately than did CA children. The children with SLI and the VS children showed similar levels of nonword repetition accuracy. Phonotactic probability affected repetition accuracy more for children with SLI and VS children than for CA children. Regression analyses showed that measures of vocabulary size were the best predictor of the difference in repetition accuracy between high- and low-probability sequences. Analyses by items showed that measures of phonotactic probability were stronger predictors of repetition accuracy than judgments of wordlikeness. Taken together, the results support research demonstrating that vocabulary size mediates the influence of phonotactic probability on nonword repetition, perhaps due to its influence on the ongoing refinement of phonological categories.

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Recent literature suggests that phonological neighborhood density and word frequency can affect speech production, in addition to the well-documented effects that they have on speech perception. This article describes 2 experiments that examined how phonological neighborhood density influences the durations and formant frequencies of adults' productions of vowels in real words. In Experiment 1, 10 normal speakers produced words that covaried in phonological neighborhood density and word frequency. Infrequent words with many phonological neighbors were produced with shorter durations and more expanded vowel spaces than frequent words with few phonological neighbors. Results of this experiment confirmed that this effect was not related to the duration of the vowels constituting the high-and low-density words. In Experiment 2, 15 adults produced words that varied in both word frequency and neighborhood density. Neighborhood density affected vowel articulation in both high-and low-frequency words. Moreover, frequent words were produced with more contracted vowel spaces than infrequent words. There was no interaction between these factors, and the vowel duration did not vary as a function of neighborhood density. Taken together, the results suggest that neighborhood density affects vowel production independent of word frequency and vowel duration. Keywordsphonological neighborhood density; word frequency; vowels; acoustic measurements; adults Knowledge of the phonological structure of language involves knowledge of both the categorical units of language and their phonetic outcomes. This relation is highly complex. Instances of the same phonemic category may be realized with qualitatively different phonetic outcomes in different words. For example, it is well known that sounds may coarticulate with adjacent sounds, so that the /s/ in words like sweet is qualitatively different ©American Speech-Language-Hearing Association

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