Many recent studies of spoken language processing by children have considered the role of phonotactic probability-the likelihood of occurrence of a sound (phoneme) sequence-and neighborhood density-the number of phonologically similar words-in word recognition (Garlock, Walley, & Metsala, 2001; MainelaArnold, Evans, & Coady, 2008;Metsala, 1997), word production (Edwards, Beckman, & Munson, 2004;Munson, Swenson, & Manthei, 2005;Newman & German, 2005;Zamuner, Gerken, & Hammond, 2004), memory (Gathercole, Frankish, Pickering, & Peaker, 1999;Thomson, Richardson, & Goswami, 2005), and learning (Alt & Plante, 2006;Storkel, 2001Storkel, , 2003Storkel, , 2004aStorkel, , 2009Storkel, Armbrüster, & Hogan, 2006;Storkel & Maekawa, 2005;Swingley & Aslin, 2007). In a number of these studies, phonotactic probability and neighborhood density were calculated using readily available American English adult corpora and online calculators (Balota et al., 2007;Davis, 2005;Vitevitch & Luce, 2004), because comparable child calculators do not exist. However, the validity of the values generated from adult online calculators for child research warrants investigation. Moreover, an understanding of the relationship between values generated from child sources compared with those from adult sources is critical for developmental research, in which researchers seek to compare phonotactic probability and neighborhood density effects across different ages as the lexicon grows.What evidence is there that child phonotactic probability and neighborhood density may differ from adult phonotactic probability and neighborhood density? To our knowledge, no researchers have investigated how phonotactic probability may change with development. However, numerous researchers have considered how neighborhood density may change from childhood to adulthood as the lexicon grows (Charles-Luce & Luce, 1990Luce, , 1995Coady & Aslin, 2003;Dollaghan, 1994). Thus, we begin by examining what is known about neighborhood density changes and then apply the observed patterns to phonotactic probability. Across studies in which lexical growth was examined, there is clear evidence that the number of neighbors increases from childhood to adulthood, meaning that the child neighborhood density for a given word will tend to be lower than the adult neighborhood density for the same word (Charles-Luce & Luce, 1990Luce, , 1995Coady & Aslin, 2003;Dollaghan, 1994). However, it is unknown whether these density differences are constant or variable across words or neighborhoods.One possibility is that child neighborhood density differs from adult neighborhood density by a relatively constant value across neighborhoods. In this case, the difference in density for stimuli identified as sparse versus dense for one age group (e.g., children) will be approximately the same as that for an older age group (e.g., adults). Consider the following hypothetical example: The word mouth, with only 5 neighbors for children, is selected as a sparse word for children, and the word tooth, with 10 neighbo...

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Purpose-The purpose of this study was to differentiate the effect of phonotactic probability from that of neighborhood density on a vocabulary probe administered to preschool children with or without a phonological delay.Method-Twenty preschool children with functional phonological delays and 34 preschool children with typical language development completed a 121 item vocabulary probe in both an expressive and receptive response format. Words on the vocabulary probe orthogonally varied on phonotactic probability and neighborhood density but were matched on age-of-acquisition, word frequency, word length, semantic set size, concreteness, familiarity, and imagability.Results-Results showed an interaction between phonotactic probability and neighborhood density with variation across groups. Specifically, the optimal conditions for typically developing children were rare phonotactic probability with sparse neighborhoods and common phonotactic probability with dense neighborhoods. In contrast, only rare phonotactic probability with sparse neighborhoods was optimal for children with phonological delays.Conclusions-Rare sound sequences and sparse neighborhoods may facilitate triggering of word learning for typically developing children and children with phonological delays. In contrast, common sound sequences and dense neighborhoods may facilitate configuration and engagement for typically developing children but not children with phonological delays due to their weaker phonological and/or lexical representations.Keywords word learning; vocabulary; neighborhood density; phonotactic probability; phonological delay Many models of spoken word recognition, production, and learning assume two types of form representations: phonological and lexical (e.g., Dell, 1988;Gupta & MacWhinney, 1997; Levelt, 1989;Luce, Goldinger, Auer, & Vitevitch, 2000;Magnuson, Tanenhaus, Aslin, & Dahan, 2003;McClelland & Elman, 1986;Norris, 1994). Phonological representations correspond to individual sounds with variation across models in the specific unit of sound chosen (e.g., phonetic features, phones, phonemes). Lexical representations NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript correspond to whole-word sound sequences as an integrated unit. A given word in a language has both a phonological and a lexical representation. For example, the word 'cat' consists of three phonological representations (assuming the phoneme is the sound unit chosen), specifically /k/, /ae/, and /t/, and one lexical representation, specifically /kaet/. As the example illustrates, words will tend to have multiple phonological representations, corresponding to the number of individual sound units in the word, but only one lexical representation.Two correlated variables have been manipulated in tandem or separately to investigate the influence of phonological and lexical representations on word recognition, production, memory, and learning by adults: phonotactic probability and neighborhood density (e.g., Roodenrys & Hinton, 2002;Sto...

The goal of this study was to examine the influence of part-word phonotactic probability/neighborhood density on word learning by preschool children with normal vocabularies that varied in size. Ninety-eight children (age 2;11 – 6;0) were taught consonant-vowel-consonant (CVC) nonwords orthogonally varying in the probability/density of the CV (i.e., body) and VC (i.e., rhyme). Learning was measured via picture naming. Children with the lowest expressive vocabulary scores showed no effect of either CV or VC probability/density, although floor effects could not be ruled out. In contrast, children with low or high expressive vocabulary scores demonstrated sensitivity to part-word probability/density with the nature of the effect varying by group. Children with the highest expressive vocabulary scores displayed yet a third pattern of part-word probability/density effects. Taken together, word learning by preschool children was influenced by part-word probability/density but the nature of this influence appeared to depend on the size of the lexicon.

This study examined the ability of 20 preschool children with functional phonological delays and 34 age-and vocabulary-matched typical children to learn words differing in phonotactic probability (i.e., the likelihood of occurrence of a sound sequence) and neighborhood density (i.e., the number of words that differ from a target by one phoneme). Children were exposed to nonwords paired with novel objects in a story and learning was measured by a picture naming task. Results showed that both groups created lexical representations for rare sound sequences from sparse neighborhoods. However, only children with typical development appeared to build on this initial lexical representation to create a full representation of the word (i.e., lexical-semantic connection and semantic representation). It was hypothesized that creating a lexical representation may be too resource demanding for children with phonological delays, leaving few resources available to create a lexical-semantic connection and/or a semantic representation.

The effect of neighborhood density on optional infinitives was evaluated for typically developing (TD) children and children with Specific Language Impairment (SLI). Forty children, 20 in each group, completed two production tasks that assessed third person singular production. Half of the sentences in each task presented a dense verb, and half presented a sparse verb. Children’s third person singular accuracy was compared across dense and sparse verbs. Results showed that the TD group was significantly less likely to use optional infinitives with dense, rather than sparse verbs. In contrast, the distribution of optional infinitives for the SLI group was independent of verb neighborhood density. Follow-up analyses showed that the lack of neighborhood density effect for the SLI group could not be attributed to heterogeneous neighborhood density effects or floor effects. Results were interpreted within the Optional Infinitive/Extended Optional Infinitive accounts for typical language development and SLI for English speaking children.

Purpose: One aspect of morphosyntax, finiteness marking, was compared in children with fragile X syndrome (FXS), specific language impairment (SLI), and typical development matched on mean length of utterance (MLU). Method: Nineteen children with typical development (mean age = 3.3 years), 20 children with SLI (mean age = 4.9 years), and 17 boys with FXS (mean age = 11.9 years) completed the Test of Early Grammatical Impairment (TEGI; Rice & Wexler, 2001), and other cognitive and language assessments. Quantitative comparisons on finiteness marking and qualitative comparisons of unscorable (i.e., nontarget) TEGI responses were conducted. Results: Children with typical development and FXS performed better on finiteness marking than children with SLI. Although unscorable responses were infrequent, boys with FXS produced more unscorable responses than children with typical development and SLI. Conclusions: Although boys with FXS have language deficits, they performed similarly to MLU-matched typically developing children on finiteness marking. This language profile differs from children with SLI, who present with a delay-within-a-delay profile with finiteness marking delays that exceed delays in MLU. Unscorable responses produced by the boys with FXS may reflect pragmatic deficits, which are prominent in this population. Assessment procedures should be carefully considered when examining language in boys with FXS.

The purpose of this study was to test the effect of manipulating verb neighbourhood density in treatment targeting the third person singular lexical affix. Using a single-subject experimental design, 6 pre-schoolers with Specific Language Impairment (SLI) were randomly assigned to one of two conditions: 1) treatment with sparse verbs or 2) treatment with dense verbs in 12 sessions. The third person singular lexical affix was targeted for 12 sessions of treatment in both conditions. Treatment gain and generalization were measured as the dependent variables. Third person singular % correct change from pre-treatment to post-treatment was measured using sentence production tasks with comparisons across the two treatment conditions. Treatment gain and generalization were greater for children enrolled in the sparse condition. Preliminary clinical recommendations are made and theoretical implications are discussed relative to neighbourhood density effects on lexical activation and storage in children with SLI.