JCPSLP VOL 15 No 1 March 2013

(Munson & Solomon, 2004), it is predicted that children in the present study will best articulate words with high ND. Similarly, it is predicted that neighbours of a word will facilitate naming at the semantic level, thereby affording words with high ND an advantage over words with low ND during retrieval. One possibility is that lexical phonological processing involves a “cascading” effect, in which nontarget words sharing a target’s phonological structure are also activated (Goldrick & Rapp, 2007). Assuming that words with high ND have more forms activated during naming, such words might be retrieved more accurately. Words may act as lexical facilitators with one another, thus resulting in more accurate naming and articulation for words with more phonologically similar forms relative to words with few neighbours. If a facilitory influence of ND is discovered, clinical implications seem possible. For example, a goal of increasing expressive vocabulary for a child with language deficits might include words with high ND. Method Participants Thirty-seven monolingual English-speaking children (20 females, 17 males) participated in the study. The average age of children participating in the study was 4;6 (years; months) ( SD = 0;8; range = 3;0–5;11). Children were recruited to participate in the study through public announcements and distribution of flyers to daycare centers and preschools. Children who were monolingual and typically developing according to parent report, using an in-depth questionnaire, were eligible to participate in the study. Additionally, each child scored within typical limits (SS 85–124) on two standardised tests of speech and language: the Goldman Fristoe Test of Articulation , 2nd edition (GFTA-2; Goldman & Fristoe, 2000), and the Peabody Picture Vocabulary Test – III (PPVT-III; Dunn & Dunn, 1997), respectively. Stimuli Thirty illustrations, half of which depicted words with low ND, and the other half of which depicted words with high ND, were used as stimuli (see Appendix A). The illustrations were selected from the Assessment of English Phonology (Barlow, 2003), a colourful picture-naming probe designed for children. Consistent with other investigations (e.g., Luce & Pisoni, 1998), ND was determined by the number of words that could be created by adding, deleting, or substituting, a single phoneme to a target item. ND was calculated with the Irvine Phonotactic Online Database (IPhOD; Vaden & Halpin, 2005), which offers information about a word’s sublexical and lexical properties. Although the database is based on an adult lexicon, previous research has demonstrated that the use of adult lexicons provides comparable measures of ND with children (Hoover, Storkel, & Kieweg, 2008); for example, words that are considered to be low in ND for adults are also low in ND for children. Stimuli in the experiment were divided at the median value for ND; all words below the median were characterised as having low ND, while those above the median value were classified as containing high ND. In the low ND condition, the mean ND was 5.5 ( SD = 2.9; range = 1–9). In the high ND condition, the mean ND was 19.7 ( SD = 10.8; range = 11–42). An independent-samples t-test confirmed that the high ND condition had significantly more neighbours than the low ND condition, t(28) = 4.91, p < .01, d = 1.79.

were named more accurately (i.e., correct lexical-semantic representations were retrieved) than words with low ND. In response, the authors acknowledged that a lack of stimuli control may have been a factor. In another picture-naming study researching effects of ND in clinical populations, Arnold, Conture, and Ohde (2005) presented 20 words varying in ND to 18 preschool children who did/did not stutter. Although some of the children’s responses contained phonological/articulatory errors, importantly these productions were discarded and only correctly articulated responses were analysed. Findings showed that all children were slower and less accurate naming words with high ND. Thus, words with more neighbours delayed naming and decreased accuracy. No difference in reaction time or accuracy was found between the two groups. Finally, while four out of nine children in each group produced more errors on words with high ND, the remaining five children did not show any difference. Perhaps then the influence of ND is more influential for some children than others. Although a semantic analysis was used to examine effects of ND in the above studies, little consideration was given to the phonological level. It is possible that more phonological measures might not have revealed effects of ND for the older children though, given that school-aged children produce target phonemes with over 90% accuracy (Waring, Fisher, & Atkin, 2001). Hence, it seems that in order to evaluate how ND affects production accuracy at the phonological level, there must be a sufficient number of (developmental) phonological production errors. Because children of younger ages such as preschoolers demonstrate numerous phonological errors (Waring et al., 2001), analysing effects of ND on production for this population would be beneficial for the current experimental question. Moreover, using measures that evaluate production at the phonological level might offer additional information about the effects of ND versus using semantic analyses alone. Models of speech production (e.g., Goldrick & Rapp, 2007) have previously attempted to understand the level of processing in which ND operates, with possibilities ranging from lexical to post-lexical and articulatory levels. Given that many studies have reported a productive advantage for words with high versus low ND (e.g., Storkel, 2004), there appears to be some support for ND operating at the lexical level. And yet, without examining actual articulatory differences between words with low and high ND, particularly at an age where developmental errors still occur, it is difficult to explore additional effects of ND at post-lexical and articulatory levels. Analyses that examine responses at the phonological level may offer such insight. The present experiment It is currently uncertain how a child’s articulation of a word during naming may be influenced by its phonological similarity to other words. The goal of this study is therefore to determine how lexical entries interact with one another during development with respect to their phonological composition. Thus, in addition to analysing productions at the semantic level, phonological measures of accuracy will also be used. This can expand our understanding of the developing lexicon, in addition to offering clinical implications. Based on previous work reporting facilitative effects of ND on production for both adults and children (Storkel et al., 2006; Storkel & Rogers, 2000), coupled with greater attention to detail when articulating words with high ND

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JCPSLP Volume 15, Number 1 2013

Journal of Clinical Practice in Speech-Language Pathology