JCPSLP VOL 15 No 1 March 2013

greater activation might be provided to words with high ND versus low ND. While such activation could potentially inhibit naming of a lexical representation (i.e., via lexical competition), it appears this relationship actually facilitates production during children’s naming. These results also support an influence of ND at the lexical level in models of speech production (e.g., Goldrick & Rapp, 2007). In addition to finding facilitative effects of ND at the semantic level, a similar pattern emerged at the phonological level. Words with high ND were articulated more accurately than those with low ND. Such productive advantages have been demonstrated previously. Recall that Munson and Solomon (2004) found that adults articulated words with high ND to a greater degree than words with low ND, related perhaps to a need for greater intelligibility when words have multiple similarly sounding forms. Based on the current results, it appears that a word’s ND can also influence young children’s articulation of a word. Note that participants in the present study did exhibit developmental production errors on this task; such errors were more likely to occur on words with low ND than on words with high ND. This is a novel finding. ND may then not only play a role in lexical processing, but also in post-lexical processing at the articulatory level. Otherwise, articulatory differences might not have been observed between words with low and high ND. Revisiting Goldrick and Rapp’s (2007) proposed “cascading” effect during phonological processing, nontarget words sharing a target’s phonological structure may also become activated during productive acquisition of a word. As mentioned above, this relationship seems to facilitate production. Words with high ND presumably have more forms activated relative to words with low ND, thereby resulting in more accurate articulation for words with more phonologically similar forms relative to Apart from theoretical contributions, there are also clinical implications of the results. Since words with high versus low ND were more accurately named at the semantic level, these words may be ideal targets for children with word- finding deficits. One might argue that having children succeed early (with high ND words) in treatment may increase motivation before presenting more challenging activities. Speech-language pathologists could match word naming strategies to target words based on their ND, with phonemic cues provided when necessary to improve naming of these forms. Future research is warranted to determine how incorporating ND into treatment may assist children with word-finding impairment. Limitations Although there was an attempt to control for many confounding stimuli factors such as imageability, information was not available for all items. It is possible that results may have been impacted by variables for which data were unavailable. Additionally, given that imitated and spontaneous productions were analysed together for the articulatory analyses, it cannot be ruled out that response accuracy may have been inflated for some children after hearing a model. Future studies of this nature can control for this possibility. Future directions Work in the future should include older participants to rule out the possibility that ND may be a developmental factor affecting articulation only at an earlier age. It is uncertain words with few neighbours. Clinical implications

used for statistical tests to allow for multiple comparisons. When applicable, spontaneous productions and imitations were analysed together given that the majority of children’s responses (> 75%) were spontaneous. Furthermore, past studies have found no significant difference in articulatory accuracy between imitations and spontaneous productions of words (Andrews & Fey, 1986; Goldstein & Fabiano, 2004). Average accuracy rates for each dependent variable are presented in Table 1 by condition. Effect sizes were calculated for all analyses. Using Cohen’s d (1988), effect sizes were considered to be small (0.2–0.3), medium (0.5), or large (0.8). Table 1. Mean percentage accuracy rates and standard deviations for children’s naming by analysis and condition Semantic Binary Segmental Semantic accuracy The first analysis was used to determine how ND might influence children’s naming according to semantic accuracy. A main effect of ND was found, t (36) = 4.55, p < .01, d = 0.61, noting a moderate-large effect size. Consistent with predictions, words with high ND were named more accurately than words with low ND. Binary articulatory accuracy The next analysis considered effects of ND on production at the phonological level using a binary measure of phonetic accuracy. There was a significant effect of ND, t (36) = 3.82, p < .01, d = 0.34. As predicted, children more accurately The third analysis investigated how effects of ND might impact production accuracy at a segmental level. Again, a main effect of ND was discovered, t (36) = 3.58, p < .01, d = 0.29. Segmental accuracy on words with high ND was greater than those with low ND. Summary of results In summary, children more accurately named (retrieved) and articulated words with high ND versus low ND. This was true at the phonological level using both a binary and segmental measure of phonetic accuracy. Discussion The current experiment was designed to shed light on how items in the developing lexicon may interact with one another as a function of their phonological similarity: competitively, facilitatively, or neither. Results will first be discussed for the semantic analysis, followed by interpretations of the articulatory findings. Regarding an influence of ND on semantic accuracy, children most successfully retrieved words with high ND. This finding revealed a facilitative nature of the lexicon during naming, such that words appeared to aid one another. Consistent with original predictions and previous findings (e.g., Storkel et al., 2006), words with many phonologically similar forms were easier to retrieve than those with few forms. Considering the possibility that lexical forms must be activated in some manner prior to retrieval, articulated words with high ND versus low ND. Segmental articulatory accuracy Low neighbourhood density High neighbourhood density 75.50 (10.31) 70.81 (21.16) 95.78 (4.37) 81.80 (10.38) 77.66 (19.19) 96.88 (3.11)

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JCPSLP Volume 15, Number 1 2013

Journal of Clinical Practice in Speech-Language Pathology