1.2.2 Abstract structural priming effect

We were particularly interested in testing whether the priming effect was larger in children than adults, because this might imply developmental differences in the strength or number of syntactic representations. It is fairly well established that less skilled speakers show larger priming effects either because they know fewer structures, so there is less competition between structures to convey meaning (Hartsuiker & Kolk, 1998; Pickering & Branigan, 1999), or because they have only weakly represented structures, which are more susceptible to change (Chang et al., 2006; Ferreira, 2003; Jaeger & Snider, 2007). These effects have been demonstrated in studies with adult aphasics (Hartsuiker & Kolk, 1998), children with specific language impairment (Leonard et al., 2000) and second language learners (Flett, 2006). However, the data from typically developing children are less clear-cut. Many existing studies report large priming effects in children (between 12% and 33% for 3- year-olds; Bencini & Valian, 2008; Shimpi et al., 2007), which are much higher than the typical 4–10% effect reported in adult studies (Chang et al., 2006). However, these differences may be due to substantial differences in methodology. For example, unlike adult studies, studies with children tend to present multiple prime sentences (Savage et al., 2003; Thothathiri & Snedeker, 2008), use slightly different coding schemes (e.g. Bencini & Valian’s (2008) ‘lax’ coding scheme), or use a between-participants or a blocked design, thus reinforcing the use of one particular structure throughout the study or block (Bencini & Valian, 2008; Savage et al., 2003; Shimpi et al., 2007). These differences make it impossible to compare the size of the priming effect in children and adults directly. In the first two studies to apply the same methodology and scoring criteria with 3-year-old children and adults, Messenger and colleagues reported no significant differences across age groups (Messenger et al., 2011, 2012). However, an inspection of their data shows some evidence for slightly larger priming effects in children than in adults, at least when utterances coded as ‘Other’ are excluded (Tables 1 and 4 in Messenger et al. (2012), Table 1 in Messenger et al. (2011)). In addition, Messenger et al. (2011) reported that children produced a greater proportion of passives than adults, which ‘‘may reflect a greater susceptibility to priming in children’’ (Messenger et al., 2011, p. 272). Thus, the current study needs to make cross-age comparisons of the size of the priming effect in order to assess whether priming effects are larger in younger children than older children.

1.2.3 Lexical boost

Besides, we need to compare the size of the priming effect in the presence and in the absence of verb overlap between the prime and target. A robust finding in the adult literature is that the size of the priming effect is greater when there is lexical overlap between prime and target, especially when prime and target share a verb. The additional priming that results when prime and target share a verb is called the lexical boost (Pickering & Branigan, 1998). We assessed priming both with and without verb overlap in our study in order to establish whether the lexical boost is present in children as well as adults and to assess whether the size of the lexical boost changes with development. This has implications for our understanding of whether children and adults differ in how they represent verbs, syntactic structure and the links between them. In particular, verb-based lexicalist accounts predict that young children should show a large lexical boost because their syntactic representations are tied to verbs or predicate-based constructions (e.g. GIVER–give–THING GIVEN to- GIVEE; Goldberg, 2006; Ninio, 1999, 2006; Tomasello, 2003). The development of abstract (lexically-independent) representations occurs as the child develops more and more verb-specific patterns with experience of the language, until she eventually generalizes across them on the basis of commonalities in form and meaning. Thus, verb-based lexicalist theories predict that very young children (2 years or younger) will not initially demonstrate verb-independent abstract priming because they possess only verb-based representations (see Savage et al., 2003). More importantly for the present study, such theories predict that there will be substantial additional priming when prime and target share a verb (a large lexical boost) in children, even in older children who have already abstracted a verb-general pattern. This is because both verb-based representations and abstract representations are available to be primed when prime and target share a verb, making priming more likely. Under early abstraction accounts, however, children are said to have categories above the level of the lexical item (i.e. abstract categories) from the beginning (e.g. Fisher, 2001; Naigles, 2002; Pinker, 1989). On this model, since children’s representations are never more lexically-dependent than those of adults, we might expect a similar sized lexical boost across development. Previous work has not provided conclusive evidence about the presence of abstract and lexically-dependent priming in young children. On the one hand, Savage et al. (2003) found that 4-year-olds were only primed to produce passive sentences when there was lexical overlap in the pronouns and grammatical markers between the prime and target sentences. Lexically independent abstract priming (i.e. priming in the absence of lexical overlap) only appeared from 6 years of age. On the other hand, Bencini and Valian (2008) reported that 3-year-olds showed significant priming effects even when prime and target shared no open class lexical items. Similarly, Thothathiri and Snedeker (2008) have reported comparable levels of priming in 3-year-olds whether or not the prime and target sentences shared a verb, although the priming effect was slightly (but not significantly) larger when prime and target shared a verb. So the present study needs to test whether younger children show a larger priming effect when prime and target share a verb (i.e. a large lexical boost), as predicted by verb-based lexicalist accounts.