Six-year-olds' comprehension of object-gapped relative clause sentences: Investigating the contribution of NP number mismatch

Comprehension of sentences with a center-embedded, object-gapped relative clause (ORC) is challenging for children as well as adults. Mismatching lexical and grammatical features of subject noun phrases (NPs) across the main clause and relative clause has been shown to facilitate comprehension. Adani et al. concluded that children's comprehension improved under conditions of NP number mismatch (e.g., singular main clause subject and plural relative clause subject) as compared with NP number match (e.g., both singular subjects). However, their stimuli provided number information on verb phrases (VPs) as well as NPs creating a confound for conclusions about facilitative effects of NP number mismatch. In this study, we isolated the contribution of NP number mismatch. Notably, 32 6-year-olds with typical language participated in a center-embedded, ORC sentence comprehension task with 4 types of stimuli: (a) NP number mismatch without VP number information (NP mismatch only), (b) NP number match without VP number information (NP match only), (c) NP number mismatch with VP number mismatch (NP + VP mismatch), and (d) NP number match with VP number match (NP + VP match). Children selected one of four pictures in an array to a verbally presented relative clause sentence; 56 sentences were presented. The within-subjects comparison for NP mismatch only and NP match only was not significant. However, the within-subjects comparison for NP mismatch only and NP + VP mismatch was significant. Children were more successful in NP + VP mismatch sentence comprehension (r(C) = 0.70).