The predictions of two contrasting approaches to the acquisition of transitive relative clauses were tested within the same groups of German-speaking participants aged from 3 to 5 years old. The input frequency approach predicts that object relative clauses with inanimate heads (e.g., the pullover that the man is scratching) are comprehended earlier and more accurately than those with an animate head (e.g., the man that the boy is scratching). In contrast, the structural intervention approach predicts that object relative clauses with two full NP arguments mismatching in number (e.g., the man that the boys are scratching) are comprehended earlier and more accurately than those with number-matching NPs (e.g., the man that the boy is scratching). These approaches were tested in two steps. First, we ran a corpus analysis to ensure that object relative clauses with number-mismatching NPs are not more frequent than object relative clauses with number-matching NPs in child directed speech. Next, the comprehension of these structures was tested experimentally in 3-, 4-, and 5-year-olds respectively by means of a color naming task. By comparing the predictions of the two approaches within the same participant groups, we were able to uncover that the effects predicted by the input frequency and by the structural intervention approaches co-exist and that they both influence the performance of children on transitive relative clauses, but in a manner that is modulated by age. These results reveal a sensitivity to animacy mismatch already being demonstrated by 3-year-olds and show that animacy is initially deployed more reliably than number to interpret relative clauses correctly. In all age groups, the animacy mismatch appears to explain the performance of children, thus, showing that the comprehension of frequent object relative clauses is enhanced compared to the other conditions. Starting with 4-year-olds but especially in 5-year-olds, the number mismatch supported comprehension—a facilitation that is unlikely to be driven by input frequency. Once children fine-tune their sensitivity to verb agreement information around the age of four, they are also able to deploy number marking to overcome the intervention effects. This study highlights the importance of testing experimentally contrasting theoretical approaches in order to characterize the multifaceted, developmental nature of language acquisition.

We elicited the production of various types of relative clauses in a group of Germanspeaking children with specific language impairment (SLI) and typically developing controls in order to test the movement optionality account of grammatical difficulty in SLI. The results show that German-speaking children with SLI are impaired in relative clause production compared to typically developing children. The alternative structures that they produce consist of simple main clauses, as well as nominal and prepositional phrases produced in isolation, sometimes contextually appropriate, and sometimes not. Crucially for evaluating the movement optionality account, children with SLI produce very few instances of embedded clauses where the relative clause head noun is pronounced in situ; in fact, such responses are more common among the typically developing child controls. These results underscore the difficulty German-speaking children with SLI have with structures involving movement, but provide no specific support for the movement optionality account.

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Purpose This study examines the contribution of number morphology to language comprehension abilities among children with specific language impairment (SLI) and age-matched controls. It addresses the question of whether number agreement facilitates the comprehension accuracy of object-initial declarative sentences. According to the predictions of the structural intervention account for German, number agreement should assist the correct interpretation of object-initial sentences. Method This study examines German-speaking children with SLI and a control group of age-matched typically developing children on their sentence comprehension skills for auditory presented subject–verb–object and object–verb–subject (OVS) sentences. The sentences were manipulated with respect to the number properties of the noun phrases (e.g., one plural and one singular, or both singular) and the number agreement of the verb. Results The group of children with SLI demonstrated poorer comprehension accuracy in comparison to controls. Comprehension difficulty was limited to OVS sentences among children with SLI. In addition, children with SLI comprehended OVS sentences in which number agreement (with plural subject and verb inflection) indicated the noncanonical word order more accurately than OVS sentences with two singular noun phrases and therein did not differ from controls. Conclusion The study suggests that number agreement helps alleviate the difficulty with OVS sentences and enhances comprehension accuracy, despite the finding that children with SLI exhibit lower comprehension accuracy and more heterogeneous interindividual differences, relative to controls. Supplemental Material https://doi.org/10.23641/asha.13718029