This study utilized a paired priming paradigm to examine the influence of input features on case assignment in typically developing English-speaking children. The Input Ambiguity Hypothesis (Pelham, 2011) was experimentally tested to help explain why children produce subject pronoun case errors. Analyses of third singular -s marking on elicited verbs with nominative and non-nominative subjects were used to test claims of the Agreement Tense Omission Model (ATOM; Schutze & Wexler, 1996). The first aim was to determine whether priming children with input featuring case contrasting pronouns (i.e., I--me and we--us) versus non-contrasting pronouns (i.e., you--you and it--it) would differentially influence children's subsequent subject pronoun productions. It was hypothesized that children would be more likely to make subject pronoun case errors when primed with non-contrasting pronouns versus contrasting pronouns. The second aim was to determine whether case contrast features in the input might also influence finiteness marking, particularly for third person singular -s forms. Following the predictions of ATOM, it was hypothesized that children would be less likely to include third person -s forms on verbs with non-nominative versus nominative subjects. The third aim was to determine if any other spontaneous or elicited language features were associated with performance on the experimental task. Thirty typically developing English-speaking children (ages 30-43 months; 15 female) participated. Utilizing a within-subjects design, the children completed both conditions of a paired priming task, counter-balanced across participants. In the contrasting pronouns condition, children were primed by imitating a pair of simple transitive phrases containing examples of case-contrasting pronouns (e.g., Dad drives us and we drive Donald Duck; Mom drives me and I drive Pluto). Then the children immediately completed a pair of sentences to elicit a third person singular subject pronoun (e.g., Dad drives her and...; Mom drives him and...). In the non-contrasting pronouns condition, children were primed with the same sentence types except the pronouns did not have case contrast (e.g., Dad drives it and it drives the pig ; Mom drives you and you drive the duck). The same subject pronoun elicitation sentences were used in both conditions. Spontaneous language samples, a pronoun elicitation task, and standardized language measures were also administered to all participants. Results indicated that children were more likely to produce him-for-he and her-for-she errors when primed with non-contrasting pronouns (it--it and you--you) versus contrasting pronouns (I--me and we--us). When children used non-nominative pronouns, they were equally likely to use or omit third person singular -s (e.g., her hug Elmo and her hugs Elmo). When children used verbs marked for third person singular -s, they were equally likely to use nominative and non-nominative case subject pronouns (e.g., him hugs Elmo and he hugs Elmo). Results of this study provide counter-evidence to claims made by ATOM and suggest a need for a theory of tense/agreement acquisition that accounts for influences of both hard-wired universal grammar principles as well as input-driven factors.
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