“Simpler is better”: Japanese children’s learning of case-markers in transitive sentences

Using the artificial language paradigm and the scenario-pointing task, the present study explored the case-marker learning of Japanese-speaking children and examined the qualitative and quantitative factors that may influence this cognitive development. In Experiment 1, participants aged five to seven years, but not those aged four years, steadily learned the novel markers for subject – object identification with simple argument-omitted sentences. However, the benefit of learning with full-argument sentences was unclear. In Experiment 2, seven-year-olds, who showed agent-first bias, were specifically studied with their artificial marker input quantitatively manipulated. The omitted and full sentences comprised 100%-0, 80%-20%, 20%-80%, and 0–100% of the four groups. The results suggested a robust case-marker learning effect even when the omitted sentences were the less probable structures in the input; such an effect was lacking, however, if only full-argument sentences were provided in the learning phase. Thus, we concluded that simple structures lead to greater benefit for case-marker learning and proposed that ages 5 and 7 may serve as developmental milestones for Japanese-speaking children in acquiring the various types of linguistic knowledge necessary for the development of the case system.