One of the fundamental questions in the field of language acquisition is a learnability problem, which considers how learners acquire certain aspects of language which are not directly provided in the input or whose referents are not readily observable. This dissertation investigates Japanese children's acquisition of various linguistic phenomena,…

In successful communication, it is critical to have the ability to identify what a speaker is referring to from previously mentioned information. This ability requires the identification of the topic initially introduced by lexical forms and its continuity in discourse expressed by anaphora such as null and pronominal forms in the subsequent…

Subject relative clauses (RCs) have been shown to be acquired earlier, comprehended more accurately, and produced more easily than object RCs by children. While this subject preference is often claimed to be a universal tendency, it has largely been investigated piecemeal and with low-powered experiments. To address these issues, this…

Contrastive focus, conveyed by prosodic cues, marks important information. Studies have shown that 6-year-olds learning English and Japanese can use contrastive focus during online sentence comprehension: focus used in a "contrastive context" facilitates the identification of a target referent (speeding up processing), whereas focus used…

Languages differ in how they encode causal events, placing greater or lesser emphasis on the agent or patient of the action. Little is known about how these preferences emerge and the relative influence of cognitive biases and language-specific input at different stages in development. In these studies, we investigated the emergence of sentence…

Syntactic bootstrapping facilitates children's initial learning of verb meanings based on syntactic information. A challenging case is the argument-drop languages, where the number of argument NPs is not a reliable cue for distinguishing between transitive and intransitive verbs. Despite this fact, the availability of syntactic bootstrapping in…

This article suggests a method to deal with cross-linguistic differences in children with Specific Language Impairment. The differences in vulnerable structures reflect typological properties of the surrounding language (e.g., Leonard 2014a, 2014b). This article adds a developmental perspective to the discussion by interpreting the vulnerable…

Much work on child sentence processing has demonstrated that children are able to use various linguistic cues to incrementally resolve temporary syntactic ambiguities, but they fail to use syntactic or interpretability cues that arrive later in the sentence. The present study explores whether children incrementally resolve filler-gap dependencies,…

The interpretation of floating quantifiers in Japanese requires knowledge of hierarchical phrase structure. However, the input to children is insufficient or even misleading, as our analysis indicates. This presents an intriguing question on learnability: do children interpret floating quantifiers based on a structure-dependent rule which is not…

Recent studies on the acquisition of semantics have argued that knowledge of the universal quantifier is adult-like throughout development. However, there are domains where children still exhibit non-adult-like universal quantification, and arguments for the early mastery of relevant semantic knowledge do not explain what causes such…

Languages differ from one another and must therefore be learned. Processing biases in word order can also differ across languages. For example, heavy noun phrases tend to be shifted to late sentence positions in English, but to early positions in Japanese. Although these language differences suggest a role for learning, most accounts of these…

A fundamental assumption regarding spoken language is that the relationship between sound and meaning is essentially arbitrary. The present investigation questioned this "arbitrariness" assumption by examining the influence of potential non-arbitrary mappings between sound and meaning on word learning in adults. Native English-speaking…

We explored children's early interpretation of numerals and linguistic number marking, in order to test the hypothesis (e.g., Carey (2004). Bootstrapping and the origin of concepts. "Daedalus", 59-68) that children's initial distinction between "one" and other numerals (i.e., "two," "three," etc.) is bootstrapped from a prior distinction between…

This paper investigates whether any difference exists in the degree of second language attrition between two siblings in terms of grammatical complexity, grammatical accuracy, lexical complexity, and lexical productivity based on their storytelling data collected over the period of 31 months. The subjects' L1 and L2 are Japanese and English,…

When can children speaking Japanese, English, or Chinese map and extend novel nouns and verbs? Across 6 studies, 3- and 5-year-old children in all 3 languages map and extend novel nouns more readily than novel verbs. This finding prevails even in languages like Chinese and Japanese that are assumed to be verb-friendly languages (e.g., T. Tardif,…