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,…

Languages spoken in larger populations are relatively simple. A possible explanation for this is that languages with a greater number of speakers tend to also be those with higher proportions of non-native speakers, who may simplify language during learning. We assess this explanation for the negative correlation between population size and…

In recent decades, a growing number of children have been diagnosed with autism spectrum disorder (ASD), a condition characterized by social interaction deficits and language impairment. Yet the precise nature of the disorder's impact on language development is not well understood, in part because of the language variability among children across…