Object and action words extracted from the observational data of 158 mother-child dyads with children aged nine, 12, 14, 18, 21, and 24 months were analyzed. The reduplication of syllables and words, including the special moras were phonological characteristics of Infant-Directed Vocabulary (IDV). Object and action words of IDV were more frequently used in morphosyntactic contexts than in isolated words.

We clarified the effects of IDV on the acquisition of object and action words using the Japanese MacArthur Communicative Development Inventories at each observation session, and at a 33-month follow-up time. IDV of object words at 14 months positively affected the acquisition of object words at 33 months. IDV of action words at 14 months positively affected the acquisition of baby-form action words. However, IDV of action words at 24 months negatively affected the acquisition of action words. A higher production of IDV at 14 months will contribute to the scaffolding effect on children’s subsequent vocabulary development, when infants map words to referents. Conversely, IDV of action words at 24 months, when verbs are being acquired, had a negative effect.

In this study, the effects of information resources on pragmatic reasoning were examined by controlling the speaker’s pointing gesture and gaze direction as nonlinguistic information, and object figures features such as shape, color, and marks. The experimenter either did or did not point to the monitor displaying three figure illustrations. Moreover, the experimenter’s gaze was either directed toward the participant or the monitor showing the stimulus. The result proved neither pointing nor gaze as effective in this experiment. Two reasons for this might be: 1) The participants could pay attention to the monitor anyway without non-linguistic cues. 2) The gaze cue might be relatively weak. However, it was also found that the participants used pragmatic reasoning better than chance level if the experimenter used pointing, suggesting that pointing is not entirely irrelevant. Further study is needed to explore the effect of non-linguistic information when people use pragmatic reasoning.

Bilingual language switching and its link to domain-general executive functions have been studied in the domain of language production, but they are seldom examined from the perspective of language comprehension. This study examined language switching using a language comprehension paradigm, and further discussed the role of working memory and inhibitory control associated with language switching in the paradigm. We focused on Japanese learners of English. In terms of response time, switching costs were not observed when leaners read a pair of two semantically related sentences presented in different languages (i.e., inter-sentential switching). Nevertheless, in such inter-sentimental switching trials, response time was positively correlated with the learners’ inhibitory control abilities when switching occurs from L2 to L1. In the opposite switching direction (i.e., from L1 to L2), on the other hand, response time was negatively correlated with their working memory capacity. Our results indicated that in comprehension, domain-general executive functions (working memory and inhibitory control) are differently associated depending on the direction of language switching.