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Extending new verbs is important to becoming a productive speaker of a language. Prior results show children have difficulty extending verbs when they have seen events with varied agents. This paper further examines the impact of variability on verb learning, and asks whether this interacts with event complexity or differs by language. Children (aged 2 ½- to 3-years) in the U.S., China, Korea and Singapore learned verbs linked to simple and complex events. Sets of events included one or three agents, and children were asked to extend the verb at test. Children learning verbs linked to simple movements performed similarly across conditions. However, children learning verbs linked to events with multiple objects were less successful if those events were enacted by multiple agents. A follow-up study rules out an influence of event order. Overall, similar patterns of results emerged across languages, suggesting common cognitive processes support children’s verb learning.

To code-switch or not to code-switch? This is a dilemma for many bilingual language teachers. In this study, the influence of teachers’ CS on bilingual children's language and cognitive development is explored within heritage language (HL) classes in Singapore. Specifically, the relationship between children's language output, vocabulary development, and cognitive flexibility to teachers’ classroom CS behavior, is examined within 20 preschool HL classrooms (10 Mandarin, 6 Malay, and 4 Tamil). Teachers’ and children's utterances were recorded, transcribed, and analyzed for CS frequency and type (i.e., inter-sentential, intra-sentential). 173 students were assessed with receptive vocabulary and dimensional card sort tasks, and their vocabulary and cognitive switching scores assessed using correlational and mixed effects analyses. Results show that inter-sentential and intra-sentential CS frequency is positively and significantly related to children's intra-sentential CS frequency. Overall, findings revealed that teachers code-switched habitually more often than for instructional purposes. Neither inter-sentential nor intra-sentential CS was significantly related to children's development in HL vocabulary, and intra-sentential CS was found to positively and significantly relate to children's growth in cognitive flexibility. These findings reveal the multi-faceted impact of teacher's CS on children's early development.

Voluntary actions are associated with both a sense of agency of the action, and with distortions of perceived duration. The present study conducted four pre-registered experiments using virtual reality to investigate whether and how perceived duration and sense of agency during voluntary action are modulated by sensorimotor coupling and visual perspective. Participants performed hand movements while observing a virtual hand moving (a)synchronously with their own hand, estimated the duration of the movements, and rated their sense of agency over the movements. Pre-registered analyses revealed that sensorimotor coupling provided by synchronous visual feedback dilates perceived duration, compared to delayed feedback or pre-recorded feedback of other’s movements (sensorimotor decoupling) in Experiments 1 and 2. Visual perspective (Experiments 1 and 2), anatomical configuration (Experiment 3), and visual eccentricity of the virtual hand (Experiment 4) did not influence duration perception. Sense of agency was also modulated by sensorimotor coupling, suggesting that sensorimotor coupling could be a shared foundation for duration perception and sense of agency. Our findings and the virtual-reality technique we developed shed new light on how humans experience time and self-agency during voluntary action.