This study compares lexical access and expressive and receptive vocabulary development in monolingual and bilingual toddlers. More specifically, the link between vocabulary size, production of translation equivalents, and lexical access in bilingual infants was examined as well as the relationship between the Communicative Development Inventories and the Computerized Comprehension Task. Twenty-five bilingual and 18 monolingual infants aged 24 months participated in this study. The results revealed significant differences between monolingual and bilinguals’ expressive vocabulary size in L1 but similar total vocabularies. Performance on the Computerized Comprehension Task revealed no differences between the two groups on measures of both reaction time and accuracy, and a strong convergent validity of the Computerized Comprehension Task with the Communicative Development Inventories was observed for both groups. Bilinguals with a higher proportion of translation equivalents in their expressive vocabulary showed faster access to words in the Computerized Comprehension Task.

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It has been suggested that infants' performance on the false belief task can be explained by the use of behavioural rules. To test this hypothesis, 18-month-old infants were trained to learn the new rule that an object that disappeared in location A could be found in location B. Infants were then administered a false belief task based on the violation of expectation (VOE) paradigm, an intention understanding task, and a modified detour-reaching task. Results revealed that infants looked significantly longer at the display when the experimenter looked for the toy in the full box (box with the toy) compared to infants who observed the experimenter search in the empty box (box without the toy). Results also revealed significant correlations between infants' looking time at the display and their scores on the intention task and on the detour-reaching task. Taken together, these findings suggest that infants possess an implicit understanding of false belief. In addition, they challenge the view that success on the implicit false belief task does not require executive functioning abilities.

There is currently a hot debate in the literature regarding whether or not infants have a true theory of mind (ToM) understanding. According to the mentalistic view, infants possess the same false belief understanding that older children have but their competence is masked by task demands. On the other hand, others have proposed that preverbal infants are incapable of mental state attribution and simply respond to superficial features of the events in spontaneous-responses tasks. In the current study, we aimed to clarify the nature of infants' performance in tasks designed to assess implicit theory of mind (ToM) by adopting a within-subject design that involved testing 18-month-old infants on two batteries of tasks measuring the same four ToM constructs (intention, desire, true belief, and false belief). One battery included tasks based on the violation-of- expectation (VOE) procedure, whereas the other set of tasks was based on the interactive, helping procedure. Replication of the original findings varied across tasks, due to methodological changes and the use of a within-subject design. Convergent validity was examined by comparing performance on VOE and interactive tasks that are considered to be measures of the same theory of mind concept. The results revealed no significant relations between performance on the pairs of tasks for any of the four ToM constructs measured. This pattern of results is discussed in terms of current conflicting accounts of infants' performance on implicit ToM tasks. A video abstract of this article can be viewed at: https://www.youtube.com/watch?v=U3vqfe_zdhA&feature=youtu.be.

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