Concurrent relations between inhibitory control, vocabulary and internal state language in 18- and 24-month-old Italian-speaking infants

The aim of this study was to investigate the concurrent relations between 18- and 24-month-olds' performance on tasks measuring inhibitory control, word production, and internal state vocabulary. Two tasks were used to measure inhibitory control, the Reverse Categorization task (a conflict task), and the Gift task (a delay task). Expressive vocabulary was assessed with the Italian version of the MacArthur Communicative Development Inventory (Words and Sentences), and internal state vocabulary was assessed with a checklist of 78 mental state terms adapted from the English Internal State Language Questionnaire. Expressive vocabulary was associated to Internal State Language and to the Reverse Categorization task, but not to the Delay task. Our findings document internal state language abilities in a sample of 61 Italian-speaking children, and show that internal state vocabulary is significantly and specifically related only to performance on the conflict measure of inhibitory control, even when vocabulary size is controlled for. Results of our study extend to an Italian sample of children previous findings on an early association between self-control and theory of mind and suggest that a link between inhibitory control processes and internal state language may be present at a very young age.