Exposure to behavioral regularities in everyday life predicts infants' acquisition of mental state vocabulary.

There are two broad views of children's theory of mind. The mentalist view is that it emerges in infancy and is possibly innate. The minimalist view is that it emerges more gradually in childhood and is heavily dependent on learning. According to minimalism, children initially understand behaviors rather than mental states, and they are assisted in doing so by recognizing repeating patterns in behavior. The regularities in behavior allow them to predict future behaviors, succeed on theory-of-mind tasks, acquire mental state words, and eventually, understand the mental states underlying behavior. The present study provided the first clear evidence for the plausibility of this view by fitting head cameras to 54 infants aged 6 to 25 months, and recording their view of the world in their daily lives. At 6 and 12 months, infants viewed an average of 146.5 repeated behaviors per hour, a rate consistent with approximately 560,000 repetitions in their first year, and with repetitions correlating with children's acquisition of mental state words, even after controlling for their general vocabulary and a range of variables indexing social interaction. We also recorded infants' view of people searching or searching for and retrieving objects. These were 92 times less common and did not correlate with mental state vocabulary. Overall, the findings indicate that repeated behaviors provide a rich source of information for children that would readily allow them to recognize patterns in behavior and help them acquire mental state words, providing the first clear evidence for this claim of minimalism. RESEARCH HIGHLIGHTS: Six- to 25-month-olds wore head cameras to record home life from infants' point-of-view and help adjudicate between nativist and minimalist views of theory-of-mind (ToM). Nativists say ToM is too early developing to enable learning, whereas minimalists say infants learn to predict behaviors from behavior patterns in environment. Consistent with minimalism, infants had an incredibly rich exposure (146.5/h, >560,000 in first year) to repeated behaviors (e.g., drinking from a cup repeatedly). Consistent with minimalism, more repeated behaviors correlated with infants' mental state vocabulary, even after controlling for gender, age, searches witnessed and non-mental state vocabulary.

Use of a head camera to examine maternal input and its relation to 10- to 26-month-olds' acquisition of mental and non-mental state vocabulary.

We examined the relation between maternal responsiveness and children's acquisition of mental and non-mental state vocabulary in 59 pairs of mothers and children aged 10 to 26 months as they engaged in a free-play episode. Children wore a head camera and responsiveness was defined as maternal talk that commented on the child's actions (e.g., when the child reached for or manipulated an object visible in the head camera). As hypothesized, maternal responsiveness correlated with both mental and non-mental state vocabulary acquisition in younger children (approximately 18 months and younger) but not older children. We posit a diminishing role for maternal responsiveness in language acquisition as children grow older.