Language input is necessary for language learning, yet little is known about whether, in natural environments, the speech style and social context of language input to children impacts language development. In the present study we investigated the relationship between language input and language development, examining both the style of parental speech, comparing ‘parentese’ speech to standard speech, and the social context in which speech is directed to children, comparing one-on-one (1:1) to group social interactions. Importantly, the language input variables were assessed at home using digital first-person perspective recordings of the infants’ auditory environment as they went about their daily lives (N =26, 11- and 14-months-old). We measured language development using (a) concurrent speech utterances, and (b) word production at 24 months. Parentese speech in 1:1 contexts is positively correlated with both concurrent speech and later word production. Mediation analyses further show that the effect of parentese speech-1:1 on infants’ later language is mediated by concurrent speech. Our results suggest that both the social context and the style of speech in language addressed to children are strongly linked to a child’s future language development.

Women are generally assumed to be more talkative than men. Data were analyzed from 396 participants who wore a voice recorder that sampled ambient sounds for several days. Participants' daily word use was extrapolated from the number of recorded words. Women and men both spoke about 16,000 words per day.

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This study tested the impact of child-directed language input on language development in Spanish-English bilingual infants (N = 25, 11-and 14-month-olds from the Seattle metropolitan area), across languages and independently for each language, controlling for socioeconomic status. Language input was characterized by social interaction variables, defined in terms of speech style ("parentese" vs. standard speech) and social context (one-on-one vs. group). Correlations between parentese one-on-one and productive vocabulary at 24 months (n = 18) were found across languages and in each language independently. Differences are highlighted between previously published monolingual samples, which used the same methods as the current study of bilingual infants. The results also suggest cultural effects on language input and language development in bilingual and bicultural infants.

In previous studies, we found that the social interactions infants experience in their everyday lives at 11- and 14-months of age affect language ability at 24 months of age. These studies investigated relationships between the speech style (i.e., parentese speech vs. standard speech) and social context [i.e., one-on-one (1:1) vs. group] of language input in infancy and later speech development (i.e., at 24 months of age), controlling for socioeconomic status (SES). Results showed that the amount of exposure to parentese speech-1:1 in infancy was related to productive vocabulary at 24 months. The general goal of the present study was to investigate changes in (1) the pattern of social interactions between caregivers and their children from infancy to childhood and (2) relationships among speech style, social context, and language learning across time. Our study sample consisted of 30 participants from the previously published infant studies, evaluated at 33 months of age. Social interactions were assessed at home using digital first-person perspective recordings of the auditory environment. We found that caregivers use less parentese speech-1:1, and more standard speech-1:1, as their children get older. Furthermore, we found that the effects of parentese speech-1:1 in infancy on later language development at 24 months persist at 33 months of age. Finally, we found that exposure to standard speech-1:1 in childhood was the only social interaction that related to concurrent word production/use. Mediation analyses showed that standard speech-1:1 in childhood fully mediated the effects of parentese speech-1:1 in infancy on language development in childhood, controlling for SES. This study demonstrates that engaging in one-on-one interactions in infancy and later in life has important implications for language development.