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The language environment is important for the development of early communication and language. In the current study, we describe the natural home language environment of 9-month-old infants in Sweden and its concurrent association with language development. Eighty-eight families took part in the study. The home language environment was measured using the Language ENvironment Analysis (LENA) system, and language development was assessed using Swedish Early Communicative Development Inventory (SECDI), a parent questionnaire. LENA measures showed dramatic variation between individuals but were comparable to and showed overlapping variance with previous studies conducted in English-speaking households. Nonetheless, there were significantly more infant vocalizations and conversational turns in the present study than in one previous study. Adult word count correlated significantly and positively with infants' Use of gestures and the subscale of that section Communicative gestures. These together with another four non-significant associations formed a consistent overall pattern that suggested a link between infants' language environment and language development. Although the direction of causality cannot be determined from the current data, future studies should examine children longitudinally to assess the directionality or the bidirectionality of the reported associations between infant's language environment and language development.

Mind-mindedness (MM), the parent’s propensity to treat their young child as an individual with a mind of their own, has repeatedly been found to be positively associated with subsequent child development outcomes. In the current Swedish study, the first aim was to investigate the main features of MM in this cultural context and the second aim was to investigate its association with early child language development. Sixty-three parent-child dyads participated. MM was assessed by videotaped laboratory-based parent-child dyad free-play sessions. Language development was assessed using the parent questionnaire Swedish Early Communicative Development Inventory (SECDI), a Swedish adaptation of the internationally used MacArthur-Bates Communicative Development Inventories (MB-CDI). The ratio between Appropriate MM and Non-attuned MM was 4:1 and there was no statistically significant correlation between these two variables. There were no statistically significant correlations between Total MM or Appropriate MM and language ability ratings at either 9 or 25 months. This may be due to methodological issues concerning elicitation of MM in a Swedish context. We emphasize the importance of further theoretical and empirical studies of cross-cultural validation of MM.

A crucial aspect of children's language development is the language environment, and parental and home environment factors are particularly important during the early years. The overarching aim of this thesis was to investigate typically developed young children's language development in relation to parental and family home language environment factors. Specifically, language development was assessed in Swedish-learning children at 9 and 25 months of age. Different research perspectives and methods were used to gain a more nuanced understanding of the contributing factors to children's language development.This thesis is based on four papers that each cover different factors in the language environment. Papers I-III are based within developmental psychology and Paper IV is based within discursive psychology. Paper I investigated the relation between several language environment factors in the home and children's language development at 9 months. The results showed that linguistic input and child vocalization were significantly and positively associated with language development. This was not the case for interaction or electronic sound. Paper II investigated parental mental state talk (MST) and its relation to children's MST and general language development at 25 months. Parental MST was not significantly associated with either children's MST nor their general language development. Paper III investigated the relation between parental mind-mindedness (MM) when children were 9 months old and child language development at 9 and 25 months old. Parental MM was not significantly associated with language development at either 9 or 25 months. Paper IV examined in detail how children used MST, specifically the word vill 'want' in parent-child interactions. The results showed that children's use of the word vill 'want' accomplished several social actions, such as requesting, rejecting, and accounting for their own behavior.The results suggest a complex interaction between language environment factors and language development that can be examined from different research perspectives. This thesis has been a first step for developmental psychology and discursive psychology to talk with each other and describe the contributions of each perspective to the phenomena of language development. How the relation between language environment and language development is researched depends on the theoretical approach and further research is needed in collaboration between approaches to gain as rich knowledge about child language as possible.