Social information processing in infancy and adolescence: Examining the role of different interaction partners

Over the course of development children learn vital communication skills from interacting with other people. However, how children learn and react might depend on the person they are interacting with. We therefore investigated the possible role of different interaction partners in two developmental samples - toddlers and adolescents. In the first part of this dissertation I examined whether familiarity of the speaker facilitated novel word learning in both a typical sample of two-year-olds and in children at increased risk for autism. Results for the typical population showed that compared to unfamiliar speakers, maternal speech indeed boosts novel word learning. This was the case both when mothers produced speech during live interaction, and when her speech was prerecorded and delivered through loudspeakers. Given these results, I next asked whether toddlers at increased risk for autism can learn novel words from their parents, as these children are typically reported to have smaller vocabularies. Although my results confirm that these high-risk infants lagged behind in their current vocabulary size compared to typically-developing peers, there was no such group difference in their ability to learn novel words from their parents. This suggests that smaller vocabularies observed in children with autism are unlikely to originate in poor word-object mapping, but rather result from deficiencies in for example consolidation of novel words or on higher level social demands of interactive communication. In the second part we examined the development of social processes over the course of adolescence, as there are extensive changes in social behavior during this period. Because of a re-orientation from parents to peers, adolescents are temporarily relatively worse in recognizing adult faces compared to child faces. I first examined whether such a dip could also be observed in other higher social processes (i.e., gaze following, emotion recognition and empathy). Both emotion recognition and empathy abilities gradually increased over adolescence, whereas gaze following did not change over this period. Thus, in contrast to basic face recognition, I did not observe any dip in performance around the onset of puberty for these higher social processes in which children viewed (parts of) adults’ faces. This begged the question whether age of the interaction partner would influence a child’s gaze following behavior. Results, however, showed similar gaze following patterns for both adult and child stimuli, which highlights that children's responses to gaze cues are not modulated by the age of the interaction partner. Based on the research described in this dissertation, I conclude that the type of interaction partner can shape early social development. Clearly familiarity with the interaction partner plays an important role in infants' language processing. Age of the interaction partner (adult versus peers) does not modulate higher social processing in adolescence. It remains an open question how familiarity affects social processing in adolescence, which is a relevant topic for future research. This knowledge is fundamental for the design of early interventions for children with communicative disorders, as it gives insights on who might be suitable to deliver these interventions to the children.