Abstract
From a young age, children have advanced social perceptual and reasoning abilities. However, the neural development of these abilities is still poorly understood. To address this gap, we used fMRI data collected while 122 3-12-year-old children (64 females) and 33 adults (20 females) watched an engaging and socially rich movie to investigate how the cortical basis of social processing changes throughout development. We labeled the movie with visual and social features, including motion energy, presence of a face and a social interaction, theory of mind (ToM) events, valence, and arousal. Using a voxel-wise encoding model trained on these features, we found that models based on visual (motion energy) and social (faces, social interaction, ToM, valence, and arousal) features can both predict brain activity in children as young as 3 years old across the cortex, with particularly high predictivity in motion-selective middle temporal region and the superior temporal sulcus (STS). Furthermore, models based on individual social features showed that while there may be some development throughout childhood, social interaction information in the STS is present in children as young as 3 years old and appears adult-like by age 7. The current study, for the first time, links neural activity in children to predefined social features in a narrative movie and suggests social interaction perception is supported by early developing neural responses in the STS.