Recent electroencephalography (EEG) data from our group indicates that infants who later develop Autism Spectrum Disorder (ASD) symptoms have altered functional brain activation in the visual cortex during global motion processing. This specific phenotype alone explained ~25-35% of the variance in ASD symptoms in toddlerhood. Yet, it is not known which underlying neural mechanisms account for differences in early visual processing in autism. Here, we address this question based on EEG and/or (functional) magnetic resonance imaging (MRI) analyses of infants (n = 924; of which 230 are at elevated likelihood of ASD) and preschoolers (n = 500, of which 200 have ASD). Specifically, we will test (1) if our previous finding can be explained by altered functional connectivity (linked to the visual cortex or more widely), and (2) the more specific hypothesis that atypicalities in global motion perception reflect elevated influence of a subcortical visual pathway. Further (3), due to the large sample size and the extensive clinical data available on the participants, we can evaluate the potential clinical utility of assessing visual perception in young children (e.g., for differential diagnosis and stratification of autistic children into more homogeneous subgroups). Because this RJ project is based on analyses of recently completed multi-site datasets collected in Europe, it will contribute to Sweden taking an important role in leveraging international efforts.