Individuals with Autism Spectrum Disorder (ASD) struggle with reciprocal social interaction in everyday life, leading to a multitude of negative outcomes. The exact reasons and neurobiological underpinnings are still unknown. To better capture the social problems in ASD, we will apply a second-person perspective approach- focusing on active engagement in social interaction- which is currently largely lacking. Not only do individuals with ASD have problems with understanding Neurotypical (NT) individuals, NT individuals also have problems with understanding individuals with ASD, referred to as the interactional heterogeneity hypothesis. According to this hypothesis, individuals who are neurologically different and have different ways of processing the world may have trouble connecting with each other. Importantly, this also implies that individuals with ASD may experience less difficulties interacting with another individual with ASD. Indeed, preliminary research findings support this view, however systematic research is lacking. We will therefore investigate social interaction between different dyads (ASD-ASD, ASD-NT, NT-NT) at the behavioral (WP1) and brain level (WP2). In WP2, we will study the between-brain communication, referred to as hyperscanning. The findings of this project will lead to fundamental new insights into the (neurobiological underpinnings of) social problems in ASD, which can be used to improve interventions and communication with individuals with ASD.