Time contingency and social engagement shape interaction choices in autism and neurotypical development.

In social interactions, the coordination of biobehavioural rhythms - interpersonal synchrony (IS) - fosters cooperation, enhances prosocial behaviours, and moulds lifelong social attitudes. At the core of synchronous interactions is the ability to detect and respond contingently to communicative signals. Atypicalities in these processes may emerge along diverse developmental trajectories and contribute to socio-communicative difficulties commonly observed in Autism Spectrum Disorder (ASD), where social disconnection is often reported. Our exploratory research simulates interactions to delve into factors influencing IS in ASD and typically developing (TD) peers, examining the impact of time contingency and social engagement on preferences for social partners across the lifespan. Using a tablet-based task, 116 participants (n = 58 ASD, n = 58 TD; age range: 3.8-33 years) repeatedly interacted with faces that transitioned from side to front upon selection. Stimuli responses varied in time contingency (immediate or delayed response) and social engagement (smiley direct gaze vs. neutral averted gaze). Our results show that TD participants consistently prioritized social engagement, even in the absence of time contingency. In contrast, ASD participants prioritized contingency as a cue but only when this was paired with social engagement. We argue that the combination of time contingency and social engagement enhances social agency, which is particularly relevant for ASD. We discuss how creating predictable and engaging social environments could help autistic individuals feel more connected in social settings.