Invariant response to faces in ASD: Unexpected trajectory of oculo-pupillometric biomarkers from childhood to adulthood

Human faces contain a large amount of information, capturing our attention and inducing physiological engagement. Oculometric (visual exploration) and pupillometric (physiological reactivity) parameters quantified by eye-tracking are potent tools for exploring attraction to human faces from an early age. Autistic people have particularities in visual exploration and physiological reactivity to faces, with reduced time spent on the eyes associated with reduced pupil dilation. To date, no study has assessed the age differences of oculo-pupillometric parameters in response to faces. This study aimed to characterize these parameters in neurotypical (n = 150) and autistic (n = 109) populations (3-34 years old). Visual stimuli were organized along a social saliency gradient, from objects to faces. Oculo-pupillometric responses to faces appear invariant across age in the autistic population, contrary to the neurotypical population that shows an increasing attentional focus on the eye region with age, and a larger pupillary sensitivity to social salient stimuli at an early age. Our results highlight an apparent lack of maturation of face processing in autismspectrum disorder (ASD) at the population level, possibly hiding atypical and complex individual trajectories. However, these findings also point to age windows in which specific parameters could be used as discriminating biomarkers of ASD.