Pupillometry reveals reduced unconscious emotional reactivity in autism

•Pupillary responses to non-consciously presented emotion found in typical children.•Reduced unconscious emotional reactivity found in children with autism.•Children with autism respond more to conscious than unconscious emotions.•Emotion processing difference in autism requiring consciousness and more time.•Eye-tracking pupillometry allows study of emotion across the entire autism spectrum.

Recent theoretical conceptualisations have suggested that emotion processing impairments in autism stem from disruption to the sub-cortical, rapid emotion-processing system. We argue that a clear way to ascertain whether this system is affected in autism is by measuring unconscious emotional reactivity. Using backwards masking, we presented fearful expressions non-consciously (subliminally) as well as consciously (supraliminally), and measured pupillary responses as an index of emotional reactivity in 19 children with autism and 19 typically developing children, aged 2–5 years. The pupillary responses of the children with autism revealed reduced unconscious emotional reactivity, with no group differences on consciously presented emotion. Together, these results indicate a hyporesponsiveness to non-consciously presented emotion suggesting a fundamental difference in emotion processing in autism, which requires consciousness and more time.