Attention to eyes is present but in decline in 2–6-month-old infants later diagnosed with autism

Abstract

A prospective longitudinal study identifies the earliest known indicator of social disability in human infancy: decline in attention to others’ eyes in infants who are later diagnosed with autism; the decline is evident already within the first 2 to 6 months of life, which reveals the early unfolding of the disorder but also offers a promising opportunity for the future of early intervention. A reduced tendency to make eye contact is a feature of autistic spectrum disorders (ASDs). It is used as a diagnostic marker, but it is not known when this behaviour arises. In a long-term study of 59 infants at high risk for ASD, and 51 at low risk, Warren Jones and Ami Klin tracked the development of eye movement in children through their first 3 years of life. Early levels of eye contact were normal in children eventually diagnosed with autism, but from soon after 2 months of age, eye contact behaviour declines. These findings may represent some of the earliest manifestations of autistic symptoms, but need to be replicated in an independent sample before being considered a potential diagnostic marker. Deficits in eye contact have been a hallmark of autism1,2 since the condition’s initial description3. They are cited widely as a diagnostic feature4 and figure prominently in clinical instruments5; however, the early onset of these deficits has not been known. Here we show in a prospective longitudinal study that infants later diagnosed with autism spectrum disorders (ASDs) exhibit mean decline in eye fixation from 2 to 6 months of age, a pattern not observed in infants who do not develop ASD. These observations mark the earliest known indicators of social disability in infancy, but also falsify a prior hypothesis: in the first months of life, this basic mechanism of social adaptive action—eye looking—is not immediately diminished in infants later diagnosed with ASD; instead, eye looking appears to begin at normative levels prior to decline. The timing of decline highlights a narrow developmental window and reveals the early derailment of processes that would otherwise have a key role in canalizing typical social development. Finally, the observation of this decline in eye fixation—rather than outright absence—offers a promising opportunity for early intervention that could build on the apparent preservation of mechanisms subserving reflexive initial orientation towards the eyes.