How infants look at the world is strongly controlled by genetics, a new study has found.
The findings illustrate how genetic and neurological differences can affect social development, and raise new avenues for research into autistic spectrum disorder (ASD).
'These new findings demonstrate a specific mechanism by which genes can modify a child's life experience,' said lead author Professor John Constantino of Washington University. 'Two children in the same room, for example, can have completely different social experiences if one carries an inherited tendency to focus on objects while the other looks at faces, and these differences can play out repeatedly as the brain develops early in childhood.'
Researchers at Washington University, St Louis and Emory University, Atlanta presented 338 toddlers aged 18 – 24 months with videos of people talking and interacting. They used eye-tracking technology to trace each infant's visual orientation to faces, eyes or objects.
The subject group included 31 pairs of identical twins and 42 sets of fraternal twins. The researchers also studied 84 unrelated children and 88 children diagnosed with ASD.
Identical twins showed almost identical degrees of attention to another person's eyes or face, even when they watched different videos. However, less than 10 percent of attention characteristics were shared between fraternal twins.
Identical twins also showed close 'mirroring' of each other's behaviour, being more likely to move their eyes at the same moments, directions, locations and content on the same videos. The differences in timing were as close as 16.7 milliseconds.
'When we started to get the results back, I thought that I had the wrong data because the match between identical twins was so strong,' senior author Dr Warren Jones of Emory University told The New York Times. 'I thought I might have mistakenly matched data from the same twin.'
When the children were tested a year later, the same findings persisted and fraternal twins showed even more differences.
As reduced attention to eyes and faces is a behaviour associated with ASD, although not exclusively, Professor Constantino suggested that tracking eye movements in infants could identify risk of ASD long before a clinical diagnosis becomes possible. The approach could also be used to test the efficacy of early interventions to target disengaged social behaviour.
Charles Nelson, professor of paediatrics and neuroscience at Harvard Medical School, who was not involved in the study, described the findings as 'convincing' and 'novel' to the New York Times. However, he cautioned that the direct role of genes should not be overemphasised. 'Twins have identical DNA, but they don’t have identical experiences and they don’t have the same brains.'
He suggested the findings could be used to identify specific genes related to visual attention, to better understand ASD and other neurological disorders.
'That would be a big advance in autism,' Professor Nelson said.