From Milliseconds to Months: Long-Term Developmental Change in Moment-By-Moment Attention to Social Stimuli in Infants with ASD
Objectives: Quantify the developmental attunement of time-varying visual salience between 2 and 24 months in infants with and without ASD.
Methods: From 2-24 months of age, children at low- and high-risk for ASD viewed video scenes of naturalistic social interaction (actresses portraying the role of caregiver and scenes of peer children at play) while eye-tracking data were collected. TD and ASD outcome groups were identified by diagnostic evaluations at 24 and 36 months. Analyses focused on low-risk TD males (n = 79) and males with ASD (n = 24). For both groups, time-varying kernel density estimation was used to quantify moment-by-moment visual scanning to eyes, mouth, face, body, and object regions, quantifying the extent to which younger infants looked at the same social content at the same moments in time.
Results: By 7 months, TD infants time their eye and mouth fixations in a manner that is not significantly different from that of TD 24-month-olds (Figure 1, statistical comparisons by bootstrap 95% confidence intervals). Likewise, by 12 months, TD infants time their face fixations in a manner that is not significantly different from that of 24-month-olds. Similar TD milestones are attained at 18 months for body and object regions. In contrast, ASD infants do not time their fixations in a typical manner for eye, face, or body and object looking at any time in the first 24 months of life. Only fixations on the mouth are timed in a manner similar to TD infants, and this similarity occurs 5-6 months later than is typical.
Conclusions: During the first two years of life, TD infants time their fixations in a manner that is increasingly similar to that of older TD children, reflecting a clear developmental progression in attention to dyadic eye and mouth cues, peer faces, bodies and objects. These moments of visual experience lay the foundation for developmental learning and future social functioning. In contrast, children with ASD deploy their attention differently across timescales short and long, creating a uniquely different experience, one which is likely to have cascading effects on future social and cognitive development.