Early-emerging gradients in children’s eye movement times in low-resource settings

Early brain development and skill formation vary along a socioeconomic gradient, with less favorable outcomes observed in more disadvantaged environments in low-resource countries. The onset and developmental origins of these variations are poorly understood, given lack of direct, quantitative measures. We used eye tracking to assess elementary visual behaviors in children at 7, 17, and 36 months in rural South Africa (N=374) and at 30 months in Zambia (N=270). The latency of saccadic eye movement responses to the appearance of visual objects was inversely associated with a proxy measure of the child’s socioeconomic environment (household asset ownership), with longer latencies observed in children from households with less asset-based wealth. This gradient was detectable at 7 months, increased between 7 and 36 months, was not explained by wealth-related differences in prior exposure to screens, and generalized to the latency of eye movements towards social cued objects (i.e., pointing gestures that directed the child’s attention to a specific object). Physical growth (height-for-age) and developmental milestone scores were lower in children from less wealthy households. The results provide novel quantitative metrics and evidence for very early emerging socioeconomic differences in behaviors that are mechanistically involved in learning and skill formation in early childhood.