Integrated global motion influences smooth pursuit in infants.

Smooth pursuit eye movements (SP) were studied in 5- and 9-month-old infants and adults in response to a rhombus oscillating horizontally behind three spatially separated vertical occluders. During motion, the rhombus vertices were never visible. Thus the perception of the global motion of the rhombus required integration of its moving visible segments. We tested whether infants were able to use such perceived global motion for SP in two different occluder conditions; one in which the occluder was clearly visible to the observer and one in which it was invisible. In adults, the presence of a visible occluder hiding the vertices of the rhombus strongly facilitates the perception of the global motion. It was found that adults and 9-month-olds performed significantly more horizontal SP in the presence of a visible occluder but not 5-month-olds. Furthermore, this tendency was strengthened over single trials, and this temporal pattern was very similar in all age groups. In the invisible occluder condition both adults and infants tracked the segments of the rhombus primarily with vertical SP. It was concluded that the ability to integrate moving object fragments into perceived global motion and use that to regulate SP develops into adult performance by 9 months of age.