Sensitivity to linear-speed-gradient of radial expansion flow in infancy.

A radial expansion flow having a linear-speed-gradient (linear-grad) creates robust perception of a rigid object moving-in-depth [Perception 19 (1990) 21]. It has been reported that sensitivity to a linear-grad of radial expansion emerges at 2 months of age [Infant Behavior and Development 17 (1994) 165]. In the present study, we examined the development of sensitivity to the linear-grad of radial expansion after 2 months of age with three experiments. A total of 197 2- to 5-month-old infants participated. The results showed that sensitivity to the linear-grad improves between 2 and 3 months of age (Experiment 1), and that the infants may discriminate between an expansion having linear-grad and that having zero-grad based on their perception of motion-in-depth (Experiments 2 and 3).