Effects of linear and angular velocity on 2-, 4-, and 6-month-olds' visual pursuit behaviors

We report on a study with 12 infants at each of 2, 4, and 6 months of age which examines the effects on infant visual pursuit of varying the target linear velocity (m/s) and the target angular velocity (deg/s) independently. Tracking performance is described in terms of five behaviors which characterize infant performance as a tracking trial unfolds: time to initial capture, duration of initial tracking, duration of initial break in tracking, frequency of interruptions in tracking, and mean duration of all tracking intervals. Interruptions in tracking become more frequent as linear velocity increases but less frequent as angular velocity increases. The mean duration of later tracking intervals is diminished relative to the duration of earlier tracking intervals in 4- and 6-month-olds, but not in the 2-month-olds. Differences in angular velocity may account for the conflicting reports of disruptions in object permanence studies relying on a visual tracking paradigm.