Time-to-contact judgment in the locomotion of adults and preschool children

The hypothesis of Lee (1976)--that approach and deceleration toward a surface can be controlled through the rate of change of the optic variable tau--was examined for natural human locomotion. In Experiment 1, 12 adults were asked to perform locomotor tasks that required running at speed and then decelerating so that either the hand or head made a controlled contact with a door. In Experiment 2, 12 preschool children performed a relay-running task that required similar control. In Experiment 3, 12 children and 12 adults ran with a stick as an extension to their arm length and performed the same task. The results supported Lee's hypothesis for the initial phase of approach, but subjects switched to a separate adjustment phase 2 to 3 arm lengths from the target. Children did not adopt an appropriate tau strategy for collision avoidance and appeared unable to modify their approach strategy to allow for a hand-held stick.