Launch effect: is the radius of action a function of the time?

In the launch effect studied by Michotte [1963 The Perception of Causality (London: Methuen)] the radius of action is a critical aspect in the perception of causality: after the contact, the second moving object, from a certain distance on, seems to move autonomously. According to Yela (1952 Quarterly Journal of Experimental Psychology 4 139^154) the radius of action is a function of the time. In the present research, we tested this hypothesis. The experimental para- digm of Michotte (1963) was used. In the experiment, the velocity of the second moving object (50, 75, 100 mm s-1) was varied. Two values (0 ms, 30 ms) of the time interval between the moment of contact of the first object and the moment when the latter begins to move were adopted. Observers indicated where the second moving object lost its passivity and started to move autonomously. The results show that the time duration of the radius of action increases with the velocity of the second moving object, whereas the time interval after the contact is not a significant factor. Our findings suggest that the radius of action is a function of the kinetic properties of the event.