Visually guided action implies the existence of information as well as a control law relating that information to movement. For ball catching, the Chapman Strategy-keeping constant the rate of change of the tangent of the elevation angle (d(tan(␣))/dt)-leads a catcher to the right location at the right time to intercept a fly ball. Previous studies showed the ability to detect the information and the consistency of running patterns with the use of the strategy. However, only direct manipulation of information can show its use. Participants were asked to intercept virtual balls in a Cave Automated Virtual Environment (CAVE) or to judge whether balls would pass behind or in front of them. Catchers in the CAVE successfully intercepted virtual balls with their forehead. Furthermore, the timing of judgments was related to the patterns of changing d(tan(␣))/dt. The advantages and disadvantages of a CAVE as a tool for studying interceptive action are discussed.The visual guidance of goal-directed movement implies the existence of information for controlling that movement as well as a control law expressing the relation between this information and the forces to be exerted by the organism to realize that movement. It is the task of the student of perception-action to discover both the implied information and the control laws for the task under study. For the specific task of catching a fly ball, some progress has been made in identifying the information as well as the control law associated with this information. In this article we argue, however, that not all alternatives have been ruled out by previous studies. To provide an unequivocal test of whether the rate of change of the tangent of the elevation angle (or, equivalently, optical acceleration; definitions are given below) is the information used in fly-ball catching, we performed experiments using virtual reality techniques while at the same time assessing the usefulness of virtual reality for the study of perception-action tasks such as catching fly balls.Most of the theoretical work on the interception of fly balls bears at least some relation to the proposal made by the physicist Seville Chapman in 1968. He considered the situation in which a ball travels along the sagittal plane toward a fielder. Chapman ignored the effects of air resistance (drag) on the ball and consequently assumed that the ball would follow a parabolic path. His mathematical analysis showed that the tangent of the angle of elevation, defined as the angle ␣ between the horizontal and the line connecting the ball with the point of observation, increases at a constant rate if the ball will land exactly at the point of observation. A constant optical velocity, that is, a constant d(tan(␣))/dt, will also occur if a catcher runs at a constant speed to arrive at the landing location of the ball at the same time as the ball does. An increasing d(tan(␣))/dt specifies that the ball will fly over the catcher's head. To catch the ball, the catcher should start running backward or, if he or she is alr...