Catching objects thrown to oneself: Testing control strategies for object interception in a novel domain.

A considerable amount of research has been performed to determine the strategies people use to intercept moving objects. Much of this research has been done using target objects such as baseballs and Frisbees that are launched to people from distances ranging from 10 m to 50 m. This research has qualified the range of domains in which each strategy is effective, but there is still controversy regarding which strategy has the most general application. The present research sought to further reduce the range of possible domains in which these strategies work by testing object interception in a situation that had never been tested before, where people launch the target objects to themselves. A strategy based on controlling optical velocity--acting to keep the optical velocity of the object at zero--provided the best match to catcher ground movements and optical trajectories. These results suggest that control of optical velocity is currently the best explanation of effective interception of both other- and self-launched objects.

Chasin' choppers: using unpredictable trajectories to test theories of object interception.

Three theories of the informational basis for object interception strategies were tested in an experiment where participants pursued toy helicopters. Helicopters were used as targets because their unpredictable trajectories have different effects on the optical variables that have been proposed as the basis of object interception, providing a basis for determining the variables that best explain this behavior. Participants pursued helicopters while the positions of both pursuer and helicopter were continuously monitored. Using models to predict the observed optical trajectories of the helicopter and ground positions of the pursuer, optical acceleration was eliminated as a basis of object interception. A model based on control of optical velocity (COV) provided the best match to pursuer ground movements, while one based on segments of linear optical trajectories (SLOT) provided the best match to the observed optical trajectories. We describe suggestions for further research to distinguish the COV and SLOT models.

Blind(fold)ed by science: a constant target-heading angle is used in visual and nonvisual pursuit.

Previous work investigating the strategies that observers use to intercept moving targets has shown that observers maintain a constant target-heading angle (CTHA) to achieve interception. Most of this work has concluded or indirectly assumed that vision is necessary to do this. We investigated whether blindfolded pursuers chasing a ball carrier holding a beeping football would utilize the same strategy that sighted observers use to chase a ball carrier. Results confirm that both blindfolded and sighted pursuers use a CTHA strategy in order to intercept targets, whether jogging or walking and irrespective of football experience and path and speed deviations of the ball carrier during the course of the pursuit. This work shows that the mechanisms involved in intercepting moving targets may be designed to use different sensory mechanisms in order to drive behavior that leads to the same end result. This has potential implications for the supramodal representation of motion perception in the human brain.

To see or not to see: effects of visual feedback on performance and intuitions of quarterbacks in American football.

We investigated the ability of quarterbacks in American football to intercept a moving receiver with a football in occluded and normal viewing conditions, and whether they can accurately predict their own success. Quarterbacks were successful in almost 80% of the trials in the occlusion condition, statistically as successful as in the normal viewing condition. Quarterbacks' predictions of their own success accounted for little variance in actual success. We propose that quarterbacks may attempt to generate a constant target-heading angle between where the football is thrown and the receiver, which may explain the high success rate in the occlusion condition.

The visual perception of lines on the road.

The present work demonstrates that observers grossly underestimate the length of lines parallel to their line of sight. In Experiment 1, observers, working from memory, estimated the length of a dashed line on the road to be 0.61 m. This result is consistent with observers' using an average visual angle converted to the physical length of visible lines on the road to estimate their length. In Experiment 2, observers gave verbal and matching estimates that significantly underestimated the length of a 3.05-m line on the ground that was parallel to their line of sight. In Experiment 3, observers significantly underestimated the length of dashed lines on the road while in a moving car. The results of Experiments 1 and 3 are described well by Euclidean geometry, whereas the tangle model that utilizes an increasing function of the visual angle to describe perceived extent best describes the results of Experiment 2.