Monocular optical constraints on collision control

A simulated ball-hitting task was used to explore the optical basis for col lision control. Ball speed and size were manipulated in Experiments 1 and 2 . Results showed a tendency for participants to respond earlier to slower a nd larger balls. Early in practice, participants would consistently miss th e slowest and largest balls. Experiments 3 and 4 examined performance as a function of the range of speeds. Performance for identical speeds differed depending on whether the speeds were fastest or slowest within a range. Asy mmetric transfer between the 2 ranges of speeds showed that those trained w ith slow speeds were very successful when tested with a faster range of spe eds. Those trained with fast speeds did not do as well when tested on slowe r speeds. The pattern of results across 4 experiments suggests that partici pants were using optical angle and expansion rate as separate degrees of fr eedom for solving the collision task.