This investigation examined short-term changes in child and adult cyclists' gap decisions and movement timing in response to general and specific road-crossing experiences. Ten-and 12-yearolds and adults rode a bicycle through a virtual environment with 12 intersections. Participants faced continuous cross traffic and waited for gaps they judged were adequate for crossing. In the control condition, participants encountered randomly ordered gaps ranging from 1.5 to 5 s at all intersections. In the high-density condition, participants encountered high-density intersections sandwiched between sets of control intersections. These high-density intersections were designed to push participants toward taking tighter gaps. Participants in both conditions were more likely to accept 3.5, 4, 4.5, and 5 s gaps during the last than the first set of intersections, whereas participants in the high-density condition were also more likely to accept very tight 3 s gaps at the last than the first set of intersections. Moreover, individuals in the high-density condition who waited less and took shorter gaps during the middle intersections were also more likely to take very tight 3 s gaps during the last intersections. Ten-year-olds in both conditions had more time to spare when they cleared the path of the oncoming car at the last intersections, whereas 12-yearolds and adults showed no change in time to spare across intersections. Discussion focuses on linking short-term change in perceptual-motor functioning to longer-term perceptual-motor development.Keywords perceptual-motor development; perception-action coupling; road crossing; practice A fundamental problem confronting the developing perceptual-motor system is learning how to bring decisions and actions tightly in line with perceptual information. This ability to fine tune judgments and actions is important both for learning new perceptual-motor skills and for improving existing ones. Becoming a skilled pedestrian, for example, involves improved use of visual information to guide gap decisions and to time interceptive movements. Clearly, experience plays a critical role in producing these kinds of changes in perception-action tuning. Probably the most important aspect of this experience is repeated practice with performing perceptual-motor skills. But how does practice with performing a

We conducted three experiments to compare distance perception in real and virtual environments. In Experiment 1, adults estimated how long it would take to walk to targets in real and virtual environments by starting and stopping a stopwatch while looking at a target person standing between 20 and 120 ft away. The real environment was a large grassy lawn in front of a university building. We replicated this scene in our virtual environment using a nonstereoscopic, large-screen immersive display system. We found that people underestimated time to walk in both environments for distances of 40 to 60 ft and beyond. However, time-to-walk estimates were virtually identical across the two environments, particularly when people made real environment estimates first. In Experiment 2, 10-and 12-year-old children and adults estimated time to walk in real and virtual environments both with and without vision. Adults underestimated time to walk in both environments for distances of 60 to 80 ft and beyond. Again, their estimates were virtually identical in the real and virtual environment both with and without vision. Twelve-yearolds' time-to-walk estimates were also very similar across the two environments under both viewing conditions, but 10-year-olds exhibited greater underestimation in the virtual than in the real environment. A third experiment showed that adults' time-towalk estimates were virtually identical to walking without vision. We conclude that distance perception may be better in virtual environments involving large-screen immersive displays than in those involving head-mounted displays (HMDS). • 217 • J. M. Plumert et al.

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This investigation tracked changes in categorical bias (i.e., placing objects belonging to the same spatial group closer together than they really are) while 7-, 9-, and 11-year-olds and adults were learning a set of locations. Participants learned the locations of 20 objects marked by dots on the floor of an open square box divided into quadrants. At test, participants attempted to place the objects in the correct locations without the dots and boundaries. In Experiment 1, we probed categorical bias during learning by alternating learning and test trials. Categorical bias was high during the first test trial and decreased over the second and third test trials. In Experiment 2, we manipulated opportunities for learning by providing participants with either one, two, three, or four learning trials prior to test. Participants who experienced one or two learning trials exhibited more bias at test than did those who experienced four learning trials. The discussion focuses on how categorical bias emerges through interactions between the cognitive system and task structure.