Changes in children’s perception-action tuning over short time scales: Bicycling across traffic-filled intersections in a virtual environment

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Abstract

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. Children (10- and 12-year-olds) 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 5.0 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-, 4.0-, 4.5-, and 5.0-s gaps at the last set of intersections than at the first set of intersections, whereas participants in the high-density condition were also more likely to accept very tight 3.0-s gaps at the last intersections than at the first intersections. Moreover, individuals in the high-density condition who waited less and took shorter gaps at the middle intersections were also more likely to take very tight 3.0-s gaps at the last intersections. The 10-year-olds in both conditions had more time to spare when they cleared the path of the oncoming car at the last intersections, whereas the 12-year-olds and adults showed no change in time to spare across intersections. The discussion focuses on linking short-term change in perceptual-motor functioning to longer term perceptual-motor development.

Introduction

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 skill lead to changes in perception-action tuning over both the short and long term? Contemporary views of perceptual-motor development suggest that short-term learning experiences accumulate to produce long-term developmental changes in the perception-action system (Berthier et al., 2005, Newell et al., 2001, Thelen and Smith, 1994). An important first step in understanding how these long-term changes occur is examining short-term changes in response to different kinds of experience. Here we examined how child and adult cyclists’ gap choices and movement timing changed over a single experimental session in response to general and specific experiences with crossing traffic-filled intersections in a virtual environment.

One way to think about experience is in terms of the amount of practice with performing a perceptual-motor skill. In general, more experience should lead to increased skill. This approach is clearly seen in recent work on the development of children’s walking skill. Using step counters in toddlers’ shoes, Adolph (2005) found that each day toddlers take more than 9000 steps and travel the equivalent of approximately 29 football fields. Another way to think about experience is in terms of the type of practice with performing a skill. Open skills such as road crossing and ball catching involve varying one’s actions to meet the demands of changing environments (e.g., the speed and distribution of traffic varies from one intersection to the next). In contrast, closed skills such as gymnastics involve performing actions in exactly the same way in an unchanging environment (e.g., doing a handspring on a standard-size balance beam). Because open skills are performed in changing environments, experience with a varied set of situations may lead to better learning, particularly in the long run.

The question of how experience affects the development of the perception-action system has been of long-standing interest to the field (e.g., Adolph, 1997, Gibson, 1988, McGraw, 1935). Past work indicates that extended practice with performing perceptual-motor skills affects judgments about possibilities for action. Studies with infants have shown that when a new action system such as crawling or walking becomes available, infants require a period of experience with the new skill to make accurate judgments about possibilities for action. Inexperienced walkers, for example, significantly overestimate the steepness of the slopes they can successfully walk down relative to experienced walkers (Adolph, 1997, Adolph, 2000). Work with older children indicates that practice with performing a skill leads to more accurate judgments (McKenzie and Forbes, 1992, Plumert, 1995). Plumert (1995) found that 8-year-olds were better able to distinguish between tasks that were just beyond and well beyond their ability when given some experience with performing the tasks first regardless of whether the experience involved success or failure. Thus, it appears that experience with learning a new action or with practicing a specific task leads to more finely attuned judgments about the relations between the self and the environment.

Past work also indicates that actions themselves become more finely tuned to perceptual information with experience. Work with adults on interception tasks, for example, indicates that movement speed becomes more precisely tuned to visual information over the course of learning (Montagne, Buekers, Camachon, de Rugy, & Laurent, 2003). Longitudinal work on infants’ prospective control over grasping also suggests that perception-action linkages become more finely tuned with age and experience (von Hofsten and Fazel-Zandy, 1984, Witherington, 2005). Similar work shows that infants’ responsiveness to optic flow becomes more closely tuned to the type of optic flow with increased crawling experience (Higgins, Campos, & Kermoian, 1996).

Despite the well-accepted notion that judgments and actions become more tightly tuned to perceptual information with long-term experience, very little developmental work has directly examined short-term changes in decisions and actions as one is gaining experience with performing a task (for an exception, see Gill, Adolph, & Vereijken, 2009). As noted above, individual infants’ ability to discriminate slopes they can successfully traverse from those they cannot successfully traverse improves as they gain experience with walking (e.g., Adolph, 1997, Adolph and Berger, 2006). Likewise, infants’ ability to bring their motor movements more tightly in line with perceptual information improves as they gain experience with self-produced locomotion (e.g., Higgins et al., 1996). However, judgments and actions might also change over shorter time scales. In particular, one might also expect to see changes over the time course of a single experimental session as children and adults gain experience with performing a task.

One perceptual-motor skill that undergoes change over childhood is road crossing. Nearly all research to date on perception of gap affordances has examined children’s road-crossing judgments while walking (Connelly et al., 1998, Demetre et al., 1992, Lee et al., 1984, Pitcairn and Edlmann, 2000, te Velde et al., 2005). Lee and colleagues (1984), for example, devised a road-crossing task in which 5- to 9-year-olds crossed a “pretend road” set up parallel to an actual road. Children watched the cars on the actual road and crossed the pretend road when they judged that they could safely reach the other side of the pretend road before the oncoming vehicle crossed their line of travel on the real road. Children were generally cautious when crossing the pretend road, but they sometimes accepted gaps that were too short. In addition, younger children were more likely than older children to make road-crossing errors. These findings suggest that younger children are less adept than older children at coordinating visual information and motor movements in the context of crossing traffic gaps.

Recent work on gap acceptance has focused on how child and adult cyclists cross traffic-filled roads in an immersive, interactive virtual environment (Plumert et al., 2004, Plumert et al., 2007). In these studies, children (10- and 12-year-olds) and adults rode a bicycle through a virtual environment consisting of a straight residential street with 6 intersections. Participants faced cross traffic from their left-hand side and waited for gaps they judged were adequate for crossing. The results clearly showed that, relative to adults, children’s gap choices and road-crossing behavior were less finely tuned. Children and adults chose the same size gaps, and yet children ended up with less time to spare when they cleared the path of the car. Thus, by the time children actually cleared the path of the oncoming car, the margin for error was very small, particularly for 10-year-olds.

These results clearly show that the perceptual-motor system is undergoing developmental change even during late childhood, particularly in terms of moving the self in relation to fast-moving objects. This raises an important question: How do gap choices and crossing behavior become more finely tuned with experience? To address this question, it is first important to understand how experience with performing a task leads to change in decisions and actions. One would expect that practice with a task helps to fine-tune the system because individuals directly experience the relation between their motor actions and the perceptual information. This provides useful information about whether the gap choice was correct and the crossing behavior was effective.

Another interesting issue is whether the type of experience matters. In particular, how does experience operating near the limits of the perceptual-motor system affect gap choices and crossing behavior? By practicing at the edge of their ability (e.g., a young pianist playing a challenging etude), novice learners may increase the precision, speed, and/or accuracy of their performance. In addition, the nature of the skill may influence the value of challenging experience. Open skills require individuals to adapt their actions to perform across a wide range of environmental circumstances. An outfielder, for example, must field balls that are traveling at different speeds, distances, and trajectories. Experiences with fielding balls that push the perceptual-motor system near the limit may be especially informative for learning about the boundary between success and failure and for bringing actions more tightly in line with perceptual information. Over time, such experiences should lead to more finely tuned decisions and actions. Road crossing also involves significant variation in environmental circumstances; traffic can differ in speed and density, and roads can vary in width and surface properties. Although pushing road-crossing actions too close to the limit in the real world can have dire consequences, experience with varying safety margins may be informative. Such experience may be particularly useful for instances in which individuals must precisely time their action (e.g., in crossing small gaps).

Our goal was to examine how general and specific experience with performing a perceptual-motor task helps children and adults to bring their decisions and actions more tightly in line with perceptual information. We addressed this issue in the context of bicycling across traffic gaps in a virtual environment. The road-crossing task is a useful model system for studying the development of perception-action tuning because we can look at how both road-crossing decisions (i.e., gap choices) and action (i.e., movement timing) change with age and experience. As with most perception-action skills studied in the laboratory, children and adults bring with them some experience with crossing roads. However, many aspects of this situation are novel and, thus, allow us to use the road-crossing task as a model system for examining change over the course of an experimental session. Moreover, road crossing in a virtual environment allows researchers to study basic questions about perception-action coupling without putting participants at risk for injury.

Children (10- and 12-year-olds) and adults bicycled across 12 intersections with continuous cross traffic coming from their left-hand side. We chose to study 10- and 12-year-olds because previous work has shown that the ability to synchronize self and object movement is undergoing change at least up until 12 years of age (Hoffmann et al., 1980, Plumert et al., 2004, Savelsbergh et al., 2003). Adults were included as a comparison group. We manipulated traffic density to examine how the experience of operating near the limit of the perceptual-motor system affected later gap choices and movement timing. Based on previous research, we expected children and adults to accept tight gaps when faced with high-density traffic (Adebisi and Sama, 1989, Guth et al., 2005, Kittleson and Vandehey, 1991). There were two conditions. In the control condition, children and adults encountered randomly ordered gaps ranging from 1.5 to 5.0 s at all intersections. In the high-density condition, children and adults encountered a set of intersections with high-density traffic sandwiched between sets of intersections with randomly ordered gaps ranging from 1.5 to 5.0 s. Thus, the first 4 and last 4 intersections were the same for both groups, but the middle 4 intersections differed. This design allowed us to directly examine the extent to which change in gap choices over the 12 intersections was due to general experience with crossing intersections or to specific experience with high-density traffic.

Our primary interest was in observing how gap choices and crossing behavior changed across the experimental session. We hypothesized that general experience with crossing intersections would be especially informative for learning how to time the movement of the self relative to the movement of the cars. Thus, although we expected to replicate previous results showing that adults had more time to spare than children when clearing the path of the car, we also expected that children would have more time to spare at the later intersections than at the earlier intersections. We also hypothesized that specific experience with crossing tight gaps in high-density traffic would be especially informative for learning about perception-action boundaries. Thus, we expected that children and adults in the high-density condition would show increased willingness to perform “tight fit” actions over the course of the session.

Section snippets

Participants

A total of 72 10-year-olds, 12-year-olds, and adults participated, with 24 participants in each age group. The mean ages of the three age groups were 10 years 11 months (range = 10 years 1 month to 11 years 0 months), 12 years 8 months (range = 12 years 6 months to 12 years 9 months), and 19 years 4 months (range = 18 years 5 months to 21 years 8 months). (No age was reported for 1 12-year-old and 2 adults). There were equal numbers of males and females in each age group. Children were recruited from a child research

Results

The results are divided into three main sets of analyses: (a) the size of the gaps participants chose to cross, (b) the time to spare when participants cleared the path of the oncoming car, and (c) head turning and veering while crossing the intersection. Unless otherwise noted, the data were analyzed using Age (10 years versus 12 years versus adults) × Condition (control versus high-density) × Intersection Set (first 4 versus middle 4 versus last 4) mixed-model analyses of variance (ANOVAs), with

Discussion

The results of this investigation clearly reveal changes in gap choices and movement timing over the course of the session. Children and adults chose smaller gaps to cross at the last set of intersections than at the first set of intersections. More specifically, participants in both conditions were more likely to accept gaps of 3.5, 4.0, 4.5, and 5.0 s at the last intersections than at the first intersections. The tendency to take smaller gaps at the last set of intersections was also

Acknowledgments

This research was supported by grants awarded to Jodie Plumert, Joseph Kearney, and James Cremer from the National Center for Injury Prevention and Control (R49-CCR721682), the National Science Foundation (EIA-0130864 and IIS 00-02535), and the National Institute of Child Health and Human Development (R01-HD052875). We thank the undergraduate research assistants for their help with data collection and coding.

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