Faculty Bibliography

The behavioral and neurobiological connections between play and the development of critical cognitive functions, such as attention, remain largely unknown. We do not yet know how these connections relate to the formation of specific abilities, such as spatial ability, and to learning in formal environments, such as in the classroom. Insights into these issues would be beneficial not only for understanding play, attention, and learning individually, but also for the development of more efficacious systems for learning and for the treatment of neurodevelopmental disorders. Different operational definitions of play can incorporate or exclude varying types of behavior, emphasize varying developmental time points, and motivate different research questions. Relevant questions to be explored in this area include, How do particular kinds of play relate to the development of particular kinds of abilities later in life? How does play vary across societies and species in the context of evolution? Does play facilitate a shift from reactive to predictive timing, and is its connection to timing unique or particularly significant? This report will outline important research steps that need to be taken in order to address these and other questions about play, human activity, and cognitive functions.

The current study investigated whether younger (college-age) and older adults (60+ years) differ in their ability to perceive safe and unsafe motor actions. Participants decided whether to walk through openings varying in width in two penalty conditions: In the doorway condition, if participants attempted to squeeze through impossibly narrow openings, the penalty for error was entrapment. In the ledge condition, if participants attempted to inch along impossibly narrow ledges, the penalty for error was falling. Results showed that across the lifespan, people consider falling to be a more severe penalty than getting stuck: Both younger and older adults made more conservative decisions when the penalty for error was falling, and older women were especially leery of falling. In both age groups, abilities and decisions were based on dynamic properties of the body, such as compressed body size in the doorway condition and balance in the ledge condition. Findings indicate that failure to perceive possibilities for action is unlikely to be the cause of the increased prevalence of falling in older adults.

Do infants, like adults, consider both the probability of falling and the severity of a potential fall when deciding whether to cross a bridge? Crawling and walking infants were encouraged to cross bridges varying in width over a small drop-off, a large drop-off, or no drop-off. Bridge width affects the probability of falling, whereas drop-off height affects the severity of the potential fall. For both crawlers and walkers, decisions about crossing bridges depended only on the probability of falling: As bridge width decreased, attempts to cross decreased, and gait modifications and exploration increased, but behaviors did not differ between small and large drop-off conditions. Similarly, decisions about descent depended on the probability of falling: Infants backed or crawled into the small drop-off, but avoided the large drop-off. With no drop-off, infants ran straight across. Results indicate that experienced crawlers and walkers accurately perceive affordances for locomotion, but they do not yet consider the severity of a potential fall when making decisions for action.

We examined several factors that affect people's ability to perceive possibilities for action. In Experiment 1, 24 participants crossed expanses of various sizes in three conditions: leaping, a familiar, launching action system; arm-swinging on monkey bars, an unpracticed skill that uses the arms rather than the legs; and crawling on hands and knees, a disused skill that involves all four limbs. Before and after performing each action, participants gave verbal judgments about the largest gap they could cross. Participants scaled initial judgments to their actual abilities in all three conditions. But they considerably underestimated their abilities for leaping, a launching action, and for arm-swinging when it was performed as a launching action; judgments about crawling, a non-launching action, and arm-swinging when it was performed as a non-launching action were more accurate. Thus, launching actions appear to produce a deficit in perceiving affordances that is not ameliorated by familiarity with the action. However, after performing the actions, participants partially corrected for the deficiency and more accurately judged their abilities for launching actions-suggesting that even brief action experience facilitates the perception of affordances. In Experiment 2, we confirmed that the deficit was due to the launching nature of the leaping and arm-swinging actions in Experiment 1. We asked an additional 12 participants to cross expanses using two non-launching actions using the legs (stepping across an expanse) and the arms (reaching across an expanse). Participants were highly accurate when judging affordances for these actions, supporting launching as the cause of the underestimation reported in Experiment 1.

Infants require locomotor experience to behave adaptively at a drop-off. However, different experimental paradigms (visual cliff and actual gaps and slopes) have generated conflicting findings regarding what infants learn and the specificity of their learning. An actual, adjustable drop-off apparatus was used to investigate whether learning to distinguish a step from a cliff transfers from crawling to walking. Experienced 12-month-old crawlers (n = 16) refused to crawl over risky drop-offs but novice 12-month-old walkers (n = 17) stepped repeatedly over the edge. Experienced 18-month-old walkers (n = 18) refused to walk over risky drop-offs but descended using alternative methods. These findings suggest that infants do not acquire generalized responses like fear or wariness of heights. Rather, infants learn to perceive affordances for the experienced action.

In light of cross-cultural and experimental research highlighting effects of childrearing practices on infant motor skill, we asked whether wearing diapers, a seemingly innocuous childrearing practice, affects infant walking. Diapers introduce bulk between the legs, potentially exacerbating infants' poor balance and wide stance. We show that walking is adversely affected by old-fashioned cloth diapers, and that even modern disposable diapers - habitually worn by most infants in the sample - incur a cost relative to walking naked. Infants displayed less mature gait patterns and more missteps and falls while wearing diapers. Thus, infants' own diapers constitute an ongoing biomechanical perturbation while learning to walk. Furthermore, shifts in diapering practices may have contributed to historical and cross-cultural differences in infant walking.

Walkers need to modify their ongoing actions to meet the demands of everyday environments. Navigating through openings requires gait modifications if the size of the opening is too small relative to the body. Here we ask whether the spatial requirements for navigating horizontal and vertical openings differ, and, if so, whether walkers are sensitive to those requirements. To test walkers' sensitivity to demands for gait modification, we asked participants to judge whether they could walk through horizontal openings without shoulder rotation and through vertical openings without ducking. Afterward, participants walked through the openings, so that we could determine which opening sizes elicited gait modifications. Participants turned their shoulders with more space available than the space they left themselves for ducking. Larger buffers for horizontal openings may reflect different spatial requirements created by lateral sway of the body during walking compared to vertical bounce. In addition, greater variability of turning from trial to trial compared with ducking may lead walkers to adopt a more conservative buffer to avoid errors. Verbal judgments accurately predicted whether openings required gait modifications. For horizontal openings, participants' judgments were best predicted by the body's dynamic abilities, not static shoulder width. The differences between horizontal and vertical openings illustrate that walkers account for the dynamic properties of walking in addition to scaling decisions to body dimensions.