Crawling versus walking infants' perception of affordances for locomotion over sloping surfaces.

14-month-old toddlers vs. 8.5-month-old crawling infants were encouraged to ascend and descend a sloping walkway (10 degrees, 20 degrees, 30 degrees, and 40 degrees). Infants in both locomotor groups overestimated their ability to ascend slopes. However, on descending trials where falling was more aversive, most toddlers switched from walking to sliding positions for safe descent, but crawlers plunged down head first and many fell at each increment. Toddlers touched and hesitated most before descending 10 degrees and 20 degrees slopes, and they explored alternative means for descent by testing out different sliding positions before leaving the starting platform. In contrast, crawlers touched and hesitated most before descending 30 degrees and 40 degrees slopes, and they never explored alternative sliding positions. In addition, we analyzed measures of locomotor skill and experience in relation to children's ability to perceive affordances. Findings indicate that children must learn to perceive affordances for locomotion over slopes and that learning may begin by fine-tuning of exploratory activity.