The affordance of barrier crossing in young children exhibits dynamic, not geometric, similarity.

Previous research has shown that adults perceive affordances like the passability of apertures, climbability or crossability of steps and graspability of objects. In this study, the affordance for stepping over or onto barriers was examined in young children. This was done by placing three distinct barriers (a foam obstacle, a gap, and a single step up), which were scaled to body size, in the walking paths of 4- and 6-year olds and adults, and observing how they crossed the barriers. Age-related differences in the scaling of these actions corresponded to levels of movement variability, indicating that children as young as 4 years old are sensitive to their own constraints and scale their actions accordingly. These results indicate that affordances are not directly related to leg geometry, but rather entail the dynamics of the developing perception-action system.