Perceiving Whether or Not the World Affords Stepping Onto and Over: A Developmental Study

Abstract

Children's perception of the critical (upper) limit of their stepping affordances, was tested at 6, 8, and 10 years of age for stepping onto (SON_max in Experiment I) and over (SOV_max in Experiment II) obstacles. Warren's (1984) proposition (similarity hypothesis) that adults perceive SON_max to be .88 of leg length (L) because the geometry of adults' legs is invariant over varying height was extended to varying height due to growth. Because the geometry of children's legs is both invariant over growth between 6 and 10 years and identical to adults, we predicted that children should both accurately perceive their critical limit and perceive it to be .88L. Experiment I confirmed these predictions and Experiment II demonstrated that children differentiate between the two stepping affordances. The similarity hypothesis is further supported by the fact that age does not interact with either observers' mean accuracy over conditions or variability within observers. This stable performance is interpreted to mean that children are continually adapted to these affordances and not continually retuning them in response to growth. The need for “action” studies to complement “perception” studies of affordances is discussed in terms of the possibility that the biodynamic effects of growth variations, such as the distribution of body mass, may affect perception only or principally when perception and action are dynamically linked in goal-directed behavior.