The effect of gap depth on the perception of whether a gap is crossable.

Four experiments were performed in order to examine the effect of gap depth on human observers' perception of whether or not a gap is crossable. Experiments 1 and 2 showed that as the gap's depth increased, observers tended to increasingly underestimate the maximum width of a gap they could step across. Experiments 3 and 4 clarified this finding: The observed covariation of perceived gap crossability and gap depth depended on the observer's direction of gaze, rather than on the physical depth of the gap. The optical relations to which observers might be attending are discussed, as well as the possibility that cognitive-affective processes might have contributed to observers' underestimation of their actual capabilities.