Carrying a biological "backpack": Quasi-experimental effects of weight status and body fat change on perceived steepness.

The apparent steepness of hills and stairs is overestimated in explicit perception. These overestimations are malleable in that when physiological resources are compromised, apparent steepness is further overestimated. An alternative explanation of these experimental findings attributes them to demand characteristics. This article tests the relationship between estimated steepness and naturally occurring differences in body composition. A quasi-experimental field study revealed more exaggerated reports of staircase steepness in overweight than in healthy-weight participants in a situation where experimental demand would be an implausible explanation for any differences. A longitudinal follow-up study used dual X-ray absorptiometry to objectively measure participants' body composition at the beginning and end of a weight-loss program (N = 52). At baseline, higher levels of body fat were associated with steeper explicit estimates of staircase steepness. At follow-up, changes in body fat were associated with changes in estimated steepness such that a loss of fat mass co-occurred with shallower estimates. Discussion focuses on the malleability of perceived steepness at an individual level and the implication of these findings for the debate surrounding "embodied" models of perception. (PsycINFO Database Record