Multimodally specified energy expenditure and action-based distance judgments.

Previous research has demonstrated that perceived self-motion can be manipulated by the relation between optic flow rate and walking rate. Other studies have revealed that verbal reports of perceived distance are influenced by the energy that would be expended to traverse the distance in question. In an effort to integrate these findings, we investigated how action-based distance judgments are influenced by multimodally specified energy expenditure (MSEE)--the metabolic cost associated with traversing an optically specified distance--using a virtual-reality treadmill environment. The energy expenditure associated with walking, measured as the volume of oxygen consumed, was manipulated by changing treadmill speed or grade. Optically specified distance was manipulated by changing the virtual optic flow rate. All three manipulations of MSEE (walking rate, grade, and optic flow rate) influenced distance reports in the predicted directions and to equivalent degrees.