Previous studies have consistently demonstrated that people's conscious perception of the slant of hills is greatly overestimated although their visually guided actions show little evidence of this bias (Bhalla & Proffitt, 1999; Creem & Proffitt, 1998; Proffitt et al., 1995). The present studies examined the influence of movement on judgments of the slant of simulated hills using a locomotion interface. This device consists of a linear treadmill capable of simulating the added forces associated with walking up hills (Hollerbach et al., 2000), surrounded by three large projection screens. In all experiments, observers were transported to a location at the bottom of each hill in a virtual environment (a simulation of a portion of the Wasatch Mountains). In Experiment 1, observers viewed a target presented on the hill while remaining stationary. In Experiment 2, they were visually moved up the hill to the target, and then transported back to the bottom. In Experiment 3, they walked up the hill to the target, and then were transported back to the bottom. Participants responded with two conscious perception judgments of slant (verbal and adjusting a pie-shape segment of disk) and a visually guided action (adjusting a palm board to correspond to the slant of the hill) while standing at the bottom of the hill. We found that walking on the hills with simulated slope forces (Exp 3) greatly increased estimations of slant for both the conscious perception and motoric measures compared to no movement or visual movement. These results differ from the previous finding that manipulations of physiological potential on a stationary observer affected conscious judgments of slant, but not motor responses (Bhalla & Proffitt). This difference may have resulted from the interaction of physical walking and the ambiguity of the graphical information in the visual display. These results have implications for a bi-directional interaction between action and perception.
This work was supported in part by NSF grants CDA-9623614 and IIS-0121084.