In the current work we investigate people's perception of their own body tilt in the pitch direction. In Experiment 1, we tilted people backward at 1 of 5 different randomly assigned angles using an inversion table. People significantly overestimated the angle at which they were tilted backward at angles from 8°to 45°. The slope of the plotted average overestimates had a gain of 1.46, fitting nicely with previously reported gains of verbal overestimates of visually perceived slant of natural outdoor geographically oriented slopes as well as man-made wooden slopes within and outside of reach in the laboratory. In Experiment 2, we showed participants a 45°line and asked them to indicate when they were positioned at that orientation. Participants again significantly overestimated the angle at which they were tilted backward. This extends work showing that a scale-expanded theory of visual space is multisensory, results in equivalent estimates for both verbal and nonverbal/nonnumeric methods, and can now be expanded to include the perceived orientation of one's own body.
Keywords Slant perception . Spatial orientation . PitchFor the last two decades, a wealth of evidence shows that people overestimate the slant of both geographical and manmade slopes by between 5°and 25° (Bhalla & Proffitt, 1999;Bridgeman & Hoover, 2008;Creem & Proffitt, 1998; CreemRegehr, Gooch, Sahm, & Thompson, 2004;Durgin & Li, 2011;Durgin, Li, & Hajnal, 2010;Hajnal, Abdul-Malak, & Durgin, 2011;Proffitt, Bhalla, Gossweiler, & Midgett, 1995;Proffitt, Creem & Zosh, 2001;Shaffer & Flint, 2011;Shaffer & McManama, 2015;Stefanucci, Proffitt, Clore, & Parekh, 2008;Witt & Proffitt, 2007). Much less work has been performed on people's perception of their own body orientation in the pitch dimension, and the results of some of this work are difficult to interpret. For instance, Cohen and Larson (1974) had participants adjust the pitch of their own body every 15°from a supine position to a prone position while restrained in a motorized hospital bed. They found systematic errors of underestimation of body tilt. For instance, when asked to place themselves at 15°backward from a vertical position, they placed themselves at 29°back-ward, and when asked to place themselves at 15°forward, they placed themselves at 23°forward. These errors were consistent but smaller as they moved in either direction in 15°increments from 15°to 60°, at which point there was almost no error. Of the studies to investigate pitch perception, this seems to be the only one where people underestimate pitch. We feel there are at least two reasons for this. First, participants were moved backward in 15°increments until they were prone, and then forward in 15°increments until they were in a supine position. They did this back and forth a total of eight times (four backward, four forward). Carryover effects from each previous estimate likely affected their subsequent estimate. Second, they were giving estimates of, say, 15°backward when they were either erect (straight up and down) o...