Pushing people to their tipping point: Phenomenal tipping point is predicted by phenomenal vertical and intuitive beliefs.

Previous work has shown that people overestimate their own body tilt by a factor of about 1.5, the same factor by which people overestimate geographical and man-made slopes. In Experiment 1 we investigated whether people can accurately identify their own and others' tipping points (TPs) - the point at which they are tilted backward and would no longer be able to return to upright - as well as their own and others' center of mass (COM) - the relative position of which is used to determine actual TP. We found that people overestimate their own and others' TP when tilted backward, estimate their own and others' COM higher than actual, and that COM estimation is unrelated to TP. In Experiment 2, we investigated people's intuitive beliefs about the TP. We also investigated the relationship between phenomenal TP and perceived vertical. Whether verbally (conceptually) estimating the TP, drawing the TP, or demonstrating the position of the TP, people believe that the TP is close to 45°. In Experiment 3, we found that anchoring influences phenomenal TP and vertical. When accounting for starting position, the TP seems to be best predicted by an intuitive belief that it is close to 45°. In Experiment 4, we show that there is no difference in phenomenal TP and vertical when being tilted about the feet or waist/hips. We discuss the findings in terms of action-perception differences found in other domains and practical implications.

Pedal and haptic estimates of slant suggest a common underlying representation.

It is well known that people verbally exaggerate the slant of visually perceived geographical, virtual, and man-made hills. More recently it has been shown that haptic and verbal estimates of slant result in similar exaggerations, supporting the proprioception calibration hypothesis-that similar biases exist in both verbal estimates of visually perceived slant and proprioceptively perceived hand orientation. This seems to point to a common underlying representation of slant. However, it is unclear if and how manual proprioceptive estimates might be relevant for perception of ground surface slant or how this might translate to pedal perception of surface orientation. In the current work we tested whether pedal perception is systematically connected to a representational system shared by haptic and visual perception. We did this by having people orient their foot to four different orientations of a ramp (Experiment 1) or to a staircase (Experiment 2) and compared these to estimates made using a free hand measure as well as to verbal estimates. Our results show that verbal, haptic, and pedal measures of visually perceived surface orientation all result in similar estimates of slant and do so across different slanted surfaces. This suggests that verbal and haptic proprioceptive estimates tap into a representational system of visually perceived surface orientation that is relevant for walking up various surface orientations.