Large perceptual distortions of locomotor action space occur in ground-based coordinates: Angular expansion and the large-scale horizontal-vertical illusion.

Abstract

What is the natural reference frame for seeing large-scale spatial scenes in locomotor action space? Prior studies indicate an asymmetric angular expansion in perceived direction in large-scale environments: Angular elevation relative to the horizon is perceptually exaggerated by a factor of 1.5, whereas azimuthal direction is exaggerated by a factor of about 1.25. Here participants made angular and spatial judgments when upright or on their sides in order to dissociate egocentric from allocentric reference frames. In Experiment 1 it was found that body orientation did not affect the magnitude of the up-down exaggeration of direction, suggesting that the relevant orientation reference frame for this directional bias is allocentric rather than egocentric. In Experiment 2, the comparison of large-scale horizontal and vertical extents was somewhat affected by viewer orientation, but only to the extent necessitated by the classic (5%) horizontal-vertical illusion (HVI) that is known to be retinotopic. Large-scale vertical extents continued to appear much larger than horizontal ground extents when observers lay sideways. When the visual world was reoriented in Experiment 3, the bias remained tied to the ground-based allocentric reference frame. The allocentric HVI is quantitatively consistent with differential angular exaggerations previously measured for elevation and azimuth in locomotor space.

A large-scale horizontal-vertical illusion produced with small objects separated in depth.

“…Our hypothesis concerning this process was based on evidence of the importance of the ground plane in defining the large-scale HVI (Klein et al, 2016). Specifically, the comparison of extents in 3D space might be susceptible to biases that are known to affect other kinds of large-scale spatial tasks.…”

“…The large-scale HVI is but one of many surprisingly large biases in the apparent surface layout of the environment that can be understood in terms of the exaggeration of angular variables in elevation and azimuth (Klein, Li & Durgin, 2016). For example, perceived egocentric distance (the distance between observer and a target on the ground) is linearly compressed whether measured directly (Foley, Ribeiro-Filho, & Da Silva, 2004; Kelly, Loomis, & Beall, 2004) or measured relative to vertical or horizontal extents (Higashiyama & Ueyama, 1988; Jackson & L. K. Cormack, 2007; Li, Phillips, & Durgin, 2011).…”

“…In this paper we consider the basis for a much larger HVI that has consistently been reported for large-scale objects (Chapanis & Mankin, 1967; Higashiyama, 1992, 1996; Klein, Li & Durgin, 2016; Yang, Dixon & Proffitt, 1999). This large-scale HVI has a magnitude of 15%–25% when large objects (e.g., 4 m tall or more) are used as stimuli.…”

“…Indeed, in their recent investigation of the large-scale HVI, Klein et al (2016) found evidence of two different contributions to the large-scale HVI, the larger of which was the orientation of the ground plane. They contrasted retinotopic components and allocentric components of the illusion by using re-oriented observers (observers lying on their sides at eye level outdoors) or re-oriented virtual environments (using head-mounted immersive simulated visual environments that had been rotated by 90°).…”

“…However, the large-scale HVI procedure used in most experiments (common to Chapanis & Mankin, 1967, Klein et al, 2016, and Yang et al, 1999) involves comparing a vertical object , with a horizontal gap between that object and another object (such as a person). This detail is a matter of practicality: Adjusting the size of a physical gap is simpler to implement in a large-scale 3D environment.…”