Visual effects on the subjective visual vertical and subjective postural head vertical during static roll‐tilt

OBJECTIVES Tilt perception is part of the perception of spatial orientation. It is determined not only by the allocentric gravity axis, but also by a second allocentric axis induced by visual information as well as by the egocentric body (head) axis induced by somatosensory information. The aim of this study was to quantify roll-tilt perception using the subjective visual vertical (SVV) and the newly developed subjective postural head vertical (SPHV) and to investigate the visual effects on both during static roll-tilt. STUDY DESIGN Basic science. METHODS Nine male volunteers participated in this study. A flight simulator was used to create several roll-tilt environments that were then combined with visual information. SVV and SPHV were evaluated in healthy participants during static roll-tilt. RESULTS The SVV evaluation revealed significant differences between the dark condition (control) and other visual conditions with respect to some of the body roll-tilt environments, and between a body roll-tilt of 0° and ≥ 20°. The SPHV evaluation revealed a significant difference between the dark condition and the visual condition that was always roll-tilted 20° to the right of the body axis. However, there were no significant differences in SPHV error between a body roll-tilt of 0° and other tilt angles for every visual condition, unlike SVV error. CONCLUSIONS Our data indicate that human susceptibility to spatial disorientation is dependent on roll-tilt angle and visual information. They also suggest that the SPHV is not affected by roll-tilt angle, and thus differs from SVV. LEVEL OF EVIDENCE NA.