Effect of head roll-tilt on the subjective visual vertical in healthy participants: Towards better clinical measurement of gravity perception

Abstract

Objective: Gravity perception is an essential function for spatial orientation and postural stability; however, its assessment is not easy. We evaluated the head-tilt perception gain (HTPG, that is, mean perceptual gain [perceived/actual tilt angle] during left or right head roll-tilt conditions) and head-upright subjective visual vertical (SVV) using a simple method developed by us to investigate the characteristics of gravity perception in healthy participants.

Methods: We measured the SVV and head roll-tilt angle during head roll-tilt within ±30° of vertical in the sitting and standing positions while the participant maintained an upright trunk (sitting, 434 participants; standing, 263 participants). We evaluated the head-upright SVV, HTPG, and laterality of the HTPG.

Results: We determined the reference ranges of the absolute head-upright SVV (<2.5°), HTPG (0.80-1.25), and HTPG laterality (<10%) for the sitting position. The head-upright SVV and HTPG laterality were not influenced by sex or age. However, the HTPG was significantly greater in women than in men and in middle-aged (30-64 years) and elderly (65-88 years) participants than in young participants (18-29 years). The HTPG, but not the head-upright SVV or HTPG laterality, was significantly higher in the standing vs sitting position.

Conclusion: The HTPG is a novel parameter of gravity perception involving functions of the peripheral otolith and neck somatosensory systems to the central nervous system. The HTPG in healthy participants is influenced by age and sex in the sitting position and immediately increases after standing to reinforce the righting reflex for unstable posture, which was not seen in the head-upright SVV, previously considered the only parameter.

Level of evidence: 4.

Keywords: gravity perception; head‐tilt perception gain; healthy participants; subjective visual vertical.

FIGURE 1

Apparatus. A, Preliminary experiment 1: The flight simulator used to generate conditions of whole‐body tilt around a front‐to‐back axis (“roll”) at various angles. B, The participant in the cockpit of the flight simulator. C, Preliminary experiment 2 and principal experiment: The examination system used to measure the subjective visual vertical and head roll‐tilt angle under static, head‐tilted conditions

FIGURE 2

Head‐tilt perception (HTP) results and illustration of experimental variables. A, HTP was calculated as the difference between the head roll‐tilt angle (HTA) and the subjective visual vertical (SVV) in all experiments. B, The average HTPs vs the average HTAs in preliminary experiments 1 (□; n = 7) and 2 (■; n = 66), superimposed. C, Representative individual data from the principal experiment. The HTP gain (HTPG) is the slope of the regression line fitted to the left or right head‐tilt data (solid and dotted lines, respectively). Left HTPG, 0.984; right HTPG, 1.025

FIGURE 3

Effects of age and sex on gravity perception. Raw absolute values of the head‐upright subjective visual vertical (HU‐SVV), A, head‐tilt perception gain (dimensionless) HTPG, B, and HTPG laterality, C, in 434 healthy participants (×, men; ○, women), plotted by age. The means of each age group (“young”: 18‐29 years, 114 men, 103 women; “middle‐aged”: 30‐64 years, 81 men, 82 women; “elderly”: ≥65 years, 29 men, 25 women) and model fits (quadratic curve) are superimposed. The means ± SD and frequency distribution histograms of the aggregated data are presented on the left and right sides of each figure, respectively

FIGURE 4

Effects of posture on gravity perception. Comparisons between the sitting and standing positions for the absolute values of the head‐upright subjective visual vertical (HU‐SVV), A, head‐tilt perception gain (dimensionless) (HTPG) B, and HTPG laterality, C, in 263 healthy participants. Fine lines: individual data; coarse lines, averages ± SD