Clinical Assessment of Subjective Visual and Haptic Vertical Norms in Healthy Adults

BACKGROUND AND OBJECTIVE: Accurate verticality perception is essential for daily life activities, such as correctly estimating object orientation in space. This study established normative data for the subjective visual vertical (SVV) and subjective haptic vertical (SHV) using the portable and self-constructable modified Bucket test and Rotating-Column test. Additionally, the contribution of age, sex, and starting position of the line/ column on SVV and SHV accuracy were evaluated. 

METHOD: This study, part of the PRECISE project (ClinicalTrials.gov ID NCT05978596), was conducted following the STROBE guidelines. Healthy adults without visual/neurological/vestibular disorders were recruited. Subjective visual vertical and SHV accuracy were described in terms of constant errors (i.e., mean deviation from 0° [true vertical] respecting its direction), unsigned errors (i.e., mean deviation from 0° irrespective of direction), and variability (i.e., intra-individual standard deviation). 

RESULTS: Sixty participants were evaluated (mean age: 41.14 [SD = 16.74] years). Subjective visual vertical constant errors between -2.82° and 2.90°, unsigned errors up to 2.15°, and variability up to 1.61° are considered normal. Subjective haptic vertical constant errors ranged from -6.94° to 8.18°, unsigned errors up to 6.66° and variability up to 4.25°. Higher ages led to higher SVV unsigned errors and variability. SHV variability was higher in females compared to males. Certain starting positions led to higher SVV and SHV constants and SVV unsigned errors. 

DISCUSSION: Normative data are provided for affordable, self-constructable, and portable SVV and SHV tools. These norms are consistent with more sophisticated equipment and can be used to distinguish between normal and abnormal values.