The subjective visual vertical: validation of a simple test.

The study sought to provide norms for a simple test of visual perception of verticality (subjective visual vertical). The study was designed as a cohort study with a balanced design. The setting was the Rehabilitation Department of a University Hospital. Twenty-two healthy adults, of 23-58 years, 11 men (three left handed) and 11 women (three left handed) were enrolled. A luminous bar was displayed on a PC screen, and rotated in steps of 0.4° until the participant perceived it as vertical. A positive sign was attributed to a clockwise rotation of the bar. The detection threshold was set at the angle corresponding to a perceived vertical, which the participant then selected out of three subsequent alternatives (each at +0.4 or -0.4°). The participant's position (sitting vs. standing) and the preset angle of presentation (clockwise vs. counterclockwise) were balanced across sex. The constant or deviation error (dE, in degrees) and the absolute errors (aE, in degrees) were computed. An analysis of variance model tested the dependence of dE on sex, posture, age, handedness, and the preset angle. Both dE and aE were unrelated to sex, posture, handedness, and the preset angle, but were dependent on age (junior, ≤43 years; senior, >43 years). The mean dE was -0.14 ± 0.60 in the junior and 0.42 ± 0.64 in the senior group, respectively. The minimal real difference of the dE was 0.75 and 0.25 in the junior and the senior group, respectively. The overall median aE was 0.4 (5th-95th percentile 0-1.2) in the junior and 0.8 (0.4-1.46) in the senior group, respectively. The whole test took no longer than 15 min in healthy participants, and 25 min in stroke patients. The test was applied to three subacute stroke patients with left hemiparesis, of whom two showed left spatial hemineglect. All three patients presented with a significant clockwise dE. This simple test appears to be valid for the routine assessment of spatial disorders in neurological impairments.