Static roll-tilt over five minutes locally distorts the internal estimate of direction of gravity

The subjective visual vertical (SVV) indicates perceived direction of gravity. Even in healthy human subjects, roll-angle dependent misestimations - roll over-compensation (A-effect, head-roll>60°&<135°) and under-compensation (E-effect, head-roll<60°) - occur. Previously, we demonstrated that, after prolonged roll-tilt, SVV estimates when upright are biased towards the preceding roll position, which indicates that perceived vertical (PV) is shifted by the prior tilt. Hypothetically, PV in any roll position could be biased towards the previous roll position. We asked whether such a "global" bias occurs or whether the bias is "local". The SVV of healthy human subjects (N=9) was measured in nine roll positions (-120° to +120°, steps=30°) after 5min of roll-tilt in one of two adaptation positions (±90°) and compared to control trials without adaptation. After adapting, adjustments were shifted significantly (p