Figure 3.

Potential effects of sensory conflict (scene tilt) applied during the movement of the head. In the memorization phase (left), subjects evaluated the orientation of the target (green beams). If a 24/15 gain between the actual and virtual head roll motion was applied when the subject tilted the head by 15° to the left (right), the gravitational and the visual vertical no longer matched and the visual scene was tilted 9° (24/15 × 15° − 15° = 9°) with respect to gravity in the opposite direction of the head tilt. If subjects used the memorized target angle with respect to the visual background, their responses would be deviated 9° in reproducing the earth-fixed target orientation. Conversely, if the target orientation was memorized and reproduced with respect to the body, gravity, or the physical world, no systematic deviation would occur.