Fig. 3.8.

Rotation of the visual scene biases estimates of the direction of gravity. Clockwise (A) and counterclockwise (B) rotation of the visual scene from the perspective of a static, upright observer. The black and white dotted arrows indicate the otolith signal (gravito-inertial acceleration: GIA). The solid blue and orange arrows indicate the estimated direction of gravity relative to the head (Ĝ), which is biased away from the otolith signal by the visual motion. (C) Clockwise (counterclockwise) visual rotation can be used to infer left (right) ear-down head tilt, and thus a rotation of the gravitational vector relative to the head in the clockwise (counterclockwise) direction away from the otolith signal (GIA). According to the gravito-inertial force resolution hypothesis, separation of the estimate of gravity relative to the head (Ĝ) from GIA results in the inference of an interaural and vertical acceleration (Â; dashed colored lines) whose magnitude and direction are given by the vector difference between GIA and Ĝ (Zupan and Merfeld, 2003). Variables with a circumflex are estimates of real-world variables.