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Orientation and posture perception requires integrating multiple sources: the vestibular system (semicircular canals for angular velocity, otoliths for gravity and inclination), vision (rotation optic flow, horizon line), and proprioception (relative position of body segments). The result is a continuous estimate of the 3D orientation of the body.

The mathematical representation of 3D orientation requires three parameters. The Euler angles (, , ) are intuitive but suffer from singularities (gimbal lock) when = ±90°. Quaternions (q, 4 parameters with constraint |q| = 1) avoid singularities and are computationally efficient: they are the standard in robotics and aeronautics.

Angular velocity integration (gyroscope or semicircular canals) accumulates drift: _ t. The noise of a typical MEMS gyro (_ 10³ rad/s/Hz) produces a drift of ~0.06°/s. Biological systems correct for this drift using vision (_vis) and otolithic gravity: the complementary filter combines the short-term precision of the gyroscope with the long-term reference of gravity.

Pure rotational optic flow generates a velocity field on the retina that depends only on , not on the distance to objects. The visual system can decompose the total optic flow into rotational (informative of angular orientation) and translational (informative of distance) components, a process implemented in the MST visual area of primates.

The somato-gravitational illusion occurs when linear acceleration (during an airplane maneuver, for example) is misinterpreted as tilt, because the otricle cannot distinguish a_lin from g·sin(). This causes pilots without visual reference to perceive that they are leaning when they are in straight horizontal flight with acceleration.

>Model

ID:('ky', 582)

Description

ID:(0, 582)