Fig. 3.6.
Framework incorporating visual and vestibular contributions to gravito-inertial force resolution based on changes in the head’s orientation in space, as summarized by Laurens and Angelaki (2011). Rotation signals originate from the semicircular canals and the visual system. Semicircular canals signals (blue lines) are combined with visual signals (gray lines) to improve the estimate of the angular velocity of the head (shown in red). Changes in the orientation of gravity relative to the head (i.e., changes in head tilt) are estimated by integrating the cross-product of the previous estimate of gravity (Ĝ) and the current estimated angular velocity of the head (shown in purple). Once the new estimate of gravity (Ĝ) is determined, the net gravito-inertial acceleration (GIA) signaled by the otoliths can be subtracted to estimate the linear acceleration of the head (Â) Somatogravic feedback (green-dashed arrow) slowly pulls the estimate of gravity towards the otolith signal to correct for drift in the gravity estimate. This feedback loop can also be formalized as a prior for zero acceleration. Rotation feedback (green vertical arrow) corrects for errant angular velocity signals by adjusting the internal estimate of the angular velocity of the head, thereby also reducing the difference between the internal estimate of gravity (Ĝ) and GIA. Variables with a circumflex are estimates of real-world variables.