Semicircular canal-otolith organ interaction during off-vertical axis rotation in humans

The aim of this study was to examine the interaction of signals from the se micircular canals and the otolith organs during off-vertical axis rotation (OVAR). We recorded horizontal eye position using electro-oculography in 22 young normal human subjects and stimulated the vestibule-ocular reflex wit h both constant velocity trapezoids and sinusoidal yaw rotations, using bot h earth-vertical axis rotation (EVAR) and OVAR. We found that per-rotatory long vestibule-ocular reflex (VOR) time constants during velocity trapezoid s were shorter for OVAR than for EVAR, suggesting a reduction in the effica cy of the velocity storage system during OVAR. However, when we tested with very-low-frequency sinusoids (0.01 Hz and below), the phase lead of the VO R re head velocity was smaller during OVAR than EVAR, suggesting a longer t ime constant and enhanced efficacy of velocity storage during OVAR. These r otational responses can be explained by two competing influences of signals from the otolith organs, one that diminishes the effectiveness of velocity storage and another that contributes to an estimate of head velocity.