New evidence for a central resolution of gravito-inertial signals
has been recently obtained by analyzing the properties of the
vestibulo-ocular reflex (VOR) in response to combined lateral
translations and roll tilts of the head. It is found that the
VOR generates robust compensatory horizontal eye movements independent
of whether or not the interaural translatory acceleration component
is canceled out by a gravitational acceleration component due
to simultaneous roll-tilt. This response property of the VOR
depends on functional semicircular canals, suggesting that the
brain uses both otolith and semicircular canal signals to estimate
head motion relative to inertial space. Vestibular information
about dynamic head attitude relative to gravity is the basis
for computing head (and body) angular velocity relative to inertial
space. Available evidence suggests that the inertial vestibular
system controls both head attitude and velocity with respect
to a gravity-centered reference frame. The basic computational
principles underlying the inertial processing of otolith and
semicircular canal afferent signals are outlined.
