Gravito-Inertial Ambiguity Resolved through Head Stabilisation
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Publisher
Journal
Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences
ISSN
1364-5021
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Show full item recordAbstract
It has been frequently observed that humans and
animals spontaneously stabilise their heads with
respect to the gravitational vertical during body
movements even in the absence of vision. The
interpretations of this intriguing behaviour have so
far not included the need, for survival, to robustly
estimate verticality. Here we use a mechanistic model
of the head/otolith-organ to analyse the possibility
for this system to render verticality ‘observable’, a
fundamental prerequisite to the determination of the
angular position and acceleration of the head from
idiothetic, inertial measurements. The intrinsically
nonlinear head-vestibular dynamics is shown to
generally lack observability unless the head is
stabilised in orientation by feedback. Thus, our study
supports the hypothesis that a central function of the
physiologically costly head stabilisation strategy is
to enable an organism to estimate the gravitational
vertical and head acceleration during locomotion.
Moreover, our result exhibits a rare peculiarity of
certain nonlinear systems to fortuitously alter their
observability properties when feedback is applied.