Effects of Orbital Space Flight on Vestibular Reflexes and Perception
We have considered the complex adaptive process of human spatial orientation in terms of a time varying optimal estimator (Borah et al., 1978,1988, Merfeld et al., 1993). According to this view, the brain is constantly attempting to make the best possible guess about where we are in the presence of parallel, at times conflicting, cues from the various sensory organs and from efferent copy of our own motor commands. Central to the optimal estimator is the Kalman filter, which is capable of determining mathematically the gains to be applied to each measurement signal in order to produce a “state estimate” which is optimal in the least squares error sense, for some given error cost function. At the heart of the optimal estimator is the “internal model”, which includes knowledge of the dynamic characteristics of the body, of the sense organs and of the random motions to which the body is subjected. This internal model appears, in part, under many different names in the evolving literature on oculomotor and postural control, including “perceptual feedback”, “corollary discharge”, “velocity storage”, “second integrator” and “body schema”. In its full implementation the mathematics for solving the Ricatti equations for the optimal gains is daunting - but the idea is actually quite simple.
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