Efforts to Quantify Adaptation in Modeling of Postural Control

Abstract

The ability to maintain stability and to withstand the effects of gravity on stance and motion is important to a large variety of human activities. It is assumed that adaptation is a necessary quality in human postural control. Studies of adaptation generally include evaluation of gain or amplitude of various parameters of the responses to repeated identical perturbations (Nashner 1976, Nashner and McCollum, 1985, Roos et al., 1988). Such a procedure will inevitably include some possibility of anticipatory action of the subject and one may have some doubts on the generality of the results. Moreover, the evaluation will concentrate on the reduction of responses more than on the time span required to achieve such a reduction. There is a multitude of studies on adaptation of the vestibular ocular reflex where one observes diminishing responses to repeated stimuli, but also over time to repeated sessions of exposure to a stimulus (c.f. Bock et al., 1979; Wilson and Melville-Jones, 1979). Furthermore, the observation of the compensatory process after acute vestibular lesions as well as of reduced symptoms of motion sickness with the adaptation to a moving surrounding or microgravity also exemplifies the conditioning of vestibular responses over time (Wilson and Melville-Jones, 1979).