Finding performance measures of a centre of mass-controlled visual tracking task: A new method

This study focused on a new method to find accurate performance measures of a mediolateral centre of mass(CoM)-controlled visual tracking task, which might be sensitive enough to detect problems in balance control early on. Visual tracking tasks, controlled by mediolateral CoM displacement, have shown promising results in this respect. The task was performed by twenty-one healthy subjects who had to track an unpredictable horizontally moving target on the screen with a tracker which was controlled by mediolateral CoM displacement. The test was performed under three conditions: The CoM displacement was controlled by either a static gain, an integrator or a double integrator before the displacement of the tracker was displayed on the screen. The results were analysed in the frequency domain. In this study the McRuer crossover-model, which was developed for aviation, was used to describe the frequency response of the participants while performing a visual tracking task in three test conditions. The three performance measures, the effective time delay, the crossover frequency and the cutoff frequency, were calculated from this estimator. The overall coherence of the double integrator condition was extremely low, so these results were not taken into discussion. Nevertheless, the McRuer crossover model appeared to be a good descriptor for the frequency response of the subjects during balance controlled visual tracking tasks in the static gain and integrator conditions. The test-retest reliability of the parameters was tested among nine of the subjects, no significant differences between the three tests were found. The crossover frequency and the cutoff frequency, of both the static gain and integrator conditions have their advantages and disadvantages on behalf of the early detection of people at risk of falling. However, the two test conditions should be repeated with a larger subject group, as well as a subject group with known impaired balance, to find out which performance measure is the most accurate and sensitive to detect problems in balance early on.BiomechatronicsBiomedical EngineeringMechanical, Maritime and Materials Engineerin