Project Virtual Balance

Abstract

This report concerns the presentation of a master thesis project accomplished, during the fall and winter of 1997-98, at the NeuroMuscular Research Center at Boston University, USA. The project concerns the implementation and an integration of a moving balance platform (BALDER, BALance DisturbER) and a set of virtual reality tools. The purpose of the system is to design a experimental tool to study human postural control and to investigate weather it is possible to affect the human balance system with the help of computer graphic. The typical experimental procedure begins with as the research subject takes place on the integrated force plate on the Balder platform. A virtual world is exposed to the subject on a large computer monitor in front of the research subject. Further the research patient is equipped with a pair of LCD shutter glasses, to get a 3D feeling of the graphical information. A glove together with a motion tracker creates a realistic eye-to-hand and line of sight relation, which increases the presents of awareness in the virtual world. All this creates an illusion of the real world into a virtual reality where the purpose is to simulate Occurrences from the real world and to investigate how the research subjects react in different situations.

Currently, the system is designed to be used in three different basic modes; first the subject can be exposed to different visual stimuli in the virtual world with Balder stationary, registrating changes of how the research subject is charging the force plate integrated in the Balder platform.; second the subject can be exposed to visual stimuli while Balder movements are controlled by the subjects center of pressure (COP). Finally the research patient and the virtual world can interact though a two-way communication. Preliminary tests were conducted on six subjects who were exposed to a 3D visual flow pattern, with a frequency of 0.2 Hz. Balder was either stationary or controlled through a weak PID controller using the subjects COP as the set point. Results indicate that the amplitudes of the COP sway decreases when the subject is exposed to a visual flow combined with a Balder movements. The conclusion of the primarily tests made so far, is that the system will be a useful tool for future studies in the field of human postural control.