Physical Aspects of Posturography in Virtual Reality

Virtual reality is a modern information technology consisting in a computer creation of an image which presents scenes with the participation of objects with the possibility of their movements in virtual space and interaction. The basis of the scene is a mathematical and/or physical model. If the observer can influence the observed scene, then the observation turns into a computer game. A force plate measures the position of the resultant pressure force on the feet (COP) of a person standing on the platform and thus evaluates the involuntary and voluntary swaying of the body, which is constantly losing and regaining its balance. A visual-motor feedback has been used in posturographic research by linking the movements of the COP of a person standing on a force plate with a movement of a virtual marker on the screen against the background of simple geometric figures. Thus, the patient is playing a computer game for which the location of the COP is the information input. The patient's task is to lean forward according to the virtual image of the geometric figure on the screen and maintain the COP marker in the given field for a few seconds. The force of inertia gives the moment of a force about the axis of rotation at the support point of the force plate. Thus, the COP is influenced by inertia forces which results in spurious COP movements at vigorous or abrupt deflections. A piece of Python software has been developed to assess the magnitude of the influence of inertia forces. The model assumes specifying the projection of the centre of gravity (COG) point at the location of the computer mouse instead. The model gives qualitative results which are very close to actual posturographic recordings.