Virtual Reality and the Crucial Problems in Motor Control

E. Otten & Th. Mulder
Movement Sciences, University of Groningen

The study of movement control in humans comes from several traditions, which have become loosely intertwined.
Physiology, especially muscle-, sensory- and neuro- physiology, has an old tradition of studying isolated processes, well clamped under experimental conditions. Observations from sports and arts (choreography) show such a rich movement vocabulary that any attempt to organize it seems futile, while no direct connection can be made with the approach in physiology. In the clinic, a separate way of looking evolved. Again, well controlled conditions as well as standardized tests form the basis of looking at human movements. In the mean time, in experimental psychology one tries to reconstruct abstract states and associations in the mind as a basis for movement control and its disorders, with only few references to the physiological processes behind the observed movements.

So the study of movement control is rich, but not very well connected. If you think about it, there are two things missing from the scene: First a well-established theory of movement control and second, the possibility to experiment with humans under natural conditions while extracting massive amounts of data.

The last two years we (Motek, AMC and RUG) have been building an environment, which can be helpful in filling in the need for the above-mentioned experiments. The system, called CAREN, which is an acronym for "Computer Assisted Rehabilitation Environment", consists of the following components:

• A large video wall on which three-dimensional scenes can be shown in motion
• A motion platform, controlled by a computer, that can be translated in three directions and rotated about three axes
• A motion capture system consisting of 6 cameras mounted to the ceiling and reflective markers affixed to the body of the subject or the patient

A human body model that can be run in real time in synchrony with the observed motion of the subject or patient A large software environment takes care of the data flow in real time and has been named D-Flow(TM). This technology allows patients to be tested in challenging new environments, or in accurate copies of known environments, such as a city bus taking corners etc. The purpose of this is to provide answers about the kind of motor strategies used in functional situations. If there are any problems, such as those occurring in motor disorders, one can pinpoint the difference with healthy subjects. So the experimental requirements can be met with this system, but it does not necessarily lead to a good theory of movement control. To put it bluntly: such a high tech environment can be a waste of time if experiments are not formulated in close association with the formation of a comprehensive theory on movement control in humans.

Lezing, te presenteren op het symposium 'Echt of Namaak: simulatie en modellering in beweging',
5 oktober 2001, University of Groningen.