Virtual Reality Systems
Virtual reality (VR) systems promise to deliver dramatic improvements to areas such as training, rehabilitation, and entertainment. Success in each of these areas is being realized by VR systems, although the reports of motion type sickness (simulator sickness) and disorientation are still prevalent among users. What is it that makes a VR system effective and pleasing for the user? This project examines the relationship between various optic flow presentations and the effect they have on a 'system user' who is attempting to synchronize their treadmill walking speed with the visual stimulus.
What exactly is Optic Flow?
Optic Flow can be defined as the relative movement of points across the visual field as a person moves through an environment. In other words, it is what you see as you move. Interestingly, as we move through the world our visual system is very effective at using elements of the optic flow field to determine which objects are stationary and which objects are in relative motion with the environment.
This experiment involves a subject on a treadmill viewing a simple computer generated optic flow pattern represented by small circular points of light. The density (number of light points) and the rate at which dots appear to move towards the observer are manipulated. The subject's goal is to synchronize their treadmill speed with their interpretation of the optic flow speed. A number of interesting findings have resulted from this study.
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View of treadmill and monitor inside of test apparatus. |
 Above is a computer model of the apparatus set-up (right rear section removed). |
Below is a representation of the visual displays and the experimental factors.
Conducting this experiment gave some of our students experience with the way optic flow information can be used by the body to provide relatively consistent mapping of a treadmill walking speed to a particular optic flow presentation. The main finding in this study was that optic flow density and expansion rate did have a positive and linear influence on the treadmill speeds chosen by subjects at the 'right' speed matching the optic flow field with their haptic and proprioceptive sensations.
Sixty randomized presentations of optic flow during 3-4 hour testing sessions for six subjects confirmed the positive and linear relationship. One interesting finding included the fact that a strong feeling of self-motion was induced for 5 of the 6 subjects. That is somewhat surprising given the small visual angle subtended by the imagery (15 degrees). It is thought that the radial optic flow pattern and the extremely dark surroundings enabled such a strong illusion of self motion when using a relatively small (21 inch along diagonal) monitor.