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Oxford University's Research into the Brain Aided by Virtalis

April 30, 2003

VIRTALIS has designed and implemented a Virtual Reality (VR) facility for a new laboratory based at the University Laboratory of Physiology, Oxford. The Wellcome Trust provided a £500,000 grant to cover the cost of the specialist equipment and its installation.

The Virtual Reality Research Group is headed by Dr. Andrew Glennerster and is formulating experiments to test alternative theories that explain how we perceive the 3D world. He explained: "Very few experiments have ever been carried out that test how the brain represents 3D while a person is moving. This forms part of a bigger question troubling neuroscience - how is information from different times and places in the brain linked together in a coherent way?"

He continued: "Normally, as we move around, our eyes jump from object to object about three times a second, yet we are quite unaware of any change. We are also unaware of the swirling patterns of motion that are generated on the retina as we move in a static environment. Of course, it would be disastrous if we did perceive the dramatic retinal changes produced by saccadic eye movements, or the subtler retinal flow produced by head movements, but the question remains: how does the brain make sense of all this rapidly changing visual information?"

Dr. Glennerster's research team consists of experts from differing spheres, including spatial vision, motor control and robotics. The experiments they have already devised rely on the "immersive virtual reality" created by the Virtalis system, where virtual environments are experienced in real time as the person moves. They can subtly alter the way images change as the observer moves so that they are no longer compatible with a real, stationary 3D scene. In this way, the researchers can begin to work out the rules or algorithms the visual system uses. It is already clear that the algorithms deployed by robots are quite unlike anything the human visual system uses. One potential application of this work is in making computer vision systems 'see' in a way that is more like human vision.

In one experiment currently taking place in the laboratory, the scene expands as the observer walks through it, but because this happens slowly, the expansion is almost imperceptible. People can be fooled into thinking that two objects are the same size when in fact one is four times larger than the other. The assumption that the room has stayed the same size is so strong, it seems to overcome evidence from binocular stereopsis and motion parallax, which are normally powerful cues telling us about 3D shape and size.

In another experiment, an object can turn towards or away from the observer as they walk around the room. It is surprisingly difficult in this situation to decide when the object really is stationary unless there are other objects nearby to compare it with. Like the expanding room experiment, these results suggest that information about the relation between objects may be more important to the visual system than a global reconstruction of the scene. A third experimental strand analyses the dynamic performance of a tracking system used for virtual reality displays.

Dr Glennerster commented: "The team from Virtalis, headed by Andy Connell, guided us through the choice of hardware for our purposes, advising us on equipment that would be upgradeable in the future. They also set up our initial software and measured the location of ultrasound emitters with a theodolite to provide an accurate tracking system.

The VR equipment at the Laboratory of Physiology consists of a Datavisor 80 Head Mounted Display unit that displays a separate image to each eye, providing a large overall Field Of View (FOV) of approximately 112o, including a 44o binocular FOV. Both images are updated at 60Hz, allowing real-time rendition of the virtual environment, as subjects move their heads freely. Position is measured using an Intersense IS-900 VET tracking system that uses time-of-flight information from a series of ultrasound emitters placed around the room, combined with an inertia-based signal about the acceleration of the tracker. The position and orientation of the head-tracker is used to calculate the two binocular optic centres, from which an SGI Onyx 3200 renders the appropriate images for each eye.

Andy Connell, Virtalis's technical director, said: "This novel solution enables the position of the users' eyes to be tracked by micro cameras which look through the specially adapted optics of the head mounted display into users' pupils. This data, when combined with the tracking information, gives the researchers insight into how the brain processes the 3D world presented by the VR system."

Cockburn-Price & Carter