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A room with a computer-generated view

* 20 May 2004 *

A room with a computer-generated view

A University of Sussex lecturer has been helping scientists in the USA to advance virtual reality research during her sabbatical at NASA.

Virtual reality (VR) simulations are used in a variety of situations, including the training of astronauts and aircraft pilots, and their success depends on convincing the human mind to accept an artificial environment, so that a "real" experience is offered.

One of the major problems for VR developers is overcoming the time delay between a person's movements and actions and the response from the system with which they are interacting. For example, someone wearing a head-mounted display that was projecting images of a pretend world in front of his eyes would expect the scenery to change instantly as he moved his head. Instead, there is a short time lag between the actual movement and the images that appear within the field of vision.

University of Sussex informatics lecturer Dr Katerina Mania researched this time delay issue - called latency - at the NASA Ames Research Centre in California, where she collaborated with the Advanced Displays and Spatial Perception group, world leaders in research on human issues related to VR, including latency. The initial findings have just been accepted for publication at the Human Factors and Ergonomics Society meeting in New Orleans, USA (September 2004).

Dr Mania says: "There is always going to be delay, however small, for a mechanical reply to a human command. Yet a virtual reality situation is sometimes required to 'feel real'. It is pointless training pilots with visually stunning flight simulation if their experiences have no meaning in a real aircraft. We need to know how much time has to elapse before this delay impacts on user performance."

For the NASA project, Dr Mania jointly conducted experiments exploring perceptual sensitivity to latency in photorealistic computer-generated "worlds" (rooms). Test subjects "explored" the rooms by wearing a projection helmet with screens in front of the eyes to immerse them in the artificial environment. A movement tracker on the back of the helmet passed details of user movement to the computer providing the images. Subjects were asked to report whether they could detect any visual consequences of latency, by means of psychophysical tests.

Dr Mania explains: "The experiment began with the minimum delay possible - 12 milliseconds - and was then stepped up, with eight milliseconds added each time. The results show people are very sensitive to picking up on delay and this stays true across different VR environments. Most people notice the visual consequences of latency at around 15 milliseconds, but some are very sensitive down to changes of five, even four milliseconds. Related  research gives VR developers a clearer idea of the limits they have to work with to improve the science further."

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