WAZZUP?
A team of York University scientists is giving new meaning to the question, “What's up?” They mean it, literally. And, using a unique, Canadian virtual reality facility, they've shown that when it comes to our perception of up from down, we can't always trust our eyes.
“People perceive a single ‘up’ direction. It is inconceivable to have more than one, but that up direction is influenced by more than one cue,” says psychology professor Dr. Laurence Harris, of York's Centre for Vision Research.
 It might seem that the question of “up” is a downright no-brainer. It's just up there! But determining up can in fact be a head-scratcher when working in zero gravity or when operating virtual reality technologies, such as pilotless aircraft that are remotely operated via video consoles.
The difficulty comes in part from the fact that our perception of up is based on the integration of a sensory threesome: our body orientation (up is above the top of our heads); gravity (up is the opposite direction of gravity's pull); and visual cues (for example, a liquid rests at the bottom of a glass). Change or remove any one of these from the sensory mix and the world can appear askew.
To explore the role of vision in determining our sense of up, the York University group used IVY (the Immersive Visual environment at York), a virtual reality “box” that's a computer gamer's dream.
The recently completed facility is Canada's only life-size virtual reality environment. Each of IVY's six 2.5-metre-long sides acts as a projection display. Participants enter IVY through a removable back panel. Once inside, what a person sees is completely at the mercy of the controllers. Objects appear so real that participants duck when they see one careening towards them.
To test the effect of altering visual up cues in virtual reality, the researchers, including IVY director and computer scientist Dr. Michael Jenkin, designed an experiment with a virtual floating ball that’s lighter in colour on one side than the other.
 “In the absence of an obvious source of light, people assume that the direction of illumination is from above. They expect shading with the lighter side on the top. So we can use how they position the ball to show us where they think 'above' is,” says Dr. Harris of the NSERC co-sponsored research, which was presented in December at the 2003 International Conference on Artificial Reality and Telexistence in Tokyo.
The virtual room orientation was tilted in increments of 10 degrees, from 90 degrees to the left and then 90 degrees to the right. (Imagine a room keeling over as if shipboard in a storm, however, the viewer remains upright). Participants were instructed to orient the two-tone ball (using hand-held controls) so that it appeared most upright at each interval of tilt.
The results? It turns out that “up” is clearly more than meets the eyes.
“When we tilt the room, they do adjust the ball to reflect that tilt, but they don't tilt it completely. They put it in an intermediate position,” says Dr. Harris. “This shows that they don't just use vision to show them where up is. Our brains are integrating our sense of gravity, body position and vision to provide a sense of orientation, which then affects how we see objects that are directly in front of us.”
Based on the results, the researchers developed a mathematical model to calculate the perceived direction of up for any angle of visual or body tilt. The results indicate it is possible to modify the visual impact of a tilt on our sense of up by using compensatory visual cues, a finding that could change the design of aircraft and spacecraft consoles.
Contact:
Dr. Laurence Harris
Tel.:
(416) 736-2100, ext. 66108
E-mail: harris@yorku.ca
A copy of the paper “In Virtual Reality, which way is up?” is available online at
http://yorku.ca/harris/pubs/icat2003.pdf.
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