Written by Oxford University Sunday, 19 March 2006
You probably think you’d notice if all the objects around you started moving, but research at Oxford University published today in Current Biology shows that in certain circumstances people do not even notice if a room grows to four times its size.
The Virtual Reality Research Group in Oxford used the latest in virtual reality technology to create a room where they could manipulate size and distance freely. They made the room grow in size as people walked through it, but subjects failed to notice when the scene around them quadrupled in size. As a consequence, they made gross errors when asked to estimate the size of objects in that room.
The lead researcher, Dr Andrew Glennerster, says: ‘This was very surprising. Normally, viewing a scene with two eyes, or walking around it, provides enough information to calculate its 3D structure, as we know from computer vision.’
Textbook wisdom says there are two key cues that tell us about size and positioning in our 3D surroundings: binocular disparity and motion parallax. Binocular disparity uses the distance between our two eyes to tell us how far away things are: each eye gives a slightly different ‘shot’ of an object, and the bigger the difference, the closer the object is. Motion parallax isthe way closer objects move faster across our field of vision than far-off objects when we are moving: for example, roadside trees whisk by when we drive compared to distant hills. However, despite there being all the normal visual cues as the virtual room changed, subjects in the experiment seemed to override them in favour of their faith that rooms stay the same.
The Virtual Reality Research Group uses state-of-the-art equipment. Subjects wear a headset and walk freely around a room fitted with sensors. As a subject walks, or tilts their head, the sensors detect the movement and feed it back to the computer, which immediately changes the images being sent to the eyes (a slightly different image to each eye, as in real life). When they tip their head up, they see a virtual ceiling. When they walk forward, they move further into a room. They are moving around both an Oxford laboratory, and a computerised room.
By changing variables in this sort of environment, the team can investigate how the brain processes a
three-dimensional world. ‘To understand the normal visual system, you create abnormal situations,’ Dr Glennerster explains. ‘Immersive virtual reality allows us to do that in new ways.’
Commenting on the findings that people ignore the evidence of their own eyes, he cites Bayes, an eighteenth-century mathematician. ‘Bayes said that what we believe to be the state of the world is the product of two things: your prior assumptions and your sensory information. If your sensory information is very specific, you’ll go with that. But if it’s poor, or confusing, you’ll go with your prior assumption. That’s what seems to be happening here.’ In other words, the subjects’ belief that rooms stay the same size is so strong that it overrides all the usual cues from binocular disparity and motion parallax.
‘These results imply that observers are more willing to adjust their estimate of the separation between the eyes or the distance walked than to accept that the scene around them has changed in size,’ says Dr Glennerster. ‘More broadly, these findings mark a significant shift in the debate about the way in which the brain forms a stable representation of the world. They form part of a bigger question troubling neuroscience – how is information from different times and places linked together in the brain in a coherent way?’
Last Updated ( Thursday, 23 March 2006 )
"I'll believe it when I see it" debunked by Oxford scientists
Linear Mode
