Cue Combination

Virtual Reality Research Group


A primary focus of the lab has been understanding how observers combine different sources of sensory information as they move naturally through their environment. Cue combination has been studied extensively with static observers, but rarely when an observer is free to move. It is this more natural situation that the lab is primarily interested in.


Perception of the world in an expanding room

A number of papers from the lab have examined peoples perception of 3D attributes when the scene around them expands or contracts. Remarkably, people do not notice anything odd is happening here, even when the expansion or contraction is dramatic e.g. a normal size room expanding to the size of a basketball court.

However, despite these surpising effects, observers judgements can be well modelled as statistically optimal decisions given the avaliable sensory data. This has important implications for understanding how humans represent the 3D layout of a scene.


How and why does the expanding room work?

The expanding room experiment exploits the unique attributes of virtual reality equipment. Just as within the film Inception, we can creat virtual, physically impossible worlds, which dynamically reconfigure as a person moves within them. 

In the case of the expanding room the centre of expansion is a point half way between the eyes. This is important since it means that the retinal projection of a virtual object remains the same irrespective of its size. For example, a wall of the room may double its distance from you but will also double in size. Alternatively, the moon is 1/400th the size of the sun, but appears to be the same size in the sky. This is because the sun is approximately 400 times further away.

As an observer walks around in the real room, the virtual room expands or contracts depending on their position. When they are in the middle of the real room, the real and virtual rooms are the same size so the observer's feet (which they cannot see) are at the same height as the virtual floor. On the left of the real room, the virtual room is half the size. On the right hand side of the real room, the virtual room has expanded to double its original size. Thus, walking from the extreme left to the extreme right of the physical room, the observer will see a four-fold expansion of the virtual room.

The key thing is, despite this massive change in scale, the pattern of light falling on the observer's retina is similar to that experienced by an observer walking through a static room, although the relationship between distance walked and image change is altered. Only stereopsis and motion parallax can give the observer any clue as to the size of the room they occupy.

These are demonstrably powerful cues under normal circumstances and contribute to our ability to grasp different sized coffee mugs, navigate across furniture filled rooms without colliding with tables, and catch balls.

Questions addressed by the labs research in the expanding room include:

  • Why does the brain place so much weight on the assumption that the scene remains a constant size?
  • Why is the brain so willing to throw away correct information from other visual and non-visual cues?
  • Can we kick the brain into using the correct cues and ignore misleading ones?
  • Are judgements about different properties of the room mutually consistent?


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