Friday, July 12, 2013

Redirected walking can save you from running into your sofa

A man is lost in the forest. No compass. No map. No phone. No GPS. He decides to walk in a straight line until he reaches a road. He walks and walks and walks until he can walk no more. When his body is found and the path he took is analyzed, it turns out that he was not actually walking in a straight, but going round and round in a big circle. Subtle visual cues - whether the forest, the earth or something else - fooled him into walking in a circle even though he intended to walk in a straight line.

There is no happy end here, but this man did not die in vein. It turns out that this same concept - of subtle visual cues - can direct a person in a virtual environment to take a certain path instead of  path that could lead to a collision.This is referred to as redirected walking.

Imagine a gamer wearing a virtual reality goggle. The true promise of goggles is in their portability and freedom of motion. Yes, most goggle users today sit deskside near a computer, but many experiences would be so much better if the user could roam around in a room, walk over, lean, pick up objects and so forth. But if a room has physical constraints to it such as a wall or a sofa, the person immersed in the goggle can collide in a way that would completely disrupt the experience, not to mention his leg or the sofa.

I had the opportunity to speak this week with Eric Hodgson, director at the Smale Interactive Visualization Center at Miami University of Ohio. Dr Hodgson is one of the leading researchers working on various aspects of redirected walking.

We got to this topic when discussing occlusion (see my previous blog post). One advantage of goggles that are not fully occluded is that the wearer feels safer when walking around because they can see the floor, some obstacles as well as other people around them. The downside of partial occlusion is that it reduces the sense of immersion. Dr. Hodgson's work shows, amongst other things, that immersion does not have to be traded off with safety. He has subjects walking around in a gym or even outside on a football field, being significantly immersed in an HMD. The visual stimuli presented in the HMD causes them to walk in a physical path that is different than what they perceive it to be.

Here is an image of a subject wearing an HMD with a computer on his back, fearlessly walking outside:

Courtesy of Dr. Eric Hodson, Miami University of Ohio
The following graph is even more interesting:
Redirected walking - Courtesy of Dr. Eric Hodson, Miami University of Ohio

The red line shows the actual physical path that a subject took. The blue line (dash-dot-dash) shows the visual path, the path that the subject thought he was taking inside the virtual world. As you can see, the subject ends up being confined in a space that is relatively small compared with the actual virtual space. 

Dr. Hodgson's research covers many aspects of this: what kind of cues are imperceptible to the person yet cause her to change her path; how is spatial memory impacted by this process of redirected walking and more.

Why is this useful? This concept is applicable to interactive games in several ways:
  • It allows experiencing a large virtual world in spite of being constricted to a smaller physical space.
  • It helps avoid physical obstacles (e.g. the sofa)
  • It allows multiple people to be immersed in the same physical space without bumping into each other.
To read more about Dr. Hodgson's work, go to his publications page, and especially check out the 2013 Hodgson and Bachmann article.

Learn to master redirected walking, or find yourself stuck in the sofa.

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