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  • Fri 23 Sep 2011

    Body representation in VR

    Published at 17:37   Category Virtual Reality  

    This is a summary of Mel Slater‘s keynote at JVRC 2011, entitled “Body representation in Immersive Virtual Reality”.

    M. Slater started his talk by stating that the goal of VR is that people act as if what they’re experiencing is real, even though they know it’s not. Your mind accepts the illusion. He insisted that this is not your imagination, it is really a perceptual illusion.

    He briefly explained his concepts of Place Illusion and Plausibility Illusion, that are actually unified in the virtual body. The virtual body is also important in that it augments the sense of presence, and improves the estimation of size and distances in VEs (which otherwise tends to be underestimated, even though we don’t know why yet. See studies from Victoria Interrante and Betty Mohler)

    Proteus effect

    Normally, when you enter a virtual world, you enter it with the same personality, the same “you” (whatever that means). But studies have shown that if you have a different representation of your self, you behave differently ! In a recent study M. Bailenson showed that improving the “attractiveness” of your avatar will transfer as self-confidence in the real world.

    This is called the Proteus effect : appearance can transform our behaviors towards other people.

    What M. Slater is most interested in is how your appearance affects your own perception, your self-image. This is of great importance for understanding how your brain actually represents your body.

    The rubber hand illusion

    To try to understand how you can transfer your body in a VE, scientists have conducted several experiments. The most famous one is the rubber hand illusion:

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    M. Slater translated this experiment in VR, replacing the rubber hand with a virtual hand and showed that it works the same as the original experiment.

    One objection against that is that the user might believe that you’re actually going to hurt his real hand, so you have no way of actually knowing if the body has really been transferred or if it’s just the fear of a real injury. They’re actually working on experiments to test this which doesn’t involve real life threat. In the meantime this can be used as a good indication and indeed not a proof of transfer.

    The question is then can you transfer your whole body and not just your hand ? Also how much latency or error can be tolerated ? How close to your body does the avatar has to be ? How close to a human does it have to be ?

    He showed two examples, the first putting you in a fat avatar, and the second where your arm is stretched and you accept it roughly until it’s three times as big as usual.


    Some answers were found in other experiments.  In an experiment conducted in 1998, Petkova and Ehrsson used a real mannequin as an avatar :

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    (oh and this one is fun too : )

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    An approaching experiment was conducted by M. Slater in which a user is put in an uncomfortable position, both in real life and in VR. In the VE, the user is alone in a gloomy room and hears strange sounds from the next room. People reported that they were very worried for their safety :

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    Here’s also how to transfer your body to the body of a young girl :

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    (and the corresponding article in PLoS ONE)

    M. Slater noted that fear is probaby easier to trigger in VR, but that inducing happiness would be quite interesting. That’s one reason a new project called VR-Hyperspace was just created: to try to make you think your body is in a more comfortable position than it is in reality, which could have applications for plane or train travellers.


    All these experiments show that virtual embodiment and transformation appears to be possible. It also shows that VR is an excellent tool for cognitive neuroscience, for example to understand how your brain but also that it broadens the possibilities for VR (raw from the presentation) :

    - Put yourself in the shoes of the other

    - Change in attitudes

    - Rehearsal and preparation for events from different standpoints

    - Changing how the body feels

    Those are really exciting possibilities. I am mostly interested to see what could be done to create empathy; experience another person’s view of a story, his life, for example as a handicapped person. Teaching social interactions could be really beneficial: a recent experiment by Benjamin Lok’s team taught new doctors to speak with a patient, and then enabled the doctor to re-live the talk from the patient’s point of view. This is really helpful to understand the impact of every word you say and how the patient receives and lives them.

    But we also have to watch out for the ethical implications of those possibilities, because it could cause even more damage than TV !

    Sun 4 Sep 2011

    Razer Hydra – Cheap magnetic tracking

    Published at 17:22   Category VR Devices, Virtual Reality  

    I just got my Razer Hydra, the new cheap (140$/€) magnetic trackers distributed by Razer, and created by Sixense.

    Magnetic tracking was the king of tracking several years ago, with Ascension and Polhemus leading the way. Magnetic tracking was expensive and widely used.

    Now it’s mostly been replaced by optical and inertial tracking (ART, Vicon, Optitrack, Wiimote, Playstation Move, Kinect…)

    My first impression is that the Razer Hydra is really nice. It comes with two tracked controllers that are identical and both look like a big Wiimote Nunchuck. Both have a joystick and several buttons, which means you don’t have to buy two packs if you want to play with a friend. The controllers are ergonomically designed for adults’ hands.

    The pack also allows you to download Portal2 for free. The game was adapted to use the Razer Hydra, and it was adapted quite well ! The movements are really smooth, and you can have some basic 3DUI interactions like moving a cube with a near 1:1 mapping to solve puzzles. It reminds me of Tumble for the PSMove.

    The SDK is quite simple to use, appart the fact that you need to point the base with both controllers to initialize the right hemisphere tracking (a typical magnetic tracking issue). I’m sure there’s a way to hardcode this once and for all if you decide that you’ll always be on the same side of the base !

    The SDK also seem to indicate that 4 players could each use two controllers ! Will it work if I buy plug more than one base ?

    It seems you can tweak or disable the internal filtering, which can be interesting to do your own filtering. The jittering is present yet really minimal. Testing with a HMD will tell if it’s acceptable.

    I haven’t measured it but the latency seems to be really low, see video :

    YouTube Preview Image

    (left hand moves the camera, right hand moves a cube)

    The two problems with magnetic tracking are 1/ if you have metal in your surrounding it will affect the magnetic field, thus your tracking and 2/ you have wires.

    The Hydra is also disturbed by metal (my desk has metal in it..)

    And why, ooooohhhh whyyyyyyy so many cables ? Why any cable at all ?

    It seems we’re back in the 90s ! Each controller is wired to the base, which is also wired to the computer. After all the efforts by other controllers to remove wires (or even the controller), that’s a big step backwards ! That said, there’s 2m of cable between the controllers and the base, and there 1.5m of cable between each controllers.

    It seems they are able to go wireless since “The Sixense wireless dev kit supports up to four controllers per base station. The Razer Hydra supports two controllers” and A 12′ diameter use zone provides ample room for full-body gaming (wireless dev kit)”.

    So maybe in the future they will lift this limitation..

    Within this range the controllers seem to perform well, but more tests would be required to know if the precision is the same if you’re further from the base. They claim a “precision to 1 mm and 1 degree” at 60 hz.

    Another small drawback is that there is no vibration in the Razer Hydra, which can always be useful for some simple tactile feedback.

    Ryan Pavlik has already reverse engineered the HID protocol and integrated the driver into VRPN.


    All in all that’s certainly an improvement upon the GameTrak + Spacepoint Fusion combo, but it could have been better without those cables. The vibration feedback would also have been a nice addition.

    The range, precision, latency and ergonomic controllers (and price!) are really interesting.

    Time will tell if it’s really usable for cheap VR. Attaching one Hydra to an HMD will certainly look ridiculous, and I hope that there won’t be any magnetic disturbance near HMDs..

    I’m happy to see more and more cheap 3d tracking, and it seems some nice cheap HMDs are also coming up (Sony’s, Vuzix VR 1200).