Path: utzoo!censor!geac!torsqnt!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!olivea!mintaka!mit-eddie!uw-beaver!milton!LHETTINGER@FALCON.AAMRL.WPAFB.AF.MIL From: LHETTINGER@FALCON.AAMRL.WPAFB.AF.MIL Newsgroups: sci.virtual-worlds Subject: Re: Motion Sickness and VR Message-ID: <14998@milton.u.washington.edu> Date: 23 Jan 91 19:44:00 GMT Sender: hlab@milton.u.washington.edu Lines: 93 Approved: cyberoid@milton.u.washington.edu Eric Pepke recently wrote: >It seems to me that there are four factors which have the capacity for >causing motion sickness in V.R.: > 1) Difference between perceived gravity and viewed "down." > 2) Difference between perceived angular velocity and acceleration > and viewed angular velocity and acceleration. > 3) Perceived linear velocity outside of normal experience. > 4) Difference between perceived linear acceleration and viewed linear > acceleration. > 5) Changes of direction at high speed. I agree. All of the things you mention involve visual-vestibular conflicts which appear to be present in most motion-sickness situations, not just flight simulator sickness. I would also suggest a sixth potential cause: head movements. Any motion of the head made in the presence of conflicting visual information for self motion (i.e., the eyes "specify" rotational motion, the inner ears "specify" some different motion) may serve to enhance the conflict. Whatever the cause - excessive head movements often lead to trouble with sickness. >1 and 2 are very easily solved. Just make the viewed orientation an accurate >representation of the actual orientation. To turn, you actually have to >turn your head; to tilt you actually have to tilt your head; the ground plane >that you see remains true. I think you could probably get away with a lot >here, such as putting a scaling factor between your real head's yaw velocity >and your virtual head's yaw velocity. I think this is a reasonable suggestion for some VR settings - for flight simulators, though, I don't think it will work. To link the simulator dynamics to head dynamics would violate the training purposes of the device. >We are relatively desensitized to 3 when we are moving in the forward direction >due to our experience driving or riding in cars. Forward motion is probably >the easiest to which to become desensitized, as it carries no message that >can be interpreted as "rotation." People who ride in trains a lot are probably >desensitized to other directions of motion as well. However, I think it's >probably a good idea to limit purely virtual motion to forward, for user >interface considerations as well as perceptual ones. The concepts of walking >and running are more easily understood than the cancrazan. It is interesting to note that experienced pilots appear to have much more difficulty with simulator sickness than inexperienced pilots. This finding appears to support what you are saying above and I think can be interpreted in the following way. Pilots become very sensitive to certain visual-vestibular consequences of controlling their self motion, and therefore can be expected to be very sensitive to violations in these relationships. Specifically, when a pilot pulls into a turn in flight it produces a characteristic pattern of visual-vestibular stimulation which is very specific to that situation. Through perceptual learning, the pilot becomes highly attuned to that pattern of stimulation. We can replicate the visual part of that pretty well in a simulator, but we can't approach the vestibular part. And therein lies the problem.... >4 is tricky, but it may not be that much of a problem. Acceleration only >need last until you get up to speed. Perhaps the disorientation can be >minimized by choosing an acceleration so that getting up to speed is neither >too abrupt nor too prolonged. If this is not sufficient, either viewed >acceleration can be mapped through a scaling factor to actual acceleration >(i.e. you have to walk forward to start accelerating, and stopping walking will >only slow you down a little bit.), or acceleration can be triggered by tilting >back the head, which emulates some of the sensations of acceleration. We >might also be able to eliminate the need for such high perceptual speeds by >compressing intervening space--do you really need to see every grain of sand >in the Arizona desert when zipping from Phoenix to Tucson? I would personally >like a set of virtual Seven League Boots. Another method of dealing with this may be to provide a brief inertial input to the user with a dynamic seat of some sort. This would provide them with a transient vestibular input that would mimic the short time constant of the vestibular system in linear acceleration. Then you can let the visual take over. >I don't know about 5, but I think that, as abrupt changes in direction at >higher than brachiating speeds haven't yet contributed to much evolutionary >pressure, this can maybe be ignored. If not, one could constrain the >direction change to be gradual enough not to matter and require a slowdown >before speedier direction changes. This would provide a nice kinesthetic >parallel to driving an automobile. Well, I don't think you want to ignore this because it's still a visual-vestibular conflict situation and therefore can't be ruled out as potentially contributing to disorientation and sickness. This may also be a potential use for a dynamic seat of some sort. >I think I'll go down to Disneyworld next weekend and do some research on >Star Tours and the World of Motion, not to mention the Interstate. :-) Just don't move your head around too much 8-) Larry Hettinger