From: LHETTINGER@FALCON.AAMRL.WPAFB.AF.MIL
Subject: Re: frame rates
Date: Wed, 6 Feb 91 15:23 EDT



John Nagle recently wrote:

>     Existing VR systems of the head-mounted display class (VPL, Autodesk)
>tend to have serious problems with a lag between head movement and display
>update.  Most of this lag is not due to the rendering system, even though
>the rendering updates are well below the 30Hz rate of ordinary TV, but
>due to the very slow and noisy Polyhemus position sensor.  Not only is
>this device only good for a few data points per second, due to noise
>problems, it is necessary to pass the data through a low-pass filter
>before using it.  This has the annoying result that when you turn your
>head, the rendered image takes a substantial fraction of a second
>to catch up.  Not only that, when it finally does catch up, it
>settles slowly, rather than matching your head's deceleration rate.
>This makes fast head motion at least counterproductive, and at
>worst may interfere with one's sense of balance.  Whether it will
>cause nausea is unclear.  But it definitely discourages rapid
>head rotation.  

        There are numerous anecdotal accounts of nausea occuring in response 
to these sorts of lags in flight simulators that use head-slaved displays of 
one sort or another.  Unfortunately, there are no hard data to talk about 
with regard to this aspect of the problem in simulators.  The closest we can 
come to this set of conditions (in regard to nausea) are experiments in which 
investigators have looked at the effect of lags between head movements and 
corresponding movements in the optic array and the effect of these conditions 
on recalibrations of the vestibular-ocular reflex.  Many of these reports have 
documented nausea as a side-effect.


                                                Larry Hettinger