From: autodesk!danr@uunet.UU.NET (Dan Rosenfeld)
Subject: Re: We need a new language
Date: 4 Feb 91 22:39:07 GMT



frerichs@ux1.cso.uiuc.edu (David J Frerichs) writes:

>In article <15594@milton.u.washington.edu> pete_leaback@cix.compulink.co.uk
(Peter Leaback) writes:

>[things wiped out]
>>A VR system has to display a frame at 50 or 60 Hz or else one tends to
>>get sick. If one standardises the object destription and rendering, each
>[things abolished]

>Your statement that one tends to get sick at a low frame rate is false
>(IMHO). Please forgive my forwardness if you have experienced this sickness
>first hand.  Low frame rates only make for choppy movement, not flickering.
>It just means that the frame stays in the buffer longer.  When you are
>doing computer animation, you don't just flash a picture and take it
>away, you hold a picture up til the next one is ready.  High frame rate
>means smoother motion, not less flicker (flicker has to do with the display
>hardware frequency).
>I think that alot of people in the newsgroup have been making statements
>that they think sound good at the time but aren't supported by any facts,
>not a good practice if we are to get to the root of some of the problems
>that face our industry.  If you are going to make wide statements about
>tech, do your homework, or make sure you say that this is your opinion,
>not a solid fact.


I believe there IS some evidence that low frame rates can cause nausea
in simulation participants.  I can't provide any references to support
this, but I knew several Psychologists at NASA (Ames) who claimed that
flight simulator subjects tended to get nauseous when imagery was
presented at too low a rate.  

The issue, I believe, is not flicker, but rather the temporary
inconsistency between sensory systems that low frame rate can cause.  
Specifically, you tilt your Polhemus-tracked head, or a flight
simulator tilts you, and your vestibular system tells your brain that
you are oriented a certain way.  Unfortunately, your visual system is
computing your head's orientation on the basis of imagery which
represents your head's "view" 100ms ago.  I have no understanding of
why this should cause nausea, and I'm not sure whether anyone else
does, but it does seem to.

BTW, I have tried three VR systems and never experienced any nausea,
but these demos never lasted more than ten minutes at a time.  

Dan


Disclaimer; I don't work on the Cyberspace project, and I am not
representing their views.

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Dan Rosenfeld   danr@autodesk.com

(    )         "Enjoy life, eat out more often."  S.I. Rykoff
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 moo
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