Do you know why some games cause motion sickness and others dont ? What can we do, when making a game, to avoid this ?
I know from my experience that Id games, in particular old ones, affect me a lot. But Unreal and UT games tend to minimize this effect.
That happens if your brain is unable to compensate the visual motion. You learn how your interaction effects the stuff on screen - then your brain adds a filtering effect which works in the opposite direction (thus nullifying the motion alltogether).
Unfortunately most games add some kind of noise to the motion in order to let it look somewhat more interesting/realistic. It’s so called “bobbing”. In Q3 it’s some rotation and up/down movement (it can be disabled via console/cfg all those commands start with cg_bob).
Older games such as Q1 or Requiem also used “leaning”, which can easily cause motion sickness. Each time you strafe you lean in that direction (rotation around the direction you are looking).
Another thing which makes motion compensation for our brain rather tricky is mouse acceleration. It’s not linear therefore you need much more time until you (your brain) is used to it.
Ha so that was the reason. Thanks, that was a very complete explanation.
Oh I forgot… watching demos is of course the worst thing you can do. The only thing your brain can do then is predicting the movement. That works to some extend, if the movement style of the player you’re watching is similar to your own.
Eg I can watch demos from “rat” without problems, but 5mins of “lsv” and I’m about to puke 
That’s why most people with car sickness don’t get sick when they’re actually driving I suppose.
Cas 
Never thought about this, but I guess it’s one of the factors.
However, the strongest factor is AFAICT that people who aren’t driving “wander around” with their eyes. Watching left, right etc… a constant stream of motion and the brain don’t get a chance to rest.
The thing which makes it usually ok-ish makes it worse then… after watching a motion for 30 to 60 seconds motion compensation kicks in. If the motion stops you can see it roll backwards for some seconds (5-10). But if the motion just changes direction (eg watching out of the window and then on the street infront), you’ll get a mix of compensation and the actual motion. It just gets worse and worse
What helps is sitting on the front seat and watching the street just as if you were driving yourself.
If you want see compensation in action just watch a big textured rotating quad for a minute. Then stop the rotation. It appears to rotate (slowly) in the other direction then. Pretty odd. That also works with scrolling or with a tunnel.
I have a nice programm floating around somewere with a rotating spiral (spirale.exe). If you watch it for a while and look then in another direction (eg out of the window) you’ll see everything warping and bending… it’s really weird
Heh well its true what oNyx says, eg what causes the effect. But why do we get sick,why do we puke?. Well the body thinks
“Hey what I see is not corresponding to what I am doing, so I must be toxicated, lets puke”
This is the same effect when you get to drunk. The body try to get rid of the toxin(alcohol IS a toxic), by emptying the stomac.
Ah… that makes perfect sense. Thanks for the additional information
I’ve also noticed that in some older games, the input system seemed to “lag” slightly behind the movement. That is, you press the “turn right” key and there would be a slight delay turning right on the screen. That is the ONLY time I would start feeling sick, no other games did it (even with bobbing heads, etc).
I also have the same problem but strangly only in newer games. Maybe because it get more realistic.
I first noticed it with halflife, then GTA3 Vice City and most recently Far Cry.
However I don’t have the problem UT2004, MAX Payne 2 or need for speed underground.
I would really like to know what causes this and if I could for instance lower the quality or disable the bobbing so I won’t get sick.
Currently I’m mostly stuck to RTS. Not that that is a bad thing but I also like a bit of fast pased action once in a while.
Something that’s not actually “motion sickness” but can have much the same effect: refresh rate. If you’re noticing a number of games that make you feel ill, try and can get into the video mode settings and see if it’s running in a low Hz.
I’m also a victim of motion sickness in games and I can tell you one thing it sucks like hell 
Yesterday I found an interesting article about this subject here:
http://www.loonygames.com/content/1.2/feat/
The article talks about how more realistic games can cause motion sickness. Although I suffer from it very much, for me the motion sickness doesn’t seem to depend on the realistics of a game…
Now to some of my expiriences:
The worst games in my opinion were the old Id games like doom1, doom2 and hexen (I didn’t play them all and didn’t play them long, you know why… ;-))
The worst thing is watching someone play these games, it makes me puke after 5 minutes.
I don’t know if that’s normal but I can normally play any 3rd person games without any problems at all. The problems are there only with 1st person games.
And even in them I can notice some differences. Outdoor-games normally don’t make me sick but as soon as it gets indoors it gets bad very soon.
Surpringly the newer Id games (Quake3, RTCW) aren’t that bad.
Somehow I found out, that it depends on the rotating the game makes (rotating left-right, looking up-down).
Only moving forward or strifing works very well but as soon as rotating comes into play it gets worse. Somehow I think that Quake3 and RTCW (which I could play for hours without any probs) has a different rotating feeling (look especially in the edges maybe you can see the differences I mean, which are perhaps only in my head ;-)) than Half-Life, Deus Ex, System Shock
2 or Far Cry (which made me sick after < 5 min)
I don’t know if anyone could share my expiriences…
IIRC Q3, RTCW etc have a considerably smaller FOV, which might be the difference for you.
I noticed because I went from being a demon deathmatch player with id games into continually getting stuck on walls, corners, statues, etc the first few weeks I played Q3.
Try increasing and decreasing the FOV (you can do it from the console if you google the commands) and see if it has an effect…