Also try to do anything you can in the room to increase your awareness of the room around the computer. Positioning the keyboard and mouse back farther from the screen (or moving the screen back farther from the keyboard), adding interestingly distracting posters to the wall behind the screen, increasing the room lighting behind the screen, etc., all of those things will help your brain realize that it's not actually inside that rendered world and not get the cue conflict problem.

And of course see if there's a way to tweak the config files to make the window even smaller.

I'm really interested in knowing how it goes.

I'll let you know as soon as I get up the motivation to tempt nausea

Oh, one thing I noticed in the settings for Portal is the FOV angle. Looks like it defaults to 75, bumping that up may also help.

The window thing worked. Once it's started, I can reenable fullscreen mode, but I do have to start in windowed mode.

I'd try going the other way, too, seeing if a lower FOV helps.

I finished the main part of Portal the other day. I'm surprised that no one I've seen on the Internet has:

Sadly, I don't think I'm even going to try the FOV change. I got through the second training objective in windowed mode and was already feeling nauseous. I guess I'm extremely sensitive to this stuff.

Oh well, at least it was free...

Did you try any of the other things I suggested? Such as tweaking the configuration files to make the window very very small, sitting farther back from the screen, and making the area behind the screen brighter and more interesting so that your eyes have something to focus on besides the screen?

I ask, not because I'm trying to pressure you, but in a genuine interest as to whether or not they worked for you. Scientific data points.

Well there's a few problems.

First off, I do have an interesting background to my monitor, because it's set in front of a corner hutch. And I actually have a light set up directly behind it so that it's backlit. One problem is that my monitor is so large it fills up my FOV even when sitting fairly far back. I'm currently sitting approximately two feet from the screen, but I've played Portal at as much as three.

I haven't made the window any smaller via config files, but I am using the smallest resolution setting, which produces a window 8.5" diagonally. If it were any smaller I simply wouldn't want to play it because I wouldn't be able to see anything.

Even with all this, the very first training exercise that rotated me through a portal really made me queasy. I've been able to play a little more, but I can feel it building...