this is indeed an artifact :O (no not like fozzer ;D )
update your drivers, and make sure your card is seated properly and is not over heating.
Tee-Hee... ;D...!
Its a funny old do...
But out of all my recent games, "S-T-A-L-K-E-R" is the only one that gives me various artifact, etc, problems..
The game seems very sensitive to in-game graphics, sound, etc, settings. I often wonder it there were difficulties during the design of the program (bugs) to cope with all the various customer's hardware...?
I can generally cure the worst of them, but it does involve a lot of fiddling about with the settings, often involving re-starting the game a few times to get it working correctly!
(There are no overheating problems in my hardware).
...no problems with "Bioshock".
...an excellent game tho'...(with the Cheats installed!...;)...)!
Paul... 8-)...nVidia 7800GS AGP 256meg...!
....>>>>"Computer Games and Software"... ::)....

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Win 8.1 64-bit. DX11. Advent Tower. Intel i7-3770 3.9 GHz 8-core. 8 GB System RAM. AMD Radeon HD 7700 1GB RAM. DVD ROM. 2 Terra Byte SATA Hard Drive. Philips 17" LCD Monitor. Saitek Cyborg X Fly-5 Joystick. ...and a Briggs and Stratton Petrol Lawn Mower.