July 16, 2000
by Denis Pelli
visitors since September 17, 1996.
July 16, 2000
COMPUTER AND VIDEO SPEED
VIDEO SYNCH
VIDEO DRIVER BUGS
Pelli-Zhang VIDEO ATTENUATOR
VIDEO CARDS
MONITORS
ARTIFACTS
STEREO
CHIN RESTS
HARDWARE NOTES
PROGRAMMING NOTES
MULTISYNCH ADAPTERS
HIGH FRAME RATES (e.g. 120 Hz)
LONG KEYBOARD (ADB) CABLES AND WIRELESS KEYBOARD
ARTIFACTS
Q: "On both monitors there is a wandering gray line in the midst of the gray screen (this wandering gray line moves slowly from the bottom of the screen to the top and then back around). It moves up on one monitor, and down on the other." (Sabina Wolfson)
A: You're almost certainly getting cross talk between the two monitors Usually, you can get it to go away by fiddling with the video cable positions. I suspect that the coupling is magnetic induction (i.e. due to current, not voltage) which is very difficult to shield effectively.
Q: My drifting grating has a break, a tear, about halfway down the screen. What's displayed above the tear is offset relative to what's below.
A: That's called "tearing". The computer is writing to video memory at the same time that it's being read out to the display. Above the tear the movie is one-frame older than below the tear. If you're using the Psychophysics Toolbox, try the MovieTearDemo for a demonstration and explanation. You can eliminate tearing by showing your movie lower on the screen, to give the computer a head start.