Screen tearing *sometimes* -- behavior inconsistent, even with psychopy

jtpar

Hi all,

I tried the little 'flicker' experiment that's at the bottom of the documentation page on timing, to test whether v-sync is on or not for my monitors. I'm not sure how to interpret my findings... here's what I've found:

• sometimes it seems to work without any horizontal lines, but only if i run it in one of the two monitors... and which monitor works changes when i unplug and replug them... but not consistently
• the rate at which the horizontal line "drifts" seems to vary. The direction of drift is also different between the two. One monitor (which I'll call monitor A) has the line always drifting up, while the other (monitor B ) has it always drifting down.
• because the rate of drift varies, i wonder if the runs on which I thought there were no horizontal lines just had a very slow drift rate and i didn't wait long enough.
• on a handful of runs, i would get a horizontal line that doesn't drift at all, but 'hangs" about 2cm from the top of the screen (this happened for both monitors at least once)
• These patterns appear to occur when using either the xpyriment or psycho backends (I didn't try with legacy)

I think maybe the short answer is that i just need to find a way to force v-sync 100% of the time, but I was wondering if my observation that v-sync seemed to be enabled some of the time could make sense?

I apologize for what I think is probably a very confusing post. Any insights at all would be hugely appreciated!

Thanks,
-Jonathan

Jarik

Hi Jonathan,

sometimes it seems to work without any horizontal lines, but only if i run it in one of the two monitors... and which monitor works changes when i unplug and replug them... but not consistently

Only one monitor can be the primary monitor and that one is in sync with v-sync. In our EEG labs we see the secondary monitor, where the researchers can track how the subject is doing, is out of sync (shows the horizontal lines). The inconsistency might be explained because video cards ale 'intelligent' these days en set the secondary monitor to be the primary monitor as soon as you unplug the first primary monitor.

I never looked into the patterns, behavior etc. of the lines on the secondary monitor. We just make sure subjects are looking at monitor number 1 (the primary monitor)!

Hope this helps,
Jarik

jtpar

Thanks, Jarik! It does help.

I'll play around with it and see if I can get it to a stable configuration... but you may hear from me again