Visual timing Error messages under Windows

Hardware
1

Hi Mario, everyone,

we’ve been getting error messages about timing problems in PTB on a number of different Windows 10 laptops connected to LCD monitors via HDMI, accompanied by the red background warning screen on the subject’s monitor.

This was kind of OK, as the warnings could be suppressed up to a point, and the experiment still worked (since timing isn’t critical for our experiment).

However, this week we have seen a more ‘fatal’ error with Screen( ) during monitor calibration - screen dump below. The code would not proceed past this point.

System info: - common to all laptops tried:
Windows 10
PTB 3.0.17 (however see screen dump below - reports 3.0.16 in the PTB warnings but 3.0.17 from PsychtoolboxVersion)
Matlab R2019b. The problem also occurred in Octave 5.1 (supposed to be compatible with 3.0.17).

Any thoughts? Is it the poor capabilities of the Intel integrated graphics, something to do with HDMI not getting the right timing info from the monitor, or even something related to the scary-looking warning “WINDOWS DWM DESKTOP COMPOSITOR IS ACTIVE” (see below)?

Many thanks,

Eric

PTB-INFO: This is Psychtoolbox-3 for Microsoft Windows, under Matlab 64-Bit (Version 3.0.16 - Build date: Apr 25 2020).
PTB-INFO: OS support status: Windows 10 (Version 10.0) supported and tested to some limited degree.
PTB-INFO: Type ‘PsychtoolboxVersion’ for more detailed version information.
PTB-INFO: Most parts of the Psychtoolbox distribution are licensed to you under terms of the MIT License, with
PTB-INFO: some restrictions. See file ‘License.txt’ in the Psychtoolbox root folder for the exact licensing conditions.

PTB-WARNING: Couldn’t determine end-line of vertical blanking interval for your display! Trouble with beamposition queries?!?
PTB-WARNING: Detected end-line is 1080, which is either lower or more than 1.250000 times higher than vbl startline 1620 → Out of sane range!

PTB-INFO: OpenGL-Renderer is Intel :: Intel(R) HD Graphics 620 :: 4.6.0 - Build 26.20.100.7872
PTB-INFO: VBL startline = 1620 , VBL Endline = 1080
PTB-INFO: Beamposition queries unsupported or defective on this system. Using basic timestamping as fallback.
PTB-INFO: Timestamps returned by Screen(‘Flip’) will be therefore less robust and accurate.
PTB-INFO: Measured monitor refresh interval from VBLsync = 16.670290 ms [59.986959 Hz]. (50 valid samples taken, stddev=0.256970 ms.)
PTB-INFO: Reported monitor refresh interval from operating system = 16.949153 ms [59.000000 Hz].
PTB-INFO: Small deviations between reported values are normal and no reason to worry.
PTB-INFO: ==============================================================================================================================
PTB-INFO: WINDOWS DWM DESKTOP COMPOSITOR IS ACTIVE. On this Windows-10 or later system, Psychtoolbox can no longer reliably detect if
PTB-INFO: this will cause trouble for timing and integrity of visual stimuli or not. You might be just fine, or you could be in trouble.
PTB-INFO: Use external measurement equipment and independent procedures to verify reliability of timing if you care about proper timing.
PTB-INFO: ==============================================================================================================================

WARNING: Couldn’t compute a reliable estimate of monitor refresh interval! Trouble with VBL syncing?!?

----- ! PTB - ERROR: SYNCHRONIZATION FAILURE ! -----

One or more internal checks (see Warnings above) indicate that synchronization
of Psychtoolbox to the vertical retrace (VBL) is not working on your setup.

This will seriously impair proper stimulus presentation and stimulus presentation timing!
Please read ‘help SyncTrouble’ for information about how to solve or work-around the problem.
You can force Psychtoolbox to continue, despite the severe problems, by adding the command
Screen(‘Preference’, ‘SkipSyncTests’, 1); at the top of your script, if you really know what you are doing.

Error using Screen
See error message printed above.

PsychtoolboxVersion

ans =

'3.0.17 - Flavor: beta - Corresponds to SVN Revision 11370
 For more info visit:
 https://github.com/Psychtoolbox-3/Psychtoolbox-3'
4

PTB is testing the variance of screen updates, and your SD is greater than the default cutoff of SD=0.2ms:

PTB-INFO: Measured monitor refresh interval from VBLsync = 16.670290 ms 
[59.986959 Hz]. (50 valid samples taken, stddev=0.256970 ms.)

I get the same problems on all my Windows systems I’ve tested, so I always use Linux to run PTB when collecting data. If you really don’t care about any timing problems, then use Screen(‘Preference’, ‘SkipSyncTests’, 1) at the top of your script (as the help text specifies)—but remember it is there and don’t drift into new experiments just copy-pasting that when future experiments may depend on reliable stimulus presentation…

5

What Ian says. Adding that a SkipSynctests setting 2 shuts it up even more completely and skips the tests and calibrations.

However if your Screen mex file reports 3.0.16 and PsychtoolboxVersion reports 3.0.17 then that probably means you have some stray old Screen mex file somewhere in your path, other than where you think it is.

And yes, Intel gfx on Windows is often horrendously broken, on Linux otoh. it is usually perfect. And dual-display on Windows often has broken timing, and HiDPI displays, and …

-mario

6

Thank you Ian and Mario. I had got around the warnings in the past by using SkipSynctests, which is fine for non-time-critical experiments. On this occasion I was trying to run someone else’s code and it was clearly trying to achieve something that depended on stimulus timing.

It sounds like linux is the way to go, if I want to run things on this laptop, especially with a second display.

Eric

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