Screen('Preference', 'SkipSyncTests', 1);
>> PerceptualVBLSyncTest
at the begining, i had this red flashing warning sign, then i got a gray rectangle in the middle and yellow lines flickring mostly at the top of the screen but also randomaly everywher.
this is the output i got,
" Perceptual synchronization test for synchronization of Screen('Flip') and
Screen('WaitBlanking') to the vertical retrace.
Arguments:
'screen' Either a single screen handle, or none (in which case the
display with the maximum id will be used), or a vector of two handles in
stereomode 10, e.g., [0 1] if you want to output to screens 0 and 1. You
can also pass a vector of two screens when stereomode is not set to 10.
In this case two separate (non-stereo) onscreen windows will be opened on
both displays and they will get flipped in multiflip mode 2. That means
that the first display (first element of 'screen') is synced to VBL, but
the 2nd one is synced to bufferswaps of the first one. This is a
straightforward test to check if two displays of a stereosetup run with a
synchronized retrace cycle (good!) or if they are phase-shifted or
drifting against each other (not good!).
'stereomode' Which stereomode to use? Defaults to zero, ie. no stereo.
'fullscreen' Fullscreen presentation? Defaults to 1 ie. yes. In
non-fullscreen mode, no proper synchronization of bufferswaps can be
expected.
'doublebuffer' Single- or double-buffering (1). Defaults to 1. In single
buffer mode there is no sync to retrace, so this is a good way to
simulate the tearing artifacts that would happen on sync failure, just to
get an impression.
'maxduration' Maximum runtime of test: Runs until keypress or maxduration
seconds have elapsed (Default is 10 seconds).
'vblSync' If 1, synchronize bufferswaps to vertical retrace of monitor,
otherwise (setting 0) swap immediately without sync, ie., usually with tearing.
'testdualheadsync' If 1, and 'vblSync' is zero, manually wait until the video
scanout position reaches half the height of the display, then swap. If this
is done on a multi-display setup and the video scanout cycles of all the
participating displays are properly synchronized, you should see a "static"
crack line roughly at half the height of the display, maybe a bit lower. If
you see a wandering crack line, at least on some displays, or you see vertical
offsets of the position of the crack line between displays, then the displays
are not properly synchronized, ie., not suitable for artifact free binocular
stimulation. Caveat: This logic has been developed and tested specifically
for testing on Linux with a single X-Screen spanning multiple displays. It may
or may not be suitable to assess other operating systems or display configurations.
After starting this test, you should see a flickering greyish background
that flickers in a homogenous way - without cracks or weird moving patterns
in the flickering area. If you see an imhogenous flicker, this means that
synchronization of stimulus onset to the vertical retrace doesn't work due
to some serious bug or limitation of your graphics hardware or its driver.
If you don't know what this means, you can test this script with parameter
doublebuffer == 0 to artificially create a synchronization failure.
On many systems you should also see some emerging pattern of yellow horizontal lines.
These lines should be tightly concentrated/clustered in the topmost area of
the screen. Lots of yellow lines in the middle or bottom area or even
randomly distributed lines indicate some bug in the driver of your graphics
hardware. This is a common problem of all ATI graphics adapters on MacOS-X
versions earlier than OS-X 10.4.3 when running a dual-display setup...
A second reason for distributed yellow lines could be bad timing on your
machine, e.g., due to background activity by virus scanners or the Spotlight
indexing service on OS-X. Turn these off for conducting your studies!
Press ENTER key to start the test. The test will stop after 10 seconds
or any keypress...
PTB-INFO: This is Psychtoolbox-3 for Microsoft Windows, under Matlab 64-Bit (Version 3.0.11 - Build date: Jul 9 2013).
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-INFO: Will disable DWM because a regular fullscreen onscreen window is opened -> We want best timing and performance.
PTB-INFO: The detected endline of the vertical blank interval is equal or lower than the startline. This indicates
PTB-INFO: that i couldn't detect the duration of the vertical blank interval and won't be able to correct timestamps
PTB-INFO: for it. This will introduce a very small and constant offset (typically << 1 msec). Read 'help BeampositionQueries'
PTB-INFO: for how to correct this, should you really require that last few microseconds of precision.
PTB-INFO: Btw. this can also mean that your systems beamposition queries are slightly broken. It may help timing precision to
PTB-INFO: enable the beamposition workaround, as explained in 'help ConserveVRAM', section 'kPsychUseBeampositionQueryWorkaround'.
PTB-INFO: OpenGL-Renderer is NVIDIA Corporation :: GeForce GT 520M/PCIe/SSE2 :: 4.3.0
PTB-INFO: VBL startline = 768 , VBL Endline = 768
PTB-INFO: Measured monitor refresh interval from beamposition = 17.343589 ms [57.658192 Hz].
PTB-INFO: Will use beamposition query for accurate Flip time stamping.
PTB-INFO: Measured monitor refresh interval from VBLsync = 16.660417 ms [60.022506 Hz]. (59 valid samples taken, stddev=0.309825 ms.)
PTB-INFO: Reported monitor refresh interval from operating system = 16.666667 ms [60.000000 Hz].
PTB-INFO: Small deviations between reported values are normal and no reason to worry.
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.
PTB-INFO: Support for fast OffscreenWindows enabled.
PTB-ERROR: Screen('Flip'); beamposition timestamping computed an *impossible stimulus onset value* of 2334.610282 secs, which would indicate that
PTB-ERROR: stimulus onset happened *before* it was actually requested! (Earliest theoretically possible 2334.615422 secs).
PTB-ERROR: Some more diagnostic values (only for experts): rawTimestamp = 2334.617202, scanline = 318
PTB-ERROR: Some more diagnostic values (only for experts): line_pre_swaprequest = 233, line_post_swaprequest = 239, time_post_swaprequest = 2334.615527
PTB-ERROR: Some more diagnostic values (only for experts): preflip_vblcount = 0, preflip_vbltimestamp = -1.000000
PTB-ERROR: Some more diagnostic values (only for experts): postflip_vblcount = 0, postflip_vbltimestamp = -1.000000, vbltimestampquery_retrycount = 0
PTB-ERROR: This error can be due to either of the following causes (No way to discriminate):
PTB-ERROR: Either something is broken in your systems beamposition timestamping. I've disabled high precision
PTB-ERROR: timestamping for now. Returned timestamps will be less robust and accurate, but if that was the culprit it should be fixed.
PTB-ERROR: An equally likely cause would be that Synchronization of stimulus onset (buffer swap) to the
PTB-ERROR: vertical blank interval VBL is not working properly.
PTB-ERROR: Please run the script PerceptualVBLSyncTest to check this. With non-working sync to VBL, all stimulus timing
PTB-ERROR: becomes quite futile. Also read 'help SyncTrouble' !
INFO: PTB's Screen('Flip', 10) command seems to have missed the requested stimulus presentation deadline
INFO: a total of 4 times out of a total of 601 flips during this session.
INFO: This number is fairly accurate (and indicative of real timing problems in your own code or your system)
INFO: if you provided requested stimulus onset times with the 'when' argument of Screen('Flip', window [, when]);
INFO: If you called Screen('Flip', window); without the 'when' argument, this count is more of a ''mild'' indicator
INFO: of timing behaviour than a hard reliable measurement. Large numbers may indicate problems and should at least
INFO: deserve your closer attention. Cfe. 'help SyncTrouble', the FAQ section at
www.psychtoolbox.org and the
INFO: examples in the PDF presentation in PsychDocumentation/Psychtoolbox3-Slides.pdf for more info and timing tips.
WARNING: This session of your experiment was run by you with the setting Screen('Preference', 'SkipSyncTests', 1).
WARNING: This means that some internal self-tests and calibrations were skipped. Your stimulus presentation timing
WARNING: may have been wrong. This is fine for development and debugging of your experiment, but for running the real
WARNING: study, please make sure to set Screen('Preference', 'SkipSyncTests', 0) for maximum accuracy and reliability."
and unfortunately i have no idea what to do with the errors (only experts, which i'm not)
if you have any idea, i'll be happy to hear