# beamposition problems

**URL:** <https://psychtoolbox.discourse.group/t/beamposition-problems/479>\
**Category:** Uncategorized\
**Created:** [October 27, 2011, 4:55pm UTC](https://psychtoolbox.discourse.group/t/beamposition-problems/479 "2011-10-27T16:55:46Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![thenekonaut](https://avatars.discourse-cdn.com/v4/letter/t/b38774/32.png) [@thenekonaut](https://psychtoolbox.discourse.group/u/thenekonaut)\
**Post date:** [October 27, 2011, 4:55pm UTC](https://psychtoolbox.discourse.group/t/beamposition-problems/479/1 "2011-10-27T16:55:46Z")

</div>

Hihi,  
  
I'm working in PTB3.0.9 on Windows 5.1 (Windows XP Professional) with a ATI Radeo HD 4550 graphics card. I've been having synchronization / beamposition problems. When I run the program, the following message appears:  
  
AFTER RUNNING PROGRAM:  
  
PTB-INFO: This is Psychtoolbox-3 for Microsoft Windows, under Matlab (Version 3.0.9 - Build date: Aug 23 2011).  
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: Some ATI graphics cards may not support proper syncing to vertical retrace when  
PTB-INFO: running in windowed mode (non-fullscreen). If PTB aborts with 'Synchronization failure'  
PTB-INFO: you can disable the sync test via call to Screen('Preference', 'SkipSyncTests', 1); .  
PTB-INFO: You won't get proper stimulus onset timestamps though, so windowed mode may be of limited use.  
  
  
OpenGL-Extensions are: GL\_AMDX\_name\_gen\_delete GL\_AMDX\_vertex\_shader\_tessellator GL\_AMD\_draw\_buffers\_blend GL\_AMD\_performance\_monitor GL\_AMD\_seamless\_cubemap\_per\_texture GL\_AMD\_shader\_stencil\_export GL\_AMD\_texture\_cube\_map\_array GL\_AMD\_texture\_texture4 GL\_AMD\_vertex\_shader\_tessellator GL\_ARB\_color\_buffer\_float GL\_ARB\_copy\_buffer GL\_ARB\_depth\_buffer\_float GL\_ARB\_depth\_clamp GL\_ARB\_depth\_texture GL\_ARB\_draw\_buffers GL\_ARB\_draw\_buffers\_blend GL\_ARB\_draw\_elements\_base\_vertex GL\_ARB\_draw\_instanced GL\_ARB\_fragment\_coord\_conventions GL\_ARB\_fragment\_program GL\_ARB\_fragment\_program\_shadow GL\_ARB\_fragment\_shader GL\_ARB\_framebuffer\_object GL\_ARB\_framebuffer\_sRGB GL\_ARB\_geometry\_shader4 GL\_ARB\_half\_float\_pixel GL\_ARB\_half\_float\_vertex GL\_ARB\_imaging GL\_ARB\_instanced\_arrays GL\_ARB\_map\_buffer\_range GL\_ARB\_multisample GL\_ARB\_multitexture GL\_ARB\_occlusion\_query GL\_ARB\_pixel\_buffer\_object GL\_ARB\_point\_parameters GL\_ARB\_point\_sprite GL\_ARB\_provoking\_vertex GL\_ARB\_seamless\_cube\_map GL\_ARB\_shader\_objects GL\_ARB\_shader\_texture\_lod GL\_ARB\_shading\_language\_100 GL\_ARB\_shadow GL\_ARB\_shadow\_ambient GL\_ARB\_sync GL\_ARB\_texture\_border\_clamp GL\_ARB\_texture\_buffer\_object GL\_ARB\_texture\_compression GL\_ARB\_texture\_compression\_rgtc GL\_ARB\_texture\_cube\_map GL\_ARB\_texture\_cube\_map\_array GL\_ARB\_texture\_env\_add GL\_ARB\_texture\_env\_combine GL\_ARB\_texture\_env\_crossbar GL\_ARB\_texture\_env\_dot3 GL\_ARB\_texture\_float GL\_ARB\_texture\_mirrored\_repeat GL\_ARB\_texture\_multisample GL\_ARB\_texture\_non\_power\_of\_two GL\_ARB\_texture\_query\_lod GL\_ARB\_texture\_rectangle GL\_ARB\_texture\_rg GL\_ARB\_texture\_snorm GL\_ARB\_transpose\_matrix GL\_ARB\_uniform\_buffer\_object GL\_ARB\_vertex\_array\_bgra GL\_ARB\_vertex\_array\_object GL\_ARB\_vertex\_buffer\_object GL\_ARB\_vertex\_program GL\_ARB\_vertex\_shader GL\_ARB\_window\_pos GL\_ATI\_draw\_buffers GL\_ATI\_envmap\_bumpmap GL\_ATI\_fragment\_shader GL\_ATI\_meminfo GL\_ATI\_separate\_stencil GL\_ATI\_texture\_compression\_3dc GL\_ATI\_texture\_env\_combine3 GL\_ATI\_texture\_float GL\_ATI\_texture\_mirror\_once GL\_EXT\_abgr GL\_EXT\_bgra GL\_EXT\_bindable\_uniform GL\_EXT\_blend\_color GL\_EXT\_blend\_equation\_separate GL\_EXT\_blend\_func\_separate GL\_EXT\_blend\_minmax GL\_EXT\_blend\_subtract GL\_EXT\_compiled\_vertex\_array GL\_EXT\_copy\_buffer GL\_EXT\_copy\_texture GL\_EXT\_draw\_buffers2 GL\_EXT\_draw\_instanced GL\_EXT\_draw\_range\_elements GL\_EXT\_fog\_coord GL\_EXT\_framebuffer\_blit GL\_EXT\_framebuffer\_multisample GL\_EXT\_framebuffer\_object GL\_EXT\_framebuffer\_sRGB GL\_EXT\_geometry\_shader4 GL\_EXT\_gpu\_program\_parameters GL\_EXT\_gpu\_shader4 GL\_EXT\_histogram GL\_EXT\_multi\_draw\_arrays GL\_EXT\_packed\_depth\_stencil GL\_EXT\_packed\_float GL\_EXT\_packed\_pixels GL\_EXT\_pixel\_buffer\_object GL\_EXT\_point\_parameters GL\_EXT\_provoking\_vertex GL\_EXT\_rescale\_normal GL\_EXT\_secondary\_color GL\_EXT\_separate\_specular\_color GL\_EXT\_shadow\_funcs GL\_EXT\_stencil\_wrap GL\_EXT\_subtexture GL\_EXT\_texgen\_reflection GL\_EXT\_texture3D GL\_EXT\_texture\_array GL\_EXT\_texture\_buffer\_object GL\_EXT\_texture\_buffer\_object\_rgb32 GL\_EXT\_texture\_compression\_latc GL\_EXT\_texture\_compression\_rgtc GL\_EXT\_texture\_compression\_s3tc GL\_EXT\_texture\_cube\_map GL\_EXT\_texture\_edge\_clamp GL\_EXT\_texture\_env\_add GL\_EXT\_texture\_env\_combine GL\_EXT\_texture\_env\_dot3 GL\_EXT\_texture\_filter\_anisotropic GL\_EXT\_texture\_integer GL\_EXT\_texture\_lod GL\_EXT\_texture\_lod\_bias GL\_EXT\_texture\_mirror\_clamp GL\_EXT\_texture\_object GL\_EXT\_texture\_rectangle GL\_EXT\_texture\_sRGB GL\_EXT\_texture\_shared\_exponent GL\_EXT\_texture\_snorm GL\_EXT\_texture\_swizzle GL\_EXT\_timer\_query GL\_EXT\_transform\_feedback GL\_EXT\_vertex\_array GL\_EXT\_vertex\_array\_bgra GL\_IBM\_texture\_mirrored\_repeat GL\_KTX\_buffer\_region GL\_NV\_blend\_square GL\_NV\_conditional\_render GL\_NV\_copy\_depth\_to\_color GL\_NV\_explicit\_multisample GL\_NV\_primitive\_restart GL\_NV\_texgen\_reflection GL\_SGIS\_generate\_mipmap GL\_SGIS\_texture\_edge\_clamp GL\_SGIS\_texture\_lod GL\_SUN\_multi\_draw\_arrays GL\_WIN\_swap\_hint WGL\_EXT\_swap\_control  
  
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 ATI Technologies Inc. :: ATI Radeon HD 4550 :: 3.2.9704 Compatibility Profile Context  
PTB-INFO: VBL startline = 768 , VBL Endline = 768  
PTB-INFO: Measured monitor refresh interval from beamposition = 13.327800 ms [75.031138 Hz].  
PTB-INFO: Will use beamposition query for accurate Flip time stamping.  
PTB-INFO: Measured monitor refresh interval from VBLsync = 13.327702 ms [75.031690 Hz]. (50 valid samples taken, stddev=0.002826 ms.)  
PTB-INFO: Reported monitor refresh interval from operating system = 13.333333 ms [75.000000 Hz].  
PTB-INFO: Small deviations between reported values are normal and no reason to worry.  
PTB-INFO: Using OpenGL GL\_TEXTURE\_RECTANGLE\_EXT extension for efficient high-performance texture mapping...  
  
  
PTB-ERROR: Screen('Flip'); beamposition timestamping computed an \*impossible stimulus onset value\* of 813788.273897 secs, which would indicate that  
PTB-ERROR: stimulus onset happened \*before\* it was actually requested! (Earliest theoretically possible 813788.276004 secs).  
  
PTB-ERROR: Some more diagnostic values (only for experts): rawTimestamp = 813788.287225, scanline = 767  
PTB-ERROR: Some more diagnostic values (only for experts): line\_pre\_swaprequest = 93, line\_post\_swaprequest = 100, time\_post\_swaprequest = 813788.276125  
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' !  
  
  
As per suggestions in this topic [http://tech.groups.yahoo.com/group/psychtoolbox/message/10703,](http://tech.groups.yahoo.com/group/psychtoolbox/message/10703,) I ran PerceptualVBLSyncTest:  
  
  
AFTER RUNNING PerceptualVBLSyncTest...  
  
OpenGL-Extensions are: GL\_AMDX\_name\_gen\_delete GL\_AMDX\_vertex\_shader\_tessellator GL\_AMD\_draw\_buffers\_blend GL\_AMD\_performance\_monitor GL\_AMD\_seamless\_cubemap\_per\_texture GL\_AMD\_shader\_stencil\_export GL\_AMD\_texture\_cube\_map\_array GL\_AMD\_texture\_texture4 GL\_AMD\_vertex\_shader\_tessellator GL\_ARB\_color\_buffer\_float GL\_ARB\_copy\_buffer GL\_ARB\_depth\_buffer\_float GL\_ARB\_depth\_clamp GL\_ARB\_depth\_texture GL\_ARB\_draw\_buffers GL\_ARB\_draw\_buffers\_blend GL\_ARB\_draw\_elements\_base\_vertex GL\_ARB\_draw\_instanced GL\_ARB\_fragment\_coord\_conventions GL\_ARB\_fragment\_program GL\_ARB\_fragment\_program\_shadow GL\_ARB\_fragment\_shader GL\_ARB\_framebuffer\_object GL\_ARB\_framebuffer\_sRGB GL\_ARB\_geometry\_shader4 GL\_ARB\_half\_float\_pixel GL\_ARB\_half\_float\_vertex GL\_ARB\_imaging GL\_ARB\_instanced\_arrays GL\_ARB\_map\_buffer\_range GL\_ARB\_multisample GL\_ARB\_multitexture GL\_ARB\_occlusion\_query GL\_ARB\_pixel\_buffer\_object GL\_ARB\_point\_parameters GL\_ARB\_point\_sprite GL\_ARB\_provoking\_vertex GL\_ARB\_seamless\_cube\_map GL\_ARB\_shader\_objects GL\_ARB\_shader\_texture\_lod GL\_ARB\_shading\_language\_100 GL\_ARB\_shadow GL\_ARB\_shadow\_ambient GL\_ARB\_sync GL\_ARB\_texture\_border\_clamp GL\_ARB\_texture\_buffer\_object GL\_ARB\_texture\_compression GL\_ARB\_texture\_compression\_rgtc GL\_ARB\_texture\_cube\_map GL\_ARB\_texture\_cube\_map\_array GL\_ARB\_texture\_env\_add GL\_ARB\_texture\_env\_combine GL\_ARB\_texture\_env\_crossbar GL\_ARB\_texture\_env\_dot3 GL\_ARB\_texture\_float GL\_ARB\_texture\_mirrored\_repeat GL\_ARB\_texture\_multisample GL\_ARB\_texture\_non\_power\_of\_two GL\_ARB\_texture\_query\_lod GL\_ARB\_texture\_rectangle GL\_ARB\_texture\_rg GL\_ARB\_texture\_snorm GL\_ARB\_transpose\_matrix GL\_ARB\_uniform\_buffer\_object GL\_ARB\_vertex\_array\_bgra GL\_ARB\_vertex\_array\_object GL\_ARB\_vertex\_buffer\_object GL\_ARB\_vertex\_program GL\_ARB\_vertex\_shader GL\_ARB\_window\_pos GL\_ATI\_draw\_buffers GL\_ATI\_envmap\_bumpmap GL\_ATI\_fragment\_shader GL\_ATI\_meminfo GL\_ATI\_separate\_stencil GL\_ATI\_texture\_compression\_3dc GL\_ATI\_texture\_env\_combine3 GL\_ATI\_texture\_float GL\_ATI\_texture\_mirror\_once GL\_EXT\_abgr GL\_EXT\_bgra GL\_EXT\_bindable\_uniform GL\_EXT\_blend\_color GL\_EXT\_blend\_equation\_separate GL\_EXT\_blend\_func\_separate GL\_EXT\_blend\_minmax GL\_EXT\_blend\_subtract GL\_EXT\_compiled\_vertex\_array GL\_EXT\_copy\_buffer GL\_EXT\_copy\_texture GL\_EXT\_draw\_buffers2 GL\_EXT\_draw\_instanced GL\_EXT\_draw\_range\_elements GL\_EXT\_fog\_coord GL\_EXT\_framebuffer\_blit GL\_EXT\_framebuffer\_multisample GL\_EXT\_framebuffer\_object GL\_EXT\_framebuffer\_sRGB GL\_EXT\_geometry\_shader4 GL\_EXT\_gpu\_program\_parameters GL\_EXT\_gpu\_shader4 GL\_EXT\_histogram GL\_EXT\_multi\_draw\_arrays GL\_EXT\_packed\_depth\_stencil GL\_EXT\_packed\_float GL\_EXT\_packed\_pixels GL\_EXT\_pixel\_buffer\_object GL\_EXT\_point\_parameters GL\_EXT\_provoking\_vertex GL\_EXT\_rescale\_normal GL\_EXT\_secondary\_color GL\_EXT\_separate\_specular\_color GL\_EXT\_shadow\_funcs GL\_EXT\_stencil\_wrap GL\_EXT\_subtexture GL\_EXT\_texgen\_reflection GL\_EXT\_texture3D GL\_EXT\_texture\_array GL\_EXT\_texture\_buffer\_object GL\_EXT\_texture\_buffer\_object\_rgb32 GL\_EXT\_texture\_compression\_latc GL\_EXT\_texture\_compression\_rgtc GL\_EXT\_texture\_compression\_s3tc GL\_EXT\_texture\_cube\_map GL\_EXT\_texture\_edge\_clamp GL\_EXT\_texture\_env\_add GL\_EXT\_texture\_env\_combine GL\_EXT\_texture\_env\_dot3 GL\_EXT\_texture\_filter\_anisotropic GL\_EXT\_texture\_integer GL\_EXT\_texture\_lod GL\_EXT\_texture\_lod\_bias GL\_EXT\_texture\_mirror\_clamp GL\_EXT\_texture\_object GL\_EXT\_texture\_rectangle GL\_EXT\_texture\_sRGB GL\_EXT\_texture\_shared\_exponent GL\_EXT\_texture\_snorm GL\_EXT\_texture\_swizzle GL\_EXT\_timer\_query GL\_EXT\_transform\_feedback GL\_EXT\_vertex\_array GL\_EXT\_vertex\_array\_bgra GL\_IBM\_texture\_mirrored\_repeat GL\_KTX\_buffer\_region GL\_NV\_blend\_square GL\_NV\_conditional\_render GL\_NV\_copy\_depth\_to\_color GL\_NV\_explicit\_multisample GL\_NV\_primitive\_restart GL\_NV\_texgen\_reflection GL\_SGIS\_generate\_mipmap GL\_SGIS\_texture\_edge\_clamp GL\_SGIS\_texture\_lod GL\_SUN\_multi\_draw\_arrays GL\_WIN\_swap\_hint WGL\_EXT\_swap\_control  
  
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 ATI Technologies Inc. :: ATI Radeon HD 4550 :: 3.2.9704 Compatibility Profile Context  
PTB-INFO: VBL startline = 768 , VBL Endline = 768  
PTB-INFO: Measured monitor refresh interval from beamposition = 13.327959 ms [75.030240 Hz].  
PTB-INFO: Will use beamposition query for accurate Flip time stamping.  
PTB-INFO: Measured monitor refresh interval from VBLsync = 13.327704 ms [75.031677 Hz]. (50 valid samples taken, stddev=0.000944 ms.)  
PTB-INFO: Reported monitor refresh interval from operating system = 13.333333 ms [75.000000 Hz].  
PTB-INFO: Small deviations between reported values are normal and no reason to worry.  
PTB-INFO: Using OpenGL GL\_TEXTURE\_RECTANGLE\_EXT extension for efficient high-performance texture mapping...  
  
  
From what I understand, these are considered as 'small deviations' and shouldn't be an issue? I then ran my program again with Screen('Preference','SkipSyncTests',1) and Screen('Preference','Verbosity',10)...  
  
AFTER RUNNING PROGRAM WITH Screen('Preference','SkipSyncTests',1) and Screen('Preference','Verbosity',10)  
  
PTB-DEBUG: PsychOSOpenOnscreenWindow: Entering Win32 specific window setup...  
PTB-DEBUG: Checking for DWM Aero desktop compositor support... ... DWM Aero desktop compositing window manager unsupported. Running on a Pre-Vista system.  
PTB-DEBUG: PsychOSOpenOnscreenWindow: Window parameters computed, display switch to fullscreen done (if needed). Registering window class...  
PTB-DEBUG: Window enumeration done. Our hostwindow is HWND=013E034A, Name: 'MATLAB 7.9.0 (R2009b)'  
  
PTB-DEBUG: PsychOSOpenOnscreenWindow: Window class registered - Creating GDI window...  
PTB-DEBUG: WndProc(): Called!  
PTB-DEBUG: WndProc(): Called!  
PTB-DEBUG: WndProc(): Called!  
PTB-DEBUG: WndProc(): Called!  
PTB-DEBUG: Created onscreen window has position -4 x -30 and a size of 108 x 134.  
PTB-DEBUG: PsychOSOpenOnscreenWindow: Window created - Pixelformat selection...  
PTB-DEBUG: PsychOSOpenOnscreenWindow: ChoosePixelFormat(), SetPixelFormat() done... Creating OpenGL context...  
PTB-DEBUG: PsychOSOpenOnscreenWindow: Context created - Activating and binding context...  
PTB-DEBUG: PsychOSOpenOnscreenWindow: Online - glewInit()...  
PTB-INFO: Using GLEW version 1.5.3 for automatic detection of OpenGL extensions...  
PTB-DEBUG: PsychOSOpenOnscreenWindow: Mastercontext created, activated and bound - Enabling multisampling if needed...  
PTB-DEBUG: Window and master OpenGL context creation finished.  
PTB-DEBUG: Before slaveWindow context sharing: glGetString reports 1E667038 pointer...  
PTB-DEBUG: After slaveWindow context sharing: glGetString reports 1E667038 pointer...  
PTB-DEBUG: Final low-level window setup: ShowWindow(), SetCapture(), diagnostics...  
PTB-DEBUG: OpenGL initialization of all master-/slave-/shared-/userspace contexts finished...  
PTB-DEBUG: Final low-level window setup: ShowWindow(), SetCapture(), diagnostics...  
PTB-DEBUG: WndProc(): Called!  
PTB-DEBUG: WndProc(): Called!  
PTB-DEBUG: WndProc(): Called!  
PTB-DEBUG: WndProc(): Called!  
PTB-DEBUG: WndProc(): Called!  
PTB-DEBUG: WndProc(): Called!  
PTB-DEBUG: WndProc(): Called!  
PTB-DEBUG: WndProc(): Called!  
PTB-DEBUG: WndProc(): Called!  
PTB-DEBUG: WndProc(): Called!  
PTB-DEBUG: WndProc(): Called!  
PTB-DEBUG: WndProc(): Called!  
PTB-DEBUG: WndProc(): Called!  
PTB-DEBUG: WndProc(): Called!  
PTB-DEBUG: WndProc(): Called!  
PTB-DEBUG: WndProc(): Called!  
PTB-DEBUG: WndProc(): Called!  
PTB-DEBUG: WndProc(): Called!  
PTB-DEBUG: WndProc(): WM\_SIZE!  
PTB-DEBUG: WndProc(): Called!  
PTB-DEBUG: No call to SetForegroundWindow() and SetFocus() on window, because trigger-conditions not satisfied.  
PTB-INFO: Some ATI graphics cards may not support proper syncing to vertical retrace when  
PTB-INFO: running in windowed mode (non-fullscreen). If PTB aborts with 'Synchronization failure'  
PTB-INFO: you can disable the sync test via call to Screen('Preference', 'SkipSyncTests', 1); .  
PTB-INFO: You won't get proper stimulus onset timestamps though, so windowed mode may be of limited use.  
PTB-DEBUG: WndProc(): Called!  
PTB-DEBUG: WndProc(): Called!  
PTB-DEBUG: WndProc(): Called!  
PTB-DEBUG: WndProc(): Called!  
PTB-DEBUG: WndProc(): WM\_PAINT!  
PTB-DEBUG: Final low-level window setup finished. Continuing with OS-independent setup.  
  
  
OpenGL-Extensions are: GL\_AMDX\_name\_gen\_delete GL\_AMDX\_vertex\_shader\_tessellator GL\_AMD\_draw\_buffers\_blend GL\_AMD\_performance\_monitor GL\_AMD\_seamless\_cubemap\_per\_texture GL\_AMD\_shader\_stencil\_export GL\_AMD\_texture\_cube\_map\_array GL\_AMD\_texture\_texture4 GL\_AMD\_vertex\_shader\_tessellator GL\_ARB\_color\_buffer\_float GL\_ARB\_copy\_buffer GL\_ARB\_depth\_buffer\_float GL\_ARB\_depth\_clamp GL\_ARB\_depth\_texture GL\_ARB\_draw\_buffers GL\_ARB\_draw\_buffers\_blend GL\_ARB\_draw\_elements\_base\_vertex GL\_ARB\_draw\_instanced GL\_ARB\_fragment\_coord\_conventions GL\_ARB\_fragment\_program GL\_ARB\_fragment\_program\_shadow GL\_ARB\_fragment\_shader GL\_ARB\_framebuffer\_object GL\_ARB\_framebuffer\_sRGB GL\_ARB\_geometry\_shader4 GL\_ARB\_half\_float\_pixel GL\_ARB\_half\_float\_vertex GL\_ARB\_imaging GL\_ARB\_instanced\_arrays GL\_ARB\_map\_buffer\_range GL\_ARB\_multisample GL\_ARB\_multitexture GL\_ARB\_occlusion\_query GL\_ARB\_pixel\_buffer\_object GL\_ARB\_point\_parameters GL\_ARB\_point\_sprite GL\_ARB\_provoking\_vertex GL\_ARB\_seamless\_cube\_map GL\_ARB\_shader\_objects GL\_ARB\_shader\_texture\_lod GL\_ARB\_shading\_language\_100 GL\_ARB\_shadow GL\_ARB\_shadow\_ambient GL\_ARB\_sync GL\_ARB\_texture\_border\_clamp GL\_ARB\_texture\_buffer\_object GL\_ARB\_texture\_compression GL\_ARB\_texture\_compression\_rgtc GL\_ARB\_texture\_cube\_map GL\_ARB\_texture\_cube\_map\_array GL\_ARB\_texture\_env\_add GL\_ARB\_texture\_env\_combine GL\_ARB\_texture\_env\_crossbar GL\_ARB\_texture\_env\_dot3 GL\_ARB\_texture\_float GL\_ARB\_texture\_mirrored\_repeat GL\_ARB\_texture\_multisample GL\_ARB\_texture\_non\_power\_of\_two GL\_ARB\_texture\_query\_lod GL\_ARB\_texture\_rectangle GL\_ARB\_texture\_rg GL\_ARB\_texture\_snorm GL\_ARB\_transpose\_matrix GL\_ARB\_uniform\_buffer\_object GL\_ARB\_vertex\_array\_bgra GL\_ARB\_vertex\_array\_object GL\_ARB\_vertex\_buffer\_object GL\_ARB\_vertex\_program GL\_ARB\_vertex\_shader GL\_ARB\_window\_pos GL\_ATI\_draw\_buffers GL\_ATI\_envmap\_bumpmap GL\_ATI\_fragment\_shader GL\_ATI\_meminfo GL\_ATI\_separate\_stencil GL\_ATI\_texture\_compression\_3dc GL\_ATI\_texture\_env\_combine3 GL\_ATI\_texture\_float GL\_ATI\_texture\_mirror\_once GL\_EXT\_abgr GL\_EXT\_bgra GL\_EXT\_bindable\_uniform GL\_EXT\_blend\_color GL\_EXT\_blend\_equation\_separate GL\_EXT\_blend\_func\_separate GL\_EXT\_blend\_minmax GL\_EXT\_blend\_subtract GL\_EXT\_compiled\_vertex\_array GL\_EXT\_copy\_buffer GL\_EXT\_copy\_texture GL\_EXT\_draw\_buffers2 GL\_EXT\_draw\_instanced GL\_EXT\_draw\_range\_elements GL\_EXT\_fog\_coord GL\_EXT\_framebuffer\_blit GL\_EXT\_framebuffer\_multisample GL\_EXT\_framebuffer\_object GL\_EXT\_framebuffer\_sRGB GL\_EXT\_geometry\_shader4 GL\_EXT\_gpu\_program\_parameters GL\_EXT\_gpu\_shader4 GL\_EXT\_histogram GL\_EXT\_multi\_draw\_arrays GL\_EXT\_packed\_depth\_stencil GL\_EXT\_packed\_float GL\_EXT\_packed\_pixels GL\_EXT\_pixel\_buffer\_object GL\_EXT\_point\_parameters GL\_EXT\_provoking\_vertex GL\_EXT\_rescale\_normal GL\_EXT\_secondary\_color GL\_EXT\_separate\_specular\_color GL\_EXT\_shadow\_funcs GL\_EXT\_stencil\_wrap GL\_EXT\_subtexture GL\_EXT\_texgen\_reflection GL\_EXT\_texture3D GL\_EXT\_texture\_array GL\_EXT\_texture\_buffer\_object GL\_EXT\_texture\_buffer\_object\_rgb32 GL\_EXT\_texture\_compression\_latc GL\_EXT\_texture\_compression\_rgtc GL\_EXT\_texture\_compression\_s3tc GL\_EXT\_texture\_cube\_map GL\_EXT\_texture\_edge\_clamp GL\_EXT\_texture\_env\_add GL\_EXT\_texture\_env\_combine GL\_EXT\_texture\_env\_dot3 GL\_EXT\_texture\_filter\_anisotropic GL\_EXT\_texture\_integer GL\_EXT\_texture\_lod GL\_EXT\_texture\_lod\_bias GL\_EXT\_texture\_mirror\_clamp GL\_EXT\_texture\_object GL\_EXT\_texture\_rectangle GL\_EXT\_texture\_sRGB GL\_EXT\_texture\_shared\_exponent GL\_EXT\_texture\_snorm GL\_EXT\_texture\_swizzle GL\_EXT\_timer\_query GL\_EXT\_transform\_feedback GL\_EXT\_vertex\_array GL\_EXT\_vertex\_array\_bgra GL\_IBM\_texture\_mirrored\_repeat GL\_KTX\_buffer\_region GL\_NV\_blend\_square GL\_NV\_conditional\_render GL\_NV\_copy\_depth\_to\_color GL\_NV\_explicit\_multisample GL\_NV\_primitive\_restart GL\_NV\_texgen\_reflection GL\_SGIS\_generate\_mipmap GL\_SGIS\_texture\_edge\_clamp GL\_SGIS\_texture\_lod GL\_SUN\_multi\_draw\_arrays GL\_WIN\_swap\_hint WGL\_EXT\_swap\_control  
  
PTB-DEBUG: Interrogating Low-level renderer capabilities for onscreen window with handle 10:  
Indicator variables: FBO's 1, ATI\_texture\_float 1, ARB\_texture\_float 1, Vendor ATI Technologies Inc., Renderer ATI Radeon HD 4550.  
Indicator variables: maxcolorattachments = 8, maxrectangletexturesize = 8192, maxnativealuinstructions = 2147483647.  
Basic framebuffer objects with rectangle texture rendertargets supported --\> RGBA8 rendertargets with blending.  
Framebuffer objects support fast blitting between each other.  
Framebuffer objects support anti-aliasing via multisampling.  
Hardware supports floating point textures of 16bpc and 32bpc float format.  
Assuming ATI R300 core or later: Hardware supports basic floating point framebuffers of 16bpc and 32bpc float format.  
Assuming ATI R500 or later (maxtexsize=8192): Hardware supports floating point blending on 16bpc float format.  
Hardware supports full 32 bit floating point precision shading.  
Assuming ATI R600 or later (Matching namestring): Hardware supports floating point blending and filtering on 16bpc and 32bpc float formats.  
No compiled in support for OpenML OML\_sync\_control extension. Using standard implementation.  
PTB-DEBUG: Interrogation done.  
  
PTB-INFO: Threshold Settings for successfull video refresh calibration are: maxStdDev = 1.000000 msecs, maxDeviation = 10.000000 %, minSamples = 50, maxDuration = 5.000000 secs.  
  
WARNING: Querying rasterbeam-position doesn't work on your setup! (Returns a constant value 96)  
  
WARNING: Couldn't determine end-line of vertical blanking interval for your display! Trouble with beamposition queries?!?  
  
WARNING: Detected end-line is -1, which is either lower or more than 25% higher than vbl startline 768 --\> Out of sane range!  
  
  
PTB-DEBUG: Output of all acquired samples of calibration run follows:  
PTB-DEBUG: Sample 0: 0.000000  
PTB-DEBUG: Sample 1: 0.013323  
PTB-DEBUG: Sample 2: 0.013327  
PTB-DEBUG: Sample 3: 0.013342  
PTB-DEBUG: Sample 4: 0.013314  
PTB-DEBUG: Sample 5: 0.013328  
PTB-DEBUG: Sample 6: 0.013328  
PTB-DEBUG: Sample 7: 0.013329  
PTB-DEBUG: Sample 8: 0.013327  
PTB-DEBUG: Sample 9: 0.013327  
PTB-DEBUG: Sample 10: 0.013329  
PTB-DEBUG: Sample 11: 0.013336  
PTB-DEBUG: Sample 12: 0.013319  
PTB-DEBUG: Sample 13: 0.013341  
PTB-DEBUG: Sample 14: 0.013315  
PTB-DEBUG: Sample 15: 0.013328  
PTB-DEBUG: Sample 16: 0.013328  
PTB-DEBUG: Sample 17: 0.013327  
PTB-DEBUG: Sample 18: 0.013337  
PTB-DEBUG: Sample 19: 0.013318  
PTB-DEBUG: Sample 20: 0.013327  
PTB-DEBUG: Sample 21: 0.013329  
PTB-DEBUG: Sample 22: 0.013328  
PTB-DEBUG: Sample 23: 0.013329  
PTB-DEBUG: Sample 24: 0.013326  
PTB-DEBUG: Sample 25: 0.013328  
PTB-DEBUG: Sample 26: 0.013328  
PTB-DEBUG: Sample 27: 0.013327  
PTB-DEBUG: Sample 28: 0.013328  
PTB-DEBUG: Sample 29: 0.013328  
PTB-DEBUG: Sample 30: 0.013327  
PTB-DEBUG: Sample 31: 0.013329  
PTB-DEBUG: Sample 32: 0.013327  
PTB-DEBUG: Sample 33: 0.013328  
PTB-DEBUG: Sample 34: 0.013327  
PTB-DEBUG: Sample 35: 0.013329  
PTB-DEBUG: Sample 36: 0.013327  
PTB-DEBUG: Sample 37: 0.013328  
PTB-DEBUG: Sample 38: 0.013328  
PTB-DEBUG: Sample 39: 0.013328  
PTB-DEBUG: Sample 40: 0.013329  
PTB-DEBUG: Sample 41: 0.013327  
PTB-DEBUG: Sample 42: 0.013328  
PTB-DEBUG: Sample 43: 0.013327  
PTB-DEBUG: Sample 44: 0.013329  
PTB-DEBUG: Sample 45: 0.013328  
PTB-DEBUG: Sample 46: 0.013327  
PTB-DEBUG: Sample 47: 0.013329  
PTB-DEBUG: Sample 48: 0.013327  
PTB-DEBUG: Sample 49: 0.013328  
PTB-DEBUG: Sample 50: 0.013329  
PTB-DEBUG: End of calibration data for this run...  
  
  
  
PTB-INFO: OpenGL-Renderer is ATI Technologies Inc. :: ATI Radeon HD 4550 :: 3.2.9704 Compatibility Profile Context  
PTB-INFO: VBL startline = 768 , VBL Endline = -1  
PTB-INFO: Beamposition queries unsupported or defective on this system. Using basic timestamping as fallback: Timestamps returned by Screen('Flip') will be less robust and accurate.  
PTB-INFO: Measured monitor refresh interval from VBLsync = 13.327716 ms [75.031612 Hz]. (50 valid samples taken, stddev=0.004758 ms.)  
PTB-INFO: Reported monitor refresh interval from operating system = 13.333333 ms [75.000000 Hz].  
PTB-INFO: Small deviations between reported values are normal and no reason to worry.  
PTB-INFO: Using OpenGL GL\_TEXTURE\_RECTANGLE\_EXT extension for efficient high-performance texture mapping...  
  
  
----- ! PTB - WARNING: SYNCHRONIZATION TROUBLE ! ----  
  
One or more internal checks (see Warnings above) indicate that  
queries of rasterbeam position are not properly working for your setup.  
  
Psychtoolbox will work around this by using a different timing algorithm,   
but it will cause Screen('Flip') to report less accurate/robust timestamps  
for stimulus timing.  
Read 'help BeampositionQueries' for more info and troubleshooting tips.  
  
  
PTB-DEBUG: Allocated unicode string: 69.000000 110.000000 100.000000 32.000000 111.000000 102.000000 32.000000 66.000000 108.000000 111.000000 99.000000 107.000000 32.000000 48.000000 32.000000 111.000000 102.000000 32.000000 49.000000 32.000000 98.000000 108.000000 111.000000 99.000000 107.000000 115.000000 46.000000   
PTB-DEBUG: In DrawTextGDI: Rebuilding font due to window switch or rebuild request: needit = 1 , oldwin = 00000000 vs. newwin = 1A1DD060   
PTB-DEBUG: Allocated unicode string: 69.000000 110.000000 100.000000 32.000000 111.000000 102.000000 32.000000 66.000000 108.000000 111.000000 99.000000 107.000000 32.000000 48.000000 32.000000 111.000000 102.000000 32.000000 49.000000 32.000000 98.000000 108.000000 111.000000 99.000000 107.000000 115.000000 46.000000   
PTB-DEBUG: Allocated unicode string: 40.000000 112.000000 114.000000 101.000000 115.000000 115.000000 32.000000 69.000000 78.000000 84.000000 69.000000 82.000000 32.000000 116.000000 111.000000 32.000000 99.000000 111.000000 110.000000 116.000000 105.000000 110.000000 117.000000 101.000000 41.000000   
PTB-DEBUG: Allocated unicode string: 40.000000 112.000000 114.000000 101.000000 115.000000 115.000000 32.000000 69.000000 78.000000 84.000000 69.000000 82.000000 32.000000 116.000000 111.000000 32.000000 99.000000 111.000000 110.000000 116.000000 105.000000 110.000000 117.000000 101.000000 41.000000   
  
  
  
Please let me know if you have any suggestions.  
  
Thank you for your help!

---

<div class="post-metadata">

**Author:** ![mariokleiner](https://avatars.discourse-cdn.com/v4/letter/m/13edae/32.png) [@mariokleiner](https://psychtoolbox.discourse.group/u/mariokleiner)\
**Post date:** [October 28, 2011, 12:56am UTC](https://psychtoolbox.discourse.group/t/beamposition-problems/479/2 "2011-10-28T00:56:01Z")

</div>

--- In [psychtoolbox@yahoogroups.com](mailto:psychtoolbox@yahoogroups.com), "thenekonaut" \<nekonaut@...\> wrote:  

> \>  
> \> Hihi,  
> \>   
> \> I'm working in PTB3.0.9 on Windows 5.1 (Windows XP Professional) with a ATI Radeo HD 4550 graphics card. I've been having synchronization / beamposition problems. When I run the program, the following message appears:  
> \>   
> \> AFTER RUNNING PROGRAM:

...  
  

> \> PTB-INFO: Some ATI graphics cards may not support proper syncing to vertical retrace when  
> \> PTB-INFO: running in windowed mode (non-fullscreen). If PTB aborts with

...  
  
-\> Your script uses a non-fullscreen window, so timing trouble is expected. It actually can also apply to other graphics cards. Windowed presentation on any operating system can cause wildly inaccurate or wrong timestamps and wrong timing for stimulus onset. It is a design limitation of all existing operating systems and graphics drivers.  
  
-\> Disable the synctests and 'vbltimestampingmode' to get rid of the warnings, but be aware that visual timing (the actual one and the reported one) can be off by dozens of milliseconds.  
  
Other than that, looks good as far as i can see.  
-mario  
  
  
'Synchronization failure'  

> \> PTB-INFO: you can disable the sync test via call to Screen('Preference', 'SkipSyncTests', 1); .  
> \> PTB-INFO: You won't get proper stimulus onset timestamps though, so windowed mode may be of limited use.  
> \>   
> \>   
> \> OpenGL-Extensions are: GL\_AMDX\_name\_gen\_delete GL\_AMDX\_vertex\_shader\_tessellator GL\_AMD\_draw\_buffers\_blend GL\_AMD\_performance\_monitor GL\_AMD\_seamless\_cubemap\_per\_texture GL\_AMD\_shader\_stencil\_export GL\_AMD\_texture\_cube\_map\_array GL\_AMD\_texture\_texture4 GL\_AMD\_vertex\_shader\_tessellator GL\_ARB\_color\_buffer\_float GL\_ARB\_copy\_buffer GL\_ARB\_depth\_buffer\_float GL\_ARB\_depth\_clamp GL\_ARB\_depth\_texture GL\_ARB\_draw\_buffers GL\_ARB\_draw\_buffers\_blend GL\_ARB\_draw\_elements\_base\_vertex GL\_ARB\_draw\_instanced GL\_ARB\_fragment\_coord\_conventions GL\_ARB\_fragment\_program GL\_ARB\_fragment\_program\_shadow GL\_ARB\_fragment\_shader GL\_ARB\_framebuffer\_object GL\_ARB\_framebuffer\_sRGB GL\_ARB\_geometry\_shader4 GL\_ARB\_half\_float\_pixel GL\_ARB\_half\_float\_vertex GL\_ARB\_imaging GL\_ARB\_instanced\_arrays GL\_ARB\_map\_buffer\_range GL\_ARB\_multisample GL\_ARB\_multitexture GL\_ARB\_occlusion\_query GL\_ARB\_pixel\_buffer\_object GL\_ARB\_point\_parameters GL\_ARB\_point\_sprite GL\_ARB\_provoking\_vertex GL\_ARB\_seamless\_cube\_map GL\_ARB\_shader\_objects GL\_ARB\_shader\_texture\_lod GL\_ARB\_shading\_language\_100 GL\_ARB\_shadow GL\_ARB\_shadow\_ambient GL\_ARB\_sync GL\_ARB\_texture\_border\_clamp GL\_ARB\_texture\_buffer\_object GL\_ARB\_texture\_compression GL\_ARB\_texture\_compression\_rgtc GL\_ARB\_texture\_cube\_map GL\_ARB\_texture\_cube\_map\_array GL\_ARB\_texture\_env\_add GL\_ARB\_texture\_env\_combine GL\_ARB\_texture\_env\_crossbar GL\_ARB\_texture\_env\_dot3 GL\_ARB\_texture\_float GL\_ARB\_texture\_mirrored\_repeat GL\_ARB\_texture\_multisample GL\_ARB\_texture\_non\_power\_of\_two GL\_ARB\_texture\_query\_lod GL\_ARB\_texture\_rectangle GL\_ARB\_texture\_rg GL\_ARB\_texture\_snorm GL\_ARB\_transpose\_matrix GL\_ARB\_uniform\_buffer\_object GL\_ARB\_vertex\_array\_bgra GL\_ARB\_vertex\_array\_object GL\_ARB\_vertex\_buffer\_object GL\_ARB\_vertex\_program GL\_ARB\_vertex\_shader GL\_ARB\_window\_pos GL\_ATI\_draw\_buffers GL\_ATI\_envmap\_bumpmap GL\_ATI\_fragment\_shader GL\_ATI\_meminfo GL\_ATI\_separate\_stencil GL\_ATI\_texture\_compression\_3dc GL\_ATI\_texture\_env\_combine3 GL\_ATI\_texture\_float GL\_ATI\_texture\_mirror\_once GL\_EXT\_abgr GL\_EXT\_bgra GL\_EXT\_bindable\_uniform GL\_EXT\_blend\_color GL\_EXT\_blend\_equation\_separate GL\_EXT\_blend\_func\_separate GL\_EXT\_blend\_minmax GL\_EXT\_blend\_subtract GL\_EXT\_compiled\_vertex\_array GL\_EXT\_copy\_buffer GL\_EXT\_copy\_texture GL\_EXT\_draw\_buffers2 GL\_EXT\_draw\_instanced GL\_EXT\_draw\_range\_elements GL\_EXT\_fog\_coord GL\_EXT\_framebuffer\_blit GL\_EXT\_framebuffer\_multisample GL\_EXT\_framebuffer\_object GL\_EXT\_framebuffer\_sRGB GL\_EXT\_geometry\_shader4 GL\_EXT\_gpu\_program\_parameters GL\_EXT\_gpu\_shader4 GL\_EXT\_histogram GL\_EXT\_multi\_draw\_arrays GL\_EXT\_packed\_depth\_stencil GL\_EXT\_packed\_float GL\_EXT\_packed\_pixels GL\_EXT\_pixel\_buffer\_object GL\_EXT\_point\_parameters GL\_EXT\_provoking\_vertex GL\_EXT\_rescale\_normal GL\_EXT\_secondary\_color GL\_EXT\_separate\_specular\_color GL\_EXT\_shadow\_funcs GL\_EXT\_stencil\_wrap GL\_EXT\_subtexture GL\_EXT\_texgen\_reflection GL\_EXT\_texture3D GL\_EXT\_texture\_array GL\_EXT\_texture\_buffer\_object GL\_EXT\_texture\_buffer\_object\_rgb32 GL\_EXT\_texture\_compression\_latc GL\_EXT\_texture\_compression\_rgtc GL\_EXT\_texture\_compression\_s3tc GL\_EXT\_texture\_cube\_map GL\_EXT\_texture\_edge\_clamp GL\_EXT\_texture\_env\_add GL\_EXT\_texture\_env\_combine GL\_EXT\_texture\_env\_dot3 GL\_EXT\_texture\_filter\_anisotropic GL\_EXT\_texture\_integer GL\_EXT\_texture\_lod GL\_EXT\_texture\_lod\_bias GL\_EXT\_texture\_mirror\_clamp GL\_EXT\_texture\_object GL\_EXT\_texture\_rectangle GL\_EXT\_texture\_sRGB GL\_EXT\_texture\_shared\_exponent GL\_EXT\_texture\_snorm GL\_EXT\_texture\_swizzle GL\_EXT\_timer\_query GL\_EXT\_transform\_feedback GL\_EXT\_vertex\_array GL\_EXT\_vertex\_array\_bgra GL\_IBM\_texture\_mirrored\_repeat GL\_KTX\_buffer\_region GL\_NV\_blend\_square GL\_NV\_conditional\_render GL\_NV\_copy\_depth\_to\_color GL\_NV\_explicit\_multisample GL\_NV\_primitive\_restart GL\_NV\_texgen\_reflection GL\_SGIS\_generate\_mipmap GL\_SGIS\_texture\_edge\_clamp GL\_SGIS\_texture\_lod GL\_SUN\_multi\_draw\_arrays GL\_WIN\_swap\_hint WGL\_EXT\_swap\_control  
> \>   
> \> 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 ATI Technologies Inc. :: ATI Radeon HD 4550 :: 3.2.9704 Compatibility Profile Context  
> \> PTB-INFO: VBL startline = 768 , VBL Endline = 768  
> \> PTB-INFO: Measured monitor refresh interval from beamposition = 13.327800 ms [75.031138 Hz].  
> \> PTB-INFO: Will use beamposition query for accurate Flip time stamping.  
> \> PTB-INFO: Measured monitor refresh interval from VBLsync = 13.327702 ms [75.031690 Hz]. (50 valid samples taken, stddev=0.002826 ms.)  
> \> PTB-INFO: Reported monitor refresh interval from operating system = 13.333333 ms [75.000000 Hz].  
> \> PTB-INFO: Small deviations between reported values are normal and no reason to worry.  
> \> PTB-INFO: Using OpenGL GL\_TEXTURE\_RECTANGLE\_EXT extension for efficient high-performance texture mapping...  
> \>   
> \>   
> \> PTB-ERROR: Screen('Flip'); beamposition timestamping computed an \*impossible stimulus onset value\* of 813788.273897 secs, which would indicate that  
> \> PTB-ERROR: stimulus onset happened \*before\* it was actually requested! (Earliest theoretically possible 813788.276004 secs).  
> \>   
> \> PTB-ERROR: Some more diagnostic values (only for experts): rawTimestamp = 813788.287225, scanline = 767  
> \> PTB-ERROR: Some more diagnostic values (only for experts): line\_pre\_swaprequest = 93, line\_post\_swaprequest = 100, time\_post\_swaprequest = 813788.276125  
> \> 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' !  
> \>   
> \>   
> \> As per suggestions in this topic [http://tech.groups.yahoo.com/group/psychtoolbox/message/10703,](http://tech.groups.yahoo.com/group/psychtoolbox/message/10703,) I ran PerceptualVBLSyncTest:  
> \>   
> \>   
> \> AFTER RUNNING PerceptualVBLSyncTest...  
> \>   
> \> OpenGL-Extensions are: GL\_AMDX\_name\_gen\_delete GL\_AMDX\_vertex\_shader\_tessellator GL\_AMD\_draw\_buffers\_blend GL\_AMD\_performance\_monitor GL\_AMD\_seamless\_cubemap\_per\_texture GL\_AMD\_shader\_stencil\_export GL\_AMD\_texture\_cube\_map\_array GL\_AMD\_texture\_texture4 GL\_AMD\_vertex\_shader\_tessellator GL\_ARB\_color\_buffer\_float GL\_ARB\_copy\_buffer GL\_ARB\_depth\_buffer\_float GL\_ARB\_depth\_clamp GL\_ARB\_depth\_texture GL\_ARB\_draw\_buffers GL\_ARB\_draw\_buffers\_blend GL\_ARB\_draw\_elements\_base\_vertex GL\_ARB\_draw\_instanced GL\_ARB\_fragment\_coord\_conventions GL\_ARB\_fragment\_program GL\_ARB\_fragment\_program\_shadow GL\_ARB\_fragment\_shader GL\_ARB\_framebuffer\_object GL\_ARB\_framebuffer\_sRGB GL\_ARB\_geometry\_shader4 GL\_ARB\_half\_float\_pixel GL\_ARB\_half\_float\_vertex GL\_ARB\_imaging GL\_ARB\_instanced\_arrays GL\_ARB\_map\_buffer\_range GL\_ARB\_multisample GL\_ARB\_multitexture GL\_ARB\_occlusion\_query GL\_ARB\_pixel\_buffer\_object GL\_ARB\_point\_parameters GL\_ARB\_point\_sprite GL\_ARB\_provoking\_vertex GL\_ARB\_seamless\_cube\_map GL\_ARB\_shader\_objects GL\_ARB\_shader\_texture\_lod GL\_ARB\_shading\_language\_100 GL\_ARB\_shadow GL\_ARB\_shadow\_ambient GL\_ARB\_sync GL\_ARB\_texture\_border\_clamp GL\_ARB\_texture\_buffer\_object GL\_ARB\_texture\_compression GL\_ARB\_texture\_compression\_rgtc GL\_ARB\_texture\_cube\_map GL\_ARB\_texture\_cube\_map\_array GL\_ARB\_texture\_env\_add GL\_ARB\_texture\_env\_combine GL\_ARB\_texture\_env\_crossbar GL\_ARB\_texture\_env\_dot3 GL\_ARB\_texture\_float GL\_ARB\_texture\_mirrored\_repeat GL\_ARB\_texture\_multisample GL\_ARB\_texture\_non\_power\_of\_two GL\_ARB\_texture\_query\_lod GL\_ARB\_texture\_rectangle GL\_ARB\_texture\_rg GL\_ARB\_texture\_snorm GL\_ARB\_transpose\_matrix GL\_ARB\_uniform\_buffer\_object GL\_ARB\_vertex\_array\_bgra GL\_ARB\_vertex\_array\_object GL\_ARB\_vertex\_buffer\_object GL\_ARB\_vertex\_program GL\_ARB\_vertex\_shader GL\_ARB\_window\_pos GL\_ATI\_draw\_buffers GL\_ATI\_envmap\_bumpmap GL\_ATI\_fragment\_shader GL\_ATI\_meminfo GL\_ATI\_separate\_stencil GL\_ATI\_texture\_compression\_3dc GL\_ATI\_texture\_env\_combine3 GL\_ATI\_texture\_float GL\_ATI\_texture\_mirror\_once GL\_EXT\_abgr GL\_EXT\_bgra GL\_EXT\_bindable\_uniform GL\_EXT\_blend\_color GL\_EXT\_blend\_equation\_separate GL\_EXT\_blend\_func\_separate GL\_EXT\_blend\_minmax GL\_EXT\_blend\_subtract GL\_EXT\_compiled\_vertex\_array GL\_EXT\_copy\_buffer GL\_EXT\_copy\_texture GL\_EXT\_draw\_buffers2 GL\_EXT\_draw\_instanced GL\_EXT\_draw\_range\_elements GL\_EXT\_fog\_coord GL\_EXT\_framebuffer\_blit GL\_EXT\_framebuffer\_multisample GL\_EXT\_framebuffer\_object GL\_EXT\_framebuffer\_sRGB GL\_EXT\_geometry\_shader4 GL\_EXT\_gpu\_program\_parameters GL\_EXT\_gpu\_shader4 GL\_EXT\_histogram GL\_EXT\_multi\_draw\_arrays GL\_EXT\_packed\_depth\_stencil GL\_EXT\_packed\_float GL\_EXT\_packed\_pixels GL\_EXT\_pixel\_buffer\_object GL\_EXT\_point\_parameters GL\_EXT\_provoking\_vertex GL\_EXT\_rescale\_normal GL\_EXT\_secondary\_color GL\_EXT\_separate\_specular\_color GL\_EXT\_shadow\_funcs GL\_EXT\_stencil\_wrap GL\_EXT\_subtexture GL\_EXT\_texgen\_reflection GL\_EXT\_texture3D GL\_EXT\_texture\_array GL\_EXT\_texture\_buffer\_object GL\_EXT\_texture\_buffer\_object\_rgb32 GL\_EXT\_texture\_compression\_latc GL\_EXT\_texture\_compression\_rgtc GL\_EXT\_texture\_compression\_s3tc GL\_EXT\_texture\_cube\_map GL\_EXT\_texture\_edge\_clamp GL\_EXT\_texture\_env\_add GL\_EXT\_texture\_env\_combine GL\_EXT\_texture\_env\_dot3 GL\_EXT\_texture\_filter\_anisotropic GL\_EXT\_texture\_integer GL\_EXT\_texture\_lod GL\_EXT\_texture\_lod\_bias GL\_EXT\_texture\_mirror\_clamp GL\_EXT\_texture\_object GL\_EXT\_texture\_rectangle GL\_EXT\_texture\_sRGB GL\_EXT\_texture\_shared\_exponent GL\_EXT\_texture\_snorm GL\_EXT\_texture\_swizzle GL\_EXT\_timer\_query GL\_EXT\_transform\_feedback GL\_EXT\_vertex\_array GL\_EXT\_vertex\_array\_bgra GL\_IBM\_texture\_mirrored\_repeat GL\_KTX\_buffer\_region GL\_NV\_blend\_square GL\_NV\_conditional\_render GL\_NV\_copy\_depth\_to\_color GL\_NV\_explicit\_multisample GL\_NV\_primitive\_restart GL\_NV\_texgen\_reflection GL\_SGIS\_generate\_mipmap GL\_SGIS\_texture\_edge\_clamp GL\_SGIS\_texture\_lod GL\_SUN\_multi\_draw\_arrays GL\_WIN\_swap\_hint WGL\_EXT\_swap\_control  
> \>   
> \> 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 ATI Technologies Inc. :: ATI Radeon HD 4550 :: 3.2.9704 Compatibility Profile Context  
> \> PTB-INFO: VBL startline = 768 , VBL Endline = 768  
> \> PTB-INFO: Measured monitor refresh interval from beamposition = 13.327959 ms [75.030240 Hz].  
> \> PTB-INFO: Will use beamposition query for accurate Flip time stamping.  
> \> PTB-INFO: Measured monitor refresh interval from VBLsync = 13.327704 ms [75.031677 Hz]. (50 valid samples taken, stddev=0.000944 ms.)  
> \> PTB-INFO: Reported monitor refresh interval from operating system = 13.333333 ms [75.000000 Hz].  
> \> PTB-INFO: Small deviations between reported values are normal and no reason to worry.  
> \> PTB-INFO: Using OpenGL GL\_TEXTURE\_RECTANGLE\_EXT extension for efficient high-performance texture mapping...  
> \>   
> \>   
> \> From what I understand, these are considered as 'small deviations' and shouldn't be an issue? I then ran my program again with Screen('Preference','SkipSyncTests',1) and Screen('Preference','Verbosity',10)...  
> \>   
> \> AFTER RUNNING PROGRAM WITH Screen('Preference','SkipSyncTests',1) and Screen('Preference','Verbosity',10)  
> \>   
> \> PTB-DEBUG: PsychOSOpenOnscreenWindow: Entering Win32 specific window setup...  
> \> PTB-DEBUG: Checking for DWM Aero desktop compositor support... ... DWM Aero desktop compositing window manager unsupported. Running on a Pre-Vista system.  
> \> PTB-DEBUG: PsychOSOpenOnscreenWindow: Window parameters computed, display switch to fullscreen done (if needed). Registering window class...  
> \> PTB-DEBUG: Window enumeration done. Our hostwindow is HWND=013E034A, Name: 'MATLAB 7.9.0 (R2009b)'  
> \>   
> \> PTB-DEBUG: PsychOSOpenOnscreenWindow: Window class registered - Creating GDI window...  
> \> PTB-DEBUG: WndProc(): Called!  
> \> PTB-DEBUG: WndProc(): Called!  
> \> PTB-DEBUG: WndProc(): Called!  
> \> PTB-DEBUG: WndProc(): Called!  
> \> PTB-DEBUG: Created onscreen window has position -4 x -30 and a size of 108 x 134.  
> \> PTB-DEBUG: PsychOSOpenOnscreenWindow: Window created - Pixelformat selection...  
> \> PTB-DEBUG: PsychOSOpenOnscreenWindow: ChoosePixelFormat(), SetPixelFormat() done... Creating OpenGL context...  
> \> PTB-DEBUG: PsychOSOpenOnscreenWindow: Context created - Activating and binding context...  
> \> PTB-DEBUG: PsychOSOpenOnscreenWindow: Online - glewInit()...  
> \> PTB-INFO: Using GLEW version 1.5.3 for automatic detection of OpenGL extensions...  
> \> PTB-DEBUG: PsychOSOpenOnscreenWindow: Mastercontext created, activated and bound - Enabling multisampling if needed...  
> \> PTB-DEBUG: Window and master OpenGL context creation finished.  
> \> PTB-DEBUG: Before slaveWindow context sharing: glGetString reports 1E667038 pointer...  
> \> PTB-DEBUG: After slaveWindow context sharing: glGetString reports 1E667038 pointer...  
> \> PTB-DEBUG: Final low-level window setup: ShowWindow(), SetCapture(), diagnostics...  
> \> PTB-DEBUG: OpenGL initialization of all master-/slave-/shared-/userspace contexts finished...  
> \> PTB-DEBUG: Final low-level window setup: ShowWindow(), SetCapture(), diagnostics...  
> \> PTB-DEBUG: WndProc(): Called!  
> \> PTB-DEBUG: WndProc(): Called!  
> \> PTB-DEBUG: WndProc(): Called!  
> \> PTB-DEBUG: WndProc(): Called!  
> \> PTB-DEBUG: WndProc(): Called!  
> \> PTB-DEBUG: WndProc(): Called!  
> \> PTB-DEBUG: WndProc(): Called!  
> \> PTB-DEBUG: WndProc(): Called!  
> \> PTB-DEBUG: WndProc(): Called!  
> \> PTB-DEBUG: WndProc(): Called!  
> \> PTB-DEBUG: WndProc(): Called!  
> \> PTB-DEBUG: WndProc(): Called!  
> \> PTB-DEBUG: WndProc(): Called!  
> \> PTB-DEBUG: WndProc(): Called!  
> \> PTB-DEBUG: WndProc(): Called!  
> \> PTB-DEBUG: WndProc(): Called!  
> \> PTB-DEBUG: WndProc(): Called!  
> \> PTB-DEBUG: WndProc(): Called!  
> \> PTB-DEBUG: WndProc(): WM\_SIZE!  
> \> PTB-DEBUG: WndProc(): Called!  
> \> PTB-DEBUG: No call to SetForegroundWindow() and SetFocus() on window, because trigger-conditions not satisfied.  
> \> PTB-INFO: Some ATI graphics cards may not support proper syncing to vertical retrace when  
> \> PTB-INFO: running in windowed mode (non-fullscreen). If PTB aborts with 'Synchronization failure'  
> \> PTB-INFO: you can disable the sync test via call to Screen('Preference', 'SkipSyncTests', 1); .  
> \> PTB-INFO: You won't get proper stimulus onset timestamps though, so windowed mode may be of limited use.  
> \> PTB-DEBUG: WndProc(): Called!  
> \> PTB-DEBUG: WndProc(): Called!  
> \> PTB-DEBUG: WndProc(): Called!  
> \> PTB-DEBUG: WndProc(): Called!  
> \> PTB-DEBUG: WndProc(): WM\_PAINT!  
> \> PTB-DEBUG: Final low-level window setup finished. Continuing with OS-independent setup.  
> \>   
> \>   
> \> OpenGL-Extensions are: GL\_AMDX\_name\_gen\_delete GL\_AMDX\_vertex\_shader\_tessellator GL\_AMD\_draw\_buffers\_blend GL\_AMD\_performance\_monitor GL\_AMD\_seamless\_cubemap\_per\_texture GL\_AMD\_shader\_stencil\_export GL\_AMD\_texture\_cube\_map\_array GL\_AMD\_texture\_texture4 GL\_AMD\_vertex\_shader\_tessellator GL\_ARB\_color\_buffer\_float GL\_ARB\_copy\_buffer GL\_ARB\_depth\_buffer\_float GL\_ARB\_depth\_clamp GL\_ARB\_depth\_texture GL\_ARB\_draw\_buffers GL\_ARB\_draw\_buffers\_blend GL\_ARB\_draw\_elements\_base\_vertex GL\_ARB\_draw\_instanced GL\_ARB\_fragment\_coord\_conventions GL\_ARB\_fragment\_program GL\_ARB\_fragment\_program\_shadow GL\_ARB\_fragment\_shader GL\_ARB\_framebuffer\_object GL\_ARB\_framebuffer\_sRGB GL\_ARB\_geometry\_shader4 GL\_ARB\_half\_float\_pixel GL\_ARB\_half\_float\_vertex GL\_ARB\_imaging GL\_ARB\_instanced\_arrays GL\_ARB\_map\_buffer\_range GL\_ARB\_multisample GL\_ARB\_multitexture GL\_ARB\_occlusion\_query GL\_ARB\_pixel\_buffer\_object GL\_ARB\_point\_parameters GL\_ARB\_point\_sprite GL\_ARB\_provoking\_vertex GL\_ARB\_seamless\_cube\_map GL\_ARB\_shader\_objects GL\_ARB\_shader\_texture\_lod GL\_ARB\_shading\_language\_100 GL\_ARB\_shadow GL\_ARB\_shadow\_ambient GL\_ARB\_sync GL\_ARB\_texture\_border\_clamp GL\_ARB\_texture\_buffer\_object GL\_ARB\_texture\_compression GL\_ARB\_texture\_compression\_rgtc GL\_ARB\_texture\_cube\_map GL\_ARB\_texture\_cube\_map\_array GL\_ARB\_texture\_env\_add GL\_ARB\_texture\_env\_combine GL\_ARB\_texture\_env\_crossbar GL\_ARB\_texture\_env\_dot3 GL\_ARB\_texture\_float GL\_ARB\_texture\_mirrored\_repeat GL\_ARB\_texture\_multisample GL\_ARB\_texture\_non\_power\_of\_two GL\_ARB\_texture\_query\_lod GL\_ARB\_texture\_rectangle GL\_ARB\_texture\_rg GL\_ARB\_texture\_snorm GL\_ARB\_transpose\_matrix GL\_ARB\_uniform\_buffer\_object GL\_ARB\_vertex\_array\_bgra GL\_ARB\_vertex\_array\_object GL\_ARB\_vertex\_buffer\_object GL\_ARB\_vertex\_program GL\_ARB\_vertex\_shader GL\_ARB\_window\_pos GL\_ATI\_draw\_buffers GL\_ATI\_envmap\_bumpmap GL\_ATI\_fragment\_shader GL\_ATI\_meminfo GL\_ATI\_separate\_stencil GL\_ATI\_texture\_compression\_3dc GL\_ATI\_texture\_env\_combine3 GL\_ATI\_texture\_float GL\_ATI\_texture\_mirror\_once GL\_EXT\_abgr GL\_EXT\_bgra GL\_EXT\_bindable\_uniform GL\_EXT\_blend\_color GL\_EXT\_blend\_equation\_separate GL\_EXT\_blend\_func\_separate GL\_EXT\_blend\_minmax GL\_EXT\_blend\_subtract GL\_EXT\_compiled\_vertex\_array GL\_EXT\_copy\_buffer GL\_EXT\_copy\_texture GL\_EXT\_draw\_buffers2 GL\_EXT\_draw\_instanced GL\_EXT\_draw\_range\_elements GL\_EXT\_fog\_coord GL\_EXT\_framebuffer\_blit GL\_EXT\_framebuffer\_multisample GL\_EXT\_framebuffer\_object GL\_EXT\_framebuffer\_sRGB GL\_EXT\_geometry\_shader4 GL\_EXT\_gpu\_program\_parameters GL\_EXT\_gpu\_shader4 GL\_EXT\_histogram GL\_EXT\_multi\_draw\_arrays GL\_EXT\_packed\_depth\_stencil GL\_EXT\_packed\_float GL\_EXT\_packed\_pixels GL\_EXT\_pixel\_buffer\_object GL\_EXT\_point\_parameters GL\_EXT\_provoking\_vertex GL\_EXT\_rescale\_normal GL\_EXT\_secondary\_color GL\_EXT\_separate\_specular\_color GL\_EXT\_shadow\_funcs GL\_EXT\_stencil\_wrap GL\_EXT\_subtexture GL\_EXT\_texgen\_reflection GL\_EXT\_texture3D GL\_EXT\_texture\_array GL\_EXT\_texture\_buffer\_object GL\_EXT\_texture\_buffer\_object\_rgb32 GL\_EXT\_texture\_compression\_latc GL\_EXT\_texture\_compression\_rgtc GL\_EXT\_texture\_compression\_s3tc GL\_EXT\_texture\_cube\_map GL\_EXT\_texture\_edge\_clamp GL\_EXT\_texture\_env\_add GL\_EXT\_texture\_env\_combine GL\_EXT\_texture\_env\_dot3 GL\_EXT\_texture\_filter\_anisotropic GL\_EXT\_texture\_integer GL\_EXT\_texture\_lod GL\_EXT\_texture\_lod\_bias GL\_EXT\_texture\_mirror\_clamp GL\_EXT\_texture\_object GL\_EXT\_texture\_rectangle GL\_EXT\_texture\_sRGB GL\_EXT\_texture\_shared\_exponent GL\_EXT\_texture\_snorm GL\_EXT\_texture\_swizzle GL\_EXT\_timer\_query GL\_EXT\_transform\_feedback GL\_EXT\_vertex\_array GL\_EXT\_vertex\_array\_bgra GL\_IBM\_texture\_mirrored\_repeat GL\_KTX\_buffer\_region GL\_NV\_blend\_square GL\_NV\_conditional\_render GL\_NV\_copy\_depth\_to\_color GL\_NV\_explicit\_multisample GL\_NV\_primitive\_restart GL\_NV\_texgen\_reflection GL\_SGIS\_generate\_mipmap GL\_SGIS\_texture\_edge\_clamp GL\_SGIS\_texture\_lod GL\_SUN\_multi\_draw\_arrays GL\_WIN\_swap\_hint WGL\_EXT\_swap\_control  
> \>   
> \> PTB-DEBUG: Interrogating Low-level renderer capabilities for onscreen window with handle 10:  
> \> Indicator variables: FBO's 1, ATI\_texture\_float 1, ARB\_texture\_float 1, Vendor ATI Technologies Inc., Renderer ATI Radeon HD 4550.  
> \> Indicator variables: maxcolorattachments = 8, maxrectangletexturesize = 8192, maxnativealuinstructions = 2147483647.  
> \> Basic framebuffer objects with rectangle texture rendertargets supported --\> RGBA8 rendertargets with blending.  
> \> Framebuffer objects support fast blitting between each other.  
> \> Framebuffer objects support anti-aliasing via multisampling.  
> \> Hardware supports floating point textures of 16bpc and 32bpc float format.  
> \> Assuming ATI R300 core or later: Hardware supports basic floating point framebuffers of 16bpc and 32bpc float format.  
> \> Assuming ATI R500 or later (maxtexsize=8192): Hardware supports floating point blending on 16bpc float format.  
> \> Hardware supports full 32 bit floating point precision shading.  
> \> Assuming ATI R600 or later (Matching namestring): Hardware supports floating point blending and filtering on 16bpc and 32bpc float formats.  
> \> No compiled in support for OpenML OML\_sync\_control extension. Using standard implementation.  
> \> PTB-DEBUG: Interrogation done.  
> \>   
> \> PTB-INFO: Threshold Settings for successfull video refresh calibration are: maxStdDev = 1.000000 msecs, maxDeviation = 10.000000 %, minSamples = 50, maxDuration = 5.000000 secs.  
> \>   
> \> WARNING: Querying rasterbeam-position doesn't work on your setup! (Returns a constant value 96)  
> \>   
> \> WARNING: Couldn't determine end-line of vertical blanking interval for your display! Trouble with beamposition queries?!?  
> \>   
> \> WARNING: Detected end-line is -1, which is either lower or more than 25% higher than vbl startline 768 --\> Out of sane range!  
> \>   
> \>   
> \> PTB-DEBUG: Output of all acquired samples of calibration run follows:  
> \> PTB-DEBUG: Sample 0: 0.000000  
> \> PTB-DEBUG: Sample 1: 0.013323  
> \> PTB-DEBUG: Sample 2: 0.013327  
> \> PTB-DEBUG: Sample 3: 0.013342  
> \> PTB-DEBUG: Sample 4: 0.013314  
> \> PTB-DEBUG: Sample 5: 0.013328  
> \> PTB-DEBUG: Sample 6: 0.013328  
> \> PTB-DEBUG: Sample 7: 0.013329  
> \> PTB-DEBUG: Sample 8: 0.013327  
> \> PTB-DEBUG: Sample 9: 0.013327  
> \> PTB-DEBUG: Sample 10: 0.013329  
> \> PTB-DEBUG: Sample 11: 0.013336  
> \> PTB-DEBUG: Sample 12: 0.013319  
> \> PTB-DEBUG: Sample 13: 0.013341  
> \> PTB-DEBUG: Sample 14: 0.013315  
> \> PTB-DEBUG: Sample 15: 0.013328  
> \> PTB-DEBUG: Sample 16: 0.013328  
> \> PTB-DEBUG: Sample 17: 0.013327  
> \> PTB-DEBUG: Sample 18: 0.013337  
> \> PTB-DEBUG: Sample 19: 0.013318  
> \> PTB-DEBUG: Sample 20: 0.013327  
> \> PTB-DEBUG: Sample 21: 0.013329  
> \> PTB-DEBUG: Sample 22: 0.013328  
> \> PTB-DEBUG: Sample 23: 0.013329  
> \> PTB-DEBUG: Sample 24: 0.013326  
> \> PTB-DEBUG: Sample 25: 0.013328  
> \> PTB-DEBUG: Sample 26: 0.013328  
> \> PTB-DEBUG: Sample 27: 0.013327  
> \> PTB-DEBUG: Sample 28: 0.013328  
> \> PTB-DEBUG: Sample 29: 0.013328  
> \> PTB-DEBUG: Sample 30: 0.013327  
> \> PTB-DEBUG: Sample 31: 0.013329  
> \> PTB-DEBUG: Sample 32: 0.013327  
> \> PTB-DEBUG: Sample 33: 0.013328  
> \> PTB-DEBUG: Sample 34: 0.013327  
> \> PTB-DEBUG: Sample 35: 0.013329  
> \> PTB-DEBUG: Sample 36: 0.013327  
> \> PTB-DEBUG: Sample 37: 0.013328  
> \> PTB-DEBUG: Sample 38: 0.013328  
> \> PTB-DEBUG: Sample 39: 0.013328  
> \> PTB-DEBUG: Sample 40: 0.013329  
> \> PTB-DEBUG: Sample 41: 0.013327  
> \> PTB-DEBUG: Sample 42: 0.013328  
> \> PTB-DEBUG: Sample 43: 0.013327  
> \> PTB-DEBUG: Sample 44: 0.013329  
> \> PTB-DEBUG: Sample 45: 0.013328  
> \> PTB-DEBUG: Sample 46: 0.013327  
> \> PTB-DEBUG: Sample 47: 0.013329  
> \> PTB-DEBUG: Sample 48: 0.013327  
> \> PTB-DEBUG: Sample 49: 0.013328  
> \> PTB-DEBUG: Sample 50: 0.013329  
> \> PTB-DEBUG: End of calibration data for this run...  
> \>   
> \>   
> \>   
> \> PTB-INFO: OpenGL-Renderer is ATI Technologies Inc. :: ATI Radeon HD 4550 :: 3.2.9704 Compatibility Profile Context  
> \> PTB-INFO: VBL startline = 768 , VBL Endline = -1  
> \> PTB-INFO: Beamposition queries unsupported or defective on this system. Using basic timestamping as fallback: Timestamps returned by Screen('Flip') will be less robust and accurate.  
> \> PTB-INFO: Measured monitor refresh interval from VBLsync = 13.327716 ms [75.031612 Hz]. (50 valid samples taken, stddev=0.004758 ms.)  
> \> PTB-INFO: Reported monitor refresh interval from operating system = 13.333333 ms [75.000000 Hz].  
> \> PTB-INFO: Small deviations between reported values are normal and no reason to worry.  
> \> PTB-INFO: Using OpenGL GL\_TEXTURE\_RECTANGLE\_EXT extension for efficient high-performance texture mapping...  
> \>   
> \>   
> \> ----- ! PTB - WARNING: SYNCHRONIZATION TROUBLE ! ----  
> \>   
> \> One or more internal checks (see Warnings above) indicate that  
> \> queries of rasterbeam position are not properly working for your setup.  
> \>   
> \> Psychtoolbox will work around this by using a different timing algorithm,   
> \> but it will cause Screen('Flip') to report less accurate/robust timestamps  
> \> for stimulus timing.  
> \> Read 'help BeampositionQueries' for more info and troubleshooting tips.  
> \>   
> \>   
> \> PTB-DEBUG: Allocated unicode string: 69.000000 110.000000 100.000000 32.000000 111.000000 102.000000 32.000000 66.000000 108.000000 111.000000 99.000000 107.000000 32.000000 48.000000 32.000000 111.000000 102.000000 32.000000 49.000000 32.000000 98.000000 108.000000 111.000000 99.000000 107.000000 115.000000 46.000000   
> \> PTB-DEBUG: In DrawTextGDI: Rebuilding font due to window switch or rebuild request: needit = 1 , oldwin = 00000000 vs. newwin = 1A1DD060   
> \> PTB-DEBUG: Allocated unicode string: 69.000000 110.000000 100.000000 32.000000 111.000000 102.000000 32.000000 66.000000 108.000000 111.000000 99.000000 107.000000 32.000000 48.000000 32.000000 111.000000 102.000000 32.000000 49.000000 32.000000 98.000000 108.000000 111.000000 99.000000 107.000000 115.000000 46.000000   
> \> PTB-DEBUG: Allocated unicode string: 40.000000 112.000000 114.000000 101.000000 115.000000 115.000000 32.000000 69.000000 78.000000 84.000000 69.000000 82.000000 32.000000 116.000000 111.000000 32.000000 99.000000 111.000000 110.000000 116.000000 105.000000 110.000000 117.000000 101.000000 41.000000   
> \> PTB-DEBUG: Allocated unicode string: 40.000000 112.000000 114.000000 101.000000 115.000000 115.000000 32.000000 69.000000 78.000000 84.000000 69.000000 82.000000 32.000000 116.000000 111.000000 32.000000 99.000000 111.000000 110.000000 116.000000 105.000000 110.000000 117.000000 101.000000 41.000000   
> \>   
> \>   
> \>   
> \> Please let me know if you have any suggestions.  
> \>   
> \> Thank you for your help!  
> \>