ssvep-scenario display problem

[jerry_lee89]

Hi everybody,

I'm trying to use the SSVEP scenario for a project at school. I've a problem with the display of the SSVEP stimulator, the figures don't seem flickering at constant frequencies. Mainly the figure with lower frequency. It will probably be a problem for on-line test.
Do you know this problem?

Here is my configuration :

- OpenVibe-0.10.0 build by my self with Visual Studio 2008 (i have the same problem with the 0.11.0 and 0.12.0 version)
- Windows Seven 64-bit
- Graphic card : Mobile Intel(R) 4 Series Express Chipset Family (I choose OpenGL option in Ogre) (when I choose 3D accelerator, the flickering square is not display, I only see the little yellow arrow)

Thank for your help.

jerry_lee89

[jlegeny]

Hello jerry_lee89,

the SSVEP stimulator is set up to work on screens with 60Hz refresh rate, this is a very important hardware limitation. Usually all standard computer flat panels support this frequency, however sometimes not on all of the resolutions.

You can set your refresh rate by right clicking on the desktop, choosing "screen resolution", then "advanced settings" and finally the "monitor" tab.

If your screen can not display image at 60Hz, you can modify the stimulation frequencies in the setting scenarios. Sometimes switching off Aero helps as well.

Hope this will help
Jozef

[jerry_lee89]

Hello,

Thanks for your answer jozef.

Yes, I have already check this setting and my screen's refresh rate is 60 Hz (like the property in the ssvep-configuration).

But it is not the origin of my problem...

Good night.

jerry_lee89

[benry]

Hi,
I have the same problem... tried to run the scenario on two different machines with different hardware and operating system and I am experiencing the same problem on both.

Looking at the PSD of the recorded EEG, a clear peak in the spectrum is found only in the 15Hz frequency... all the configurations of the scenario were left as default ones and the screen refresh was 60Hz. In the Ogre window I selected OpenGL too and the 60Hz refresh rate.

p.s.
I do not know Ogre at all, but in OpenGL I am quite sure that the OpenGL buffers swapping could be synched with the screen refresh, how is this accomplished in this implementation? I guess that it is not working for me, for some reasons...

[jlegeny]

Hello,

in Ogre there are several ways to set the VSync flag to synchronize the buffer swapping with the screen. (Setting in Plugins.cfg, setting when creating a new window, etc.) This setting however only works reliably on Windows when the application is run in fullscreen mode. On Linux, it is important to disable the compositing extensions of the window manager which is used, or again use the application in fullscreen.

In the current release there is no flag to set the full screen on however. In the current SVN version you can use the

Code: Select all

SSVEP_Ogre_FullScreen = true

configuration token to make the ssvep application fullscreen. Put this into your openviberc or openvibe.conf file, note that on Linux the place has changed in the SVN (to ~/.config/openvibe)

Cheers
Jozef