Hi Olaf, 

as you already guessed, our lab encountered the same trigger issue as yours. During discussions with the Elekta-Neuromag team, it seems that this is a hardware limitation that we have to live with. However, we could team up and send them a request to see whether this could be solved within the acquisition software? 

Best wishes,
Virginie


Virginie van Wassenhove
CEA/SAC/DSV/I2BM/NeuroSpin Center
Unité de Neuroimagerie Cognitive (U562)
Bât 145 - Point Courrier 156 
F-91191 GIF sur YVETTE
FRANCE 
Ph:  33 (0)16.908.9498
Fax: 33 (0)16.908.7973

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http://sites.google.com/site/virginievanwassenhove/



-------- Message d'origine--------
De: Announcement for the Neuro MEG list de la part de Olaf Hauk
Date: ven. 19/06/2009 12:14
À: [log in to unmask]
Objet : +BESA Re: problems with trigger sampling
 
Hi,

thanks for all your comments and suggestions. Of course, once we had 
noticed the problem, we developed the appropriate software solutions. We 
were just wondering whether this problem is specific to our 
installation, whether other labs are aware of it, and if there's a way 
of avoiding it.

For those using BESA for analysis: BESA did not take this problem into 
account before we notified them, i.e. it may read incorrect trigger 
values based on the first trigger samples. They've updated their 
"Neuromag data reader", but as far as I can see it's not on their 
web-page for updates yet. If you need it, either contact them directly, 
or I can send it to you as well.

Regards,

Olaf




Matti Hamalainen wrote:
>
> On Jun 17, 2009, at 9:29 AM, VAN WASSENHOVE Virginie wrote:
>
>> On behalf of Ghislain de Frescheville:
>>
>>> Hello,
>>> I had this problem of multiple steps in the increase/decrease of 
>>> ttl, which >are visible with graph...
>>>
>>> For those who use mne's matlab toolbox, here is my personal solution 
>>> : in >matlab, I write the events of the files with 
>>> 'mne_make_combined_event_file' >into a text file, I remove/modify by 
>>> hand the 'wrong' events (thoses which >don't begin from 0), and I 
>>> use this txt file as event file.
>>> For example, in the case below, I change the text :
>>> 'time1   0 -> 240   
>>> time2   240 -> 255'
>>>   into :
>>> 'time1  0 -> 255'   (time1 and time2 are currently just 1ms different)
>>>
>>> !!! : please notice that the last version of 
>>> 'mne_make_combined_event_file' >will only detect '0->240' and you 
>>> will never be able to see that it's a >wrong event. You have also to 
>>> modify this matlab program on your own, so it >detects all the 
>>> changes in the trigger line, and not only those which come >from 0.
>>>
>>> Regards,
>>>
>>> Ghislain de Frescheville
>
> You can also save all events from mne_browse_raw and see what is 
> happening (File/Save events (text)...)
>
> The same can be done (at least) in the newest version of mne_process_raw:
>
> mne_process_raw --raw <raw data file> --allevents --eventsout <name>.eve
>
> I hope this helps.
>
> - Matti
>
>
>
>
> ---------
>
> Matti Hamalainen, Ph.D.
> Athinoula A. Martinos Center for Biomedical Imaging
> Massachusetts General Hospital
>
> [log in to unmask] <mailto:[log in to unmask]>
>
>
>
>
>
>