[FieldTrip] Biosemi eventtype problem

[Vitória Piai]

Hi all,

I managed to gather more information regarding this issue and I thought 
I'd post the resolution here just in case someone bumps into the same 
problem in the future.
The issue is indeed caused by not having set E-prime to work correctly 
with Biosemi. I use Presentation, and that goes flawlessly with Biosemi. 
But these data were acquired by someone else in E-prime. The reply from 
Biosemi's CEO below may be helpful in case you use E-prime.
Thanks for all the thoughts, Vitoria

 >>>>>>>>>>>>>>>>>>>>>>>>>>
First rule of triggering from E-Prime to ActiveTwo is that you must 
reset the port to zero after each non-zero code. Hold values high on the 
port for 10 msec or so and return to zero after and you will not see any 
of the problems you describe. E-Prime will not do this automatically 
(though it would seem logical for the software to do it) -- you must 
write a zero to the port after each code.

Random codes occur when you do not follow the above rule if you have 
told ActiView to decimate EEG and triggersamples by some fraction other 
than 1 (e.g. 1/4th).  By doing this you leave it to ActiView what value 
to assign to the trigger channel at samples bordering the
intersection between two non-zero values.  ActiView performs a logical 
AND between trigger bits in the high state on samples to be combined.  
So, if you had a 1 followed by a 2 with no zero in between and you 
decimate by 1/4 you will end up with 1 - 3 - 2. 3 is the logical AND of 
1 and 2 in binary.

ActiveTwo has a 16 bit trigger port.  Your triggers are all on bits 0-7, 
probably because you are using a standard parallel port with only 8 
bits.  The value on the upper half of the Trig1-8 field is the value at 
the rising edge of the trigger and the value on the lower half of the 
Trig1-8 field is the value at the falling edge. This should be zero if 
you are resetting the port correctly.
 >>>>>>>>>>>>>>>>>>>>




On 1/23/2015 11:54 AM, Vitoria Piai wrote:
> Thanks, Ricarda and JM!
> JM, I know for sure it's not a FT problem :)
>
> I checked the E-prime scripts used and all the markers were sent 
> (according to the E-prime code). What I'm trying to figure out is what 
> kind of conversion was applied between E-prime and Biosemi so I can 
> work backwards and still detect my events. It doesn't seem to be a 
> linear transformation between what E-prime sent and Biosemi coded...
> Anyways, thanks a lot for your thoughts!
> Vitoria
>
> On 1/23/2015 9:09 AM, Schoffelen, J.M. (Jan Mathijs) wrote:
>> Hi V.,
>>
>>> With this new Biosemi dataset (programmed by someone else in 
>>> E-prime, it's not my data):
>> Have you consulted with this ‘someone else’? From the looks of it, it 
>> doesn’t seem a FieldTrip issue per se.
>>
>>
>> Best,
>> JM
>>
>>
>>
>>
>>> cfg=[];
>>> cfg.dataset = dataset;
>>> cfg.trialdef.eventtype = 'STATUS';
>>> cfg.trialdef.eventvalue = '?';
>>> ft_definetrial returns markers that were not sent, and doesn't 
>>> return markers that were sent. (The same occurs if I read the data 
>>> in EEGlab by the way).
>>> It doesn't look like there's a linear transformation between what 
>>> was sent and what FT finds. For example, markers sent were 1:21; FT 
>>> returns [3:23 29:31], but I'll definitely look into the suggestion 
>>> that maybe 1:21 was sent but for some reason recorded as 3:23 and 
>>> the 29:31 are coming from somewhere else.
>>>
>>> Thanks a lot!
>>> Vitoria
>>>
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>>> fieldtrip mailing list
>>> fieldtrip at donders.ru.nl
>>> http://mailman.science.ru.nl/mailman/listinfo/fieldtrip
>>
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>