too many trials/overlapping trials

[Christian Hesse]

Hi Sameer,

as far as I can follow the discussion there appear to be quite a few
triggers in your data whose values are not 7 or 11 ... I assume you
know where they come from?

What might be helpful is if you could provide a little more detail
about your data collection and especially the triggers on each trial.

Thanks,
Christian


On 7 Feb 2007, at 17:30, Sameer Walawalkar wrote:

> Thanks for the reply Robert. here's some more info.
>
>> Dear Sameer,
>>
>> Maybe you could try
>> cfg =  []    ;
>> cfg.dataset = 'JD_012507_Beeps_One.fif' ;
>> cfg.trialdef.eventtype  = '?';
>> dum =  definetrial(cfg);
>> and look what is printed on screen.
>
> evaluating trialfunction 'trialfun_general'
> the following events were found in the datafile
> event type: 'STI101' with event values: 5      6      7      8
> 9 11     15  16388  16391  16392  16396
> event type: 'STI301' with event values: 5.0003      5.0018 ...(many
> more...)
> event type: 'trial' with event values:
> no trials have been defined yet, see DEFINETRIAL for further help
> found 61361 events
> created 0 trials
>
> (I address another point at the bottom of the email. I have left
> the following paragraphs in for refrence)
>
>>> My first problem is, I should have 30 trials for this event. The
>>> file
>>> contains a total of 60 trials, but the other 30 are for eventtype
>>> = 11
>>> So it is clearly doing something wrong.
>>
>>> Next, I decided to see what is in cfg.trl and I get the Nx3
>>> matrix that I find the following problems with it
>>> 1> each trial should be 4000 milli seconds long. That happens here,
>>> however, there seem to be overlap between trials which does not make
>>> sense. This is what leads to the double counting. Thus I get 4000
>>> msec long trials bunched in group of two where the second trial
>>> starts about 1000 to 1300 msecs after the beginning of the first
>>> trial.
>>
>> Please have a look in cfg.event.
>>
>>> 2> If the first trial is at 8502, all subsequent trials should be in
>>> increments of integral multiples of 4000 ( plus or minus a few).
>>> But that does not seem to happen (and I am looking at on the
>>> leading trial of the pair and discounting the trials that follow
>>> 1000 msecs later.)
>>
>> That means that there are events detected that are not supposed to
>> be there according to your knowledge of the dataset. Could it be
>> that both the positive and the negative flank of the trigger are
>> detected?
>
>
> I have looked into this as it was the first thing I suspected. What
> has been confusing me is that it seems to be counting the rising
> flank of the correct trigger and the falling flank of the earlier
> trigger, even though the event type for the earlier trigger is
> different. I am looking for
> cfg.trialdef.eventtype = 'STI101' and
> cfg.trialdef.eventvalue = 7 or 11.
> The earlier falling trigger  is 5,6 or 8.9 and so should not be
> considered at all. I never use STI301
>
> sameer
>

----------------------------------------------------------------------
Christian Hesse, PhD, MIEEE

F.C. Donders Centre for Cognitive Neuroimaging
P.O. Box 9101
NL-6500 HB Nijmegen
The Netherlands

Tel.: +31 (0)24 36 68293
Fax: +31 (0)24 36 10989

Email: c.hesse at fcdonders.ru.nl
Web: www.fcdonders.ru.nl
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