too many trials/overlapping trials

[Sameer Walawalkar]

Thanks for your email. I tried to look into trialfun_general.m file, but
the one I have is only 286 lines long. I looked into preprocessing.m, just
in case you meant it rather than trialfun_general.m and it is 432 lines
long.


sameer

On Fri, 9 Feb 2007, Christian Hesse wrote:

> Hi Sameer,
>
> thanks for the additional info and data from the STI101 channel you sent me.
>
> I think that the double counting of your triggers must be caused by the way
> that the function "trialfun_general.m" computes the (valid) flanks for your
> data format (e.g., line 467, and see all the comments in lines nearby). Using
> the content of your STI101 channel (referred to as x below) I was unable to
> reproduce the double counting using a slightly simpler approach:
>
> d = [0, diff(x)];
> ii = find((d~=0) & (x==7));
> % length(ii) gives 30
> ii = find((d~=0) & (x==11));
> % length(ii) gives 30
>
> For the time being, the easiest solution (in my view, since you have the
> STI101 channel) is to construct the "trl" matrix from the content of the ii
> arrays above for each trigger, and copy this into the cfg structure used to
> call preprocessing.m:
> cfg.trl = trl;
>
> The more elegant solution in a Fieldtrip sense is to write your own trialfun,
> which would consist of wrapper code around the essential operations outlined
> above. I suggest you have a closer look at the code and documentation in
> preprocessing.m and definetrial.m if you decide to pursue this route.
>
> Hope this helps,
> 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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