too many trials/overlapping trials

[Robert Oostenveld]

Dear Sameer,

On 6 Feb 2007, at 14:32, Sameer Walawalkar wrote:
> I use the first three lines to set up cfg, and then issue the command
> definetrial(cfg);
> Note: the data is from Elekta Neuromag 306 channel MEG.
>
> It returns some thousand odd events and finds STI 101 and STI 301
> as Stim channels.
>
> So next I do the following:
>
>>> cfg =  []    ;
>>> cfg.dataset = 'JD_012507_Beeps_One.fif' ;
>>> cfg.trialdef.eventtype  = 'STI101'  ;
>>> cfg.trialdef.eventvalue = 7    ;
>>> cfg.trialdef.prestim = 1.500;
>>> cfg.trialdef.poststim = 2.501;
>>> cfg =  definetrial(cfg);
> evaluating trialfunction 'trialfun_general'
> found 61361 events
> created 60 trials

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.

> 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?

Robert