importing CTF data

[Robert Oostenveld]

Hi Thomas

On 10 May 2005, at 11:57, Thomas Thesen wrote:
> When trying to use definetrial.m/preprocessing.m to load in the dataset
>
> cfg = [];
> cfg.dataset = 'sub12_SAM_a_C1_A1.ds';
> cfg.trialdef.eventtype = '?'
> cfg.trialdef.eventtype = 'C1_A1'
> cfg.trialdef.prestim   = 0;    % trial starts at time t=0 at the marker
> cfg.trialdef.poststim  = 0.5;  % trial ends at t=0.5 sec
>
> and adding the line:
>
> cfg.trialdef.excludeConditions = {'BAD'};
>
> and running:
> cfg = definetrial(cfg);
> raw = preprocessing(cfg);
>
> the trials marked 'BAD' are not excluded. However, when doing the same
> procedure on the FieldTrip workshop data set for example, where the
> trials
> are defined through a trigger, the marked trials are removed.

The fieldtrip tutorial that you refer to uses an old CTF-format
specific trialfunction that is not in the release version. This type of
"combinatorial" definition of events (include the trials with marker
C1_A1 and exclude the trials with classification BAD) is not supported
any more. Furthermore, the underlying code of that tutorial section
only worked for a trial-based file format without markers...

As you can see, it is quite difficult to combine all the different
types of information (trials, triggers, classifications, markers) and
especially sinc e every file format has it's own way of dealing with
them. Therefore I decided not to support all of them. There is a common
way of handling them all, and that is through using the read_fcdc_event
function, which results in a well-defined collection of all information
which you can to cut up your data into pieces of interest. Using the
event structure (i.e. the output from read_fcdc_event), you can create
your own trialfunction.

Please read the documentaion on read_fcdc_event, try it out on your
data, and then read the documentation in definetrial about the custom
trialfunction. A short example of a custom trialfunction was given in
the clusterstatistics tutorial.


> Do you have any suggestions on how to exclude 'BAD' trials before they
> are
> loaded? Or is my only option to remove these 'BAD' trials after they
> have
> been loaded into FieldTrip format? In that case would you advise to
> remove
> the appropriate columns (trials) by hand or rather use the artifact
> rejection option?

No, you should not remove them afterwards, but you should use the
custom trialfunction to prevent them from being read in the beginning.

Robert