eep and brainvision definetrial

Robert Oostenveld r.oostenveld at FCDONDERS.RU.NL
Fri May 9 09:19:34 CEST 2008

Hi Susana

On 6 May 2008, at 19:33, Susana Silva wrote:
> In the mean time, I finally succeed in reading all brainvision
> files (yes, there should have been a problem with bv format,
> because I had to change the name of a field - to nChans- in the m
> file).

Can you upload one of your problematic files to
incoming, or if it is less <1MB send it as email attachement to my
personal email account?

> However, after rereading the documentation, I still have a local
> (and very basic) question on the cfg for definetrial: what is a
> "dataset" when we are using brainvision files? Can it be replaced
> by the header file, the data file and the event/marker file? If so,
> what should bi included in the cfg (cfg.datafile, cfg.headerfile,
> cfg.event?) I tried that but it did not work out.

You can specify cfg.datafile and cfg.headerfile seperately, or in
your case you can specify cfg.dataset=yourfile.vhdr. Also for the
events (which are read using read_fcdc_event) you can specify the
header file, because that file contains the name of the accompanying
event file.

> Concerning the arrangement of data so as to match definetrial
> output, I also did this, based upon the documentation. However,
> this solution does not give a prestimulus time, to be seen in each
> trial as referenced to a negative time (eg: time -0.2 up to time
> 0) . I believe this is necessary to view the baseline later.

This is from the definetrial documentation

% The trial definition "trl" is an Nx3 matrix, N is the number of
% The first column contains the sample-indices of the begin of each
% relative to the begin of the raw data, the second column contains the
% sample-indices of the end of each trial, and the third column contains
% the offset of the trigger with respect to the trial. An offset of 0
% means that the first sample of the trial corresponds to the trigger. A
% positive offset indicates that the first sample is later than the
% a negative offset indicates that the trial begins before the trigger.

The trl matrix is used to read in the interesting segments of the
data with the preprocessing function (using the first and second
column of trl) and to attach a timeaxis to each trial (using the
third column).

best regards,

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