Reading in Neuroscan files

[Robert Oostenveld]

Hi Monika,

On 30 Jun 2008, at 13:21, Monika Mellem wrote:
> I have noticed some things when reading in both Neuroscan .eeg
> and .cnt files.
>
> 1) When reading a Neuroscan .eeg file, read_event.m seems to put
> either
> "accept" or "reject" into the field event.value.  According to how
> event.field is used later on, it should be putting the trigger
> values in
> this field which are in tmp.sweep.type.  I modified the code as
> shown below.

Thanks for the suggestion. I have changed it into the following

    for i=1:hdr.nTrials
       % the *.eeg file has a fixed trigger value for each trial
       % furthermore each trial has the label 'accept' or 'reject'
       tmp = read_ns_eeg(filename, i);
       % create an event with the trigger value
       event(end+1).type     = 'trial';
       event(end  ).sample   = (i-1)*hdr.nSamples + 1;
       event(end  ).value    = tmp.sweep.type;  % trigger value
       event(end  ).offset   = -hdr.nSamplesPre;
       event(end  ).duration =  hdr.nSamples;
       % create an event with the boolean accept/reject code
       event(end+1).type     = 'accept';
       event(end  ).sample   = (i-1)*hdr.nSamples + 1;
       event(end  ).value    = tmp.sweep.accept;  % boolean value
indicating accept/reject
       event(end  ).offset   = -hdr.nSamplesPre;
       event(end  ).duration =  hdr.nSamples;
     end

This encodes both the event value (trigger code) and the accept/
reject state, albeit in different events. The two events can be
combined in a trialfun of course.

> 2) When reading in a Neuroscan .cnt file, read_header.m puts some bad
> channel labels into hdr.label using what it gets from the
> read_ns_cnt.m file
> (around line 564).  Whatever is in orig.chan.names starts with the
> correct
> channels (about 10 of them) and then has blank values or odd
> characters for
> the rest of the channel labels.

This seems like a bug w.r.t. the reading of the header in general. I
was not able to reproduce the problem. Could you send me the .cnt
file that has the problem, e.g. using yousendit.com or on
ftp.fcdonders.nl?

best regards,
Robert



> As a quick fix for just the channel labels,
> I just took the channel labels that read_ns_hdr.m finds and
> substituted them
> into hdr.label.  See below.  This doesn't fix the underlying
> problem in
> read_ns_cnt.m though which seems to be with the variables chandat and
> r.chan.names (lines 140-141).
>
> orig = read_ns_hdr(filename);
> hdr.label = orig.label;
> hdr.orig.chan.names = orig.label;

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