[Eeglablist] File editing and epoching

[Stephen Politzer-Ahles]

Hello Elia,

It's not entirely clear to me what you are asking for help with, perhaps
I've misunderstood. It sounds like your data will consist of epochs where
the time-locking event for each epoch (i.e., the '0 ms' of the epoch) is
S1, and the epoch also includes an S2 event later. (I'm not sure why you
need to remove the boundary markers.)

To get epochs like that, you just choose S1 as the stimulus event when you
epoch, there's no need to say anything about S2. But you will need to
choose a large enough epoch that it will always fit S2; I'm not sure how
much time there was between your S1 and S2, and whether that time was fixed
or variable. If the amount of time is variable, you should just make sure
your epoch is big enough to capture the S2 in the trial where it had the
longest latency. (Or, I may be mistaken about this, but I think ERPLAB
allows for epochs of varying lengths?).

To baseline-correct both events to the pre-stimulus interval before S1,
just do a baseline correction using the default pre-stimulus interval after
you've epoched the data. If you baseline-correct using the portion of the
epoch before S1, that baseline is subtracted from the whole epoch, and thus
S2 also gets baseline-corrected relative to that.

Best,
Steve

On Mon, Oct 1, 2012 at 2:59 PM, Elia Valentini
<elia.valentini at uniroma1.it>wrote:

> Dear EEGlabers,
>
> I'm looking for the expert list help on some difficulties I'm having on
> adding and deleting markers to my data files, and baseline correcting
> epoched data.
>
> As a premise our design implies:
> a) two different set of files where a different cognitive manipulation is
> administered (factor 'mind-set')
> b) two different type of blocks, pre-post manipulation (factor
> 'manipulation')
>
> within each block we have two different sensory modalities delivered in
> pairs - S1,S2 - (we are interested in studying ERPs).
>
> I did the following:
> 1) Marge all the single subject datasets (4 neuroscan .cnt files per
> session).
> 2) Downsample to 250 Hz (originally 1000 Hz).
> 2) Re-reference to the average (excluding mastoid and EOG electrodes).
> 3) Bandpass filter 0.5-30 Hz.
> 4) Manually reject gross artifacts from the continuous large datafile
> 5) Remove baseline and run ICA
> 6) Reject components by maps
>
> I'm in the process of
> 7) Removing "boundary markers" produced by the manual rejection procedure
> (deleted one by one from the "Event values" interface. I guess this could
> be automated but I'm doing it manually).
> 8) Add markers (or rather labels as this are not phasic EEG events) for
> the levels of the variable 'mind-set' and 'manipulation' (I guess this
> could be automated but I'm doing it manually).
> 9) Then I need to generate epoched files from this large file according to
> the two modalities and locked to the first stimulus of each couple.
> However, while the first stimulus is baseline corrected to its relative
> pre-stimulus time, the second stimulus (S2) should be baseline corrected to
> the S1 prestimulus time (I did not come out yet with a scripting of it -  I
> guess may not be possible from the GUI).
>
> Perhaps I have missed some important past discussion in the list, if this
> is the case please forgive me.
> Thanks very much in advance for your time.
>
> Elia
>
>
>
>
> _______________________________________________
> Eeglablist page: http://sccn.ucsd.edu/eeglab/eeglabmail.html
> To unsubscribe, send an empty email to
> eeglablist-unsubscribe at sccn.ucsd.edu
> For digest mode, send an email with the subject "set digest mime" to
> eeglablist-request at sccn.ucsd.edu
>



-- 
Stephen Politzer-Ahles
University of Kansas
Linguistics Department
http://people.ku.edu/~sjpa/
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://sccn.ucsd.edu/pipermail/eeglablist/attachments/20121001/89c2d1bc/attachment.html>