[Eeglablist] File editing and epoching

[Elia Valentini]

Dear Stephen,

On 2 October 2012 04:27, Stephen Politzer-Ahles <politzerahless at gmail.com>wrote:

> 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.)
>
> Yes, you are right.


> 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?).
>
> The tima lag is fixed and thus does not require particular effort in
epoching.


> 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.
>
> Ok, then this what I've been doing.

Thanks for replying!
Best,

e


> 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
>>
>>
>>
>>
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>
>
>
> --
> Stephen Politzer-Ahles
> University of Kansas
> Linguistics Department
> http://people.ku.edu/~sjpa/
>



-- 
Elia Valentini PhD

Social and Cognitive Neuroscience Laboratory - SCNLab
Sapienza University of Rome
Department of  Psychology
Via dei Marsi 78 - 00185 - Roma
Phone: (+39) 06-49917635
Fax: (+39) 06-49917635
e-mail: elia.valentini at uniroma1.it;
Web:  http://w3.uniroma1.it/scnl/index.php/elia-valentini/
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