[Eeglablist] Epoching eeg data

[Mikołaj Magnuski]

Dear Karlo,

there is a case when dividing your whole 15 min. into smaller epochs (say 1
or 2 seconds long)
is quite convenient with respect to ICA:
--> cleaning data before ICA is easy if you just have to click bad epochs
instead of marking
bad periods in continuous data - although this is just my personal feeling.
Nevertheless, you can also use automatic artifact rejection methods
available in EEGlab this way. These methods require epoched data.
(it is also easy to reconstruct your rejections later if you do them
on epochs - you can just save the indices of windows that you removed [by
coping relevant field in EEG structure after marking bad epochs,
but before rejecting them]).
--> Then, after your first IC decomposition, if you are not satisfied with
its results and observe that
some parts of your data may be responsible for poor results - you can remove
epochs containing these data easily and perform ICA again.

So, just as Makoto wrote, ICA does not care whether data are epoched but
you may -
because in some cases it is convenient in preprocessing or 'postprocessing'
(correcting
ICA decomposition).
If you need any extra help with this - let me know (I have some scripts and
functions to do this).

Mikolaj


W dniu środa, 5 czerwca 2013 użytkownik Makoto Miyakoshi napisał:

> Dear Karlo,
>
> If you want to epoch your data into 3-min blocks, for example, put event
> markers every 3 minutes then epoch the data.
>
> ICA does not care temporal continuity of the data since it shuffles them
> up differently for every iteration as a preprocess. That means, if the
> total number of datapoints are the same before and after the epoching, the
> ICA results should be the same.
>
> Makoto
>
>
> 2013/6/3 karlo gonzales <thats_karlo at yahoo.com <javascript:_e({}, 'cvml',
> 'thats_karlo at yahoo.com');>>
>
>> Dear EEGlab experts,
>>
>> I need you help regarding an eeg data files which was recorded during
>> eye closed state (15 min long).  Thus, there is no event to epoch the data.
>> 1) How do you epoch such data?  2) should we epoch data before running
>> ica (dose more epoch means better results?)
>> Thanks in advance
>>
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>
>
>
> --
> Makoto Miyakoshi
> Swartz Center for Computational Neuroscience
> Institute for Neural Computation, University of California San Diego
>


-- 
Pozdrawiam,
Mikołaj Magnuski
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