[Eeglablist] Epoching eeg data

[Stephen Politzer-Ahles]

Hi Karlo,

In EEGLAB you can also epoch data based on times (e.g. the first 1000 ms,
the next 1000 ms, etc.). I  guess it all depends on what you are trying to
analyze about the data; I only have experience with ERPs, so I don't know
of a purpose for epoching other than to epoch around events, but if there
is another reason to epoch your data based on times then it is at least
possible.

As for epoching before ICA, as far as I know from reading the tutorial and
the mailing list I don't think there's a reason to expect the ICA to be
better just from epoching. (ICA is often better when you remove periods of
irrelevant data, such as breaks when the participant was not on-task; but
that's not a result of the epoching per se, it's a result of removing the
noisy data.) Often the reason for epoching before ICA is to make the data
more manageable (continuous data can be very large, and the analysis could
take a long time). But if you do ICA on epoched data, the epochs need to be
long enough to give the ICA sufficient data; what has been recommended to
me is to use epochs that are at least several seconds long. You can check
some of the previous discussions on this mailing list regarding the topic
of epoching before ICA, such as this one:
http://sccn.ucsd.edu/pipermail/eeglablist/2011/003670.html.

Best,
Steve


On Mon, Jun 3, 2013 at 1:59 PM, karlo gonzales <thats_karlo at yahoo.com>
wrote:
>
> 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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--
Stephen Politzer-Ahles
University of Kansas
Linguistics Department
http://people.ku.edu/~sjpa/
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