[Eeglablist] epoch extracting

Stephen Politzer-Ahles politzerahless at gmail.com
Mon Jun 24 13:51:09 PDT 2013


Hi Tahani,

Based on your description of your dataset, it sounds like it might not be
necessary to use variable length epochs--if you are interested in the ERP
relative to the
onset of the stimulus, people often used a fixed epoch duration around that
stimulus even if the participant's response had a variable latency. (I
think the same often applies to response-locked ERPs, although I'm less
familiar with those.)

That being said, if you really do need to use epochs of variable
lengths.... I'm not sure if it's straigthforward to do within EEGLAB (it
might be possible, I'm just not aware of ways to do it; this message on the
eeglablist [http://sccn.ucsd.edu/pipermail/eeglablist/2008/002587.html]
suggests that it's not possible to do in one dataset, but it's an old
message so things may have changed.) Fieldtrip, however, does allow epochs
of varying length (
http://fieldtrip.fcdonders.nl/faq/what_is_the_relation_between_events_such_as_triggers_and_trials),
and I think ERPLAB (http://erpinfo.org/erplab) might as well (but I have
not used the latter, so I can't guarantee).

Best,
Steve


On Mon, Jun 24, 2013 at 12:33 AM, T. Almabruk <t.almabruk at yahoo.com> wrote:
>
> Dear Makoto
>
> I want to know if there is a possibilities to extract epochs with
inconstant lengths.
> I have a continues EEG dataset where the participant can spend as long
time as he/she wants before responding (press the button) to the presented
stimuli. So based on that, this dataset contains  stimuli with very quick
responses and others with very late responses(in some cases more than 2.5
min).
> Can you please suggest me how to deal with this case
>
> Cheers,
> Tahani
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