[Eeglablist] pre-stimulus baseline for response-locked epoch?

Tarik S Bel-Bahar tarikbelbahar at gmail.com
Mon Aug 28 10:54:40 PDT 2017

Hello Xinyi,

It's best if you epoch your continuous data with epoch settings that
include the necessary baseline.
At least try to do it within eeglab first, and if you have at least 500 ms
(or longer) before the response, then that should be okay for epoching
within eeglab.

If you want to "add your own baseline to EEG.data" then it's tricky, and
requires good knowledge of eeglab and matlab. It is generally possible to
recreate EEG.data in the way you want, but you have to do it by hand/code,
and this capability does not exist in eeglab. Alternatively you could do
the baselining yourself (not using an eeglab function) by computing a
general baseline, and then subtracting that from each of your epochs
(again, by hand/code within matlab, not using eeglab functions). In order
to do this you need to have a clear idea of the necessary computations for
baselining, need to do it for all channels, etc.. You could review the
baselining function in eeglab for ideas. Also you have to make sure you
have chosen and computed a correct/proper/valid baseline for your use.

You an review the time-frequency functions in eeglab, and you might see a
way to provide a precomputed baseline to those functions, though I doubt
that this exists. Overall, it is something that would be useful for eeglab,
so if you build a solution, let the eeglablist know about it, and/or add it
as an eeglab plugin.

If you haven't had a chance to, google eeglablist + your topic and you'll
find some eeglablist posts on this topic. If you are copying methods from a
published article, you can also try contacting authors who have already
done this.

On Sun, Aug 27, 2017 at 8:14 PM, Xinyi Li <lxykh0700073 at outlook.com> wrote:

> Hi,
> I want to do response-locked epoching but also add a period before each
> stimulus as baselines for later time-freq analysis.
> I noticed that if I manually edit EEG.data to add baseline before each
> epoch, the latencies in the event field (and maybe some other things) won't
> change accordingly. And I think I cannot directly use the EEGlab epoch
> function to add the baseline since the reaction time of each trial varies
> so I won't know the prestimulus time period with regard to responses.
> So I'm wondering if you have any advice on how I could do this? Or is it
> possible to achieve this when doing time-frequency analysis?
> Thank you!
> Best,
> Xinyi
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