[Eeglablist] Is short epoch necessary for all types of experiment ?

[Stephen Politzer-Ahles]

The short answer is, no, a short epoch is not necessary for all types of
experiment, but it is necessary for many types of experiment.

If you are analyzing event-related potentials, it is not meaningful to
analyze more than a short epoch, because beyond the first couple seconds
the EEG signal will be affected by so many subsequent events it will be
impossible to tell what's going on. I recommend you read Luck's *An
Introduction to the Event-Related Potential Technique *(2005/2014) to
better understand this concept. On the other hand, for experiments where
the research question is not about what the brain does in response to a
certain stimulus, but is about patterns of brain activity over a longer
period of time, event-related potential analysis may not be necessary. It
really depends what research question you are hoping to answer.

---
Stephen Politzer-Ahles
The Hong Kong Polytechnic University
Department of Chinese and Bilingual Studies
http://www.mypolyuweb.hk/~sjpolit/
<http://www.nyu.edu/projects/politzer-ahles/>


On Fri, Sep 21, 2018 at 2:38 PM Vibra Lab <labvibra at gmail.com> wrote:

> Dear Colleagues of EEGLAB,
>
> I need your help to strengthen my understanding so that it can sharpen my
> analysis.
>
> Let me describe my study. A person is given 4 sections (in total around 60
> minutes for all sections for each participant). For each section,
> participant is given various questions that they need to answer. i.e. it's
> like a conversation. Due to the nature of the experiment, the length of
> each section for each participant varies. For instance, for section *one *(for
> 4 participants) there are *4 different lengths* of time window (10
> minutes, 15 minutes, 20 minutes, and 25 minutes). In relation to that, I
> have several questions as follow :
>
> 1. Can I just *directly *analyze such full length of time window
> (considering after pre-processing the data), *e.g. 10 minutes*, instead
> of dividing them into 30 - 40 epochs out of 10 minutes  ?
>
> 2. Something that I still don't get the reason behind epoch is, *why do
> we have to create data into epochs ?* since the tutorial always uses
> epoch. I really appreciate if you could give me such reasoning for this.
> Since the beginning I learn ERP I still don't understand the significance
> of creating epoch.
>
> 3. Why is the duration of epoch is always short ? I rarely find epoch for
> more than 1 minute.
>
> 4. If I need to create epochs (30 - 40), *3 seconds each*, how can I do
> that ? since I have only 4 markers (considering there are 4 sections for
> the whole experiment for each participant) in my original data ?
>
> I would like to thank you in advanced for your help. Look forward to your
> answer.
>
> Sincerely,
> Ihshan
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