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

[Vibra Lab]

Thank you very much for your answer

Cheers,
Ihshan

On Fri, Sep 21, 2018 at 4:14 PM Stephen Politzer-Ahles <
politzerahless at gmail.com> wrote:

> 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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>
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