[Eeglablist] (ask) about averaging and ICA
Bagas Isadewa
izadewa at yahoo.com
Thu Dec 30 11:32:09 PST 2010
hello,
thank you for the answers, especially for Mr. Andrew Hill and Mr. Tarik S
Bel-Bahar
I apologize for my ambiguous and unclear question. It caused by my English is
bad, i'm sorry.
I will explain about my experiment, now i'm doing my final project to get
bachelor degree's. I try to generate ERP with subject read an alphabet/letter
in a slideshow ( I chosed a/i/u/e/o letter for stimuli). My goal is to get a
ERP waveform related to a certain alphabet which subject has read. Note that
subject only thinking reading a words not speak it and not produce any sound.
The subject just say (or think) the letter in mind.
for my question number :
1.thank you for the suggestion, I take just 20 trials for each letter, actually
I wanted to do experiment (record many trials) again but i'm facing a bit of
problem here. To do an experiment, I must rent an EEG in medical clinic which I
must paid some money (unfortunately it quite expensive). because of that I
can't do an experiment as many as I wanted.
2. I mean many N trials in many N epoch (is that right ?) and single-trial in 1
epoch.
3. Let me try to explain what I understand. To extract ERP there are two ways
: a. Do the averaging many trials and b. run ICA to the data. And what I'm
going to do is run ICA first, then I will average the result of ICA
decomposition
I admit I do not fully understand ICA, but I still try reading the literature
(it's little hard in English, hehehe). There is a question in my mind, how do
we prove the result of ICA decomposition is right ? I mean, do the result will
one hundred percent represent the true neural signal ?
thank you very much
regards,
bagas isadewa
________________________________
From: Tarik S Bel-Bahar <tarikbelbahar at gmail.com>
To: Bagas Isadewa <izadewa at yahoo.com>
Cc: EEGLAB <eeglablist at sccn.ucsd.edu>
Sent: Mon, December 27, 2010 8:45:01 AM
Subject: Re: [Eeglablist] (ask) about averaging and ICA
Greetings Bagas,
1. Yes, there are multiple papers that refer to this issue. I would suggest you
start
with the HANDBOOKS by Tom Handy or Steve Luck, and these will answer your basic
questions about the relations
between trial counts, averaged ERPs, and the resultant signal-to-noise ratios.
You can find these books by doing a Google search, and you can order them from
Amazon or another bookseller.
Here's the link for the Handy handbook:
http://mitpress.mit.edu/catalog/item/default.asp?tid=10253&ttype=2
2. Your second question is not clear. It's not clear what you mean by "many
trials" or only "single-trials" in one epoch.
For information about best practice using EEGLAB and ICA, please read through
the EEGLAB tutorial online.
A general rule of thumb is that more single trials are better than fewer single
trials, for an accurate ICA decomposition of the data.
3. Again, you should read and learn basic information about ERP techniques from
handbooks mentioned in Point 1 above,
or in articles that use ERPs (please search on Google Scholar for examples that
relate to your research questions).
It also not clear what you mean by using "only one technique".
You can generate average ERPs without using ICA, and you can also generate ERPs
after using ICA.
Please be aware that the emphasis in EEGLAB is on single-trial analysis,
although it can certainly be used for single subject average ERPs.
4. In the future please try to be more specific about what you are trying to do,
what kind of ERPs you are trying to generate.
Also it seems that you are unaware of the the many potential uses of ICA (for
artifact detection, for detection of independent modulators, etc..)
Please read through the articles describing EEGLAB (which you can find at the
EEGLAB site, or via Google Scholar).
Please also read through and do the EEGLAB tutorial, which will answer some of
your questions.
Then feel free to send some more questions after that.
Good luck Bagas!
On Thu, Dec 23, 2010 at 1:09 AM, Bagas Isadewa <izadewa at yahoo.com> wrote:
hello,
>
>i have several questions,
>
>1. if I wanted to average EEG data to yields good ERP, how many minimum trials
>do I needed ? is there any paper or journals that explained about it ?
>2. then, if I wanted to run ICA to extract ERP, do I need many trials or only
>single-trials in one epoch will be enough ??
>3. is it necessary to run ICA first then do averaging or it is enough to use
>only one technique for extracting ERP ?
>
>if you don't mind please give me an explanation
>thank you very much
>
>
>regards,
>bagas isadewa
>
>
>
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