[Eeglablist] ICA assumption (independence of sources)

[Makoto Miyakoshi]

Dear Ali,

> Do you mean that: when we record an EEG, with for example visual
stimulation and apply ICA to EEG, we get a number of sources each
corresponds to a physiological activity. For example, we could get sources
correspond to eye movement, muscle activity, visual task, heart beat and
etc.

That's true if and only if you have 1) enough number of channels, 2) clean
signal, 3) as little noise as possible.

> The brain sources are not independent in reality but because the
physiological activities are independent (e.g. eye movement, muscle
activity, visual task, heart beat and etc), then we could say ICA
assumption can work for EEG.

We are not sure how completely independent the brain activities are. Our
assumption is that they are independent, but for example, if you think
about visual cortex and visuo-motor association cortex, how confident are
we to say that they are also independent?

But we would say that they are mostly independent anyways. It's an useful
assumption.

> And in this case, we are not talking about the brain sources of each
physiological activity, we only consider each physiological activity as an
independent source that could be estimated by ICA.

That's one way of interpreting what we see in the ICA results.
ICA is a filter in a broad sense. Filter is like a lens. When you choose a
lens, you choose what you see.

Makoto



On Fri, Jan 27, 2017 at 5:10 PM, ali zahedi <ali.zahedi.bham at gmail.com>
wrote:

> Dear Makoto,
>
> Thank you for your reply.
> I am sorry I am little bit confused...
> Do you mean that: when we record an EEG, with for example visual
> stimulation and apply ICA to EEG, we get a number of sources each
> corresponds to a physiological activity. For example, we could get sources
> correspond to eye movement, muscle activity, visual task, heart beat and
> etc. The brain sources are not independent in reality but because the
> physiological activities are independent (e.g. eye movement, muscle
> activity, visual task, heart beat and etc), then we could say ICA
> assumption can work for EEG. And in this case, we are not talking about the
> brain sources of each physiological activity, we only consider each
> physiological activity as an independent source that could be estimated by
> ICA.
> Did I understand correctly?
>
> Kindest regards,
> Ali
>
> On Thu, Jan 26, 2017 at 9:34 PM, Makoto Miyakoshi <mmiyakoshi at ucsd.edu>
> wrote:
>
>> Dear Ali,
>>
>> > the brain sources are not independent in reality,
>>
>> That may be true. In that case, ICA is extracting independent part of
>> brain activity.
>>
>> However, at least in a standard psychological assumptions, when you are
>> performing visual task, your auditory cortex is not directly engaged,
>> therefore EEG from the visual cortex and the auditory cortex should be
>> independent. Don't you agree?
>>
>> Makoto
>>
>>
>>
>> On Tue, Jan 24, 2017 at 5:30 AM, ali zahedi <ali.zahedi.bham at gmail.com>
>> wrote:
>>
>>> Hi all,
>>>
>>> I have a question about one of the assumptions of the ICA on estimated
>>> sources; "the sources estimated by ICA are statistically independent". If
>>> we want to apply ICA to EEG data, does this assumption make sense for brain
>>> sources? the brain sources are not independent in reality, so how does ICA
>>> work for EEG data?
>>>
>>> Thank you in advance,
>>> Ali
>>>
>>> _______________________________________________
>>> Eeglablist page: http://sccn.ucsd.edu/eeglab/eeglabmail.html
>>> To unsubscribe, send an empty email to eeglablist-unsubscribe at sccn.uc
>>> sd.edu
>>> For digest mode, send an email with the subject "set digest mime" to
>>> eeglablist-request at sccn.ucsd.edu
>>>
>>
>>
>>
>> --
>> Makoto Miyakoshi
>> Swartz Center for Computational Neuroscience
>> Institute for Neural Computation, University of California San Diego
>>
>
>


-- 
Makoto Miyakoshi
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://sccn.ucsd.edu/pipermail/eeglablist/attachments/20170130/ac4b0f17/attachment.html>