[Eeglablist] Similar ICA components

mahsa shalchy mahsa.shalchy at gmail.com
Wed Oct 11 10:22:45 PDT 2017


Hi Jumana,

When I use average of all channels as my reference I am losing one unit of
my rank compared to the case, which I use average mastoid as reference. So,
I guess somehow using the average of all electrodes is introducing a kind
of dependence between my data matrix rows (channels)! So, I guess I should
either use pca to discard the bogus IC or use average mastoid as my
reference. My question is which method is preferred? Should I maybe go with
the average reference and just discard the bogus IC manually in Ic
rejection step?

In addition, when I change the reference many of my ICs change (please see
here:
https://www.dropbox.com/s/7zo1epdjn82apij/Screen%20Shot%202017-10-11%20at%2010.16.54%20AM.png?dl=0
).
Is this suppose to happen?

Many thanks,
Mahsa

On Wed, Oct 11, 2017 at 9:51 AM, Ahmad, Jumana <jumana.ahmad at kcl.ac.uk>
wrote:

> Hi Mahsa,
> Can you calculate your data rank?
> It should equal the number of non interpolated electrodes put into the
> ICA. Did you average reference first? Maybe you average referenced, then
> ran ICA..... in which case your rank would be out by 1, and you'd get a
> bogus component. If this happens then I normally see the second component
> as the inverse of the first.
> Let me know if any of this is the case, and I can help further if required.
> Best wishes,
> Jumana
>
>
> On 11 Oct 2017, at 17:39, mahsa shalchy <mahsa.shalchy at gmail.com> wrote:
>
> Dear Experts,
>
> I collected some data using Biosemi system (32 channels) and after doing
> pre-processing steps (resampling, filtering, re-referencing), I epoched the
> data and applied ICA.
>
> My problem is that, I'm getting two similar components in my ICA results
> (IC3 and IC4).
>
> I uploaded related images here:
>
> https://www.dropbox.com/sh/etjkwjrse12lu5j/AABpJvKmKWY5n69eER1GrPGka?dl=0
> <https://emea01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.dropbox.com%2Fsh%2Fetjkwjrse12lu5j%2FAABpJvKmKWY5n69eER1GrPGka%3Fdl%3D0&data=01%7C01%7Cjumana.ahmad%40kcl.ac.uk%7C4ae8a136541542300a9608d510c6a063%7C8370cf1416f34c16b83c724071654356%7C0&sdata=NWHt%2FlvryzXHmM41KmtBR%2B7JtVm7bZRCij7V76kFGRU%3D&reserved=0>
>
>
> Could you please help me with this?
>
> Many thanks,
> Mahsa
>
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