[FieldTrip] fieldtrip Digest, Vol 141, Issue 4

Elif Tülay e.eliftulay at gmail.com
Fri Aug 5 14:46:30 CEST 2022


Thank you for your response. However, I believe and am almost sure that it
is not related to the data (P.S. it is from an open EEGdateset which has
already been published). By the way, I also tried to perform fastica in
EEGlab toolbox and attach the result of it as well. Red line represents
after ica, and I put 2 rectangles to show the differences. Is it normal or
not?

Moreover, I repeat my second question " Also I wonder one more thing, what
is the mission of cfg.updatesens parameter in ft_ componentanalysis
function? "

many thanks again

Elif

On Fri, Aug 5, 2022 at 2:12 PM Tineke Grent-'T-Jong via fieldtrip <
fieldtrip at science.ru.nl> wrote:

> I feel something might be wrong with your input data. It is very unlikely
> that an eyeblink shows up with a similar amplitude across all channels.
> Typically, it has a topographic distribution, with smaller amplitudes the
> further away from the source, in this case the eyes.
>
> Hope this helps,
> Best wishes,
> Tineke Grent-'t-Jong
>
> -----Original Message-----
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> Sent: Freitag, 5. August 2022 12:35
> To: fieldtrip at science.ru.nl
> Subject: fieldtrip Digest, Vol 141, Issue 4
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> Today's Topics:
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>    1. Why does applying fastica change the form of EEG data?
>       (Elif Tülay)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Fri, 5 Aug 2022 13:34:50 +0300
> From: Elif Tülay <e.eliftulay at gmail.com>
> To: FieldTrip discussion list <fieldtrip at science.ru.nl>
> Subject: [FieldTrip] Why does applying fastica change the form of EEG
>         data?
> Message-ID:
>         <CALtq08VJsc_qb2dm+cPSA=
> zKhW_sphCXDgEbe7ws7y5R8Yeh-g at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> Dear Fieldtrippers,
>
> Now, I work on EEG data which is exported from EEGlab as segmented data. I
> try to remove eye blinks from the data and I wonder something about
> ft_componentanalysis function. When I performed fastica to remove the eye
> blink component, I realized that it changes the form of EEG in addition to
> removing the related component (please see the attached files, before and
> after; scales are the same). I cannot understand the reason. It is not
> because demean application, I checked it.
>
> Do you have any other idea? By the way, I used averaged referencing on
> EEGlab. Also please find the script that I used below.
>
>
>
> cfg            = [];
>
> cfg.method     = 'fastica';
>
> cfg.channel       = {'all', '-VEOG'};
>
> comp           = ft_componentanalysis(cfg, data);
>
>
>
> cfg = [];
>
> cfg.component = [5];
>
> data = ft_rejectcomponent(cfg, comp, data)
>
>
>
> Also I wonder one more thing, what is the mission of cfg.updatesens
> parameter in ft_ componentanalysis function?
>
>
>
> Many thanks in advance,
> Elif
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