[FieldTrip] Automatized artifact rejection in FT

[Ricarda Braukmann]

Hi Jim,

Thanks for the quick reply, this is really helpful.
I will try your suggestion for number three.

Regarding the second criteria, we indeed want to exclude changes of more
than 3uV between t and t+200ms.
So if you have any suggestion of how we might be able to implement this as
well, that would be great!

Thanks!
Ricarda

On Wed, Nov 18, 2015 at 2:14 PM, Herring, J.D. (Jim) <
j.herring at donders.ru.nl> wrote:

> Hi Ricarda,
>
>
>
> All three criteria have a certain threshold that has to be met in order
> for a trial to be marked as containing artifacts so for all criteria you
> could use ft_artifact_threshold (or ft_artifact_zvalue). The difference
> will be how you preprocess the signal. You would need to transform the
> signal so that for criteria nr. 2 the signal represents the potential
> difference over a 200ms window?, and for nr. 3 the potential difference per
> sampling point.
>
>
>
> Number 3 is relatively easy, you can calculate the first temporal
> derivative (ie. the difference between two consecutive samples) with
> cfg.artfctdef.threshold.derivative = ‘yes’ (or ….threshold.absdiff = ‘yes’,
> if you want the absolute difference). So something like this should work:
>
>
>
> cfg.artfctdef.threshold.channel   = cell-array with channel labels
>
> cfg.artfctdef.threshold.bpfilter  = 'no';
>
> cfg.artfctdef.threshold.absdiff = ‘yes’;
>
> cfg.artfctdef.threshold.max       = 50;
>
>
>
> Number 2 is slightly more difficult because you want to integrate over a
> larger window. I don’t fully understand what you want to avoid, should the
> signal at time X stay within 3uV of the signal at time X + 200ms?
>
>
>
> Best,
>
>
>
> Jim
>
>
>
>
>
>
>
> *From:* fieldtrip-bounces at science.ru.nl [mailto:
> fieldtrip-bounces at science.ru.nl] *On Behalf Of *Ricarda Braukmann
> *Sent:* woensdag 18 november 2015 12:58
> *To:* FieldTrip discussion list
> *Subject:* [FieldTrip] Automatized artifact rejection in FT
>
>
>
> Hi everyone,
>
> I would like to implement an automatized artifact rejection procedure for
> my EEG data and compare this to manual rejection.
>
> I would like to use the following criteria for rejection of a segment:
>
> 1. amplitudes below -150 or above 150 µV
> 2. a difference of 3 µV per 200 ms,
> 3. or a voltage change of 50 µV per sampling point
>
> Is there a function in fieldtrip that I can use for implementing these
> different criteria?
>
> I know that FT_ARTIFACT_THRESHOLD can reject segments on basis of the
> first criteria but I am unsure how to implement the second two.
>
> Any help would be highly appreciated.
>
> Thanks!
>
> Ricarda
>
>
>
> --
>
>
> Ricarda Braukmann, MSc
> PhD student
>
> Radboud University Medical Centre & Baby Research Center
>
> Donders Institute for Brain, Cognition and Behaviour,
> Centre for Neuroscience & Centre for Cognition
>
> Room B.01.22
> Phone: +31 (0) 24 36 12652
> Email: r.braukmann at donders.ru.nl
>
> Website: http://www.zebra-project.nl/
>



-- 

Ricarda Braukmann, MSc
PhD student

Radboud University Medical Centre & Baby Research Center

Donders Institute for Brain, Cognition and Behaviour,
Centre for Neuroscience & Centre for Cognition

Room B.01.22
Phone: +31 (0) 24 36 12652
Email: r.braukmann at donders.ru.nl
Website: http://www.zebra-project.nl/
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