[FieldTrip] about when to filter

[Roemer van der Meij]

Hi Lin,

That depends on what kind of filters you use, and how you remove your
ocular artifacts. Obviously, if you are removing ocular artifacts by hand
any filtering that will help you in detecting eye movements will be of
course be of benefit. If you use a blind decomposition technique such as
ICA to try and remove ocular artifacts, it's a bit more tricky. Some
specific filters might help depending on what kind of other artifacts are
present, but it's important for example not to smear out your eye
movements. Before ones does ICA to remove artifacts it's a good idea to
remove trials that are unfixable, like trials with jumps in them (i.e.
hitting the ceiling of the amplifier).

I can only help you further if you more precisely describe what you mean
with filtering and ocular artifact removal. There are many many ways to go
about these two.

All the best,
Roemer


On Tue, Dec 18, 2012 at 11:00 AM, Roemer van der Meij <
r.vandermeij at donders.ru.nl> wrote:

> Hi Lin,
>
> Could you provide a little more information? How did you reduce your
> ocular artifacts? How did you filter your data? What kind of fieldtrip
> settings did you use, and what fieldtrip version were you using? Adding a
> picture of the artifacts you're referring to might also help.
>
> All the best,
> Roemer
>
>
> On Tue, Dec 18, 2012 at 2:55 AM, 蔡林 <bertram0611 at pku.edu.cn> wrote:
>
>> Hi all,
>>
>>     Now I have an urgent problem about how to filter EEG data recorded in
>> NeuroScan. I don't know the distiction between raw data(ie. cnt file)and
>> the data after ocular artifact reduction. I filtered these two different
>> data, and then I got diffrent results. Especially, I found many vertical
>> lines after filtering the data through ocular artifact reduction, but I
>> didn't find vertical lines filtering raw data.
>>     Please give me some advice about how to filter offset. Thank you in
>> advance.
>>
>> --
>> Lin Cai
>> Department of Psychology, Peking University, Beijing 100871, P.R.China
>>
>> Spam detection software, running on the system "kompost.science.ru.nl",
>> has
>> identified this incoming email as possible spam.  The original message
>> has been attached to this so you can view it (if it isn't spam) or label
>> similar future email.  If you have any questions, see
>> postmaster at science.ru.nl for details.
>>
>> Content preview:  Hi all, Now I have an urgent problem about how to
>> filter EEG
>>
>>    data recorded in NeuroScan. I don't know the distiction between raw
>> data(ie.
>>    cnt file)and the data after ocular artifact reduction. I filtered
>> these two
>>    different data, and then I got diffrent results. Especially, I found
>> many
>>    vertical lines after filtering the data through ocular artifact
>> reduction,
>>    but I didn't find vertical lines filtering raw data. Please give me
>> some
>>   advice about how to filter offset. Thank you in advance. [...]
>>
>> Content analysis details:   (6.2 points, 5.0 required)
>>
>>  pts rule name              description
>> ---- ----------------------
>> --------------------------------------------------
>>  3.2 CHARSET_FARAWAY_HEADER A foreign language charset used in headers
>>  3.0 BAYES_95               BODY: Bayesian spam probability is 95 to 99%
>>                             [score: 0.9800]
>>
>>
>>
>> _______________________________________________
>> fieldtrip mailing list
>> fieldtrip at donders.ru.nl
>> http://mailman.science.ru.nl/mailman/listinfo/fieldtrip
>>
>
>
>
> --
> Roemer van der Meij M.Sc.
> PhD Candidate
> Donders Institute for Brain, Cognition and Behaviour
> Centre for Cognition
> P.O. Box 9104
> 6500 HE Nijmegen
> The Netherlands
> Tel: +31(0)24 3655932
> E-mail: r.vandermeij at donders.ru.nl
>
>


-- 
Roemer van der Meij M.Sc.
PhD Candidate
Donders Institute for Brain, Cognition and Behaviour
Centre for Cognition
P.O. Box 9104
6500 HE Nijmegen
The Netherlands
Tel: +31(0)24 3655932
E-mail: r.vandermeij at donders.ru.nl
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.science.ru.nl/pipermail/fieldtrip/attachments/20121219/e4f6a82a/attachment.html>