[FieldTrip] about detrend

Mon Dec 8 10:19:56 CET 2014

oh and another thing: in FieldTrip, detrending inherently also demeans, or
in other words, if the fitted first order polynomial is removed, also the
zeroth order polynomial is.

--

Jörn M. Horschig, Software Engineer

 <http://www.artinis.com/> Artinis Medical Systems  |  +31 481 350 980 

From: fieldtrip-bounces at science.ru.nl
[mailto:fieldtrip-bounces at science.ru.nl] On Behalf Of Yun Wen
Sent: Sunday, December 7, 2014 11:53 AM
To: FieldTrip discussion list
Subject: Re: [FieldTrip] about detrend

Hi, Alexander. Thank you for your help. Do you suggest that I do baseline
correction plus detrend, e,g,  cfg.blc = 'yes' & cfg.detrend = 'yes' on
epoched data? 

Best,

Yun

From: fieldtrip-bounces at science.ru.nl
<mailto:fieldtrip-bounces at science.ru.nl>
[mailto:fieldtrip-bounces at science.ru.nl] On Behalf Of Alexander Nakhnikian
Sent: Saturday, December 06, 2014 1:14 AM
To: FieldTrip discussion list
Subject: Re: [FieldTrip] about detrend

It looks as though the take home message is that in theory high pass filters
remove DC but you can't be sure how they will interact with empirical data
since there is no perfect filter in the real world.  If other people report
substantial artifacts after filtering data without removing the DC component
I suggest getting rid of it.  To answer your original question, assuming
you're detrending each epoch individually it should remove the DC component
or at least reduce it substantially.   

I hope that helps.

On 12/5/14, 6:20 PM, Yun Wen wrote:

Hi, Alexander & Rodrigo. Thank you very much for your help. I collected my
data with DC recordings (BioSemi system). I have seen some discussion on the
DC offset:

http://sccn.ucsd.edu/pipermail/eeglablist/2014/008068.html

http://sccn.ucsd.edu/pipermail/eeglablist/2008/002229.html

http://sccn.ucsd.edu/pipermail/eeglablist/2010/003315.html

http://erpinfo.org/erplab/erplab-documentation/manual/Filtering.html

It seems to me that Id better remove DC offset of continuous data before
high-pass filter. Am I right?

Best,

Yun

From: fieldtrip-bounces at science.ru.nl
<mailto:fieldtrip-bounces at science.ru.nl>
[mailto:fieldtrip-bounces at science.ru.nl] On Behalf Of Alexander Nakhnikian
Sent: Friday, December 05, 2014 10:19 PM
To: FieldTrip discussion list
Subject: Re: [FieldTrip] about detrend

Hello Again,

I think there's an error in my response. I think removing the linear trend
should also set the mean to zero already since the best fit line
incorporates vertical offset.  Sorry about that.  

A

On 12/5/14, 4:20 PM, Yun Wen wrote:

Hi all, I want to remove DC offset before applying the high-pass filter. I
was wondering if I can achieve that by putting cfg.detrend = 'yes' before
cfg.hpfilter = 'yes', something like:

cfg = []; 

cfg.dataset = filename_raweeg;

cfg.detrend = 'yes'; 

cfg.hpfilter = 'yes';

cfg.hpfiltord = 2; % Order of the filter = 2.

cfg.hpfreq = 0.1; % High-pass cutoff at 0.1 Hz;

[data] = ft_preprocessing (cfg);

Thank you in advance.

Best,

Yun

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