[FieldTrip] about detrend

[Alexander Nakhnikian]

I would.  Baseline correction removes background components from the ERP 
but it does remove linear offset that is part of the post-stimulus time 
series.  In addition to getting ride of DC, detrending also removes 
certain non-stationarities and reduces the severity of edge effects.  I 
use it as a matter of course unless there is a compelling reason to omit 
it from the analysis pipeline.

On 12/7/14, 5:53 AM, Yun Wen wrote:
>
> 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] *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 I’d 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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