detrend/partial artefact rejection

[J.M. Schoffelen]

Dear Dasha and Ole,

Thanks a lot for this question. Indeed it is very true that in theory
detrending prior to the partial rejection of artifacts could lead to little
subtrials having a DC-offset. It is also very true that a detrend-operation
after the identification of artifacts is helpful to get rid of these
potential confounds for your further frequency analysis.
This is exactly what is done in preprocessing! The artifact-rejection
routines that are provided by fieldtrip, read in the data and does a lot of
fancy stuff with it, one of the things is detrending. However, once the data
has been read in in one of these routines and the artifacts are detected,
the data itself is discarded again.
The real reading in of the data takes place after the artifact-detection,
and the cfg.detrend = 'yes' option takes proper care that all the separate
subtrials will be detrended. At least, that is what it should do...

Yours,

Jan-M

-----Original Message-----
From: FieldTrip discussion list [mailto:FIELDTRIP at NIC.SURFNET.NL] On Behalf
Of Daria Osipova
Sent: Monday, May 16, 2005 3:47 PM
To: FIELDTRIP at NIC.SURFNET.NL
Subject: [FIELDTRIP] detrend/partial artefact rejection

Hi,

We have a question on detrend in preprocessing.m in relation to partial
artifact
rejection. As we understand detrend is first applied and then the partical
rejection is performed. This results in some subtrials in which for instance
a
DC offset is present. Would it not be more optimal to perform another
detrend
prior to the calculation of the wavelet/fourier transforms to avoid boundary
effects?

Dasha and Ole