Re: [Marsbar-users] filter effects in Plot Data (full)

[<gla...@hs...>]

Dear Matthew,

thank you so much for you immediate and helpful response. May I ask a=20
couple of quick follow-up questions ...

Matthew Brett wrote:
>> 1. Is this a visualization effect, because it's part of the "Plot=20
>> Data" and
>> not "Extract Data"?
>=20
> Yes - probably - try plotting the extracted data in matlab outside
> marsbar, I think you will probably see that the effect is gone...

You are absolutely right, but this makes me wonder about a related issue:=
 I=20
believe that most people you are doing PPI analyses use spm_regions to=20
extract their data ... and spm_regions returns the first eigenvariate whi=
ch=20
displays those edge effects of the whitening filter. However, the design =

matrix does not have the edge effects, so it seems that there is a obviou=
s=20
mismatch between the data (eigenvariate) and the model, thus creating lar=
ge=20
residuals and a bad model fit which might influence the statistics. I=20
wonder if you can comment on this ...

Maybe I should also post this question on the SPM mailing list and see wh=
at=20
the folks at the FIL have to say about this ...

>=20
>> 2. What is really the underlying time course like in the "Extract Data=

>> (default)" and in the "Extract Data (full)"? Are the filters of the SP=
M
>> design applied (e.g. HPF and AR(1))?
>=20
> No - the SPM design filters are not used for the extract data options.

So, does MarsBaR access the images via the SPM.xY.VY handle or rather=20
directly? The reason I am asking is, that the global scaling factor is on=
ly=20
written to SPM.xY.VY(i).pinfo(1,:), but not to the images themselves. Thu=
s,=20
when you DO NOT you access the images through SPM.xY.VY then you don't ge=
t=20
the global scaling ...

see http://www.jiscmail.ac.uk/cgi-bin/webadmin?A2=3Dind0701&L=3DSPM&P=3DR=
41923

Thanks a lot,
Jan


--=20
Jan Gl=E4scher, Ph.D.         Div. Humanities & Social Sciences
+1 (626) 395-4976 (office)  Caltech, Broad Center, M/C 114-96
+1 (626) 395-2000 (fax)     1200 California Blvd
gla...@hs...    Pasadena, CA 91125