AFNI Message Board

Dear AFNI users-

We are very pleased to announce that the new AFNI Message Board framework is up! Please join us at:

https://discuss.afni.nimh.nih.gov

Existing user accounts have been migrated, so returning users can login by requesting a password reset. New users can create accounts, as well, through a standard account creation process. Please note that these setup emails might initially go to spam folders (esp. for NIH users!), so please check those locations in the beginning.

The current Message Board discussion threads have been migrated to the new framework. The current Message Board will remain visible, but read-only, for a little while.

Sincerely, AFNI HQ

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Lee Friedman
September 26, 2003 04:33PM
We are using 3dFourier to filter out low frequency drift.

If we include the retrend opton on it, everythings works as expected.

If we don't retrend the data, then when we do a fim we get a lot of pixels whose correlation
is 0.

The same pixels in the retrended data have non-zero correlations.

Since fim removes a linear trend (my understanding) then the correlation coefficients should be
identical regardless of whether or not we retrend after FFT filtering.

But they are clearly not. We looked at histograms of the correlation subbrick and it differs
also depending on whether or not the analysis is performed on retrended data.

Lee
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correlaton r = 0 if no retrend after fourier

Lee Friedman September 26, 2003 04:33PM

Re: correlaton r = 0 if no retrend after fourier

bob cox September 29, 2003 11:49AM

Re: correlaton r = 0 if no retrend after fourier

Lee Friedman October 01, 2003 11:26AM