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

History of AFNI updates  

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September 12, 2003 09:37AM
Liz,

Sorry that my response was not clear enough to you. Let me try it again.

The output from 3dDeconvolve includes the statistics, beta coefficients, and the modelled signal (the original signal with noise removed). As you said, the statistics would not be affected by how you create your regressors. The same holds for the modelled signal. Only the beta coefficients would depend on the scaling of the regressors.

I am not so sure what results from 3dDeconvolve you would like to report. If you want to detect activation regions and/or compare the % change of the modelled signal among different voxels, there is no need to concern about the scaling.

As your experiments with different scaling showed, the beta coefficients are inversely proportional to the magnitudes of your regressors: peak 1 ==> beta =8.0817, peak 2 ==> beta=4.014718. As I said in my previous message, beta's are quite arbitrary because they depend on the scaling of your stimulus files. Therefore if you want to compare the relative values of beta among different voxels or across different subjects, you'd better convert the beta's into their % change instead of using their arbitrary values. The % changes of beta then become a common currency for comparison. In this sense, you don't need to worry about the magnitude of your regressors when you calculate the % change of beta's, because your irf's (basis function of gamma variates) have a peak of one ( the option -peak 1 in waver).

Gang
Subject Author Posted

waver -peak

Elizabeth Felix September 10, 2003 02:48PM

Re: waver -peak

rick reynolds September 10, 2003 04:34PM

Re: waver -peak

Elizabeth Felix September 10, 2003 04:56PM

Re: waver -peak

Gang Chen September 11, 2003 08:35AM

Re: waver -peak

Elizabeth Felix September 11, 2003 10:13AM

Re: waver -peak

Gang Chen September 11, 2003 10:31AM

Re: waver -peak

rick reynolds September 11, 2003 11:31AM

Re: waver -peak

Elizabeth Felix September 11, 2003 02:32PM

Re: waver -peak

Gang Chen September 11, 2003 04:33PM

Re: waver -peak

Elizabeth Felix September 11, 2003 07:24PM

Re: waver -peak

Gang Chen September 12, 2003 09:37AM

Re: waver -peak

rick reynolds September 12, 2003 10:26AM

Re: waver -peak

Elizabeth Felix September 12, 2003 10:36AM

Re: waver -peak

rick reynolds September 19, 2003 04:22PM