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
May 04, 2006 11:39AM
Question is: How should regressors be scaled ?
Lets assume a simple block design, convolved with a
simple gamma HRF as provided by waver.

Let's further assume that we want to use the beta-weights and the
intercept estimate to give us percent change, as in 100*beta/intercept.

Obviously, this will only work with 1 particular scaling of the regressor.

Two options: scale the regressor so that the peak is = 1 or
scale the regressor so that its integral is 1.0

Keith Worsley, in fmristat, does the latter. Here is a quote for how
he calculates is double gamma HRF:

"The final hrf is: gamma1/max(gamma1)-DIP*gamma2/max(gamma2) scaled so that its total integral is 1."

But if I want to get percent change at the peak of the response, using 100*beta/intercept, don't I need to have the peak == 1 ?

If I use waver with -peak 1 will that give me a peak of 1.0, an integral of 1.0 or
what?

Lee
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Subject Author Posted

scaling regressors

Lee Friedman May 04, 2006 11:39AM

Re: scaling regressors

Gang Chen May 04, 2006 05:02PM

Re: scaling regressors

Lee Friedman May 04, 2006 08:01PM