Hi Matthew and Yanmei,
Just to add, the last comment in that cited post:
"Having said all this. It is still *BETTER* to use an F-test whenever you
are encoding a condition using more than one basis function (the reason
for explained above). And since we can now (as of proper variance
component estimation) bring all the parameter estimates (or rather
contrasts thereof) to the second level, it is *always* the recommended
thing to do."
is not correct. You can dilute your statistical effect size (regression sums
of squares) across the multiple dimensions of an F-contrast. It is better to
use a one-dimensional contrast when you know what you are looking for
(matched filter idea). So, for time-series statistical inference I would
suggest using either (a) a one-dimensional contrast estimating the original
effect in the presence of orthogonalized nuisance terms such as derivatives,
as Jesper mentioned in the model (Zarahn, 2002), or even better (b) an
estimate of amplitude based on both the original and derivative terms
(Calhoun et al, 2004). As an aside, approaches like (a) don't matter to 2nd
level analyses, while (b) will affect 2nd level estimators (beneficially)
Eric.
Calhoun, V.D., Stevens, M.C., Pearlson, G.D., Kiehl, K.A., 2004. fMRI
analysis with the general linear model: removal of latency-induced amplitude
bias by incorporation of hemodynamic derivative terms. Neuroimage 22, 252-7.
Zarahn, E., 2002. Using larger dimensional signal-subspaces to increase
sensitivity in fMRI time series analyses. Human Brain Mapping 17, 13-16.
----- Original Message -----
From: "Matthew Brett" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, March 16, 2006 5:11 PM
Subject: Re: [SPM] time derivative for block design fMRI???
Hi,
> I have a very naive question about inclusion of time derivative in
> analysing block design fMRI data (TR = 2s, block duration = 20s). Is it
> suggested to include time derivative for block design or it is only used
> for event-related?
I think the answer to that would be that it is basically only used for
event-related. There is a characteristically clear explanation from
Jesper Andersson here:
http://www.jiscmail.ac.uk/cgi-bin/webadmin?A2=ind04&L=SPM&P=R351987&I=-3
Best,
Matthew
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