Hi.
On Fri, 29 Mar 2002, Souheil Inati wrote:
> Quick question: I've run an analysis for a simple block design
> experiment. One thing I don't understand is why there is a little bit
> of a roll in the first rest block and the last
> task block in the first column of the design matrix.
You're right - this isn't related to the HRF convolution - it is indeed a
result of applying the highpass filter to the model in order to mimick the
effect that the highpass filter has on the data, to get a better match
between the model and the data - this is normal and improves the stats
slightly. Another nice benefit of applying the filter to the model is
that if somehow you choose a "wrong" hp cutoff (eg too small) it will
probably be apparent in the filtered model.
> Or am I being an airhead?
not at all!
ttfn :)
Stephen M. Smith
Head of Image Analysis, FMRIB
Oxford University Centre for Functional MRI of the Brain
John Radcliffe Hospital, Headington, Oxford OX3 9DU, UK
+44 (0) 1865 222726 (fax 222717)
[log in to unmask] http://www.fmrib.ox.ac.uk/~steve
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