Hi - in order to interpret the absolute size of estimated PE values, you
need to first multiply them by the peak-to-peak height in the model (i.e.,
look inside design.mat) - after doing this, regardless of the convolution
type, you know the fitted peak-to-peak height. In none of this, at this
point, are things normalised into percentages (etc.).
On Wed, 8 Dec 2004, Ramapriyan Pratiwadi wrote:
> We recently ran an analysis using the FIR basis set, rather than the the
> double-gamma HRF. To our surpise, the range of values for the pe images
> were much much lower than expected; in fact, they look like percent
> signal change. And when the betas for the basis set were graphed, they
> indeed looked like a typical HRF.
> Do the pe images need to be scaled in some way, or are they already in
> percent deviation from baseline.
> Ram Pratiwadi
> Research Assistant
> University of Pennsylvania, Brain Behavior Laboratory
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Stephen M. Smith DPhil
Associate Director, FMRIB and Analysis Research Coordinator
Oxford University Centre for Functional MRI of the Brain
John Radcliffe Hospital, Headington, Oxford OX3 9DU, UK
+44 (0) 1865 222726 (fax 222717)
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