Hi - you are unlikely to be able to predict the potentially varying
HRF via a reaction-time (etc) covariate with any accuracy. What you
can do is to use a more flexible HRF model such as FLOBS (see the FEAT
documentation), and if you decide that you do need that, have a look
at emails on the archive / the literature on the possibility of
passing up an F on the FLOBS to a higher-level analysis via randomise
(though this is not yet trivial with the software).
Cheers.
On 19 Jun 2008, at 07:57, Moria Smoski wrote:
> As a newcomer both to the list and to neuroimaging, I hope this is an
> appropriate question!
>
> I am primarily interested in fMRI studies comparing psychiatric and
> control
> groups in both younger and older adult populations. Because of a
> general
> physiological slowing or differences in global CBF (due to age or
> psychiatric status), it is conceivable that I will have group
> differences
> in the speed of hemodynamic responses, but not necessarily their
> intensity
> or location. (e.g., the shape of a hemodynamic response curve to a
> stimulus would be the same in both groups in a given voxel, but the
> peak of
> that curve would be slightly delayed in one group vs. another.) How
> would
> that difference be reflected in FSL/FEAT results, if at all? If I
> wanted to
> control for that difference, what would be the best way to go about it
> (e.g., entering a behavioral reaction time score as a covariate?)
>
> Thanks for your help and advice,
>
> --Moria Smoski
>
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Stephen M. Smith, Professor of Biomedical Engineering
Associate Director, Oxford University FMRIB Centre
FMRIB, JR Hospital, Headington, Oxford OX3 9DU, UK
+44 (0) 1865 222726 (fax 222717)
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