Hi Donovan,
Without an "off" condition, BOLD imaging data is pretty uninterpretable -
there is no useful information you can get from it. In order to get
something from this data, you will _have_ to include the preliminary rest
condition in your design, and even then you will find it hard to
distinguish on-off contrast from signal drift.
Regards, Steve.
On Fri, 7 Nov 2003, Donovan Rebbechi wrote:
> Hi. I'm trying to do a between subjects analysis. What it amounts to in
> this case is doing an analysis on the mean volumes for each subject. The
> problem is that there really isn't any within-subject design (well, it's
> "on" all the time for any given subject, which means that you don't get
> meaningful t-statistics out of it, and more to the point, feat doesn't
> produce cope images) It's pretty clear how to do the high
> level analysis, but I don't know how I'm supposed to proceed with the
> lower level analysis. Obviously, registration etc is necessary, but I
> don't see how I can produce cope images without setting up a design
> matrix, and there really isn't a within-subject design in this case. For
> now, I've sidesteped the problem by setting up a design that distinguishes
> between a short (30s) preliminary rest period and the stimulus, but I'd
> rather not do this.
>
> PS I noticed that feat does not apply bet to the structural images by
> default for registration, even when the 'bet' button is checked. This was
> a source of some confusion for a little while -- it may be a good idea to
> consider putting an 'apply bet to structural image' button in the reg
> dialog in feat. Seems to make sense since the choice of template appears
> to assume that the structural image has been appropriately scalped.
>
> Cheers,
> --
> Donovan Rebbechi, PhD
> Research Associate, Dept of Psychology
> Smith Hall #340, 101 Warren Street
> Newark NJ 07102
> 973 353 5440 x240
> http://pegasus.rutgers.edu/~elflord
>
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)
[log in to unmask] http://www.fmrib.ox.ac.uk/~steve
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