> 1) can anyone recommend a REAlly EASY paper on how SPM tackles motion
> correction. If anyone can explain it to me in 3/4 sentences that would be
> even better
Easiest level of description:
It wobbles the images about until the difference between them
is smallest.
Slightly harder version:
Realignment involves matching each of the images to the same reference
image. The movement is parameterised by three translations and three
rotations, and the objective is to find (for each image) the values of
these rotations and translations that best matches the images. The
quality of the matching is based on the square of the difference between
the images. The algorithm that the realignment uses to search for the best
parameters is Gauss-Newton optimisation.
Harder version:
http://www.fil.ion.ucl.ac.uk/~john/thesis/chapter2.pdf
>
> 2) What sources of systematic bias does SPM routinely examine and adjust
> for?
Whatever is entered into the design matrix as a confounding effect. This
could be anything, but typically includes things like a constant background,
a subject specific background, "globals", low frequency drifts, age, sex,
handedness, etc...
>
> 3) Is there any formal way of analysing between group differences in
> motions and rotations?
Differences among the parameters themselves, or differences in the effect
they have on the data? It also depends on what you mean by "different".
Maybe you want to asses movement in a particular direction, or you may want
to look for total amount of rotation or translation, or maybe the maximum of
these. A more useful measure may be about how much of the movement is
correlated with the actual experimental design.
>
> 4) Finally, bearing in mind I AM NOT A STATISTICIAN, can anyone recommend
> any REALLY EASY TO UNDERSTAND comparisons of parametric and non-parametric
> analysis
Parametric statistics assume Gaussian (bell shaped) distributions, whereas
non-parametric ones don't make this assumption. If you want to know more,
then have a quick flick through the introductory chapters of:
http://www.fil.ion.ucl.ac.uk/spm/papers/APH_thesis/ch6.pdf
Good luck,
-John
--
Dr John Ashburner.
Wellcome Department of Cognitive Neurology.
12 Queen Square, London WC1N 3BG, UK.
tel: +44 (0)20 78337491 or +44 (0)20 78373611 x4381
fax: +44 (0)20 78131420
http://www.fil.ion.ucl.ac.uk/~john
mail: [log in to unmask]
