Dear Tony,
> I have smoothed my normalised images to 4mm and looked at data for
> individuals. Now I wish to go through to a second level, random effects,
> analysis.
> 1) Can I simply smooth the con* images before entering them into the
second level?
Yes
> 2) Suppose it is OK to smooth the con* images by X mm. Is it true that
> the 'total' smoothing would be the root of 4*4 + X*X ?
Yes
> 3) Finally, what is the current consensus on the appropriate amount
> of 'total' smoothing, when the areas of interest are in DLPFC?
No hard and fast rule on this but 8 or 10 mm 'total smoothing' seems to work well.
Phillipe - Tony's motivation for further smoothing is that his data are not sufficiently smoothed for a RFX analysis. Smoothing the con images avoids re-smoothing normalised functional images and re-estimating the first-level model.
Best regards,
Bryan
Bryan Strange
Wellcome Dept Cognitive Neurology
Institute of Neurology
12 Queen Square
London WC1N 3BG
+44 (0) 207 833 7485
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and
Institute of Cognitive Neuroscience
University College London
17 Queen Square
London WC1N 3AR
+44 (0) 207 679 5431
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