Dear Jon,
> I have recently been experimenting with a random effects analysis of
> several trials in an fMRI study. I have 18 subjects, so I guess this is
> the right analysis to use. Basically, I was wondering whether I should
> use a corrected height threshold in the generation of the SPMs? If I do
> I get no supra-threshold clusters.
>
> Is it appropriate to use an uncorrected p, given that the random
> effects analysis is quite stringent? Is there any general consensus on
> the best approach to choosing p-levels in this situation?
I am afraid exactly the same inference criteria apply to first and
second level analyses. I would think about any anatomical priors that
could be used to provede small volume correction to the p values. One
point you might want to take forward is that inter-subject differences
may include anatomical variations in the response profile. Increasing
the smoothing (of the con??? or beta???.img) prior to the 2nd level
analysis might improve your sensitivity (e.g. 8mm FWHM).
I hope this helps - Karl
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
|