"PS Regarding the implicit assumption that error variance is constant across subjects, could this be addressed through a mixed-effects analysis in SPM? i.e. Friston et al (2005) Mixed-effects in fMRI studies. NeuroImage 24, 244-252. http://dx.doi.org/10.1016/j.neuroimage.2004.08.055"
I think that's right. I haven't looked into the issue enough to really decide though.
Best,
S
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