Yes, this is possible. If your threshold at the single-subject level
is, say, t=3.09 and every subject has an activation in the same place
but at a maximum of t = 3.05, you will not see anything on the
individual subject analysis but you will see activation in the RFX
analysis because it is consistent across subjects.
The most likely interpretation for such an outcome (RFX activation
without associated single-subject activation) is that the activations
were subthreshold in the individuals. You can test that by looking at
the single-subject data with a more lenient threshold, or by doing ROI
analyses on the region in question.
russ
Priyantha Herath MBBS wrote:
> Dear all,
>
> I was just wondering whether it is possible to have a situation where
> one finds no consistent activations in any given cortical region
> reflecting the activity for a given contrast it the subject level
> analysis, and yet to have a robust , significant activity when an RFX
> analysis is performed on the same set of subjects for that same
> contrast?
> If this is possible, what will the interpretation be?
>
> Thanks,
>
> Priyantha Herath
--
Russell A. Poldrack, Ph. D.
MGH-NMR Center
Building 149, 13th St.
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Phone: 617-726-4060
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Web Page: http://www.nmr.mgh.harvard.edu/~poldrack
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