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Hi Iselin,

This can happen and suggests that the significant results found in the
whole-brain analysis were "enhanced" by areas of sub-threshold signal that
were connected to them in the TFCE's support region. A smaller ROI cuts
this support region, then the findings may no longer be significant.

Hope this helps.

All the best,

Anderson

On 17 August 2017 at 05:22, Iselin Meluken <[log in to unmask]>
wrote:

>
>
> Dear experts
>
>
>
> In an experiment testing activity to emotional faces over baseline I am
> concerned that significant clusters observed at whole brain level does not
> reach significance in ROI analysis, although the ROI mask includes the
> specific area (insula and amygdala) using PALM and the TFCE option. Trying
> to understand why, I tried to rerun the same analysis with C=3.1 instead of
> TFCE, and then these areas do reach cluster-wise significance within the
> ROI mask as in whole brain analysis.
>
>
>
> Could you help me understand why this discrepancy happens? Sorry if this
> is a naive question. My theory is that this somehow happens because the
> clusters disappearing are part of a larger cluster significant at whole
> brain level, where part of this larger area is NOT included in the ROI mask
> (e.g. putamen), and that this is somehow treated differently in the TFCE
> approach compared with the traditional cluster threshold defining method.
>
>
>
> All the best
>
>
>
> Iselin
>
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