Hi Cédric,
> The question of how to deal with subjects not activating the ROI remains...
>
> -set the threshold to 1 and extract the VOI time-series ?
>
> -choose a liberal threshold (say 0.1) and exclude subjects without
> activation ?
I'm no expert on this, but I think that either should be okay...
I think the former would be more in keeping with standard statistical
practice. For example, in a summary statistic approach where straight
lines where fitted to within-subject data, and then slopes compared
across e.g. groups of subjects, I *think* it would be very
non-standard to exclude any subjects from the group analysis if their
regression slopes where insignificant according to any criterion.
However, I think the key idea behind spm_regions is that the contrast
you subsequently investigate over the VOI is orthogonal to the
contrast used to select the VOI (e.g. define VOI based on main effect
of slope, then test the orthogonal slope-group interaction). So I
think you can therefore exclude subjects without biasing the
subsequent analysis.
So I think my answer to this might have to be the rather woolly
"you'll have to decide based on what makes more sense to you in your
experimental context". Though I do hope that more statistically
knowledgeable people post more clear-cut answers to the list!
Ged
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