In an event related fMRI study I am interested in EVs where the value of the input (I am using the 3 column format to specify my EVs) varies across the experiment.
I decided to input one EV where the value of the input was always positive (varying between 0 and 1 as I'm looking for activations) and one EV where the value of the input was always negative (varying between 0 and -1 as I'm looking for deactivations).
However, on re-reading the Feat-in-detail webpage, I see that "ALL columns are demeaned before model fitting".
So, it seems I can't obtain my original goal of finding areas where there are activations (relative to the unmodeled baseline) and those activations vary in magnitude in a way that proportional to a behavioural variable and other areas where there are deactivations (relative to the unmodeled baseline) and the deactivations are variable in magnitude proportional to a behavioural variable.
In case it is of help in clarifying my study, my aim is to look for areas where signal strength correlates with positive and negative prediction error value (different value for every trial) in an associative learning experiment.
Any comments most welcome
Thanks
Graham
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