Dear all,
I am trying to analyse an fMRI study where two groups of subjects
performed 4 conditions: 2 active conditions (say A and B) each with a
corresponding baseline (C1 and C2).
I am particularly interested in regions which respond to BOTH A and B
relative to their controls and therefore want to do a conjunction of
A-C1 and B-C2.
I have read various previous responses from Karl to this kind of
query and the suggestion for performing such an analysis in one group
seems to be as follows: At the first level, get con* images
corresponding to A-C1 and B-C2 for each subject. Assume
sphericity. Put all the con* images into a "simple regression"
analysis at the second level, with a covariate of [1,.....1, -1,
......-1] to look after the constant term. Then test for a
conjunction of contrasts [1 1] and [-1 1].
So far so good, and that tells me where each group shows responses to
both A and B. My question is how to then look for between group
differences in this common response to A and B. The prior hypothesis
is that one group will show a greater degree of commonality than the
other. But I am not sure how to test for this. Any tips would be
greatly appreciated. Sorry if this has been asked before but I
couldn't find it in the archives!
Many thanks
Rebecca
Dr Rebecca Elliott
Neuroscience and Psychiatry Unit
Room G907, Stopford Building
University of Manchester
Oxford Road
Manchester
M13 9PT
Phone: 0161 275 7433
Fax: 0161 275 7429
e-mail: [log in to unmask]
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