That looks correct. Look at the beta values for those conditions. Maybe e.g. the parameter estimate for the TD for condition 4 is high, making the con value close to 0.
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From: SPM (Statistical Parametric Mapping) [[log in to unmask]] On Behalf Of megha sharda [[log in to unmask]]
Sent: Thursday, September 09, 2010 2:30 AM
To: [log in to unmask]
Subject: [SPM] Specifying F contrast for hrf with time derivative
Hi all,
I'm trying to analyse data from a sparse sampled event related design. I have four conditions for which I'm modelling the canonical hrf with time derivative. When I simply model the hrf (using t-test in contrast) I get some activations. However, when i'm trying to use the hrf with time derivative, I get no activations at all. I specified the F-contrast using two vectors - [ 1 0 0 0 0 0 -1 0]; [ 0 1 0 0 0 0 0 -1] to look at the contrast between condition 1 and condition 4. (c1-c4). Any suggestions?
Thanks!
Megha
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Megha Sharda
Graduate Student
National Brain Research Centre
Manesar, Gurgaon -122050
India
Ph: +919810943202
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