Dear SPMers,
I want to examine common activity during 3 task conditions (A, B, C) separately for neutral & negative material. (NEU / NEG). On the first level I build the contrasts against implicit baseline (A_NEU, B_NEU, C_NEU, A_NEG, B_NEG, C_NEG).
On the second level I build a flexible factorial Model with the factors
1) Subject (number of subjects = No)
>> independence yes / variance equal
2) Emotion (2 levels)
>> Independence no, variance equal
3) Condition (3 levels)
>> Independence no, variance equal
For each subject – I entered the following information
Order of first level images to include:
A_NEU, B_NEU, C_NEU, A_NEG, B_NEG, C_NEG
Conditions:
1 1; 1 2; 1 3; 2 1; 2 2; 2 3
Main effects & interactions:
1) Main effect = 1
2) Interaction = 2 3
To assess the common activity within a conjunction I initially set-up the condition-specific contrasts across participants (example N = 4 participants)
For emotion a conjunction of all conditions I build the three contrasts
1 0 0 0 0 0 0 ¼ ¼ ¼ ¼
0 1 0 0 0 0 0 ¼ ¼ ¼ ¼
0 0 1 0 0 0 0 ¼ ¼ ¼ ¼
Next I use the conjunction contrast of these contrasts on the 2nd level to evaluate common activity for Neutral stimuli in the three conditions.
My questions:
1.) Is this analysis approach generally valid? I read about some methodological issues of the conjunction analysis.
2.) Which option in SPM12 to choose: conjunction or global Null?
Thanks in advance & best regards
Ben
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