Hi,
2 Questions:
In a quite complicated design where we finished all first level analyses, I created (among others) 7 contrasts that produced the accompanying COPE images.
Contrast 1 - 4 consist of contrasting 4 different categories of stimuli presented to a repeating baseline condition in which grey screens were presented. (cat1>BL, cat2>BL etc.)
Contrast 5-7 consist of contrasting category1 to cat2, 3 and 4 respecively. (cat2>1, Cat3>1, cat4>1)
All subjects had ConditionA during session 1 and ConditionB during session 2 or vice versa (crossed-over of course).
1) We first want to find out if fMRI activitity during ConditionA differs from ConditionB
2) If the effect of ConditionA versus ConditionB varies across the categories.
3) Subjects differ (between) on one other personal variable (factor C): what is the effect on main effect or on the interaction effect of this factor
We now plan for a MAIN effect analysis and want to
1) enter all cope images from contrasts 1-4 of all subjects vertically
2) Create EV 1: to create a difference between Condition A versus B
3) Create EV 2-5 : to check if Condition is interacting with different categories
QUESTION 1: How do we enter the Between-factorC to make a within subjects comparison of Condition and Between subjects comparison of Factor C + interaction effects; how can we proceed ?
QUESTION 2: Can we expect a difference if we first analyse contrasts 1-4 and then create new contrasts between each of them,
from a second procedure: directly entering contrasts 5-7 in the higher level analysis.
Or: is the contrast to a baseline (grey screens) condition with later 'subtraction' of each 'df category - baseline' different from comparing the categories directly with each other ?
how are variances etc. involved here ?
Thanks,
Anda van Stegeren
Drs. Anda van Stegeren, VUMC &University of Amsterdam
Department of Clinical Psychology
Roetersstraat 15
1018 WB Amsterdam
The Netherlands
tel. ++ 31 20 525 6799
fax. ++31 20 639 1369
E-mail: [log in to unmask]
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