I have followed the tutorial for DCM analysis and I have a question regarding 1st level contrasts. The example in the manual (see below) shows that contrasts vectors include values based on the order of trials in the session.
think of the contrast vector as a concatenated vector for all sessions - i.e. if session 1 has 36 trials, and session 2 has 11, then the 37th entry in the contrast vector refers to the first trial of session 2, and the 48th entry to the first trial in session 3.
Hope this helps
Dominik
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Hello,
I have followed the tutorial for DCM analysis and I have a question regarding 1st level contrasts. The example in the manual (see below) shows that contrasts vectors include values based on the order of trials in the session.
1st level model specification:
Condition
· Name: CS+|US-
· Index: 6 7 11 14 16 18 26 29 38 40 Condition
· Name: CS+|US+
· Index: 13 17 19 20 21 24 28 31 32 37
* Condition
· Name: CS-
· Index: 1 2 3 4 5 8 9 10 12 15 22 23 25 27 30 33 34 35 36 39
1st level contrasts:
Contrast
Name: Fear Learning (CS+|US- > CS-)
* Contrast Vector: -1 -1 -1 -1 -1 2 2 -1 -1 -1 2 -1 0 2 -1 2 0 2 0 0 0 -1 -1 0 -1 2 -1 0 2 -1 0 0 -1 -1 -1 -1 0 2 -1 2
In my experiment I have multiple sessions and each session has a different trials order. How do I specify contrasts vectors? Am I missing something?
Many thanks and best,
Ambra
Hi Ambra
think of the contrast vector as a concatenated vector for all sessions - i.e. if session 1 has 36 trials, and session 2 has 11, then the 37th entry in the contrast vector refers to the first trial of session 2, and the 48th entry to the first trial in session 3.
Hope this helps
Dominik