Dear Karl, Dear SPM users
We recently asked you for advice concerning our prepulse inhibition
(PPI)-H2O-PET study.
May we bother you again with some basic questions:
This PET study includes 9 scans/3conditions per subject. So far we have
measured two
goups of subjects (a and b). The group a and b have been stimulated using a
different number but identical startling acoustic pulses and prepulses
respectively per scan.
We wish to address the question whether the different number of stimuli used
between group a and b lead to different activation patterns.
So far we tried to use a multigroup design and the following contrasts to
assess the differences between group a and b for the pulse alone conditions:
1a 2a 3a 4a 5a 6a 7a 8a 9a 1b 2b 3b 4b 5b 6b 7b 8b 9b
NS NS NS PP PP PP P P P NS NS NS PP PP PP P P P
0 0 0 0 0 0 1 1 1 0 0 0 0 0 0 -1 - 1 - 1
similarly, for the differences base on prepulse plus pulse (PP) we used:
1a 2a 3a 4a 5a 6a 7a 8a 9a 1b 2b 3b 4b 5b 6b 7b 8b 9b
NS NS NS PP PP PP P P P NS NS NS PP PP PP P P P
0 0 0 1 1 1 0 0 0 0 0 0 -1 -1 -1 0 0 0
However, the program did not accept this contrast settings!!!
What might be the appropriate contrast settings to investigate the effect of
the different numbers of pulses and prepulses used between the two groups
???
Could it make sens to use a design where we treat the two groups (a and b)
as one
group of 18 scans ti investigate this effects?
for example for the pulse condition:
1a 2a 3a 4a 5a 6a 7a 8a 9a 10b 11b 12b 13b 14b 15b 16b 17b 18b
NS NS NS PP PP PP P P P NS NS NS PP PP PP P P P
0 0 0 0 0 0 1 1 1 0 0 0 0 0 0 -1 -1 -1
Thank you very much for advice
Sincerely yours
Daniel
Daniel Bächle
Psych. Uni-Klinik Zürich
Forschungungsabteilung
Lenngstr. 31
Postfach, CH-8029 Zürich
Tel. +41 (0)1 384 23 10
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