Dear All!
I read the 1997 Friston PPI paper and couldn't find a solution to this
special problem in the helpline:
How can I test with psychophysiological interaction whether brain area A
differentiates between high and low levels of X (e.g., memory load or
bananas) only when activity in brain area B is *low*,
that is, whether there is an *inhibitory* influence of area B on high vs
low level encoding of X in area A?
The problem is, I don't want area A to ever differentiate low>high X
significantly, but rather high>low sensitivity to fade when area B
activity is high.
Should I do that by selecting area B as VOI and
a) assigning [1] to high X and [-1] to low X as contrast weights when
setting up PPI.ppi and then testing the [-1] contrast in the
subsequent spm model or rather by
b) assigning [-1] to high X and [1] to low reward as contrast weights
when setting up PPI.ppi and then testing the [1] contrast in the
subsequent spm model?
Any advice appreciated
Best wishes
Markus
--
Dipl.-Psych. Markus Staudinger
Social Cognitive Affective Neuroscience Group
Department of Psychiatry
Division of Medical Psychology
University of Bonn
Sigmund-Freud-Strasse 25
D- 53105 Bonn
Germany
Tel: +49 (0)228 287 19704
Fax: +49 (0)228 287 19125
E-mail: [log in to unmask]
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