Hi,
after looking through a lot of documentation and spm-mail archives I
still don't understand the scaling of the event related PSTH Plot.
For a test I took one session of an event related fMRI with one
condition (call it "go") and concentrated on the activated voxel with
the highest T-value using spm99 with all updates and a slightly
modified version of Kalina Christoff's extractYmad. The results are
confusing to me:
The global intesity varies between 274.1 and 277.4 (mean 275.4712)
The voxel intesity (from Y.mad with no filtering) shows on average an
event with baseline 229.5 and peak of 232.3 which I interpret as signal
change around 1% scaled to session global mean as it should be in the
"unscaled" condition.
beta1 is 0.91 beta2=230.55(=session confound)
plotting event/epoch-related fitted response and PSTH directly in spm99
shows me a signal change of about 2.5% for the fitted and the PSTH though.
Am I doing something completely wrong here?
In hope of enlightenment,
RM Rutschmann
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