Dear Torben and Jason,
> One thing to point out is that the [Y.mad] file created from SPM is in a
> compressed format. So be careful what you're dealing with. If you need
Perhaps others can comment or correct me on this, but is seems the main
question is what exactly it is that one would be doing with the extracted
data. If the goal is simply to plot the average timecourse and look at
that plot, it seems quite unlikely that the compression in the Y.mad file
would make any difference.
The compression would be relevent, however, if the goal is to compute
some statistics on the extracted data that would involve taking sums of
squares (e.g. standard error estimates, or parameter fits). In this case
using the Y.mad file should probably be avoided and the data should be
extracted from the V*.img files.
In both cases, however, the important thing to keep in mind about Y.mad
file is that the data stored in it are already scaled as specifed during
the design specification stage. That is, it contains data that
are scaled either to the global mean or to the session specific
grand mean, depending on whether global scaling was selected or not.
This maybe useful or not, depending on how far back to the raw data one
would like to get.
Best,
-k.
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Kalina Christoff Email: [log in to unmask]
Office: Rm.478; (650) 725-0797
Department of Psychology Home: (650) 497-7170
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Stanford, CA 94305-2130 http://www-psych.stanford.edu/~kalina/
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