Dear Markus,
>after carefully reading the SPM99 manual and an intensive search on the
>mailing list I still do not understand the so-called peri-stimulus time
>histogram (PSTH).
The PSTH (peristimulus-time histogram) option provides a finite impulse
response (FIR) estimate of the trial-specific evoked response as a function
of peristimulus time. This is estimated by refitting a convolution model
to the selected voxel using an FIR basis set. This is simply a set of
small boxes covering successive time bins after trial onset. The width
of each bin is usually the TR. This option provides a more time-resolved
quantitative characterisation of the evoked hemodynamic response. However,
it should not be over-interpreted because inference is usually made using a
simpler and more efficient basis set (e.g., canonical hrf, or canonical
plus time derivative).
>How to chose a reasonable bin size? Does it make sense to chose a time bin
>of 3 sec if the TR was 3 sec?
Yes.
>What is the unit of "response at [...]"?
The units are a-dimensional and correspond to percent whole brain mean.
>Where could I find the values of the PSTH in the matlab workspace?
You will not. If you would like to see them, you will have to modify the
code in spm_graph. Use something like:
save PSTH PST PSTH
and load PSTH after plotting.
>Have a nice weekend!
Thank you.
Karl
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