Hi Joseph,
Using AM1 simply applies the modulators to the individual
responses, rather than allowing for a mean response along
with modulation responses. The single regressor in AM1
should be the sum of the modulation regressors (including
the mean, so 3 in your case).
Note that when the stimulus events are so very long (2-3
minutes?), the main regressor would likely eat up much
more variance than the modulation terms, though that
depends on the strength of the modulation response, of
course. Also, be very careful with the baseline model.
Having only 3 long events in a run makes distinguishing
baseline from task more difficult.
Getting to the implied question, I am not sure what you
might want with only 2 regressors. Would one be the
mean and the other a combined modulation? To compare
with the SPM result, how many betas did the other one
generate, 1 or 2?
- rick
