> First level Analysis:
> I have the following questions:
> (1) Is there task related activity? I am setting this up as shown in the attached diagram
> with a '1' for the task and all zeros for the rest of the parameters.
Yes, that's right.
> (2) Does the addition of the custom regressor (R) change my activation? That's a more
> tricky question and I am not quite sure about it. Should I set that one up as a '1 1
> followed by zeros' - contrast or a '0 1 followed by zeros' - contrast?
Ignoring motion regressors, you have 2 columns per session: the first
is the main task, and the second the additional regressor R. I would
think of it like this: A contrast of 1 0 (as you noted above) gives
you mean activity related to your task across all levels of your
custom regressor. A contrast of 0 1 gives you activity related to
your regressor that deviates from the mean: if you perform this
contrast and don't see anything, it would suggest that this custom
regressor is not resulting in any extra neural activity. (This is
assuming you mean-center your custom regressor, which is the default
and makes sense in this case.)
A contrast of 1 1 is probably not very meaningful, because it
essentially takes the average of the main task and your custom
regressor. If you get a significant result you don't know which of
the two it comes from; and if you don't get one, it is hard to know
> Alternatively, should I run 2 models, one including the custom regressor 'R' and one
> without it and I am getting two .mat files in my 1st level analysis, how do I then set up
> my model comparison in SPM? I understand that comparing nested models would be an F-
> test, but how do I enter two .mat files in the contrast manager?
I don't see how this would give you anything additional; if you
include your regressor in your original model, the simple 0 1 contrast
should tell you if it is contributing.
> (3) If I figured out the proper way at the subject (1st) level, how do I use this information
> at the second level. Presumably, this depends on the approach at the first level.
If your questions on the group level are the same as those for the
single subject level (as you explain above), and you have one group of
subjects, you can just enter each of those contrasts in a 1 sample
t-test. So, one t-test to look for a group effect of task, and a
second one to look for a group effect of your custom regressor.
Good luck! Hope this helps.