Hi Panda,

> (1) Which is the correct way when I want to get the areas which is modulated
> by the semantic distance? AM1 OR AM2? What's the difference between the
> modulated areas we got from AM1 and AM2?

If you want to find out the brain regions whose modulation effects are associated with the semantic distance, AM2 is what you looking for. More specifically, it's the second regressor from each AM2 that indicates the modulation effect.

The difference between AM1 and AM2 is subtle. With AM1 you assume a standard response magnitude that corresponds to one unit of the semantic distance. In the end you would only get ONE effect estimate that corresponds to one unit measure of your modulation parameter (semantic distance).

With AM2 you model the response of each condition with TWO effects: the first one shows the brain response that corresponds to the AVERAGE semantic distance of all trials for that subject, and the second effect reflects the modulation of the semantic distance in percent signal change per unit of semantic distance.

> (2) Should we aplly the same thresold to the modulated areas from AM2? In my
> case, when I apply the same threshold as the activation map to the modulated
> areas from AM2, no cluster will survive.

Individual subject or group level? You should adopt the same thresholding, although the significance may depend on the power of the experiment design. Also you should pay more attention to the group analysis results because that's what matters in the end.

> (3) something I'd like to confirm: when doing group analysis after apllying AM1
> or AM2 to individual subject, is it just the same as usual? I mean, we just need
> to apply 3dttest++ to test the significant of the modulated or unmodulated areas?

For AM1 or for the modulation effect (2nd effect) of AM2, the group analysis should be pretty straightforward.

For the average effect (1st effect) of AM2, you may consider to use the AVERAGE semantic distance from each subject as a covariate in your group analysis because the average semantic distance could vary a lot from subject to subject.

Gang



Edited 1 time(s). Last edit at 08/31/2012 01:28PM by Gang.