Hi Panda,

> When the three conditions differ in semantic distance but semantic
> distance is not what we are interested in, is it better for us to use
> AM2 so that we can discriminate the areas which is sensitive and
> insensitive to semantic distance? In this case, should I define each
> condition in a separate "stim_times_AM2"?

Your situation does sound like that you should use the AM2 approach. However, it's a misconception that you can "discriminate" the effects between one that is sensitive to modulation effect (e.g., semantic distance) and the one that is not. The subtle issue here is that the former characterizes the marginal effect (the amount of brain activation per unit of the variable), while the latter is the brain response corresponding to the *average* value of the variable (e.g., average semantic distance across all trials). This subtlety has significant impact when you compare and interpret the comparisons across conditions at individual subject level and when you run group analysis across subjects.

Gang



Edited 1 time(s). Last edit at 07/09/2012 09:48PM by Gang.