Hi Megan,
Long story short: I think you should be using -regress_stim_types AM2 (rather than AM1).
Long story long: Amplitude modulation and duration modulation are somewhat different beasts.
AM1 means to _assume_ any modulation effects (amplitude or duration), and make only 1 regressor, which contains both the mean and modulation effects. Making that assumption is uncommon (for the case of an actual amplitude modulator), one generally wants to see main effects and modulation effects separately.
Duration modulation never adds an extra regressor. It convolves the current ones to be for events of the given durations. So when doing DM, is it very common to use AM1 (if there are no actual amplitude modulators).
Use of AM2 is explicitly for the case where there is at least one modulation term attached to events (not including duration modulation). When using AM2, modulators will be modeled separately from the average response.
Since you have a modulation term, you should use AM2. Having a DM term does not really affect this.
To summarize:
If you only have DM, use AM1.
If you ever have a modulation term, use AM2 (probably).
Does this seem reasonable?
- rick
