Question 1: Is IM capable (I am referring to when it is used in 3ddeconvolve the typical LSA approach not LSS) of using auxiliary data for amplitude modulation? So you would have betas for each trial and each trial could be modulated by something like RT, difficulty, stimulus intensity, etc…
Question 2: When it comes to LSS it seems that only one IM file can be read unless I am misunderstanding the documentation. Is this the case and if so how should I keep track of my trials conditions and is 3dLSS capable of amplitude modulation?
Q1: It does not make sense to use amplitude modulation with IM, since computing the coefficient (beta) for the AM component requires at least TWO events – one for the beta describing the mean response, and one for the beta describing the variable response. With IM, there is only one event per regressor. Instead of AM, you get a different beta for each event time in the same stimulus file – and then have to combine those betas somehow to get useful information.
Q2: Yes, only one IM regressor is allowed in 3dLSS. This program was a quick implementation for someone (and now I don’t even remember why I wrote this code). I am unlikely to make any changes to it, since 3dLSS is very low priority for me.