Christine,

The situation for Accuracy is indeed a little tricky: each trial is either correct or incorrect, so, if you want to handle the situation at the trial level, you would essentially have to model with two types of trials (correct and incorrect) separately. If you make the assumption that the average response across the trials for each subject is proportional to their accuracy, then handle the accuracy variability at the group level by using the accuracy percentage as a covariate in 3dLME (centering accuracy within each condition).

> Or should I simply use 3dLME to handle all of the nuisance variables and forget the amplitude-modulated approach?

That should be fine since you would have to deal with accuracy at the group level anyway.

Gang