I have an experiment in which events of interest are of different durations 1 s to 15 s. I want to look for brain regions that show increase or decrease in activity at the onset, during, and end of these events. Since events are of different duration and numbers, I am wondering what is the best way to model onset transient, sustained, and end transient activity for this experiment. My approach is to have three different regressors:
The first regressor will be an impulse regressor which models transient activity at the onset of all events.
The second regressor will be a variable epoch regressor which models sustained activity at longer events (> 2.5 s) .
The third regressor will be an impulse regressor which models transient activity at the end of longer events (>2.5 s).
Three contrast, [1 0 0], [0 1 0], and [0 0 1] will give me brain regions active at onset, during, and end of these events.
Is this a valid approach?