Hello FSL experts,
I'm setting up a model with FIR basis functions for the first time and have some general questions.
My task is a simple autobiographical memory recall task. Each trial has 3 epochs:
epoch 1: view memory cue (10 sec)
epoch 2: recall details of memory (30 sec)
epoch 3: rate subjective valence/arousal (10 sec)
A long ITI (30sec) separates each trial, and my TR=2sec. I also have two groups of participants: patients and controls; I would like to use FIR so that I can examine, in addition to a main effect of group at epoch 2, group by time interactions occurring in epoch 2.
My initial plan was to set -within the FIR basis function series of inputs- Phase=0, Number=15, Window=30 - with the thought that I could capture activation occurring roughly every 2 sec (time locked to the TR) throughout epoch 2 (for a total of 15 events within each 2nd epoch of a trial). However, I see that to do that, I must also set epoch 1 and epoch 3 to also have 15 events. In trying to force epoch 1 and epoch 3 to do otherwise (e.g., phase/number/window=0/5/10 instead of 0/15/30), I get an error message: "In order to setup contrasts in 'Original EVs' mode whilst using basis functions or sinusoidal harmonics, all the original EVs must be the same basic shape and generate the same number of real EVs. Please change the EV setup."
To unequally divide each epoch into separate FIR bins seems counterintuitive. Can you please advise on how to proceed? How are these basic modeling steps typically handled with FIR basis functions?
Many thanks in advance,
Lara
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