Dear SPMers,
My experiment consists of two conditions: A and B with 3 levels each. I ran my experiment in two separate but identical sessions. I realized now that some subjects simply did not respond in some of the conditions (eg, A1B1) in just one of the sessions (eg, session 1) which means that I have no onsets to input for that condition for that session. I'm planning to average the responses fr the two sessions together, eg [0.5 0 0 0.5 0 0], and I would like to create a factorial design 3x3 at second level so didn't really want to exclude the conditions where subjects did not respond.
I thought that maybe I could use NaN as the unique onset value in those conditions where subjects didn't make any response. SPM doesn't seem to complain, but I don't know if it's a valid way of doing this.
Also, if I collapsed my data into one single session then I wouldn't have this problem, but as far as I'm aware I should be modelling the two sessions separately, is this right?
Thank you in advance,
Angela
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