Dear SPMers,
My experiment contains different sessions (the scanner was switched off between sessions) in which subjects performed the same task. In the design specification, should I add a regressor that corresponds to each specific session, or does SPM take care of that implicitly?
In the simplest case of 2 sessions I created a session-specific regressor session1 = zeros(nbVolSession1),1)' for the first session and session2 = ones(nbVolSession2),1)' for the second session.
However, the session2 regressor does not show up in the design matrix, although I get two gray bars in the parameter estimability saying that there are betas not uniquely specified. Am I doing something wrong?
Thank you very much in advance,
Angela
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