Hello SPM users,
I have a 2X2X2 within-subject design. Ultimately my goal is to test main effects and interactions at the group-level.
I understand that I can model the different factors at the 1st level design, and that SPM will automatically identify the conditions that comprise the different factors and compute the relevant F-contrasts for main effects and interactions.
However, in addition to the 8 conditions that comprise the levels of the factorial design, I have an additional regressor which represents the appearance of an instruction phase throughout the task. As far as I know such an instruction phase should be modelled in the GLM even though it's not a part of the experimental conditions.
Will the software recognize that this condition isn't a part of the factorial design, as it appears after the first 8 conditions I defined? Should this condition be defined where confound regressors are added – because it seems that it will not be convolved with the HRF if it's defined there; Or should such a factorial design only be defined in the 2nd level analysis?
Thanks,
Ofir
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