Dear SPMers:
We are working on continuous spin labeling data where we are acquiring sessions during which a task is applied.
There is a session of a baseline resting state and three sessions during which a task is applied.
Each sessions consists of 30 volumes (since in cont. spin labelling the TR is very long).
Is it appropriate to concatenate the four session into one and then make up the contrasts by assigning onset and duration times that correspond to the appropriate position in the concatenated series of volumes, as if we had one very long session.
This approach would of course be problematic if SPM used a special covariance structure like an autoregressive covariance but it probably would not matter if SPM was using a compound symmetry covariance structure. I am not sure what's "under the hood".
Any thoughts on this?
Regards,
Michael Froelich
University of Alabama
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