What exactly is SPM.Sess.U.u? I know the help file says "(t x j) inputs or stimulus function matrix", but what does this mean? Is this related to the time points? For example the example attention dataset has 360 time points, but SPM.Sess.U(1).u has 5792 rows.
Also why does it start with "(193,1) 1", and not with "(1,1) 1"?