Dear all,

I have taken this statement from SPM manual.

In this way SPM can account for possible "non-sphericity" in the data. This is implemented in SPM using a set of matrices (bases) that characterise the covariance matrix. The first three correspond to the variance of each of the canonical, temporal and dispersion derivatives: SPM.xVi.Vi{1}, SPM.xVi.Vi{2}, and SPM.xVi.Vi{3}.
The next three correspond to covariances: SPM.xVi.Vi{4} (covariance between canonical and temporal derivative), SPM.xVi.Vi{5} (covariance between canonical and dispersion derivative), and SPM.xVi.Vi{6} (covariance between temporal and dispersion derivatives).
After estimation the actual covariance values (hyper-parameters) are given by SPM.xVi.h (the six entries correspond to the above bases).

According to above statement if you have two conditions and you are taking 3 basis functions, canonical, temporal and dispersion derivative then you should have SPM.xVi.Vi{1} - SPM.xVi.Vi{6} (Six vectors).

But I am taking the same design matirx, 2 conditions and 3 basis functions but I have only two vectors. SPM.xVi.Vi{1} and SPM.xVi.Vi{2}. So I have only 2 values of hyper-parameters (SPM.xVi.h).

Please tell me where I am wrong.

Thanks in advance

Regards

NUML