Dear spm experts,

 

I am using the EEG dataset from the website (mismatch negativity) to see how dcm works and what I can expect when applying it on my own dataset.

 

It is repeatly asked if I want to use the previous posteriors and/or previous priors when inverting another dcm. I can understand that you want to start the next dcm with the same priors but the question about the posteriors is not clear to me. These are not used as priors for the next model?

 

I tried to see how minimal changes in position of the sources could affect the estimated parameters. I looked for example to the delays DCM.Ep.D when doing this. I randomly moved a source with 0.5cm from the original position as mentioned in the reproducibility study and spm manual. I did the same for using the previous posteriors and priors and on the other hand only using the previous priors.

See attached the results. Why do I get so much fluctuation in the estimation using only the previous priors? And what is the role of the posterior for calculating the next dcm. It is not clear to me from the papers of kiebel 2006, david 2006.

 

Many thanks,

Best regards,

Prejaas Tewarie