Reply-To: | | [log in to unmask][log in to unmask], 2 May 2012 14:53:07 +00002340_utf-8 Dear Martin,
To my knowledge there are a number of papers on your last topic.
Synthetic data with different neural parameters (connectivity structures):
W.D. Penny, K.E. Stephan, A. Mechelli, and K.J. Friston. Comparing Dynamic Causal Models. NeuroImage, 22(3):1157-1172, 2004.
W. Penny (2011). Comparing Dynamic Causal Models using AIC, BIC and Free Energy. Neuroimage. Available online 27 July 2011.
Synthetic data with different hemodynamic models:
K.E. Stephan, N. Weiskopf, P.M. Drysdale, P.A. Robinson, and K.J. Friston. Comparing hemodynamic models with DCM. NeuroImage, 38:387-401, 2007
Best, Will
> -----Original Message----- > From: SPM (Statistical Parametric Mapping) [mailto:[log in to unmask]] > On Behalf Of Martin Pyka > Sent: 02 May 2012 12:41 > To: [log in to unmask] > Subject: Re: [SPM] DCM fails to select model that generated the data > > > That makes sense that my problem might have something to do with the > EM algorithm settling on a relatively poor local maximum for the > correct model. How can one mitigate this risk? If the EM algorithm > starts at an arbitrary point, then it would seem that increasing > subject or run number would help. Are there properties of a specific > model structure (or space) that would make one more or less susceptible > to this? > > This is a good question. I don't know how important this problem in DCM > actually is and (if it is important) how to avoid it. Maybe, there is > already an article about it that I am not aware of. > > If you have more detailed pre-assumptions about the real neural and > hemodynamic paramaters of your model it could help to start the EM with > those values. If this is not possible, it can help to run the EM a few > times with different starting positions. > > In general, I think, it is necessary to test if model selection works > properly using synthetic data generated with various (!) neural and > hemodynamic parameters. I would like to know if this has been done > before. > > Best, > Martin > > > > -- > SPM for programmers > http:[log in to unmask] |