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Dear Wang,
My apologies, I forgot that a change was made in DCM a year or two ago (thanks to my colleague Adeel Razi for pointing this out). The
self-connections in the A-matrix are scaling parameters rather than in units of Hz (regardless of whether you use the 2-state option). A value of 1 in DCM.Ep.A(x,x) for region x means -0.5Hz. The reason for this change was to ensure that the self-connections
are always negative. In case you’re interested in the code, it is implemented on line 106 of spm_fx_fmri.m .
Please let us know if you have any further queries.
Best,
Peter
From: SPM (Statistical
Parametric Mapping) [mailto:[log in to unmask]] On Behalf Of ??
Sent: 15 April 2015 11:33
To: [log in to unmask]
Subject: [SPM] 回复：RE: [SPM] question about
DCM in SPM12: the value in mEp
Dear experts:
Yes, I talked about SPM for fMRI. I have checked my DCM.mat and I'm sure that option for two-state is still closed. What puzzled me most is why some value on diagonal of mEp.A would be positive.
Wang Yi
2015.4.15
------------------ 原始邮件 ------------------
发件人: "Zeidman, Peter";<[log in to unmask]>;
发送时间: 2015年4月15日(星期三)
晚上6:18
收件人: "晓翌"<[log in to unmask]>;
"[log in to unmask]"<[log in to unmask]>;
主题: RE:
[SPM] question about DCM in SPM12: the value in mEp
Dear Wang,
I assume you are referring to SPM for fMRI. The self-connections on the A matrix have the same definition in SPM8 and SPM12, except for the situation where you use the two-state
DCM option. In this case, they are scaling parameters and you should take the exponential when you interpret them: exp(DCM.Ep.A).
Hope that helps, let me know if anything else is unclear.
Best,
Peter
From: SPM (Statistical Parametric Mapping) [mailto:[log in to unmask]]
On Behalf Of ??
Sent: 14 April 2015 03:07
To: [log in to unmask]
Subject: [SPM] question about DCM in SPM12: the value in mEp
Dear experts:
Recently I use DCM in SPM12 to calculate some models. When checking the estimated and BMAed value of model, I find that on the diagonal of mEp.A the values are far from -0.5, which
is just the case in SPM8, and even some values are positive but not negative.
I just want to ask whether the definition of the values in mEp and sEp or so on are changed from SPM8 to SPM12, and if so how to understand the meaning of values in DCM calculated
by SPM12.
Great thanks
Wang Yi
2015.4.14