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Bug 1321 - projectmom in ft_sourcedescriptives suboptimal for time domain methods?
| Status | CLOSED WONTFIX |
| Reported | 2012-02-09 11:24:00 +0100 |
| Modified | 2018-11-12 10:56:41 +0100 |
| Product: | FieldTrip |
| Component: | core |
| Version: | unspecified |
| Hardware: | PC |
| Operating System: | Mac OS |
| Importance: | P3 normal |
| Assigned to: | Jan-Mathijs Schoffelen |
| URL: | |
| Tags: | |
| Depends on: | |
| Blocks: | |
| See also: |
Jan-Mathijs Schoffelen - 2012-02-09 11:24:30 +0100
ft_sourcedescriptives uses svdfft for the estimation of the optimal orientation, both for frequency domain and time domain source reconstruations. Internally, the csd/covariance is computed, and an svd is performed. As far as the frequency domain is concerned, the csd is correctly estimated from f*f' where f are the 'raw' fourier coefficients. Yet, it is questionable whether the same applies for the covariance, (mom*mom') where mom is the 3D-dipole moment as a function of time. The mom is not necessarily zero mean. Does this yield a sub-optimal covariance estimate? (and thus a sub-optimal estimate of the optimal dipole orientation?). Note: this non-zero mean issue also arises in the computation of the source.avg.cov (mom*mom'), and the determination of optimal orientation in ft_sourceanalysis (cfg.fixedori = 'yes'). I would suggest to adjust svdfft with an optional extra flag which specifies whether the data need to be de-meaned, or to implement a svdmom (probably cleaner, because svdfft is specifically designed for freq-domain analysis and it hacked its way into the time-domain code too).
Robert Oostenveld - 2012-02-09 15:11:52 +0100
Hi JM I just finished discussions with the FIL team on SPM12. There are some relevant plans that also impact fieldtrip, esp. on the source estimation (ft_inverse_xxx) and the post-processing of the estimations. Please postpone any actions until we have discussed this in detail (i.e next week). best Robert
Jan-Mathijs Schoffelen - 2018-10-09 12:38:12 +0200
not for now.