[Eeglablist] How many dipoles to fit?

[Arnaud Delorme]

Dear Igor,

we fit 95%-99% of the components using a single equivalent dipole. We only fit 2 symmetrical dipoles for bilateral occipital alpha ICA components which are easily recognizable. Note that a large number of components cannot be fitted well with a single dipole (or 2 bilateral dipoles). These include artifactual components, or components that do not account for much of the data variance and reflect noise in the EEG data or in the ICA algorithm optimization procedure.

Best regards,

Arno

On May 27, 2011, at 6:06 AM, Igor Riecansky wrote:

>  
> Dear EEGLAB community,
>  
> I am starting to use DIPFIT2 to localize brain sources of PCA/ICA EEG components. I face a problem to decide how many dipoles to fit, i.e. one unilateral vs two bilateral symmetrical. Some papers simply always assume 2 symmetrical sources. However, if component's topography is highly asymmetric, this seems not to be justified. Furthermore, in case of a symmetric topography one could often reasonably assume both one unilateral or two bilateral sources both originating from brain structures close to the midline. Of course, solutions may substantially differ for one and two sources. What is you experience and practice? How do you solve this problem? Do you use any quantitative test? Residual variance is always lower when two sources are fitted compared to one source. Is there some rule to consider this reduction as significant, or can the reduction of residual variance be statistically tested?
>  
> I will greatly appreciate any feedback and help. Thanks.
>  
>  
> Igor
>  
> -----------------------------
> Igor Riecansky, MD PhD
> SCAN-Unit
> Institute of Clinical, Biological and Differential Psychology
> Faculty of Psychology
> University of Vienna
> Liebiggasse 5, A-1010 Austria
> Tel.: +43-1-4277-47 509
> Room No. O3.28
> E-mail: igor.riecansky at univie.ac.at
>  
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