Hi
By default, melodic removes the each voxels' mean value over time, i.e. removes the mean image - so the data is zero centred. The degree of spatial smoothness is controlled for in the pre-proc tab in the GUI - if you set this to 0 then no additional spatial smoothing will be done. There is no temporal smoothing. Melodic will estimate the data smoothness in order to get a more accurate estimation of the number of underlying components. And no, the first set of estimates are not saved.
cheers
Christian
On 30 Nov 2009, at 21:18, Srinivas wrote:
> Hi all,
>
> I have questions in the pre-processing and PPCA stages?
>
> 1. Data - Is the mean removed per image or per voxel before doing PPCA? I
> see that "Estimating data smoothness" message appears before doing PCA.
> What kind of smoothing is done (Spatial or temporal)? Is there a way to turn
> off that option.
>
> 2. PPCA - Only PCA results in the 2nd reduction stage are saved. Is there a
> way to get the PCA information (whitening) in the first data reduction stage of
> the temporal concatenation method?
>
> Thanks for the great software.
>
> Rnsk. Srinivas
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