You might find our brief technical report and the references
in that (particularly Kiebel et al 1999) to be useful in
explaining exactly what GRF does.  The report is at:

Matthew Brett also has an excellent web page explaining GRF
and cluster-based inference at:

Hope these help.
All the best,

On 21 Dec 2004, at 00:07, Fornito, Alexander wrote:

> That worked -thanks!
> You're answer raised another issue for me. I'm still trying to 
> understand how thresholding is achieved in FEAT. Let me see if I 
> understand...
> For voxel-based thresholding, is each voxel treated independently?
> Is the corrected p-value set by the user corrected according to GRF 
> theory (eg., if I set the value to .05, the threshold is corresponds 
> to a GRF corrected .05. In this case, is there any way of determining 
> what the actual threshold is?
> For cluster-based thresholding, are the voxels smoothed according to 
> the FWHM set in the pre-stats tab of the FEAT GUI? Thus, for eg., if 
> the FWHM is 5mm then the stats are run on clusters of 5 or more 
> contiguous voxels?
> What do the Z values and p values represent in cluster based 
> thresholding, and are there any rules of thumb for determining what 
> the appropriate values for these are?
> Once again, many thanks for your assistance,
> Alex
> -----Original Message-----
> From: Andreas Bartsch [mailto:[log in to unmask]]
> Sent: Monday, December 20, 2004 8:01 PM
> To: [log in to unmask]
> Subject: [FSL] AW: [FSL] Timeseries in FSL view
> Hi Alex,
> ok - this one is easy:
> Load the 4D-file (e.g., filtered_func_data) into FSLView. The selected 
> file appears in the lower box on the left. Once you have loaded the 
> stats image (e.g., thresh_zstat1) you need to select the 4D-file in 
> the box again to view the time series. I assume you had the stats 
> image selected (which is 3D), so you could not access the time series 
> of the 4D file.
> And yes - all clusters surviving the threshold are listed. But note 
> that are always some stipulations involved in defining what is 
> regarded as a cluster (which depend on the precise approach chosen). 
> To define contiguous clusters, FEAT applies an initial Z-threshold you 
> choose.
> Best regards-
> Andreas
>         -----Ursprüngliche Nachricht-----
>         Von: Alex Fornito [mailto:[log in to unmask]]
>         Gesendet: Mo 20.12.2004 03:39
>         An: [log in to unmask]
>         Cc:
>         Betreff: [FSL] Timeseries in FSL view
>         Hi,
>         I'm having trouble accessing timeseries data in FSL view.
>         I load the 4D image, and add the thresh_zstat image for the 
> contrast of
>         interest. The stat image gets overlaid on the 4D image, but I 
> am uable o
>         select "Timeseries" from the "View" menu. Am I missing 
> something?
>         Also, as an aside, in the report.html page, do the cluster 
> lists obtaine
>         by clicking on a contrast image represent an exhaustive list 
> of all
>         clusters that syurvived thresholding?
>         Many thanks for your help,
>         Alex