The extent threshold is the number of contiguous (edge-connected in SPM) voxels needed to retain a cluster after applying the voxel-wise p-value criteria.

When you first click results, it should ask you for an extent threshold after the voxel threshold.

Best Regards, 

Donald McLaren, PhD

On Tue, Aug 11, 2015 at 12:15 PM, Joelle Zimmermann <[log in to unmask]> wrote:

Hi Experts,

I've run a second-level analysis, and am looking at the statistics output in the results. I see that, at the bottom, the Extent threshold is k = 0 voxels.

I'm wondering what the Extent threshold actually means? And also how to adjust it in the SPM GUI?

Thanks,

Joelle