Does running 3dclust 1.42 100 MannWhitneytest+tlrc report clusters smaller than 1992 microliters? This program just finds the clusters and (with these options) will print out a table of all clusters larger than 100 microliters.

You can use the reported locations of the clusters from 3dclust to set your crosshair locations to see what is at those places. In particular, the right-click popup menu in an image window has the "Jump to (xyz)" item -- this gives a little window into which you can paste a set of "x y z" coordinates (select them from the 3dclust table using mouse Button-1, then paste them into the AFNI coordinate window with Button-2).

When you do this, you often find that thing which look like small clusters in a 2D view are actually a part of a complex shape in 3D.

Another useful thing is to use the volume renderer in ShowThru mode to see all the activation at once. Switching between datasets (maybe with the crosshairs on in the renderer as well) can help pinpoint the differences between the datasets. Of course, this requires learning how to use the renderer, which is a non-trivial (but rewarding) task.

bob cox