Sally and Gang,
Thanks for the hints. I sorted out, though it is looking a bit crowded with so many overlapping voxels.
Gang,
you are right about overwhelming possibilities, but the point is to show exact overlapping voxels across all 4 tasks. I was not sure if it is valid way of comparison, but seems it works.
Or maybe I can I try something esle instead? I need to show the activation elicited by each task, the common areas between pairs of tasks and the common areas between all 4 tasks - and all this on one overlay.
Thanks
Kristina