SHOWING ONE EFFECT IN THE FILTER GALLERY

The idea behind the Filter Gallery (under the Filter menu) is the stacking up of one filter on top of the next, but if you want to see any one of the filters by itself, just Option-click (PC: Alt-click) on the Eye icon beside that filter in the filter stack, and all the other filters will be hidden from view. Option-click (PC: Alt-click) on the same Eye icon to bring them all back into view.