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It is described here: viewtopic.php?f=9&t=335#p3884
By the way, the lighting in your scene is set up a bit strange.
For example the huge sphere light. It seems way too big, it even clips into the ceiling and ground. It is like having a giant glowing ball hanging in the room.
I would shrink this sphere light radius down to the size of a usual lamp.
Stuff like normal maps depend a bit on the lighting. If the whole room is lit very uniformly, it seems like the normalmaps are not visible.
But if you have lighting with more contrast, casting dark shadows, you will see the normalmaps better.