Corners?

We have inherited a home that was bulit in the 50's. The walls in every room minus the kitchen and bathroom are textured plaster. We have primed the bedroom twice, 2 coats cut in and on the walls. The corners all around the room seem hollow, I don't know how else to explain it. I have noticed this in all the other rooms as well but they just seemed dirty and unable to get clean. Now that we have primed this room it seems like its the walls not a poor paint job.

What could cause this? Is it light reflection off the smoother corners or do the corners just need more coats of primer?