When I use soft brush to paint I got a result like this:

You can see the rings in the red circle.This is just a simple dot drew by the standard soft brush.
What could cause this kind of problem? It is suddenly appeared and I don’t think I changed any settings of photoshop or my monitor.Well, maybe I just didn’t notice it before…
I searched the Internet and find some people got the same problem with me but it seems no solution.So I try to ask at here again to see if anyone could help me.It is really painful that I can’t go on with my work… 