Additionally What you are going for is, if you hold up lined paper so the lines are going vertically, to let your eyes out of focus so that you would start seeing double, ((as if looking at something through and passed the page) and then focus your eyes where the doubled lines of the page overlap. You can then play with bringing into focus lines that are two lines apart, three lines apart, 4 and so on. The action of seeing past the page and focusing on the doubled image made by the overlapping is what you are going for.