How to train your vision?

We have acknowledged that it is a good idea to train your vision. But how do you do that? I have done an enormous load of tactical exercises and chess play, according to hundreds of different regimens, but almost none of this contributed to my vision in a measurable way. Extreme fast, extreme slow, extreme many, extreme many repetitions, without repetition, blindfold, cc, blitz, rapid, OTB, Stoyko exercise, extreme difficult, extreme easy, all kind of scanning techniques, all kinds of thought processes, all kinds of board vision exercises, exercises for specific pieces, themed exercises, random exercises, and I exaggerated each exercise into absurdum in order to be able to draw a definite conclusion. None of these exercises enhanced my vision.

With three exceptions.
Polgars first brick (5333+1) learned me to look at the covered squares in stead of the pieces.
The first time that I did the Steps Method (basic exercises with explanation). With none of these exercises I worked with repetition, btw.
The third exercise was Troyis, what enhanced my ability to move around with the knight. A very specific result, which is handy, but doesn't contribute much to OTB play.

In general it can be said that by far, most exercises don't contribute to your vision, and if they do, it is by accident, and only if the material you work with is relatively new to you. In fact, doing the wrong kind of training, which is, as I showed you, almost any kind of training, proofs that your vision will deteriorate during the training. Probably not due to the training itself, but due to the fact that your vision needs maintenance, and the exercises don't provide that.

So what's the best way to train your vision? It looks like every motif-based-vision requires specific training, dedicated to that exact motif. Although different kinds of motifs can appear in the same problem.

At the moment I try to visualize the motifs that occur in a problem. But is that really the best way to train your vision?