John Fairbairn wrote:
This discussion seems to lack an agreement on what is meant by visualisation, and the last example perhaps muddies the waters even further. It would be fascination to hear theories on what it is.
Moi, when I talk about conscious visualization I mean having a more or less clear and distinct mental image. That's all.
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Visualisation presumably is some combination of at least a couple of processes. I'd guess it starts with recognition, a variable skill that increases with grade and which must be extremely high in pros. There is then some skill that enables one to set a goal (as Bill describes) and to work towards it. Stiil, while iff you have the subsequent skill set you can really get to work, you can't do anything if there is no recognition to start with.
I mentioned the goal position to jlt because he said he had trouble with visualization around move 10, even though he had seen the solution. If he had visualized the position after move 12, IMX, he would have found it relatively easy to work out the variation to get there.

I did not mean to imply that he should somehow have seen the goal state to start with.
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But this example seems to suggest at least two kinds of recognition. I recognised it instantly as a blunder by a very eminent player (and so also knew the answer instantly). That kind of whole-shape recognition is actually quite common even among amateurs (L group, notchers etc) and the fame element is just icing on the cake here.
In bridge there is an advanced play called a squeeze. It used to be the mark of a master, but nowadays the level of play has improved so that the equivalent of 2 kyus can run squeezes. But there are a number of squeezes, some quite advanced, so that the order of play is very important. There are rules about how to decide the correct order of play, and learning those rules can be quite a challenge. But there is a technique, discovered, I believe, by Sidney Lenz, called visualizing the squeezed position. I found that, if I learned the squeezed positions of these advanced squeezes, I could work out the order of play to get there. For go problems, I have found that visualizing the goal position also helps to figure out how to play. OC, the goal position is not always obvious.

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But unlike us, the player concerned here would not have seen the position before and so could not recognise it in that sense. Yet clearly it was expected of him that he should have recognised something there, otherwise it wouldn't have gone down in history as a famous blunder, and he wouldn't have felt so mortified afterwards. The question then is what was he meant to recognise?
My guess is that if he had seen the first play he would have found it easy to read the position out, given his level of play. The goal position is of a kind that he would have been familiar with. (Not that he would have seen it before doing any reading.)
Knowing that this was a problem, I had no trouble finding the first play. Would I have found it in a real game? Probably not.
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The elements of what he is supposed to have recognised (topological features?) are probably listable.
Black has two strings, each of which has 3 dame, but they share 2 of those dame, so that together, they have only 4 dame. (Wilcox points out that with only 4 dame they may be vulnerable.) Furthermore, one of those shared dame is adjacent to two White stones, so connecting the two strings on that shared dame will leave them with only 3 dame. And if White puts a stone on the other shared dame, then if they make that connection they will have only 2 dame, and Black to play can put them in atari and then capture them. That other shared dame is the first play.
If White makes that first play, Black will have to capture that played White stone in order to connect the two strings. That being the case, there are other familiar features to the play. And in addition there are other familiar features, such as an atari with sente that takes away a liberty, and a connect-and-die of the sort that occurs in many tsumego.
Edit: Actually, that atari is not necessarily sente, is it?