JUST AS I PICTURED IT ...
Visualization is a form of concentrative meditation that is a movie-style use of imagination - turning a thought or emotion or expectation into visual form or images. This is not quite the same as a dream, in that it is intentionally directed - your mind thinks it and wills it. Like with so much else that people see as 'paranormal', there's really not that much that's unusual about visualization once the malarkey is stripped away.
One of the best uses of visualization is to picture something you're about to do, taking yourself through the steps, anticipating the problems before they occur, and testing out what you could do. Say, you're a basketball player. You're headed for the big game, and your main task is to defend against the other team's scoring star. You've watched endless videotapes to learn how that player acts and reacts. You also know the way you play. By focusing your imagination on it, you can do the brain's version of a computer simulation game, picturing how you'd play in order to succeed. You might even do it while you're asleep, while dreaming, if your focus is strong. The result is that you'll know and anticipate the opponent's moves, and be ready to make your own moves, making you a more effective player.
Christians throughout the ages have used concentrated visualization to set themselves into the stories of Scripture, so that they can feel and sense and 'see' what went on as if they were there. This form of visualization can be very vivid and exciting, and can open up many sides to Scripture that you might otherwise had missed. Sometimes, you're a disciple hearing Jesus teach, or you're someone in the crowd. Maybe you envision it as Baruch delivering a real Jeremiad to the king, or as the one who cuts each piece of that scroll and throws it into the fire. Maybe as a child watching a battle from a hilltop; maybe as Jacob when he first lays eyes on Rachel; maybe as the eunuch Elnathan who asks the king to take Jeremiah out of the well; maybe as the rich young man as Jesus tells him to sell all he has; maybe as the Samaritan woman at the well, or as Paul making his escape from an angry town. The human mind is packed with the ability to do this. It's a wonderful way to draw from the riches of Scripture.
There are, unfortunately, harmful versions of the same process. It happens when the information that goes into the visualization is a lie : garbage in, garbage out. Most often, it's a lie you tell yourself over and over again. It can be something you're trying to convince yourself, for your own self-image. You play the movie in your head, with scenes that show how awful your spouse treats you, how generous and kind you are, how great you look. The movie does not show that you live more like a two-timing con man with a beer gut. Go back to the basketball game for a moment. Let's say, the player does not do the game's disciplines (such as study his opponents, think through his moves, keep in shape, practice, etc.), and projects a sop opponent that he beats with ease. What happens? His confidence will be laid waste by any disciplined opponent. What he pictures is a mere fantasy which deceives him. Visualization is no short cut; only the truth will do. Visualization is not about fantasy. It is never the whole story; it can be a good part of it.
Sometimes, the lie is told to you by someone else. Cults and self-styled gurus especially use visualization this way. You are told to concentrate deeply on the word/lie, as a "spiritual technique" to get in touch with your supposed inner self. The lie gets taken down deep when it's used this way. Even a seemingly innocent word or image can become the highway for a collapse of resistance. Which is exactly what the cult wants.
It's in vogue right now to use visualization as a mind-over-matter concentrative technique. For instance, a cancer patient pictures the tumor, then pictures and directs the natural defenses or the drug rushing to it. Advocates of this kind of visualization believe that envisioning the healing process helps to bring it about. Lying behind this is the idea that the mind has the power to mentally direct the body's healing activities. The research on this is mixed, and is mostly done by those with an interest in showing its benefits. This kind of visualization, at least, does no harm as long as it's done with other treatments, and can help the patient feel like more of a part of the healing process, which itself may be of help. Mind-over-matter theories take a small truth (frame of mind affects overall health) and make a vastly overblown claim (that the mind can determine and direct one's health and bodily condition).
Others of a new-age sort think you help attain world peace by visualizing it. Get large numbers of people to visualize, they say, and it will sway the vast unity of all things that lies behind what exists. It's certainly far better than visualizing war or terrorist attacks. (Perhaps visualization can become hostage to our fears.) But there are those who are hell-bent on making us think with hate and fear, and you won't visualize these guys away. You can't just pray them away, either. We not only have to pray for God to take action, we ourselves have to live right and live together as Jesus has taught us, in a way that responds directly to their challenge. And we can do that in unity with the visualizing new agers and anyone else who stands against terror.