"Though a theoretical understanding of random-dot stereograms came only in the nineteen-sixties, they are akin to the stereo illusions described by David Brewster, the inventor of another early stereo viewer, as early as 1844. Gazing at wallpaper with small repetitive motifs, he observed that the patterns might quiver or shift, and then jump into startling stereoscopic relief, especially if the patterns were offset in relation to one another. Such 'autostereograms' have probably been experienced for millennia, with the repetitive patterns of Islamic art, Celtic art, the art of many cultures. Medieval manuscripts such as the Book of Kells or the Lindisfarne Gospels, for example, contain exquisitely intricate designs done so exactly that whole pages can be seen, with the unaided eye, as stereoscopic illusions. (John Cisne, a paleobiologist at Cornell, has suggested that such stereograms may have been 'something of a trade secret among the educated elite of the seventh and eighth century British Isles.')" - Oliver Sacks

Another lesson from Magic Eye pictures: everything the mind "sees" is not what the eye sees. The eye might "see" wallpaper with repetitive motifs, or intricate patterns in art, or, in the case of Magic Eye pictures, seemingly random dots. But the mind takes the raw visual input from the eyes, processes it, and then decides what it wants to "see." So, in my co-worker's Magic Eye image of a large-breasted woman, where was the image - on the page, or in my mind?

Several years ago, sitting in zazen for long periods at a Zen retreat, I was facing a wooden wall. After a while, the grain of the wood began to seem to wiggle and move, and all sorts of strange shapes began to emerge from the pattern of the wood grain. At times, the shapes looked like flames, at other times mountains and sheer cliffs, and at other times strange animal bodies and human torsos. The grain on the parallel boards in front of me were probably creating an accidental "autostereogram," similar to that observed by David Brewster. What I was seeing was not a "trick of the eyes" so much as a "trick of the mind," as the brain tried to reconcile the essentially two-dimensional input the eyes were receiving from the wall into a three-dimensional image.

Nor was it a "hallucination," an image created out of whole cloth by the mind. The mind was relying on the input it was getting from the eyes, it was not making up its own data to process. But since the input it normally got from the eyes was not an essentially static, flat image of wood grain on a wall, it was seeking new and different ways to interpret and process the input, lest it miss some important data on the surrounding conditions.

A similar thing happened to me in Alaska. After several days of backpacking with a friend, I set out on my own for some solo hiking in Peters Hills, essentially the foothills of Mount Denali. This terrain would most likely be called "mountains" anywhere else in the country, but in relation to Denali, which towered over them, they are termed Peters "Hills."

Anyway, I was up above the tree line, walking across more or less open tundra. There were no marked trails, because everything was so open and visible that it was always apparent where you were headed - Denali loomed before you, and the low country behind. If you want to hike toward Denali, there it was - just go toward it - what need is there for trails in such country?

But the sheer enormity of the landscape was unsettling to my mind. Denali was larger than anything I had ever seen standing by itself before, and I was not able to judge my distance from it. And with the lack of trees or anything else taller than myself around me, I soon found judging the distance to any object challenging. I felt like one of those natives of the densest rainforests, who have never seen anything more distant than about six or eight feet away, and who simply cannot perceive more-distant objects when first brought into a large clearing.

At one point, in a basin off to my right, I saw a small pond (or was it a large lake? I couldn't tell) and decided to walk to its shore. But I had become so unsure of my judgment of distance that even my depth perception began to wildly swing one way to another, and walking toward the pond I literally could not tell if it was a mile away, or if my very next step would splash in to it. Like in a dream where things move close and then suddenly far away, either option alternately seemed entirely possible to me as I gingerly took small, tentative steps forward, until I was able to actually touch the shore with my toe.

Disoriented, I hiked back to my car soon afterwards.

But meanwhile, back at the Zen retreat, my restless mind, bored with the great effort of hours and hours of zazen, entertained itself with the three-dimensional illusions it "saw" in the woodgrain. I could soon create whole murals in the wall, of strange Hieronymus Bosch-like creatures throwing dismembered torsos off of cliffs into lakes of fire below. But then the bell would ring, and I would suddenly snap back into the here and now.

Lest I be misunderstood, seeing strange visions in walls is not the object of zazen. It is not a "vision quest." The practice is observing that the restless mind, ever leaning toward that which it finds "interesting" or "fun," can go to great lengths to amuse and distract itself when bored, and that on an even deeper level, all that we think that we "see" is not what our eyes perceive, but how our minds interpret what our eyes see.

"The things we see are the mind's best bet as to what is out in front" - Adelbert Ames (1835-1933)

Don't be so sure that what you are "seeing" right now is that which is in front of you. It's all in the mind. As the Diamond Sutra concludes, "So you should see all of this fleeting world: a star at dawn, a bubble in the stream, a flash of lightning in a summer cloud, a flickering lamp, a phantom and a dream."