The Blind Spot - Part One  (Thomas Fraps)

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To ignore questions of why we are so easily fooled
by conjuring is a serious oversight of psychologists,
for there is far more to it than mere sleight of hand,
or the hand moving faster than the eye can follow.

Richard L. Gregory

"Magic takes place in the spectator's head." One often runs into this sentence in books or lectures on magic. In a trivial way it's true—there is no magical effect without a spectator. No magic occurs when one practices at home in front of a mirror. Not until the minds of spectators become involved do such ordinary things as a top change or a false transfer become magic.

Exactly what happens in the minds of the spectators? What causes a spectator to believe that the coin which appeared under the salt shaker is the same one which disappeared from the performer's hand? Why does a lemon "appear" under a cup, although it was only transferred from a jacket pocket into the cup?

Misdirection, timing, and technique are a few terms capable of explaining why it's possible to distract the spectator against his will. Why are certain actions and movements cut out (i.e., not observed), although they take place before our eyes? The answer is only hinted at in the volumes of literature on magic: "It works," that's the important thing.

A few exceptions are, for example: The Psychology of Deception—Why Magic Works, Randall, 1982; The works of Arturo de Ascanio in Ascanio's Magic, as well as Conjuror's Psychological Secrets, Sharpe, 1992. "Directing Attention" in Card College, Vol. 2, Giobbi, 1996. See also Richard L. Gregory, Odd Perceptions, Routledge, London, 1986.

With equal validity the opening quotation, from one of the most famous researchers on the mysteries of perception, can be applied to magicians as well. In fact, it's a grave omission of magicians to ignore this question. Our explanations, with few exceptions, are merely more discriminating versions of those proposed by laymen. What is remarkable is that the explanation for what happens is sought in the magician, as if he alone were responsible for the illusion's occurrence.

We do the necessary absurd things—like doing a pass, wearing a thumbtip, or sewing in a Topit—in order to give the impression of magic. But without the active help of the viewer's perceptive faculties, this impression couldn't be made at all. Why not turn things around and look for the explanation in the spectator. The world acts crazy in his head, not ours.

This leads us to the question of how the signals from our environment are put together in our heads to form a picture of reality. In order to throw a little light on why magic as such works, a few cross-references to research on perception follow. This will not directly improve your stage presence, but it might give you a deeper understanding of what a magician actually does when he performs. This helps to increase the magical content of the individual tricks and their impact on the audience, a goal which no magician should forget.

Seeing is Believing

Although all five senses contribute to our perception of the outer world, vision dominates. The following illustrations are, therefore, limited to the visual system.

At first glance, perception appears to be a passive process comparable with photography. One assumes the outer world is pictured on the retina (the way a film is exposed in a camera) and the incoming information must only be decoded. But this first glance deceives. The analogy to a camera is, at best, valid only for the first step of perception, the focusing of light rays through the lens on the retina. Several complex switching mechanisms take place in the retina which are representative of the entire perceptive process; research has shown that at this stage more has already happened than the mere copying of a picture of the outer world.

On the contrary, from the incoming physical stimulation—in this case, lightwaves—our brain actually constructs its own picture of its surroundings. This picture does not necessarily coincide with physical reality. As a simple example, consider your first glance in the mirror in the morning. After you have recognized the person in the mirror, measure the length of your face on the plane of the mirror. You will discover that it's only half as long as that of your actual face. Obviously, there is something wrong with our perceptive facility which makes the face in the mirror appear to be actual size. This has nothing to do with how tired you are, but with the way we perceive the size of things, i.e., the way the brain calculates the actual perceived picture from the visual input (retina picture). Such "calculation processes" usually occur unconsciously: they take place without our willful control.

Comment: Not only is the size of the corresponding retina picture used in the estimation of an object's size, but also its distance. This has the advantage that the object's size remains constant while it moves toward or away from us. If we estimate the distance of an object incorrectly, this directly effects the perceived size. In case of the mirror, our face appears twice as large because we estimate the distance to be twice as large. A further example is the "moon illusion." A moon rising on the horizon in the early evening appears many times larger when in the night sky. (See Perception by Irvin Rock, W H Freeman & Co., 1995)

Look at the two tables in figure 1 At first glance you won't notice anything unusual, but if you measure the edges of these tables, you will be astonished to discover that both are identical. This example illustrates that between the original sensory stimulation and the conscious perceived picture, mental processes (of which we are not conscious) automatically take place. These processes are capable of creating an illusion all by themselves.

See Mind Sights: Original Visual Illusions, Ambiguities, and Other Anomalies, With a Commentary on the Play of Mind in Perception and Art by Roger N. Shepard, W. H. Freeman & Co., 1990 See also Sam H. Sharpe Conjuror's Optical Secrets, Hades Publications, 1992.

Although these mechanisms fabricate a false picture of the outer world under certain circumstances, they work very well for everyday use, and are needed to compensate for the insufficient data at the lowest level of visual perception—the eye.

Figure 2 shows a schematic of the eye. Outside light passes through both the cornea and the lens before falling onto the retina. The latter consists of rows of cells of which the most important are light receptors. There are two types. About 120 million "rods" are responsible for black-white vision under limited lighting.

The "cones," on the other hand, are responsible for colored vision and the recognition of details under normal illumination. The distribution of the two types of receptors on the retina is interesting. The rods are concentrated at the edge, whereas the cones are almost exclusively concentrated at one point, the Fovea centralis. This tiny area, which has a diameter of only 2 mm, is responsible for clear vision. If we want to observe an object precisely, we fix our eyes so that the object's image falls in the area of the Fovea. At the same time we see another part of the object, which is pictured in the peripheral area of the retina, unclearly.

Comment: Stretch your right arm in front of you with the thumb pointing upward and close the left eye. If you now look at another object in the room, the size of your thumb is approximately the area in the field of vision which you can see sharply.

This is the physiological basis for the "tube effect," was first described in the magical literature by the late Arturo Ascanio. The attempt to divide your attention between light and dark areas corresponds to the two types of receptors in the retina and their distribution.

See: The Psychology of Palming, p.4, Ascanio (translation by R. Giobbi), 1982.

In general we are not aware of how narrow the area of clear vision is, we always see the entire picture sharply—at least it appears so. We have this impression, however, because our eyes constantly shift from one point to another while probing our surroundings, making snapshots during the short fixation phases. While the eyes move, the picture on the retina is blurred and useless as a source of information for further perceptive mechanisms.

A shift in attention always accompanies eye movement, regardless of whether it's the reflex from a stimulation in the peripheral area of the retina (for example, seeing a tiger in the corner of the eye) or consciously controlled (as in looking at a painting). Therefore, the eye movements indicate the focus of our attention. One of the first measurements of the path of eye movement in observing a face show clearly that the eyes are a center of attention (figure 3).

See A. L. Yarbus Eye Movements and Visions, Plenum Press, 1965.

This proves the rule that the performer can direct the audiences' eyes with his own. A perfect application of this principle based on the physiological characteristics discussed is the "crossing the gaze" technique proposed by Slydini and Tamariz.

An extended discussion can be found in The Five Points of Magic, Tamariz, 1988, as well as in The Best of Slydini and More, Fulves, 1976.

The organization of the retina is, therefore, responsible for two central principles of misdirection, and what is needed for a successful application already exists at the lowest level of physical perception.

A Blind Spot

Right next to the Fovea centralis, however, there is another area whose existence we don't even suspect. For this reason, it illustrates how we perceive best. It's an area in which there are no receptors at all, the point where the optic nerve exits the eye to connect with the brain (see figure 2). The lack of light sensitive receptors in this area has given it the name "Blind Spot." The fascinating thing is that we don't even see that we don't see at this point. If perception functioned like a camera, we would constantly have a black hole in our field of vision, however, the brain automatically fills this hole for us on its own.

To prove the existence of the Blind Spot, close your left eye and fix your right eye on the black "plus" sign of figure 4 Now move your head close to the screen until the black dot suddenly disappears. Since the missing information is "patched in" from the surrounding parts of the retina, you see only a white area.

If you do the same thing with a white "plus" sign, you'll discover that your brain completes the disappearance of the white dot by filling in black. This shows that the process of completion, an extremely complex ability of the visual system is dependent on the context of the picture. This has far reaching consequences for the entire perceptive system. Your brain "patches" the hole caused by the lack of receptors in the Blind Spot with information it gleans from adjacent receptors: the "completion process."

See: V. A. Ramachandran, "Compensation of the Blind Spot," Scientific American, June, 1992.


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