Can You Believe Your Eyes?

J. Richard Block, Harold Yuker

• Éditeur: Routledge
• Année: 2013
• ISBN:
  9781134857012
• Édition: 1
• Sujet: Psychology
• Sous-sujet: Psychotherapy

Published in 1989, Can You Believe Your Eyes? is a valuable contribution to the field of Psychotherapy.

CHAPTER 1

INTRODUCTION

This is a book which requires you to participate in more ways than simply reading. To really enjoy it you will have to do a great many things with it that you don't do with other books.

For example, when you get to Chapter 17, you will be constantly turning the book upside down and then right side up to see what is there. In some cases, you will have to turn the book left or right to see the effect.

There are several chapters where you will have to use a ruler to convince yourself that what you see is really not true (Chapters 9, 10 and 11).

In Chapter 6, you cannot simply look at the illustrations to see the illusions. You must stare at them for approximately 30 seconds. Even then, to see the illusion you do not look at the book. You must shift your gaze to a blank sheet of paper, or the wall, or some other blank space to see the effect.

For most of Chapter 18 you have to cross your eyes to see the illusions.

You have to move away from the book to see two illusions (5.18 and 5.19) but, you have to put the book practically up against your nose to see two others (19.15 and 19.16).

To see several of the illusions, you will have to xerox the illustration, paste it on a piece of cardboard, and then spin it on the end of a paper clip (6.8, 6.9, 7.5, 7.6, and 7.7). There is another which you can only see by looking at it through a pin hole.

You have to wiggle the book slightly to see several illusions (7.1, 7.2, 19.8, 19.9 and 19.10), while for others you will have to tilt the book away from you so that it is almost horizontal, and look at them from the edge of the page (12.8, 12.9 and 18.9).

Several of the visual oddities we have included in Chapter 16 deal with words. To be appreciated, they will have to be read aloud.

Some of the illusions included here are “one-time” illusions. That is, once you have seen them, the novelty is gone. Indeed, in many cases, whatever you thought you saw before the visual principle was made known to you, will never be seen again! In these illustrations the pleasure you will experience after that lies in showing it to others. Other illusions are perpetual. That is, although you know your perception is incorrect, you will still be unable to change it! In that sense, this is a book you will be able to go back to over and over again for years to come.

This book doesn't really have a beginning, a middle, or an end. With few exceptions each chapter can stand on its own, and even each illustration can be enjoyed separately from the others. You can start anywhere and go either forward or backward.

Basically this book is about vision. Vision is one of our most important means of getting information from the world around us. But what is vision? It is a process that involves the reception of electromagnetic energy by the eyes. This kind of energy travels in waves, which vary greatly in length. Some electro-magnetic waves, called gamma waves, are extremely short, measuring only about 4 ten-trillionths of an inch in length! In contrast, some are over 18 miles long! These are the electro-magnetic waves used for trans-oceanic broadcasts. In between are the wave lengths used for X-rays, infra-red radiation, short wave and regular broadcast radio signals.

The wave lengths your eyes receive make up what is called the visible spectrum. They are relatively short waves, somewhat longer than X-rays. They range from 16 millionths of an inch to about 32 millionths of an inch in length. Receptors in the eye are sensitive to this band of radiation, much as radio tuners are sensitive to wave lengths of the same kind of energy, but of lengths of from about a tenth of a mile to a third of a mile.

Sensation results when this energy is received by the eye and transmitted to the brain. The receptors in the eyes, called rods and cones, convert the energy into nerve impulses and send it on to the brain. The brain connects these impulses with other brain processes to make them meaningful. This is called perception. This book is about visual perception—the interpretation of the visible spectrum.

The book is not intended to be scholarly. Though there are occasional explanations of visual principles, they are not presented in great detail. There are several reasons for this. First, we wanted the book to have a broad range of appeal, from professionals to laypersons. Second, many principles underlying the illustrations here are not understood even today, although as you will see, many of the illusions in this book have been around for over a century, and a few are thousands of years old! Finally, where explanations are available, they often are very complex and require specialized knowledge.

The book focuses on many pleasurable and interesting aspects of vision. We have tried to concentrate on those visual principles we think people will find most intriguing rather than to attempt balanced coverage. We present a wide range of examples of visual principles, but focus most on illusions.

Illusions are misperceptions. They are interpretations of stimuli that do not follow from the sensations received by the eye. When we witness an illusion, we perceive something that does not correspond to what is actually out there—what exists in the real world. Illusions fool us; they convince us of things that are not true. The interesting thing is we seem to enjoy being fooled in this way!

Magicians use illusions all the time. In fact, magicians are sometimes referred to as illusionists. Famous magicians, like the great Harry Houdini, admit that what they do is create illusions. They do not do the impossible, they just seem to do it.

Illusions are different from both hallucinations and delusions. Illusions are misperceptions that are perceived by most people, and that are based on a specific stimulus viewed under certain conditions. Some experiments with animals indicate that several species of mammals and birds are “fooled” by illusions in much the same way we are. Not all human beings are fooled by illusions. For example, persons who come from cultures in which there are few straight lines and angles would not be fooled by several of the illusions in this book.

Hallucinations are usually seen by only one individual. Most often they are experienced by people who suffer from specific kinds of mental illness, or who are influenced by drugs or extreme amounts of alcohol. Hallucinations are false perceptions that occur in the absence of appropriate external stimuli, whereas illusions are misinterpretations of external stimuli that are, in fact, present.

Although we shall discuss and illustrate visual illusions, illusions and hallucinations can involve any of our senses—sight, sound, touch, taste, or smell.

Delusions are different from both illusions and hallucinations. They are beliefs, not perceptions. Like hallucinations, they tend to be found in people who are mentally ill. A person may have delusions of grandeur (believing that he or she is a very important person) or delusions of persecution (believing someone or something is out to harm him or her), when the facts clearly do not support these beliefs.

Many common perceptions involve illusions although most people are not aware of it. That is, much of what we perceive does not correspond to the stimulation of our sense organs. Thus, for example, we do not see a person who is walking away from us as getting smaller and smaller, even though the image in our eyes rapidly decreases in size. Yet anthropologists have described tribes that are greatly puzzled by this phenomenon when they first perceive it.

We also get illusions of depth in paintings, 3-D movies, stereopticons, and holographs, even though these are presented to us on two-dimensional surfaces.

The “moon illusion” discussed in Chapter 10 is a familiar natural illusion. The moon illusion refers to the fact that when the moon is on the horizon it appears to be quite large, but when it is overhead, it seems very much smaller. Philosophers and scientists have been trying to explain this since Ptolemy, an astronomer who lived in Alexandria in the second century.

One very powerful illusion is called the size-weight illusion. However, since it involves the use of containers, we cannot present it in this book. We can describe it, though, and you can demonstrate it for yourself and your friends.

Take a small attache case, a small over-night bag, and a large three-suiter suitcase, and fill the attache case with some heavy material such as books. After you have determined its weight, put books of the same weight in the over-night case and the three-suiter. Ask someone to lift each case and tell you which is the heaviest. We virtually guarantee that the attache case will be judged to be much heavier than the others, even though they all weigh exactly the same.

In part this is explained by our expectations. When we see the large case, we prepare our muscles to lift something heavy. When it is only filled to a portion of its capacity, it goes up easily. On the other hand, we don't expect to have a particularly difficult time lifting the small attache case, and we are suprised by the weight.

You can get the same effect using food containers. For example, you can use cans holding 8 ounces, 16 ounces, and 32 ounces of material. Put dirt or pebbles into each can so that all three are exactly the same weight, and cover them with tin foil. Most people will swear that the smallest weighs the most, and the largest the least. Even though you prepared them yourself, you too may have difficulty accepting that they are all the same weight!

Perception may also be distorted in other ways. One such distortion results from what is called selective perception. Selective perception is a result of the influence of personal factors on perception. What a person perceives reflects that person's past learning and present state of mind, as well as what is actually “out there.” A Republican and a Democrat who listen to the same political speech will “hear” and remember different things. If you ask them about it afterwards, it may be hard to believe they listened to the same speech.

Being aware of these various types of perceptual distortions should make people less willing to believe their eyes—or any of their other senses. What you perceive does not always correspond to reality.

Optical illusions are related to the way the brain processes incoming information. As the brain receives impulses from the eye, it tries to make the information meaningful. Factors such as prior learning, and the total visual context, in addition to the object upon which we focus, and the extent to which we are prepared to receive specific information, all play important roles in interpretation.

The process usually involves two steps. First, drawing attention to an object, and second, making it meaningful. This book presents examples of these factors, many of which are very useful in such fields as advertising, art, fashion design, equipment design, and stage design. In fact, some of the basic principles go beyond vision. Some relate to hearing, and others to social behavior.

However, most of the book deals with the misperceptions called illusions. Although we have included over 250 illustrations, this is not an exhaustive presentation. Many illusions have not been included here. Some, such as the size-weight illusion described earlier, require equipment which goes beyond the limits of the printed page. Other illusions are not visual. They may involve hearing, the sense of touch, or other nonvisual sensations.

As we stated earlier, not all illusions are universal. There may be some that you or your friends do not see, or some that one person sees, but another does not. There is no simple explanation for this variability in perception. Nonetheless, there are enough illustrations that we believe you will find many hours of pleasure in going through these pages.

CHAPTER2

AMBIGUOUS FIGURES

The first set of illustrations we present is among those that are perpetual. Once you see them they will persist forever. In each drawing in this chapter there are at least two different figures. You may not see both initially. Therefore, we will provide cues for you to differentiate one from the other. Once you see each separate figure, you should have no difficulty in seeing both—or, in one case, all three.

Some people, on first exposure, apparent...