  A physician who wishes to use psychotherapy effectively should know something about physiological psychology, or analytical or experimental psychology, as it is variously called, because of the help that he will derive from it in understanding many of his patients' symptoms. Fortunately this branch is now being taught in some of the medical schools, and the greater requirements for preliminary training bring to the medical school men who have already had a course in this subject. The chapter on Illusions is particularly important because it affords many illustrations of how easy it is to be deceived by the senses and, therefore, how many precautions have to be taken in order to be sure that impressions produced on patients' minds that seriously disturb them may not merely be due to exaggeration of the significance of information brought them by their senses. These illusions are of special interest because they represent not only failures of the senses to convey truth, but because they illustrate how easy it is for the mind to be led astray by the senses. People often declare that they have seen things with their own eyes or in some other way have definite sensory knowledge of them, yet these illusions make it clear that it is perfectly possible for such sensory phenomena to convey quite mistaken information. People who are suffering from many symptoms are persuaded that they must pay attention to their sensations. The main purpose of the psychotherapeutist often is to have them neglect their sensations and correct them by means of information gathered from other sources. We do this with regard to our sensory illusions, why not also with regard to many sensations which are probably quite as mistaken, in certain individuals at least, as these universal illusions of mankind. The argument from analogy holds very well and can be used to decided advantage in many cases. A startling illusion which makes it clear that care is needed in interpreting our sensations, is the so-called tube illusion or experiment. If a sheet of note paper be rolled into a tube of something less than an inch in diameter and then held close to one eye, both eyes being kept open, while the hand opposite to the eye before which the tube is held is placed palm faceward against the side of the tube about its middle, a hole will be seen, as it were, through the palm of the hand. This false vision is as clear as can be and persists after any number of repetitions of the experiment. It merely illustrates two-eyed vision. We have a picture in each eye and we combine them. When the pictures cannot be combined for any reason, optical illusions result. There are many more optical illusions than we think and there are many reasons besides two-eyed vision for them. Other illusions of two-eyed vision may be illustrated rather easily. If
After an interval four dots will be seen—each of the dots having a picture in each eye. Then only one dot may be seen because the pictures combine. Sometimes three dots will be seen. When the dots swim toward one another, a curious feeling of insecurity comes over the experimenter, showing how much our sense of stability is dependent on vision and illustrating why vision from a height is so disturbing because objects cannot be properly fixed on the distant background.
Just as the two dots may be made to come together, so, after a little practice, a bird may be made to go into a cage (Fig, 27) or an apple made to go onto a plate (Fig. 28),
These illusions show how many things that people
There are, however, a number of optical illusions which illustrate certain defects of our vision that cannot be corrected, no matter how much we may desire to see correctly. We continue to see them not as they are but as they seem, and we must correct our vision by information from other sources. The MÜller-Lyer lines are familiar and are given here (Fig. 29) because
Figure 30 illustrates how easy it is to be deceived by the juxtaposition of different portions of objects. I have had a woman who had cut out high collars for children and who happened to put them in the juxtaposition of the sketch here given think that she was either losing her sight or her judgment was being affected by the nervous condition in which she was. Nothing would persuade her that some serious development was not taking place until I showed her this illustration. In this illusion the juxtaposition of the short curved line to the long curved line of the other figure produces all the disturbance of judgment of size. The illusions of filled and unfilled space are interesting and are quite inevitable. They are due to physiological visual effects and are very strikingly illustrated by what is known as the sun and moon illusion. Both these luminaries seem larger at the horizon than they are at the zenith. This is entirely an optical illusion. The horizon seems farther away than the zenith because vision to it is interrupted. The heavens appear not to be a half sphere, but more like an old-fashioned watch glass.
Since the sun and moon occupying the same space on the retina are, because of this apparent difference of distance, judged to be farther away at the horizon than they are at the zenith, we are inevitably forced to the conclusion that they are larger in size than when in the other position. The over-estimation of filled space as compared with Illusions of size are even more startling than illusions of distance. It is perfectly possible to take three spaces, each exactly a square inch, and by drawing lines in two of them in different directions to make the figures appear of
Other illusions of size are quite frequent. It is rather hard for the ordinary observer to think that the half circles, a and a' (Fig. 32), are the same size, or that b and b' in the same chart are the same curve. The interruption in the circles c and c' produce very curious erroneous impressions which require a knowledge of this illusion to correct. Optical illusions with regard to directions of lines are extremely common. Quite unconsciously we translate directions into special meanings. This is what enables perspective to be effective in drawings. It has many disturbing features, however. Some of these are striking illustrations of the defects of our vision.
Poggendorf's illustration of the displacement of oblique lines (Figure 33) These optical illusions might seem to be of little significance, but the Greeks thought them of so much importance and recognized so thoroughly that they could not be corrected, and that the distortions and displacements would inevitably take place, that they deliberately put certain optical corrections into their great architectural monuments in order to avoid these false appearances. These have been traced very accurately in the Parthenon, for instance. In a word, the Greeks, knowing of these optical illusions, in order to make the lines of their buildings appear correct, deliberately made them wrong to a sufficient degree to correct the optical illusion; This frank mode of yielding to a limitation of human nature is a fine lesson for patients to learn if they can only be made to learn it from these illustrations. It is with regard to colors, however, that we have the best examples of optical illusions depending on the individual and his special anatomy and physiology. Color-blind people are quite sure that they see color, just as other people do, until their defect is demonstrated to them. A man who is color blind for red thinks that he sees that color as other people do, while all that he sees is a particular shade of brightness which, because other people call it red, he has come to call red. When asked to pick out red from a series of other colors he may often succeed. When asked, however, to take a skein of red wool selected for him to a basket containing a number of different colored wools, and to bring back all those that are of the same color, he will select grays and browns and sometimes greens as well as reds, and present them as all matched colors. A man who is color blind for all colors will still think that he sees colors as other people do. The ingenious illustration of the American flag as it appears to people suffering from different forms of color blindness, though they are all persuaded that they see the same kind of flag, is an interesting example of how different may be people's sensations, though their conclusions are the same. It may be seen in many of the text books of analytical or experimental psychology. Dalton, to whom we owe the atomic theory, was himself color blind for red and made the first investigations in that subject. He was of Quaker origin and found that a great many of his brethren were deficient in color vision. It becomes much easier from this to understand why they resolved to wear nothing but gray. They did not see colors as other people do and therefore could not understand nor sympathize with the joy of other people in color. Dalton tells the story of a Quaker prominent in his sect who once went to town to buy a gray waistcoat and purchased instead one of bright red. When he appeared at meeting in this he was promptly tried for heresy and violation of church regulations. There is an interesting tendency on the part of people who are themselves defective in certain faculties of sensation, to conclude that when other people are wrapt in admiration of something that they cannot perceive, it is because these other people have some mental defect that leads them to enthuse too easily over their sensations. A story is told of a newspaper man who used to insist that all that was said about the beauty of the song of birds was due to the vivid imagination of the writers, for he could find nothing to admire about the songs of birds. He was placed in a room with a number of fine song birds all round him and it proved that he could not hear any of the higher notes at all. It was easy, then, to understand his condemnation of the enthusiasm of others as hysterical and imaginative. Nearly this same thing is true of many quite intelligent people with regard to music. They hear ordinary sounds, as did the newspaper man, very well. They are tone-deaf however, that is, they are quite unable to hear and appreciate combinations of sounds or even to catch melodious successions of single notes. They cannot recognize one tune from another and often do not know "Yankee Doodle" from the "Doxology," or, at most, know only the most familiar tunes, but they set themselves up very calmly as judges of the intellects of others and conclude that music lovers are really a hysterical set of people who go into ecstasies over certain quite insignificant sensations. These interesting tendencies are helpful in enabling the physician to understand his patients better. They often serve as texts from which the physician can explain curious things to patients who are prone to draw wrong conclusions from them and often suggestions unfavorable to their health. These illustrations and their discussion serve to make very clear the distinction between illusions, delusions and hallucinations, which are often confounded. Illusions are deceptions of the senses. If a man walking along a country road where he fears the presence of snakes sees in the gathering twilight a piece of rope coiled, he will almost surely mistake it for a snake. This is an illusion produced by the conditions in which the object is seen. If walking along the same road the next day, more timorous than ever as to snakes, he should see in broad daylight the same coil of rope, he might in his fright not stay long enough to decide whether it was a snake or not, and his illusion would continue, though it would partake somewhat of the nature of a delusion due to fright disturbing his judgment. If, in spite of careful examination, however, of it, such as would satisfy any ordinary mind that it was a coil of rope and not a snake, he should still insist in believing that it was a snake, this would be a delusion. There is always a mental element in delusions. If, having seen nothing, he should insist, owing to fright and Illusions may be quite inevitable. Most of the optical illusions continue to appeal to us as truths even when we know that they represent errors of vision. In spite of the fact that we know that the sun and moon are not larger at the horizon than they are at the zenith, by optical illusion we continue to see them of larger size. It is our duty to correct such illusions by information gathered from other sources. To follow an illusion, that is, to give it credit, when we should correct it, is a delusion. To think that because we cannot see red that therefore there is no red, or because we do not hear the sounds of notes of birds that they do not utter any notes, in spite of the fact that we have the testimony of nearly the whole human race to the contrary, is a delusion. When, using the verb in its broadest sense, as "perceive," we seem to see things very differently from the generality of people around us, there is every reason to suspect that there is some specific or individual limitation of our senses which makes us fail to perceive these things as others do. We have to suspect our sources of information then and to correct them by what we can learn from the experience of others. These are important considerations for many of the ideas that patients cherish with regard to themselves and their ills. Hallucinations are entirely mental. But the phenomena that sometimes appear to be hallucinations may be due to illusions of the senses within the organism. For instance, those who indulge in cocaine often have the feeling of having a veil over the face, or of having run into a cobweb or something of that kind. The presence of the veil or the cobweb on the face is probably not an hallucination, but is due to certain disturbances in the circulation, or perhaps in the nerves themselves, which affect the nerve endings of the face, causing them to tingle in a particular way, and this sensation is translated as coming from without in terms of something that has been felt before. Some of the appearances of muscae volitantes, or of specks before the eyes, or occasionally of wavy lines, are due to disturbances of the circulation within the eyeball which cause corresponding disturbances of the optic nerve, with consequent apparent visions. When the eyeball is pressed upon, the sensation first produced is that of light and not of pain, because whenever a nerve of special sense is irritated, it produces its own specific sensation in the brain. The chilly stage in malaria is a typical example of a physical condition having an effect upon sensory nerves that more or less necessarily produces a delusion. The patient is actually at the height of his fever when the chilliness and shivering come on and when he demands a larger amount of covers in order to protect himself from the cold he will often have a temperature of 104 degrees Fahrenheit, or even higher. What has happened is that the little blood vessels at the surface of the body are shut up by the effect of the plasmodium upon the system. Whenever we are cold these little blood vessels shut up in order to protect the blood from being chilled by the external atmosphere. The shutting up of the little blood vessels deprives, for the time being, the terminal nerves in the neighborhood of some of their nourishment. Their response is to set up a tremor or shivering, which will mechanically tend |
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