Fig. 1.Fig. 1.
Fig. 2.Fig. 2.
Aërial perspective has a great influence on the determination of these phenomena, particularly such as occur in the open and at great distances. The influence is to be recognized through the various appearances of distant objects, the various colors of distant mountains, the size of the moon on the horizon, and the difficulties which aërial perspective offers painters. Many a picture owesits success or failure to the use of aërial perspective. If its influence is significant in the small space of a painting, the illusions in nature can easily become of enormous significance, particularly when extremes are brought together in the observations of objects in unknown regions. The condition of the air, sometimes foggy and not pellucid, at another time particularly clear, makes an enormous difference, and statements whether about distance, size, colors, etc., are completely unreliable. A witness who has several times observed an unknown region in murky weather and has made his important observation under very clear skies, is not to be trusted.
An explanation of many sensory illusions may be found in the so-called illusory lines. They have been much studied, but Zöllner[313]has been the first to show their character. Thus, really quite parallel lines are made to appear unparallel by the juxtaposition of inclined or crossing lines. In figures 1 and 2 both the horizontal lines are actually parallel, as may be determined in various ways.
The same lines looked at directly or backwards seem, inFig. 1, convex, inFig. 2concave.
Fig. 3.Fig. 3.
Still more significant is the illusion inFig. 3, in which the convexity is very clear. The length, etc., of the lines makes no difference in the illusion.
On the other hand, inFig. 4the diagonals must be definitely thicker than the parallel horizontal lines, if those are to appear not parallel. That the inclination is what destroys the appearance of parallels is shown by the simple case given inFig. 5, where the distance from A to B is as great as from B to C, and yet where the first seems definitely smaller than the second.
Still more deceptive isFig. 6, where the first line with the angle inclined inwards seems incomparably smaller than the second with the angle inclined outwards.
Fig. 4.Fig. 4.
Fig. 5.Fig. 5.
Fig. 6.Fig. 6.
All who have described this remarkable subject have attempted to explain it. The possession of such an explanation might put us in a position to account for a large number of practical difficulties. But certain as the facts are, we are still far from theirwhyandhow. We may believe that the phenomenon shown in Figs. 1 and 2 appears when the boundaries of a field come straight up to a street with parallel sides, with the result that at the point of meeting the street seems to be bent in. Probably we have observed this frequently without being aware of it, and have laid no particular stress on it, first of all, because it was really unimportant, and secondly, because we thought that the street was really not straight at that point.
In a like manner we may have seen the effect of angles as shown in Figs. 5 and 6 on streets where houses or house-fronts were built cornerwise. Then the line between the corners seemed longer or shorter, and as we had no reason for seeking an accurate judgmentwe paid no attention to its status. We simply should have made a false estimate of length if we had been required to judge it. It is also likely that we may have supposed an actual or suppository line on the side of the gables of a house enclosed by angles of the gables, to be short,—but until now the knowledge of this supposition has had no practical value. Nevertheless, the significance of these illusions should not be underestimated. They mean most of all the fact that we really can be much deceived, even to the degree of swearing to the size of a simple thing and yet being quite innocently mistaken. This possibility shows, moreover, that the certainty of our judgment according to sensible standards is inadequate and we have no way of determining how great this inadequacy is. We have already indicated that we know only the examples cited by Zöllner, Delboeuf and others. It is probable that they were hit upon by accident and that similar ones can not be discovered empirically or intentionally. Hence, it may be assumed that such illusions occur in great number and even in large dimensions. For example, it is known that Thompson discovered his familiar “optical circle illusion” (six circles arranged in a circle, another in the middle. Each possesses bent radii which turn individually if the whole drawing is itself turned in a circle) by the accident of having seen the geometrical ornament drawn by a pupil. Whoever deals with such optical illusions may see very remarkable ones in almost every sample of ladies’ clothes, particularly percale, and also in types of carpets and furniture. And these are too complicated to be described. In the course of time another collection of such illusions will be discovered and an explanation of them will be forthcoming, and then it may be possible to determine how our knowledge of their existence can be turned to practical use.
Fig. 7.Fig. 7.Fig. 8.
Practical application is easier in the so-called inversion of the visual object.Fig. 7shows the simplest case of it—the possibility of seeing the middle vertical line as either deeper or higher than the others. In the first instance you have before you a gutter, in the second a room. Similar relations are to be observed in the case of a cube in which the corneramay be seen as either convex or concave according asyou think it behind or before the background of the angles from whichaproceeds. It is still clearer when, in a rhomboid, the lineXYis drawn. Thenxorymay be seen alternately as nearer or further and the figure can thereby be brought into a different position. (Fig. 9.) Done once it may be repeated voluntarily.
Fig. 9.Fig. 9.
Fig. 10.Fig. 10.
There are many practical examples of these illusions. Sinsteden saw one evening the silhouette of a windmill against a luminous background. The arms seemed now to go to the right, now to the left—clearly because he did not make out the body of the mill and might equally assume that he saw it from the front or from the rear, the wheels going toward the right in the first, and toward the left in the other case. An analogous case is cited by Bernstein. If (Fig. 10) the cross made of the thin lines stand for the bars of a weather vane and the heavy lines represent the weather vane itself, it may be impossible under the conditions of illumination for an eye looking from N to distinguish whether the weather vane points NE or SW; there is no way of determining the starting point of motion. All that can certainly be said is that the weather vane lies between NE and SW and that its angle is at the crossing of the two lines, but the direction in which its heads point can not be determined at even a slight distance. Both forms of this illusion may occur in a criminal trial. If once a definite idea of some form of order has been gained, it is not abandoned or doubted, and is even sworn to. If asked, for example, whether the mill-wheel moved right or left, the observer will consider hardly one time in a hundred whether there might not have been an optical illusion. He will simply assureus that the thing was as he thinks he saw it, and whether he saw it correctly is purely a matter of luck.
To all these illusions may be added those which are connected with movement or are exposed by movement. During the movement of certain bodies we can distinguish their form only under definite conditions. As their movement increases they seem shorter in the direction of movement and as it decreases they seem broader than normally. An express train with many cars seems shorter when moving directly near us, and rows of marching men seem longer. The illusion is most powerful when we look through a stationary small opening. The same thing occurs when we move quickly past bodies, for this makes them seem very short as we go by.
Of such cases sense-illusion does not constitute an adequate explanation; it must be supplemented by a consideration of certain inferences which are, in most instances, comparatively complex.[314]We know, e.g. that objects which appear to us unexpectedly at night, particularly on dark, cloudy nights, seem inordinately magnified. The process is here an exceedingly complex one. Suppose I see, some cloudy night, unexpectedly close to me a horse whose environment, because of the fog, appears indistinct. Now I know from experience that objects which appear from indistinct environments are as a rule considerably distant. I know, further, that considerably distant objects seem much smaller, and hence I must assume that the horse, which in spite of its imaginary distance appears to retain its natural size, is really larger than it is. The train of thought is as follows: “I see the horse indistinctly. It seems to be far away. It is, in spite of its distance, of great size. How enormous it must be when it is close to me!” Of course these inferences are neither slow nor conscious. They occur in reflection with lightning-like swiftness and make no difference to the certainty of the instantaneous judgment. Hence it is frequently very difficult to discover the process and the mistake it contains.
If, however, the observer finds an inexplicable hiatus in an event he happens to notice, he finds it strange because unintelligible. In this way is created that notion of strangeness which often plays so great a rôle in the examination of witnesses. Hence when under otherwise uncomfortable conditions, I see a horse run without hearing the beat of his hoofs, when I see trees sway without feeling any storm; when I meet a man who, in spite of the moonlight, has no shadow, I feel them to be very strange because something is lackingin their logical development as events. Now, from the moment a thing becomes strange to an individual his perceptions are no longer reliable, it is doubtful whether he knows what he has really experienced before his world became strange to him. Add to this that few people are unwilling to confess that they felt ill at ease, that perhaps they do not even know it,[315]and you get the complicated substitution of sensory illusions and uncanny sensation, the one causing the other, the other magnifying the one, and so on until the whole affair is turned into something quite unrecognizable. So we find ourselves in the presence of one of the inexplicable situations of the reality of which we are assured by the most trustworthy individuals.
To magnify this phenomenon, we need only think of a few slightly abnormal cases. It has already been indicated that there are many such which are not diseased, and further, that many diseased cases occur which are not known as such, at least, as being so much so as to make the judge call in the doctor. This is the more likely because there are frequently, if I may say so, localized diseases which do not exhibit any extraordinary symptoms, at least to laymen, and hence offer no reason for calling in experts. If we set aside all real diseases which are connected with optical illusions as not concerning us, there are still left instances enough. For example, any medical text-book will tell you that morphine fiends and victims of the cocaine habit have very strong tendencies to optical illusions and are often tortured by them. If the disease is sufficiently advanced, such subjects will be recognized by the physician at a single glance. But the layman can not make this immediate diagnosis. He will get the impression that he is dealing with a very nervous invalid, but not with one who is subject to optical illusions. So, we rarely hear from a witness that he knows such people, and certainly not that he is one himself. A very notable oculist, Himly, was the first to have made the observation that in the diseased excitability of the retina every color is a tone higher. Luminous black looks blue, blue looks violet, violet looks red, red looks yellow. Torpor of the retina inverts the substitution.
Dietz[316]tells of color-illusions following upon insignificant indigestion; Foderè of hysterics who see everything reversed, and Hoppe[317]says, “If the order of the rods and cones of the retina is somewhat disturbed by an inflammatory touch, the equilibrium of vision isaltered and changes in size, in form, or appearance occur.” Naturally the criminalist can not perceive slight indigestion, weak hysteria, or an inflamed area in the retina when he is examining witnesses, yet false observations like those described may have a definite influence upon the decision in a case.
If such abnormal occasions are lacking the reasons for optical illusions are of another nature. As a rule optical illusions occur when there is an interruption in the communication between the retina, the sense of movement, and the sense of touch, or when we are prevented from reducing the changes of the retinal image to the movement of our body or of our eyes. This reduction goes on so unconsciously that we see the idea of the object and its condition as a unit. Again, it is indubitable that the movement of the body seems quicker when we observe it with a fixed glance than when we follow it with our eyes. The difference may be so significant that it is often worth while, when much depends on determining the speed of some act in a criminal case, to ask how the thing was looked at.
Fechner has made a far-reaching examination of the old familiar fact that things on the ground appear to run when we ride by them rapidly.[318]This fact may be compared with the other, that when you look directly into swift-moving water from a low bridge, the latter seems all of a sudden to be swimming rapidly up stream, though the water does not appear to stand still. Here some unknown factor is at work and may exercise considerable influence on many other phenomena without our being able to observe the results. To this class may be added the extraordinary phenomenon that from the train objects easily seem too near and hence appear smaller than they are. It may be, however, that the converse is true and objects appear smaller, or at least shorter, and that inasmuch as we are in the habit of attributing the diminution of size in objects to their distance, we tax the latter as false. So much is certain—that whenever we ourselves move quickly we make false judgments of size, distance, and even color. The last may be due to the fact that during a quick passage, colors may so compose themselves, that green and red become white, and blue and yellow, green, etc. I believe that all these illusions are increasing in connection with the spread of bicycling, inasmuch as many observations are made from the fleeting wheel and its motion tends to increase the illusions considerably. Concerning the differences in movement Stricker[319]says: “If I lie on my back and see a bird fly in the uniformly blue heaven, I recognize the movement although I have no object with which to compare it. This can not be explained by the variety of points on the retina which are affected, for when the bird pauses and I turn my eye, I know that it is not moving.” The last argument is not correct. If the bird is sitting on a branch I know, in spite of all my occipital movement, that it is quiet, but only because I perceive and observe the bird’s immobility. If, however, I lie on my back like Stricker and see above me a bird of the class that, so to speak, swim motionless in the air for minutes at a time, and if then I turn my head, I can not tell when the bird begins to move. Here then we have no exception to the general rule and can always say that we are speaking of movement optically perceived when the rays issuing from any body progressively touch various points on the retina. And since this occurs when we are in motion as well as when the object is in motion it happens that we can not locate the movement, we cannot say whether it be in us or in the object.
Of course, the possibility that fanciful images may appear during movement is familiar. If I sit quietly in the forest and at some distance see a stone or a piece of wood or a little heap of dried leaves, etc., it may be that, because of some illusion, I take it to be a rolled up hedgehog, and it may happen that I am so convinced of the nature of the object while I am looking at it that I see how the hedgehog stretches itself, sticks out its paws and makes other movements. I remember one winter when, because of some delay, a commission on which I was serving had failed to reach a village not far from the capital. We had gone to investigate a murder case and had found the body frozen stiff. The oven in the room was heated and the grave-digger placed the stiff body near the oven in order to thaw it out. We at this time were examining the place. After a while I was instructed by the examining justice to see about the condition of the corpse, and much to my disgust, I found it sitting near the oven, bent over. It had thawed out and collapsed. During the subsequent obduction I saw most clearly how the corpse made all kinds of movements, and even after the section, during the dictation, of the protocol, my imagination still seemed to see the corpse moving a hand or a foot.
The imagination may also cause changes in color. Once, I saw on my desk, which stood next to a window, a great round drop of water on the left side of which the panes of the window were reflected. (Fig. 11). The whole business was about a meterfrom my eye. I saw it repeatedly while working and it finally occurred to me to inquire how such a great drop of water could get there. I had sat at my desk for hours without moving. I must have observed it if it had dropped there. Refraining intentionally from going closer, I started, without avail, to consider how it could have come. Some time after I examined the drop of water and found it to be an ink-blot, long ago completely dried, and bearing on its left side a few grains of white cigar ash. I had taken these to be the image of the window, and hence, had immediately attached to it the idea of the shining, raised drop of water. I had altogether overlooked the deep black color of the drop. On the witness stand I would have sworn that I had seen a drop of water, even if I had known the evidence on the matter to be important.
Fig. 11.Fig. 11.
In many cases it is possible to control the imagination, but only when it is known that the images can not be as they are seen. Everybody is aware how a half-covered object at a distance, or objects accidentally grouped in one way or another, are taken for God knows what. Thus once, looking from my desk to my smoking table, I saw an enormous pair of tailor’s scissors half-covered by a letter. It remained identical under a number of repeated glances. Only when I thought vigorously that such a thing could not possibly be in my room did it disappear. A few scales of ashes, the lower round of the match safe, the metal trimmings of two cigar boxes half-covered by a letter and reflected by the uncertain light breaking through the branches of a tree, were all that the tailor’s scissors was composed of. If there had been such a thing in the house, or if I had believed something like it to exist in the house, I should have sought no further and should have taken my oath that I had seen the thing. It is significant that from the moment I understood the phenomenon I could not restore the image of the scissors. How often may similar things be of importance in criminal trials!
The so-called captivation of our visual capacity plays a not unimportant part in distinguishing correct from illusory seeing. In order to see correctly we must look straight and fully at the object. Looking askance gives only an approximate image, and permits the imagination free play. Anybody lost in a brown study who pictures some point in the room across the way with his eyes can easily mistake a fly, which he sees confusedly askance, for a great big bird. Again, the type of a book seems definitely smaller if the eyes are fixed on the point of a lead pencil with a certain distancebefore or above the book. And yet again, if you stand so that at an angle of about 90 degrees from the fixation point, you look at a white door in a dark wall, observing its extent in indirect vision, you will find it much higher than in direct vision.
These examples indicate how indirect vision may be corrected by later correct vision, but such correction occurs rarely. We see something indirectly; we find it uninteresting, and do not look at it directly. When it becomes of importance later on, perhaps enters into a criminal case, we think that we have seen the thing as it is, and often swear that “a fly is a big bird.”
There are a number of accidents which tend to complete illusion. Suppose that the vision of a fly, which has been seen indirectly and taken for a big bird happens to be synchronous with the shriek of some bird of prey. I combine the two and am convinced that I have seen that bird of prey. This may increase, so much so that we may have series of sense-illusions. I cite the example of the decorative theatrical artist, who can make the most beautiful images with a few, but very characteristic blots. He does it by emphasising what seems to us characteristic, e.g., of a rose arbor, in such a way that at the distance and under the conditions of illumination of the theatre we imagine we really see a pretty rose arbor. If the scene painter could give definite rules he would help us lawyers a great deal. But he has none, he proceeds according to experience, and is unable to correct whatever mistakes he has committed. If the rose arbor fails to make the right impression, he does not try to improve it—he makes a new one. This may lead to the conclusion that not all people require the same characteristics in order to identify a thing as such, so that if we could set the rose arbor on the stage by itself, only a part of the public would recognize it as properly drawn, the other part would probably not recognize it at all. But if, of an evening, there is a large number of decorations on the stage, the collective public will find the arbor to be very pretty. That will be because the human senses, under certain circumstances, are susceptible to sympathetic induction. In the case of the rose arbor we may assume that the artist has typically represented the necessary characteristics of the arbor for one part of the audience, for another part those of a castle, for another part those of a forest, and for a fourth those of a background. But once an individual finds a single object to be correct, his senses are already sympathetically inductive, i.e., captivated for the correctness of the whole collection, so that the correctness passes from one object to the totalnumber. Now, this psychic process is most clear in those optical illusions which recently have been much on public exhibition (the Battle of Gravelotte, the Journey of the Austrian Crown Prince in Egypt, etc.). The chief trick of these representations is the presenting of real objects, like stones, wheels, etc., in the foreground in such a way that they fuse unnoticeably with the painted picture. The sense of the spectator rests on the plastic objects, is convinced of their materiality and transfers the idea of this plasticity to the merely pictured. Thus the whole image appears as tri-dimensional.
The decorations of great parks at the beginning of the last century indicate that illumination and excited imagination are not alone in causing such illusions. Weber tells ecstatically of an alley in Schwetzing at the end of which there was a highly illuminated concave wall, painted with a landscape of mountains and water-falls. Everybody took the deception for a reality because the eye was captivated and properly inducted. The artist’s procedure must have been psychologically correct and must have counted upon the weakness of our observation and intellection. Exner points to the simple circumstance that we do not want to see that things under certain conditions must terminate. If we draw a straight line and cover an end with a piece of paper, every one wonders that the line is not longer when the paper is removed.
I know of no case in criminal procedure where illusions of this kind might be of importance, but it is conceivable that such illusions enter in numberless instances. This is especially susceptible of observation when we first see some region or object hastily and then observe it more accurately. We are astonished how fundamentally false our first conception was. Part of this falseness may be adduced to faults of memory, but these play little or no part if the time is short and if we are able to recall that the false conception appeared just as soon as we observed the situation in question. The essential reason for false conception is to be found only in the fact that our first hasty view was incorrectly inducted, and hence, led to illusions like those of the theatre. Thus, it is possible to take a board fence covered at points with green moss, for a moss-covered rock, and then to be led by this to see a steep cliff. Certain shadows may so magnify the size of the small window of an inn that we may take it to be as large as that of a sitting room. And if we have seen just one window we think all are of the same form and are convinced that the inn is a mansion. Or again, we see, half-covered, through the woods, a distant pool, and in memory we then see the possibly,but not necessarily, present river. Or perhaps we see a church spire, and possibly near it the roof of a house rises above the trees; then we are inducted into having seen a village, although there really are visible only the church and the house.
These illusions again, I must repeat, are of no importance if they are at all doubted, for then the truth is ascertained. When, however, they are not doubted and are sworn to, they cause the greatest confusion in trials. A bar-room quarrel, a swung cane, and a red handkerchief on the head, are enough to make people testify to having seen a great brawl with bloody heads. A gnawing rat, a window accidentally left open through the night, and some misplaced, not instantaneously discovered object, are the ingredients of a burglary. A man who sees a rather quick train, hears a shrill blowing of the whistle, and sees a great cloud, may think himself the witness of a wreck. All these phenomena, moreover, reveal us things as we have been in the habit of seeing them. I repeat, here also, that the photographic apparatus, in so far as it does not possess a refracting lens, shows things much more truly than our eye, which is always corrected by our memory. If I permit a man sitting on a chair to be photographed, front view, with his legs crossed and stretched far out, the result is a ludicrous picture because the boots seem immensely larger than the head of the subject. But the photograph is not at fault, for if the subject is kept in the same position and then the apparent size of head and boot are measured, we get accurately the same relation as on the photograph. We know by experience how big a head is. And hence, we ordinarily see all relations of size in proper proportion. But on the photograph we can not apply this “natural” standard because it is not given in nature, and we blame the camera.
If, in a criminal case, we are dealing with a description of size, and it is given as it is known from experience, not as it really appears, then if experience has deceived us, our testimony is also wrong, although we pretend to have testified on the basis of direct sense-perception.
The matter of after-images, probably because of their short duration, is of no criminalistic importance. I did once believe that they might be of considerable influence on the perception of witnesses, but I have not succeeded in discovering a single example in which this influence is perceptible.
On the other hand, the phenomenon of irradiation, the appearance of dark bodies as covered with rays of light by adjacent luminosities,is of importance. This phenomenon is well-known, as are Helmholtz’s and Plateau’s explanations of it. But it is not sufficiently applied. One needs only to set a white square upon the blackest possible ground and at the same time a similar black square of equal size on a white ground, and then to place them under a high light, to perceive how much larger the white square appears to be. That such phenomena often occur in nature need not be expounded. Whenever we are dealing with questions of size it is indubitably necessary to consider the color of the object and its environment with respect to its background and to the resulting irradiation.
From the point of view of the criminalist, auditory illusions are hardly less significant than visual illusions, the more so, as incorrect hearing is much more frequent than incorrect seeing. This is due to the greater similarity of tones to each other, and this similarity is due to the fact that sound has only one dimension, while vision involves not only three but also color. Of course, between the booming of cannons and the rustling of wings there are more differences than one, but the most various phenomena of tones may be said to vary only in degree. For purposes of comparison moreover, we can make use only of a class of auditory images on the same plane, e.g., human voices, etc. Real acoustic illusions are closely connected with auditory misapprehension and a distinction between these two can not be rigorously drawn. A misapprehension may, as a rule, be indicated by almost any external condition, like the relations of pitch, echo, repetition, false coincidence of waves of sound, etc. Under such circumstances there may arise real illusions.
The study of auditory illusions is rendered especially difficult by the rarity of their repetition, which makes it impossible reliably to exclude accidents and mistakes in observation. Only two phenomena are susceptible of accurate and sufficient study. For three summers a man used to ride through the long street in which I live. The man used to sell ice and would announce himself by crying out, “Frozen,” with the accent on the Fro. This word was distinctly audible, but if the man came to a definite place in the street, there were also audible the words “Oh, my.” If he rode on further the expression became confused and gradually turned into the correct, “Frozen.” I observed this daily, got a number of others to do so, without telling them of the illusion, but each heardthe same thing in spite of the distinct difference between “frozen,” and “oh, my.”
I made a similar observation at a bicycle school. As is known, beginners are able frequently to ride by themselves but need help in mounting and dismounting their machines. To do so they call a teacher by crying out: “Herr Maier.” At a certain place this sound would seem distinctly to be “mamma.” I was at first much surprised to hear people of advanced age cry cheerfully, “mamma.” Later I discovered what the word really was and acquaintances whose attention I called to the matter confirmed my observation. Such things are not indifferent, they show that really very different sounds may be mistaken for one another, that the test of misunderstandings may often lead to false results, since only during the test of an illusion are both auditor and speaker accurately in the same position as before. Finally, these things show that the whole business of correcting some false auditions is very difficult. Yet this work of correction may be assumed to be much more easy with respect to hearing than with respect to seeing. If, e.g., it is asserted that the revolver has been seen somewhere, and if it has been known that the sight was impossible, it becomes just as impossible, almost, to determine what the object seen really was. In the rarest cases only will it be something altogether similar, e.g., a pistol; most of the time it will be an object which could not be inferred from no matter what combinations. In hearing, on the contrary, if once it is determined that there has been a false audition, the work of placing it, though difficult, need not be unprofitable. This work is often compulsory upon the criminalist who receives protocols which have not been read aloud, and in which mistakes of hearing and dictation have been made. Such mistakes are considerably disturbing, and if the case is important their source and status must be inferred. This may almost always be done. Of course, strange, badly heard proper names can not be corrected, but other things can.
As regards the general treatment of auditory illusions, it is necessary, first of all, to consider their many and significant differences. In the first place, there are the varieties of good hearing. That normal and abnormal hearers vary in degree of power is well known. There are also several special conditions, causing, e.g., the so called hyper-auditive who hear more acutely than normal people. Of course, such assertions as those which cite people who can hear the noise of sulphur rubbed on the poles of quartz crystals and so on, are incorrect, but it is certain that a little attention will reveal asurprising number of people whose hearing is far acuter than that of normal individuals. Apart from children, the class is made up of musicians, of young girls, and of very nervous, excitable, and sickly persons. The musicians in fact have become so because of their ears; the young girls hear well largely because of their delicate organization and the very fine construction of their ears; and the nervous people because of their sensibility to the pain involved in loud noises. Many differences of perception among witnesses are to be explained by differences of audition, and the reality of apparent impossibilities in hearing must not be denied but must be tested under proper conditions. One of these conditions is location. The difference between hearing things in the noisy day and in the quiet night, in the roar of the city, or in the quiet of the mountains, is familiar. The influence of resonance and pitch, echo and absorption of tones, i.e., the location of the sound, is of great importance. Finally, it must not be forgotten that people’s ability to hear varies with the weather. Colds reduce the power, and not a few people are influenced by temperature, atmospheric pressure, etc. These considerations show the degree in which auditory illusions can be of importance even in tests of their nature and existence. They show above all that the same object of comparison under the same circumstances must be used in every test. Otherwise much confusion inevitably results.
The presence of auditory illusions in diseases, fever, hysteria, nervousness, alcoholism and its associates, mental disturbances, hyperæmia, diseases of the ear, etc., is well known, but concerns us only as pointing to the necessity of calling in the physician immediately. They have their definite characteristics and rarely leave the layman in doubt of his duty in that direction. The great difficulty comes in dealing with diseases or apparent diseases while it is still impossible to know of their existence, or where the pain is of such character that the layman does not know of its presence and thus has no ground for consulting the doctor. For example, it is well known that a large amount of ear wax in the aural passage may cause all sorts of ringing and sighing in the ear, and may even produce real hallucinations. Yet a person having an abnormal amount of ear wax may be otherwise absolutely sound. How is the need of a physician to be guessed in such a case? Again, the perforation of the drum, especially when it follows a catarrh, may cause a definite auditory illusion with regard to the sound of voices, or the illusion may be effected by the irritation of the skin in the ear passage, orby anemia, or by a strong carotid pulse and a distention of the bloodvessels, as happens in alcoholism. Many people become abnormally sensitive to sound at the beginning of fevers. Women at the time of their climacterium hear all kinds of voices. Inasmuch as this soon stops, the abnormality and incorrectness of their audition is hard to establish. Childbirth, too, makes a difference. Old, otherwise conscientious midwives claim to have heard unborn children breathe and cry.
Examples of this sort of thing are innumerable and they teach that whenever any questionable assertion is made about a thing heard the doctor must be called in to determine whether the witness heard it under abnormal, though not diseased conditions. Again, merely accidental or habitual general excitability tends to intensify all sounds, and whether the witness under consideration was in such condition can be determined only by the expert physician.
The illusions of hearing which completely normal people are subject to are the most difficult of all. Their number and frequency is variously estimated. The physician has nothing to do with them. The physicist, the acoustician and physiologist do not care about the criminalist’s needs in this matter, and we ourselves rarely have time and opportunity to deal with it. As a result our information is very small, and no one can say how much is still undiscovered. One of my friends has called my attention to the fact that when the beats of the clock are counted during sleepiness, one too many is regularly counted. I tested this observation and my experience confirmed it. If, now, we consider how frequently the determination of time makes the whole difference in a criminal case and how easily it is possible to mistake a whole hour, we can get some notion of the importance of this illusion. Its explanation is difficult and it may be merely a single instance of a whole series of unknown auditory illusions resting on the same basis. Another and similar phenomenon is the “double beat of the hammer.” If you have an assistant strike the table with a hammer while you hold both ears with your fingers and then open them half a second or a second after the blow, you hear the blow again. And if you open and shut your ears quickly you can hear the blow several times. This is explained through the fact that a number of reflections of the sound occur in the room, and that these are perceivable only by the unfatigued ear. The explanation is unsatisfactory because the experiment is sometimes successful in the open. Taken in itself, this matter seems very theoretical and without practical value. But this kind of action may occurautomatically. It is well known that swallowing closes the Eustachian tubes for a moment, especially if done when lying down. Now, if this occurs during a blow, a shot, etc., the sound must be heard twice. Again, it may easily happen that because of the noise a man wakes up half asleep and, frightened, swallows the collected saliva; then this accident, which in itself seems unimportant, may lead to very significant testimony. Such occurrences are not infrequent.
The intensity of a sound already heard may be of considerable influence. Certain experimenters have indicated the remarkable character of slightly intensive effects of sound. If you hold a watch so far from the ear as to hear it clearly but weakly, the sound decreases until finally it is not heard at all, and after awhile it is again heard, etc. This may lead to hearing distinct sounds made up of many tones, and need not evince any great illusion with regard to the ticking of a watch. But the thing may occur also in connection with more powerful and more distant sounds, e.g., the murmur of a brook, the rush of a train, the pounding in a distant factory. Noises far removed are influenced by reflections of sound, waves of air, etc., and it is possible that all kinds of things may be heard in a completely monotonous noise. This can be easily learned by listening to the soft murmur of a distant brook at night. Given the disposition and supposing the existence of the brook unknown, it is easy to hear in its monotonous murmur, human voices, sighs, shrieks, etc.
Another remarkable observation shows that in the dark very distinct things are heard during the playing of delicate instruments, such as mouth-organs. The humming approaches and withdraws, then it comes on various sides, and finally one has the feeling that the whole room is full of humming and winging insects. And this may go on indefinitely. There is a large collection of reasons for this reduplication of monotonous sounds. Everybody knows the accord of the æolian harp which consists of identical notes, and the melodies which seem to lie in the pounding of the train on the rails. This can become especially clear when one is half asleep. If ever thinking begins to be ousted by slumber, the rhythmic pound begins to dominate consciousness. Then the rhythm gets its appropriate melody which becomes progressively more intense, and if one grows suddenly wide awake one wonders why the clearly-heard music is missing. Similarly, it is often asserted that a row of travelling wild swans make pleasant chords, although each swan is able to utteronly one cry. Difference in distance and alterations in the air cause the chords.
The difficulties in distinguishing the intensity or weakness of a sound are of importance. Fechner learned from the violinist Wasilewski that he observed that a male choir of four hundred voices did not sound essentially louder than one of two hundred. At the same time one clock is not heard at a great distance, a hundred clocks are heard. One locust can not be heard eating; when 1000 eat they are heard; hence each one must make a definite noise.[320]Early authorities have already indicated how difficult it is to distinguish the number of bells ringing together. Even musicians will often take two or three to be five or six.
Certain dispositions make some difference in this respect. The operating physician hears the low groaning of the patient after the operation without having heard his loud cries during the operation. During the operation the physician must not hear anything that is likely to disturb his work, but the low groan has simply borne in upon him. The sleeping mother often is deaf to considerable noise, but wakes up immediately when her child draws a deeper breath than usual. Millers and factory hands, travellers, etc., do not hear the pounding of their various habitual environmental noises, but they perceive the slightest call, and everybody observes the considerable murmur of the world, the sum of all distant noises, only in the silence of the night that misses it.
Illusions of direction of sound are very common. It is said that even animals are subject to them; and everybody knows how few human beings can distinguish the source and direction of street music, a rolling wagon, or a ringing bell. Even when long practice enables one to determine direction with correctness, an accidental event, perhaps the weather, especial sounds, a different grouping of individuals on the street, may result in serious mistakes. I tried to learn to judge from my office-desk whether the ring of the horse-car came from above or below. I succeeded so well that I could not understand how it was difficult not to learn the difference, and yet I failed many a time altogether in judgment. The reason for it I do not know.
All these enumerated circumstances must show how very uncertain all acoustic perceptions are, and how little they may be trusted if they are not carefully tested under similar conditions, and if—what is most important—they are not isolated. We are here led backto the old principle that every observation is not proof but means of proof, and that it may be trusted only when it is confirmed by many parallel actions which are really consistent. That even after that mistakes are possible, is true, but “after that” is when we have done all that lies within human power.
The high standing of the sense of touch which make it in certain directions even the organ of control of the sense of sight, is well known, and Condillac’s historic attempt to derive all the senses from this one is still plausible. If what is seen is to be seen accurately there is automatic resort to the confirmatory aid of the sense of touch, which apprehends what the eye has missed. Hence we find many people touching things, whose vision is not altogether reliable—i.e., people of considerable age, children unpracticed in seeing, an uneducated people who have never learned to see quickly and comprehensively. Moreover, certain things can be determined only by touching, i.e., the fineness of papers, cloth, etc., the sharpness or pointedness of instruments, or the rawness of objects. Even when we pat a dog kindly we do so partly because we want to see whether his skin is as smooth and fine as the eye sees it; moreover, we want to test the visual impression by that of touch.
But important and reliable as the sense of touch is, it is nevertheless not to be trusted when it is the sole instrument of perception. We must never depend on the testimony of a witness based entirely on perceptions by touch, and the statements of a wounded person concerning the time, manner, etc., of his wound are unreliable unless he has also seen what he has felt. We know that most knife and bullet wounds, i.e., the most dangerous ones, are felt, in the first instance, as not very powerful blows. Blows on the extremities are not felt as such, but rather as pain, and blows on the head are regularly estimated in terms of pain, and falsely with regard to their strength. If they were powerful enough to cause unconsciousness they are said to have been very massive, but if they have not had that effect, they will be described by the most honest of witnesses as much more powerful than they actually were. Concerning the location of a wound in the back, in the side, even in the upper arm, the wounded person can give only general indications, and if he correctly indicates the seat of the wound, he has learned it later but did not know it when it occurred. According to Helmholtz,practically all abdominal sensations are attributed to the anterior abdominal wall. Now such matters become of importance when an individual has suffered several wounds in a brawl or an assault and wants to say certainly that he got wound A when X appeared, wound B when Y struck at him, etc. These assertions are almost all false because the victim is likely to identify the pain of the moment of receiving the wound with its later painfulness. If, for example, an individual has received a rather long but shallow knife wound and a deep stab in the back, the first will cause him very considerable burning sensation, the latter only the feeling of a heavy blow. Later on, at the examination, the cut has healed and is no longer painful; the dangerous stab which may have reached the lung, causes pain and great difficulty in breathing, so that the wounded man assigns the incidence of the stab to the painful sensation of the cut, and conversely.
Various perceptions of victims on receiving a wound are remarkable, and I have persuaded a police surgeon of considerable learning and originality to collect and interpret his great mass of material. It is best done by means of tabulation, accurate description of wounds according to their place, size, form, and significance, the statement of the victim concerning his feeling at the moment of receiving the wound, the consequences of healing, and at the end explanatory observations concerning the reasons for true or incorrect sensations of the victim. As this work is to have only psychological value it is indifferent whether the victim is veracious or not. What we want to know is what people say about their perception. The true and the false will distinguish themselves automatically, the material being so rich, and the object will be to compare true subjective feelings with true subjective deeds. Perhaps it may even be possible to draw generalizations and to abstract certain rules.
There are many examples of the fact that uncontrolled touch leads to false perceptions. Modern psychophysics has pointed to a large group of false perceptions due to illusions of pressure, stabs, or other contact with the skin. The best known, and criminalistically most important experiments, are those with open compasses. Pressed on the less sensitive parts of the body, the back, the thigh, etc., they are always felt as one, although they are quite far apart. The experiments of Flournoy, again, show how difficult it is to judge weights which are not helped by the eye’s appreciation of their form and appearance. Ten objects of various forms were judged by fiftypeople for their weight; only one discovered that they all had the same weight.
Similarly, mere touch can not give us proper control over the organs of the body. Sully says that in bed we may voluntarily imagine that a leg has a position quite different from that it really has. Let me cite some similar examples from my “Manual for Investigating Judges.” If we take a pea between the thumb and the index finger, we feel the pea simply, although its tactile image comes to us through two fingers, i.e., double. If now we cross the third finger over the fourth and hold the pea between the ends of these two fingers, we feel it to be double because the fingers are not in their customary positions and hence give double results. From one point of view this double feeling is correct, but when we touch the pea naturally, experience helps us to feel only one pea. Another example consists in crossing the hands and turning them inward and upward, so that the left fingers turn to the left and the right fingers to the right. Here the localization of the fingers is totally lost, and if a second person points to one of the fingers without touching it, asking you to lift it, you regularly lift the analogous finger of the other hand. This shows that the tactile sense is not in a very high stage of development, since it needs, when unhelped by long experience, the assistance of the sense of sight. Perceptions through touch alone, therefore, are of small importance; inferences are made on the basis of few and more coarse characteristic impressions.
This is shown by a youthful game we used to play. It consisted of stretching certain harmless things under the table—a soft piece of dough, a peeled, damp potato stuck on a bit of wood, a wet glove filled with sand, the spirally cut rind of a beet, etc. Whoever got one of these objects without seeing it thought he was holding some disgusting thing and threw it away. His sense of touch could present only the dampness, the coldness, and the motion, i.e., the coarsest traits of reptilian life, and the imagination built these up into a reptile and caused the consequent action. Foolish as this game seems, it is criminalistically instructive. It indicates what unbelievable illusions the sense of touch is capable of causing. To this inadequacy of the tactile imagination may be added a sort of transferability of certain touch sensations. For example, if ants are busy near my seat I immediately feel that ants are running about under my clothes, and if I see a wound or hear it described, I often feel pain in the analogous place on my own body. That this may lead to considerable illusion in excitable witnesses is obvious.
Finally, this dependence of the sense of touch may be supplemented by the fact that it is counted only relatively, and its value varies with the individual. We find the cellar warm in winter and cold in summer, because we only feel the difference with the outer air, and when we put one hand in hot, and the other in cold water, and then put both in tepid water one finds the tepid water cold, the other warm. The record of tactile sensations is frequent in our protocols and requires constant consideration of the sense’s unreliability.
Diseased conditions are of course to be referred to the physician. I need only mention that slight poisonings by means of chloroform, morphine, atropine, daturine, decrease, and that strychnine increases the sensitivity of the touch organ.
Illusions of taste are of importance for us only in cases of poisoning in which we want the assistance of the victim, or desire to taste the poison in question in order to determine its nature. That taste and odor are particularly difficult to get any unanimity about is an old story, and it follows that it is still more difficult clearly to understand possible illusions of these senses. That disease can cause mistaken gustatory impressions is well known. But precedent poisoning may also create illusions. Thus, observation shows that poisoning by rose-santonin (that well-known worm remedy to which children are so abnormally sensitive) causes a long-enduring, bitter taste; sub-cutaneous morphine poisoning causes illusory bitter and sour tastes. Intermittent fevers tend to cause, when there is no attack and the patient feels comparatively well, a large number of metallic, particularly coppery tastes. If this is true it may lead to unjustified suspicions of poisoning, inasmuch as the phenomena of intermittent fever are so various that they can not all be identified.
Imagination makes considerable difference here. Taine tells somewhere of a novelist, who so graphically described the poisoning of his heroine that he felt the taste of arsenic and got indigestion. This may be possible, for perhaps everybody has already learned the great influence of the false idea of the nature of a food. If some salt meat is taken to be a sweet pastry, the taste becomes disgusting because the imaginary and the actual tastes seem to be mixed. The eye has especial influence, and the story cited and denied a hundred times, that in the dark, red wine and white wine, chicken and goose,can not be distinguished, that the going out of a cigar is not noted, etc., is true. With your eyes closed it may be possible to eat an onion instead of an apple.
Prior tastes may cause significant gustatory illusions. Hence, when assertions are made about tastes, it is always necessary to inquire at the outset what had been eaten or drunk before. Experienced housewives take this fact into consideration in setting their tables and arranging their wines. The values of the wines are considerably raised by complete illusions of taste. All in all, it must not be forgotten that the reliability of the sense of taste can not be estimated too low. The illusions are greatest especially when a thing has been tasted with a preconceived notion of its taste.
Olfactory illusions are very rare in healthy people and are hence of small importance. They are frequent among the mentally diseased, are connected in most cases with sexual conditions and then are so vivid that the judge can hardly doubt the need of calling in the physician. Certain poisons tend to debauch the olfactory sense. Strychnine, e.g., tends to make it finer, morphine duller. People with weak lungs try, in most cases, to set their difficulty of breathing outside themselves and believe that they are inhaling poisoned air, coal-gas, etc. If one considers in this connection the suspiciousness which many people suffering from lung trouble often exhibit, we may explain many groundless accusations of attempted murder by stifling with poisonous or unbreathable gas. If this typical illusion is unknown to the judge he may find no reason for calling in the physician and then—injustice.
The largest number of olfactory illusions are due to imagination. Carpenter’s frequently cited case of the officials who smelled a corpse while a coffin was being dug up, until finally the coffin was found to be empty, has many fellows. I once was making an examination of a case of arson, and on approaching the village noted a characteristic odor which is spread by burned animals or men. When we learned that the consumed farm lay still an hour’s ride from the village, the odor immediately disappeared. Again, on returning home, I thought I heard the voice of a visitor and immediately smelled her characteristic perfume, but she had not been there that day.
Such illusions are to be explained by the fact that many odors are in the air, that they are not very powerfully differentiated andmay hence be turned by means of the imagination into that one which is likely to be most obvious.
The stories told of hyper-sensitives who think they are able to smell the pole of a magnet or the chemicals melted into a glass, belong to this class. That they do so in good faith may be assumed, but to smell through melted glass is impossible. Hence it must be believed that such people have really smelled something somewhere and have given this odor this or that particular location. Something like this occurs when an odor, otherwise found pleasant, suddenly becomes disgusting and unbearable when its source is unknown. However gladly a man may eat sardines in oil he is likely to turn aside when his eyes are closed and an open can of sardines is held under his nose. Many delicate forms of cheese emit disgusting odors so long as it is not known that cheese is the source. The odor that issues from the hands after crabs have been eaten is unbearable; if, however, one bears in mind that the odor is the odor of crabs, it becomes not at all so unpleasant.
Association has much influence. For a long time I disliked to go to a market where flowers, bouquets, wreaths, etc., were kept because I smelled dead human bodies. Finally, I discovered that the odor was due to the fact that I knew most of these flowers to be such as are laid on coffins—are smelled during interment. Again, many people find perfumes good or bad as they like or dislike the person who makes use of them, and the judgment concerning the pleasantness or unpleasantness of an odor is mainly dependent upon the pleasantness or unpleasantness of associative memories. When my son, who is naturally a vegetarian and who could never be moved to eat meat, became a doctor, I thought that he could never be brought to endure the odor of the dissecting room. It did not disturb him in the least, however, and he explained it by saying: “I do not eat what smells like that, and I can not conceive how you can eat anything from the butcher shops where the odor is exactly like that of the dissecting room.” What odor is called good or bad, ecstatic or disgusting, is purely a subjective matter and never to be the basis of a universal judgment. Statements by witnesses concerning perceptions of odor are valueless unless otherwise confirmed.
The limits between illusions of sense and hallucinations and illusions proper can in no sense be definitely determined inasmuchas any phenomena of the one may be applied to the other, and vice versa.[321]Most safely it may be held that the cause of illusions of sense lies in the nature of sense-organs, while the hallucinations and illusions are due to the activity of the brain. The latter are much more likely to fall within the scope of the physician than sense-illusions, but at the same time many of them have to be determined upon by the lawyer, inasmuch as they really occur to normal people or to such whose disease is just beginning so that the physician can not yet reach it. Nevertheless, whenever the lawyer finds himself face to face with a supposed illusion or hallucination he must absolutely call in the physician. For, as rarely as an ordinary illusion of sense is explicable by the rules of logic or psychology, or even by means of other knowledge or experience at the command of any educated man, so, frequently, do processes occur in cases of hallucination and illusion which require, at the very least, the physiological knowledge of the physician. Our activity must hence be limited to the perception of the presence of hallucination or illusion; the rest is matter for the psychiatrist. Small as our concern is, it is important and difficult, for on the one hand we must not appeal to the physician about every stupid fancy or every lie a prisoner utters, and on the other hand we assume a heavy responsibility if we interpret a real hallucination or illusion as a true and real observation. To acquire knowledge of the nature of these things, therefore, can not be rigorously enough recommended.
Hallucination and illusion have been distinguished by the fact that hallucination implies no external object whatever, while in illusion objects are mistaken and misinterpreted. When one thing is taken for another, e.g., an oven for a man, the rustle of the wind for a human song, we have illusion. When no objective existence is perceived, e.g., when a man is seen to enter, a voice is heard, a touch is felt, although nothing whatever has happened, we have hallucination. Illusion is partial, hallucination complete, supplementation of an external object. There is not a correct and definite difference between illusion and hallucination inasmuch as what is present may be so remotely connected with what is perceived that it is no more than a stimulus, and thus illusion may be turned into real hallucination. One authority calls illusion the conception of an actually present external event which is perceived by the peripheral organs in the form of an idea that does not coincide with theevent. The mistake does not lie in the defective activity of the senses so much as in the fact that an apperceptive idea is substituted for the perceptive view. In hallucination every external event is absent, and hence, what is seen is due to a stimulation of the periphery. Some authorities believe hallucination to be caused by cramp of the sensory nerve. Others find illusions to be an externally stimulated sense-perception not corresponding to the stimulus, and still others believe it to be essentially normal. Most human beings are from time to time subject to illusions; indeed, nobody is always sober and intelligent in all his perceptions and convictions. The luminous center of our intelligent perceptions is wrapped in a cloudy half-shadow of illusion.
Sully[322]aims to distinguish the essential nature of illusion from that characterized by ordinary language. Illusion, according to him, is often used to denote mistakes which do not imply untrue perceptions. We say a man has an illusion who thinks too much of himself, or when he tells stories otherwise than as they happen because of a weakness of memory. Illusion is every form of mistake which substitutes any direct self-evident or intuitive knowledge, whether as sense-perception or as any other form.
Nowadays the cause of hallucination and illusion is sought in the over-excitement of the cerebro-spinal system. As this stimulation may be very various in its intensity and significance, from the momentary rush of blood to complete lunacy, so hallucinations and illusions may be insignificant or signs of very serious mental disturbances. When we seek the form of these phenomena, we find that all those psychical events belong to it which have not beenpurposelyperformed or lied about. When Brutus sees Cæsar’s ghost; Macbeth, Banquo’s ghost; Nicholas, his son; these are distinctly hallucinations or illusions of the same kind as those “really and truly” seen by our nurses. The stories of such people have no significance for the criminalist, but if a person has seen an entering thief, an escaping murderer, a bloody corpse, or some similar object of criminal law, and these are hallucinations like classical ghosts, then are we likely to be much deceived. Hoppe[323]enumerates hallucinations of apparently sound (?) people. 1. A priest tired by mental exertion, saw, while he was writing, a boy’s head look over his shoulder. If he turned toward it it disappeared, if he resumed writing it reappeared. 2. “A thoroughly intelligent” man always was seeing a skeleton. 3. Pascal, after a heavy blow, saw a fiery abyss into which he was afraid he would fall. 4. A man who had seen an enormous fire, for a long time afterward saw flames continually. 5. Numerous cases in which criminals, especially murderers, always had their victims before their eyes. 6. Justus Möser saw well-known flowers and geometrical figures very distinctly. 7. Bonnet knows a “healthy” man who saw people, birds, etc., with open eyes. 8. A man got a wound in his left ear and for weeks afterward saw a cat. 9. A woman eighty-eight years old often saw everything covered with flowers,—otherwise she was quite “well.”
A part of these stories seems considerably fictitious, a part applies to indubitable pathological cases, and certain of them are confirmed elsewhere. That murderers, particularly women-murderers of children, often see their victims is well known to us criminalists. And for this reason the habit of confining prisoners in a dark cell for twenty-four hours on the anniversary of a crime must be pointed to as refined and thoroughly mediæval cruelty. I have repeatedly heard from people so tortured of the terror of their visions on such days of martyrdom. Cases are told of in which prisoners who were constipated had all kinds of visual and auditory hallucinations and appeared, e.g., to hear in the rustling of their straw, all sorts of words. That isolation predisposes people to such things is as well known as the fact that constipation causes a rush of blood to the head, and hence, nervous excitement. The well-known stories of robbers which are often told us by prisoners are not always the fruit of malicious invention. Probably a not insignificant portion are the result of hallucination.
Hoppe tells of a great group of hallucinations in conditions of waking and half-waking, and asserts that everybody has them and can note them if he gives his attention thereto. This may be an exaggeration, but it is true that a healthy person in any way excited or afraid may hear all kinds of things in the crackling of a fire, etc., and may see all kinds of things, in smoke, in clouds, etc. The movement of portraits and statues is particularly characteristic, especially in dim light, and under unstable emotional conditions. I own a relief by Ghiberti called the “Rise of the Flesh,” in which seven lemurs dance around a corpse and sing. If, at night, I put out the lamp in my study and the moon falls on the work, the seven lemurs dance as lively as may be during the time it takes my eyes to adapt themselves from the lamplight to the moonlight. Something similarI see on an old carved dresser. The carving is so delicate that in dim light it shows tiny heads and flames after the fashion of the Catholic church pictures of “poor souls,” in purgatory. Under certain conditions of illumination the flames flicker, the heads move, and out of the fire the arms raise themselves to the clouds floating above. Now this requires no unusual excitement, simply the weary sensing of evening, when the eyes turn from prolonged uniform reading or writing to something else.[324]It has happened to me from my earliest childhood. High bodily temperature may easily cause hallucinations. Thus, marching soldiers are led to shoot at nonexisting animals and apparently-approaching enemies. Uniform and fatiguing mental activity is also a source of hallucination. Fechner says that one day having performed a long experiment with the help of a stop-watch, he heard its beats through the whole evening after. So again when he was studying long series of figures he used to see them at night in the dark so distinctly that he could read them off.
Then there are illusions of touch which may be criminalistically important. A movement of air may be taken for an approaching man. A tight collar or cravat may excite the image of being stifled! Old people frequently have a sandy taste while eating,—when this is told the thought occurs that it may be due to coarsely powdered arsenic, yet it may be merely illusion.
The slightest abnormality makes hallucinations and illusions very easy. Persons who are in great danger have all kinds of hallucinations, particularly of people. In the court of law, when witnesses who have been assaulted testify to having seen people, hallucination may often be the basis of their evidence. Hunger again, or loss of blood, gives rise to the most various hallucinations. Menstruation and hæmorrhoids may be the occasions of definite periodic visions, and great pain may be accompanied by hallucinations which begin with the pain, become more distinct as it increases, and disappear when it ceases.
It might seem that in this matter, also, the results are destructive and that the statements of witnesses are untrue and unreliable. I do not assert that our valuation of these statements shall be checked from all possible directions, but I do say that much of what we have considered as true depends only on illusions in the broad sense of the word and that it is our duty before all things rigorously to test everything that underlies our researches.
Illusions of sense, hallucinations, and illusions proper taken as a group, differ from imaginative representations because the individual who has them is more or less passive and subject to the thing from which they arise, while with the latter the individual is more active and creates new images by thecombinationof existing or only imagined conditions. It does not matter whether these consist of the idea only, or whether they are the product of word, manuscript, picture, sculpture, music, etc. We have to deal only with their occurrence and their results. Of course there is no sharp boundary between imaginative ideas and sense-perception, etc. Many phenomena are difficult to classify and even language is uncertain in its usage. The notion “illusion” has indicated many a false ideal, many a product of incoherent fancy.
The activity of the imagination, taken in the ordinary sense, requires analysis first of all. According to Meinong[325]there are two kinds of imaginative images—a generative, and a constructive kind. The first exhibits elements, the second unites them. Thus: I imagine some familiar house, then I reproduce the idea of fire (generative), now I unite these two elements, and imagine the house in question in flames (constructive). This involves several conditions.