DEPTH AND MOVEMENT
The problem is now quite clear before us. Do the photoplays furnish us only a photographic reproduction of a stage performance; is their aim thus simply to be an inexpensive substitute for the real theater, and is their esthetic standing accordingly far below that of the true dramatic art, related to it as the photograph of a painting to the original canvas of the master? Or do the moving pictures bring us an independent art, controlled by esthetic laws of its own, working with mental appeals which are fundamentally different from those of the theater, with a sphere of its own and with ideal aims of its own? If this so far neglected problem is ours, we evidently need not ask in our further discussions about all which books on moving pictures have so far put into the foreground, namely the physical technique of producing the pictures on the film or of projecting the pictures on the screen, or anything else which belongs to the technical or physical or economic aspect of the photoplay industry. Moreover it is then evidently not our concern to deal with those moving pictures which serve mere curiosity or the higher desires for information and instruction. Those educational pictures may give us delight, and certainly much esthetic enjoyment may be combined with the intellectual satisfaction, when the wonders of distant lands are unveiled to us. The landscape setting of such a travel film may be a thing of beauty, but the pictures are not taken for art's sake. The aim is to serve the spread of knowledge.
Our esthetic interest turns to the means by which the photoplay influences the mind of the spectator. If we try to understand and to explain the means by which music exerts its powerful effects, we do not reach our goal by describing the structure of the piano and of the violin, or by explaining the physical laws of sound. We must proceed to the psychology and ask for the mental processes of the hearing of tones and of chords, of harmonies and disharmonies, of tone qualities and tone intensities, of rhythms and phrases, and must trace how these elements are combined in the melodies and compositions. In this way we turn to the photoplay, at first with a purely psychological interest, and ask for the elementary excitements of the mind which enter into our experience of the moving pictures. We now disregard entirely the idea of the theater performance. We should block our way if we were to start from the theater and were to ask how much is left out in the mere photographic substitute. We approach the art of the film theater as if it stood entirely on its own ground, and extinguish all memory of the world of actors. We analyze the mental processes which this specific form of artistic endeavor produces in us.
To begin at the beginning, the photoplay consists of a series of flat pictures in contrast to the plastic objects of the real world which surrounds us. But we may stop at once: what does it mean to say that the surroundings appear to the mind plastic and the moving pictures flat? The psychology of this difference is easily misunderstood. Of course, when we are sitting in the picture palace we know that we see a flat screen and that the object which we see has only two dimensions, right-left, and up-down, but not the third dimension of depth, of distance toward us or away from us. It is flat like a picture and never plastic like a work of sculpture or architecture or like a stage. Yet this is knowledge and not immediate impression. We have no right whatever to say that the scenes which we see on the screen appear to us as flat pictures.
We may become more strongly conscious of this difference between an object of our knowledge and an object of our impression, if we remember a well-known instrument, the stereoscope. The stereoscope, which was quite familiar to the parlor of a former generation, consists of two prisms through which the two eyes look toward two photographic views of a landscape. But the two photographic views are not identical. The landscape is taken from two different points of view, once from the right and once from the left. As soon as these two views are put into the stereoscope the right eye sees through the prism only the view from the right, the left eye only the view from the left. We know very well that only two flat pictures are before us; yet we cannot help seeing the landscape in strongly plastic forms. The two different views are combined in one presentation of the landscape in which the distant objects appear much further away from us than the foreground. We feel immediately the depth of things. It is as if we were looking at a small plastic model of the landscape and in spite of our objective knowledge cannot recognize the flat pictures in the solid forms which we perceive. It cannot be otherwise, because whenever in practical life we see an object, a vase on our table, as a solid body, we get the impression of its plastic character first of all by seeing it with our two eyes from two different points of view. The perspective in which our right eye sees the things on our table is different from the perspective for the left eye. Our plastic seeing therefore depends upon this combination of two different perspective views, and whenever we offer to the two eyes two such one-sided views, they must be combined into the impression of the substantial thing. The stereoscope thus illustrates clearly that the knowledge of the flat character of pictures by no means excludes the actual perception of depth, and the question arises whether the moving pictures of the photoplay, in spite of our knowledge concerning the flatness of the screen, do not give us after all the impression of actual depth.
It may be said offhand that even the complete appearance of depth such as the stereoscope offers would be in no way contradictory to the idea of moving pictures. Then the photoplay would give the same plastic impression which the real stage offers. All that would be needed is this. When the actors play the scenes, not a single but a double camera would have to take the pictures. Such a double camera focuses the scene from two different points of view, corresponding to the position of the two eyes. Both films are then to be projected on the screen at the same time by a double projection apparatus which secures complete correspondence of the two pictures so that in every instance the left and the right view are overlapping on the screen. This would give, of course, a chaotic, blurring image. But if the apparatus which projects the left side view has a green glass in front of the lens and the one which projects the right side view a red glass, and every person in the audience has a pair of spectacles with the left glass green and the right glass red—a cardboard lorgnette with red and green gelatine paper would do the same service and costs only a few cents—the left eye would see only the left view, the right eye only the right view. We could not see the red lines through the green glass nor the green lines through the red glass. In the moment the left eye gets the left side view only and the right eye the right side view, the whole chaos of lines on the screen is organized and we see the pictured room on the screen with the same depth as if it were really a solid room set on the stage and as if the rear wall in the room were actually ten or twenty feet behind the furniture in the front. The effect is so striking that no one can overcome the feeling of depth under these conditions.
But while the regular motion pictures certainly do not offer us this complete plastic impression, it would simply be the usual confusion between knowledge about the picture and its real appearance if we were to deny that we get a certain impression of depth. If several persons move in a room, we gain distinctly the feeling that one moves behind another in the film picture. They move toward us and from us just as much as they move to the right and left. We actually perceive the chairs or the rear wall of the room as further away from us than the persons in the foreground. This is not surprising if we stop to think how we perceive the depth, for instance, of a real stage. Let us fancy that we sit in the orchestra of a real theater and see before us the stage set as a room with furniture and persons in it. We now see the different objects on the stage at different distances, some near, some far. One of the causes was just mentioned. We see everything with our right or our left eye from different points of view. But if now we close one eye and look at the stage with the right eye only, the plastic effect does not disappear. The psychological causes for this perception of depth with one eye are essentially the differences of apparent size, the perspective relations, the shadows, and the actions performed in the space. Now all these factors which help us to grasp the furniture on the stage as solid and substantial play their rôle no less in the room which is projected on the screen.
We are too readily inclined to imagine that our eye can directly grasp the different distances in our surroundings. Yet we need only imagine that a large glass plate is put in the place of the curtain covering the whole stage. Now we see the stage through the glass; and if we look at it with one eye only it is evident that every single spot on the stage must throw its light to our eye by light rays which cross the glass plate at a particular point. For our seeing it would make no difference whether the stage is actually behind that glass plate or whether all the light rays which pass through the plate come from the plate itself. If those rays with all their different shades of light and dark started from the surface of the glass plate, the effect on the one eye would necessarily be the same as if they originated at different distances behind the glass. This is exactly the case of the screen. If the pictures are well taken and the projection is sharp and we sit at the right distance from the picture, we must have the same impression as if we looked through a glass plate into a real space.
The photoplay is therefore poorly characterized if the flatness of the pictorial view is presented as an essential feature. That flatness is an objective part of the technical physical arrangements, but not a feature of that which we really see in the performance of the photoplay. We are there in the midst of a three-dimensional world, and the movements of the persons or of the animals or even of the lifeless things, like the streaming of the water in the brook or the movements of the leaves in the wind, strongly maintain our immediate impression of depth. Many secondary features characteristic of the motion picture may help. For instance, by a well-known optical illusion the feeling of depth is strengthened if the foreground is at rest and the background moving. Thus the ship passing in front of the motionless background of the harbor by no means suggests depth to the same degree as the picture taken on the gliding ship itself so that the ship appears to be at rest and the harbor itself passing by.
The depth effect is so undeniable that some minds are struck by it as the chief power in the impressions from the screen. Vachel Lindsay, the poet, feels the plastic character of the persons in the foreground so fully that he interprets those plays with much individual action as a kind of sculpture in motion. He says: "The little far off people on the oldfashioned speaking stage do not appeal to the plastic sense in this way. They are by comparison mere bits of pasteboard with sweet voices, while on the other hand the photoplay foreground is full of dumb giants. The bodies of these giants are in high sculptural relief." Others have emphasized that this strong feeling of depth touches them most when persons in the foreground stand with a far distant landscape as background—much more than when they are seen in a room. Psychologically this is not surprising either. If the scene were a real room, every detail in it would appear differently to the two eyes. In the room on the screen both eyes receive the same impression, and the result is that the consciousness of depth is inhibited. But when a far distant landscape is the only background, the impression from the picture and life is indeed the same. The trees or mountains which are several hundred feet distant from the eye give to both eyes exactly the same impression, inasmuch as the small difference of position between the two eyeballs has no influence compared with the distance of the objects from our face. We would see the mountains with both eyes alike in reality, and therefore we feel unhampered in our subjective interpretation of far distant vision when the screen offers exactly the same picture of the mountains to our two eyes. Hence in such cases we believe that we see the persons really in the foreground and the landscape far away.
Nevertheless we are never deceived; we are fully conscious of the depth, and yet we do not take it for real depth. Too much stands in the way. Some unfavorable conditions are still deficiencies of the technique; for instance, the camera picture in some respects exaggerates the distances. If we see through the open door of the rear wall into one or two other rooms, they appear like a distant corridor. Moreover we have ideal conditions for vision in the right perspective only when we sit in front of the screen at a definite distance. We ought to sit where we see the objects in the picture at the same angle at which the camera photographed the originals. If we are too near or too far or too much to one side, we perceive the plastic scene from a viewpoint which would demand an entirely different perspective than that which the camera fixated. In motionless pictures this is less disturbing; in moving pictures every new movement to or from the background must remind us of the apparent distortion. Moreover, the size and the frame and the whole setting strongly remind us of the unreality of the perceived space. But the chief point remains that we see the whole picture with both eyes and not with only one, and that we are constantly reminded of the flatness of the picture because the two eyes receive identical impressions. And we may add an argument nearly related to it, namely, that the screen as such is an object of our perception and demands an adaptation of the eye and an independent localization. We are drawn into this conflict of perception even when we look into a mirror. If we stand three feet from a large mirror on the wall, we see our reflection three feet from our eyes in the plate glass and we see it at the same time six feet from our eye behind the glass. Both localizations take hold of our mind and produce a peculiar interference. We all have learned to ignore it, but characteristic illusions remain which indicate the reality of this doubleness.
In the case of the picture on the screen this conflict is much stronger. We certainly see the depth, and yet we cannot accept it. There is too much which inhibits belief and interferes with the interpretation of the people and landscape before us as truly plastic. They are surely not simply pictures. The persons can move toward us and away from us, and the river flows into a distant valley. And yet the distance in which the people move is not the distance of our real space, such as the theater shows, and the persons themselves are not flesh and blood. It is a unique inner experience, which is characteristic of the perception of the photoplays. We have reality with all its true dimensions; and yet it keeps the fleeting, passing surface suggestion without true depth and fullness, as different from a mere picture as from a mere stage performance. It brings our mind into a peculiar complex state; and we shall see that this plays a not unimportant part in the mental make-up of the whole photoplay.
While the problem of depth in the film picture is easily ignored, the problem of movement forces itself on every spectator. It seems as if here the really essential trait of the film performance is to be found, and that the explanation of the motion in the pictures is the chief task which the psychologist must meet. We know that any single picture which the film of the photographer has fixed is immovable. We know, furthermore, that we do not see the passing by of the long strip of film. We know that it is rolled from one roll and rolled up on another, but that this movement from picture to picture is not visible. It goes on while the field is darkened. What objectively reaches our eye is one motionless picture after another, but the replacing of one by another through a forward movement of the film cannot reach our eye at all. Why do we, nevertheless, see a continuous movement? The problem did not arise with the kinetoscope only but had interested the preceding generations who amused themselves with the phenakistoscope and the stroboscopic disks or the magic cylinder of the zoötrope and bioscope. The child who made his zoötrope revolve and looked through the slits of the black cover in the drum saw through every slit the drawing of a dog in one particular position. Yet as the twenty-four slits passed the eye, the twenty-four different positions blended into one continuous jumping movement of the poodle.
But this so-called stroboscopic phenomenon, however interesting it was, seemed to offer hardly any difficulty. The friends of the zoötrope surely knew another little plaything, the thaumatrope. Dr. Paris had invented it in 1827. It shows two pictures, one on the front, one on the rear side of a card. As soon as the card is quickly revolved about a central axis, the two pictures fuse into one. If a horse is on one side and a rider on the other, if a cage is on one and a bird on the other, we see the rider on the horse and the bird in the cage. It cannot be otherwise. It is simply the result of the positive afterimages. If at dark we twirl a glowing joss stick in a circle, we do not see one point moving from place to place, but we see a continuous circular line. It is nowhere broken because, if the movement is quick, the positive afterimage of the light in its first position is still effective in our eye when the glowing point has passed through the whole circle and has reached the first position again.
We speak of this effect as a positive afterimage, because it is a real continuation of the first impression and stands in contrast to the so-called negative afterimage in which the aftereffect is opposite to the original stimulus. In the case of a negative afterimage the light impression leaves a dark spot, the dark impression gives a light afterimage. Black becomes white and white becomes black; in the world of colors red leaves a green and green a red afterimage, yellow a blue and blue a yellow afterimage. If we look at the crimson sinking sun and then at a white wall, we do not see red light spots but green dark spots. Compared with these negative pictures, the positive afterimages are short and they last through any noticeable time only with rather intense illumination. Yet they are evidently sufficient to bridge the interval between the two slits in the stroboscopic disk or in the zoötrope, the interval in which the black paper passes the eye and in which accordingly no new stimulus reaches the nerves. The routine explanation of the appearance of movement was accordingly: that every picture of a particular position left in the eye an afterimage until the next picture with the slightly changed position of the jumping animal or of the marching men was in sight, and the afterimage of this again lasted until the third came. The afterimages were responsible for the fact that no interruptions were noticeable, while the movement itself resulted simply from the passing of one position into another. What else is the perception of movement but the seeing of a long series of different positions? If instead of looking through the zoötrope we watch a real trotting horse on a real street, we see its whole body in ever new progressing positions and its legs in all phases of motion; and this continuous series is our perception of the movement itself.
This seems very simple. Yet it was slowly discovered that the explanation is far too simple and that it does not in the least do justice to the true experiences. With the advance of modern laboratory psychology the experimental investigations frequently turned to the analysis of our perception of movement. In the last thirty years many researches, notably those of Stricker, Exner, Hall, James, Fischer, Stern, Marbe, Lincke, Wertheimer, and Korte have thrown new light on the problem by carefully devised experiments. One result of them came quickly into the foreground of the newer view: the perception of movement is an independent experience which cannot be reduced to a simple seeing of a series of different positions. A characteristic content of consciousness must be added to such a series of visual impressions. The mere idea of succeeding phases of movement is not at all the original movement idea. This is suggested first by the various illusions of movement. We may believe that we perceive a movement where no actual changes of visual impressions occur. This, to be sure, may result from a mere misinterpretation of the impression: for instance when in the railway train at the station we look out of the window and believe suddenly that our train is moving, while in reality the train on the neighboring track has started. It is the same when we see the moon floating quickly through the motionless clouds. We are inclined to consider as being at rest that which we fixate and to interpret the relative changes in the field of vision as movements of those parts which we do not fixate.
But it is different when we come, for instance, to those illusions in which movement is forced on our perception by contrast and aftereffect. We look from a bridge into the flowing water and if we turn our eyes toward the land the motionless shore seems to swim in the opposite direction. It is not sufficient in such cases to refer to contrasting eye movements. It can easily be shown by experiments that these movements and counter-movements in the field of vision can proceed in opposite directions at the same time and no eye, of course, is able to move upward and downward, or right and left, in the same moment. A very characteristic experiment can be performed with a black spiral line on a white disk. If we revolve such a disk slowly around its center, the spiral line produces the impression of a continuous enlargement of concentric curves. The lines start at the center and expand until they disappear in the periphery. If we look for a minute or two into this play of the expanding curves and then turn our eyes to the face of a neighbor, we see at once how the features of the face begin to shrink. It looks as if the whole face were elastically drawn toward its center. If we revolve the disk in the opposite direction, the curves seem to move from the edge of the disk toward the center, becoming smaller and smaller, and if then we look toward a face, the person seems to swell up and every point in the face seems to move from the nose toward the chin or forehead or ears. Our eye which watches such an aftereffect cannot really move at the same time from the center of the face toward both ears and the hair and the chin. The impression of movement must therefore have other conditions than the actual performance of the movements, and above all it is clear from such tests that the seeing of the movements is a unique experience which can be entirely independent from the actual seeing of successive positions. The eye itself gets the impression of a face at rest, and yet we see the face in the one case shrinking, in the other case swelling; in the one case every point apparently moving toward the center, in the other case apparently moving away from the center. The experience of movement is here evidently produced by the spectator's mind and not excited from without.
We may approach the same result also from experiments of very different kind. If a flash of light at one point is followed by a flash at another point after a very short time, about a twentieth of a second, the two lights appear to us simultaneous. The first light is still fully visible when the second flashes, and it cannot be noticed that the second comes later than the first. If now in the same short time interval the first light moves toward the second point, we should expect that we would see the whole process as a lighted line at rest, inasmuch as the beginning and the end point appear simultaneous, if the end is reached less than a twentieth of a second after the starting point. But the experiment shows the opposite result. Instead of the expected lighted line, we see in this case an actual movement from one point to the other. Again we must conclude that the movement is more than the mere seeing of successive positions, as in this case we see the movement, while the isolated positions do not appear as successive but as simultaneous.
Another group of interesting phenomena of movement may be formed from those cases in which the moving object is more easily noticed than the impressions of the whole field through which the movement is carried out. We may overlook an area in our visual field, especially when it lies far to one side from our fixation point, but as soon as anything moves in that area our attention is drawn. We notice the movement more quickly than the whole background in which the movement is executed. The fluttering of kerchiefs at a far distance or the waving of flags for signaling is characteristic. All indicate that the movement is to us something different from merely seeing an object first at one and afterward at another place. We can easily find the analogy in other senses. If we touch our forehead or the back of our hand with two blunt compass points so that the two points are about a third of an inch distant from each other, we do not discriminate the two points as two, but we perceive the impression as that of one point. We cannot discriminate the one pressure point from the other. But if we move the point of a pencil to and fro from one point to the other we perceive distinctly the movement in spite of the fact that it is a movement between two end points which could not be discriminated. It is wholly characteristic that the experimenter in every field of sensations, visual or acoustical or tactual, often finds himself before the experience of having noticed a movement while he is unable to say in which direction the movement occurred.
We are familiar with the illusions in which we believe that we see something which only our imagination supplies. If an unfamiliar printed word is exposed to our eye for the twentieth part of a second, we readily substitute a familiar word with similar letters. Everybody knows how difficult it is to read proofs. We overlook the misprints, that is, we replace the wrong letters which are actually in our field of vision by imaginary right letters which correspond to our expectations. Are we not also familiar with the experience of supplying by our fancy the associative image of a movement when only the starting point and the end point are given, if a skillful suggestion influences our mind. The prestidigitator stands on one side of the stage when he apparently throws the costly watch against the mirror on the other side of the stage; the audience sees his suggestive hand movement and the disappearance of the watch and sees twenty feet away the shattering of the mirror. The suggestible spectator cannot help seeing the flight of the watch across the stage.
The recent experiments by Wertheimer and Korte have gone into still subtler details. Both experimenters worked with a delicate instrument in which two light lines on a dark ground could be exposed in very quick succession and in which it was possible to vary the position of the lines, the distance of the lines, the intensity of their light, the time exposure of each, and the time between the appearance of the first and of the second. They studied all these factors, and moreover the influence of differently directed attention and suggestive attitude. If a vertical line is immediately followed by a horizontal, the two together may give the impression of one right angle. If the time between the vertical and the horizontal line is long, first one and then the other is seen. But at a certain length of the time interval, a new effect is reached. We see the vertical line falling over and lying flat like the horizontal line. If the eyes are fixed on the point in the midst of the angle, we might expect that this movement phenomenon would stop, but the opposite is the case. The apparent movement from the vertical to the horizontal has to pass our fixation point and it seems that we ought now to recognize clearly that there is nothing between those two positions, that the intermediate phases of the movement are lacking; and yet the experiment shows that under these circumstances we frequently get the strongest impression of motion. If we use two horizontal lines, the one above the other, we see, if the right time interval is chosen, that the upper one moves downward toward the lower. But we can introduce there a very interesting variation. If we make the lower line, which appears objectively after the upper one, more intense, the total impression is one which begins with the lower. We see first the lower line moving toward the upper one which also approaches the lower; and then follows the second phase in which both appear to fall down to the position of the lower one. It is not necessary to go further into details in order to demonstrate that the apparent movement is in no way the mere result of an afterimage and that the impression of motion is surely more than the mere perception of successive phases of movement. The movement is in these cases not really seen from without, but is superadded, by the action of the mind, to motionless pictures.
The statement that our impression of movement does not result simply from the seeing of successive stages but includes a higher mental act into which the successive visual impressions enter merely as factors is in itself not really an explanation. We have not settled by it the nature of that higher central process. But it is enough for us to see that the impression of the continuity of the motion results from a complex mental process by which the various pictures are held together in the unity of a higher act. Nothing can characterize the situation more clearly than the fact which has been demonstrated by many experiments, namely, that this feeling of movement is in no way interfered with by the distinct consciousness that important phases of the movement are lacking. On the contrary, under certain circumstances we become still more fully aware of this apparent motion created by our inner activity when we are conscious of the interruptions between the various phases of movement.
We come to the consequences. What is then the difference between seeing motion in the photoplay and seeing it on the real stage? There on the stage where the actors move the eye really receives a continuous series. Each position goes over into the next without any interruption. The spectator receives everything from without and the whole movement which he sees is actually going on in the world of space without and accordingly in his eye. But if he faces the film world, the motion which he sees appears to be a true motion, and yet is created by his own mind. The afterimages of the successive pictures are not sufficient to produce a substitute for the continuous outer stimulation; the essential condition is rather the inner mental activity which unites the separate phases in the idea of connected action. Thus we have reached the exact counterpart of our results when we analyzed the perception of depth. We see actual depth in the pictures, and yet we are every instant aware that it is not real depth and that the persons are not really plastic. It is only a suggestion of depth, a depth created by our own activity, but not actually seen, because essential conditions for the true perception of depth are lacking. Now we find that the movement too is perceived but that the eye does not receive the impressions of true movement. It is only a suggestion of movement, and the idea of motion is to a high degree the product of our own reaction. Depth and movement alike come to us in the moving picture world, not as hard facts but as a mixture of fact and symbol. They are present and yet they are not in the things. We invest the impressions with them. The theater has both depth and motion, without any subjective help; the screen has them and yet lacks them. We see things distant and moving, but we furnish to them more than we receive; we create the depth and the continuity through our mental mechanism.
[1] Readers who have no technical interest in physiological psychology may omit Chapter III and turn directly to [Chapter IV on Attention].