Other psychical phenomena, as self-reflection, emotional activity, and so on, appear in dream-life, but they do so in close connection with these quasi-perceptions. The name "vision," given by old writers to dreams, sufficiently points out this close affinity of the mental phenomena to sense-perception; and so far as science is concerned, they must be regarded as a peculiar variety of sense-illusion. Hence the appropriateness of studying them in close connection with the illusions of perception of the waking state. Though marked off by the presence of very exceptional physiological conditions, they are largely intelligible by help of these physiological and psychological principles which we have just been considering.
_The State of Sleep._
The physiological explanation of dreams must, it is plain, set out with an account of the condition of the organism known as sleep. While there is here much that is uncertain, there are some things which are fairly well known. Recent physiological observation has gone to prove that during sleep all the activities of the organism are appreciably lowered.
Thus, for example, according to Testa, the pulse falls by about one-fifth. This lowering of the organic functions appears, under ordinary circ.u.mstances, to increase towards midnight, after which there is a gradual rising.
The nervous system shares in this general depression of the vital activities. The circulation being slower, the process of reparation and nutrition of the nerves is r.e.t.a.r.ded, and so their degree of excitability diminished. This is clearly seen in the condition of the peripheral regions of the nervous system, including the sense-organs, which appear to be but very slightly acted on by their customary stimuli.
The nervous centres must partic.i.p.ate in this lethargy of the system. In other words, the activity of the central substance is lowered, and the result of this is plainly seen in what is usually thought of as the characteristic feature of sleep, namely, a transition from vigorous mental activity or intense and clear consciousness, to comparative inactivity or faint and obscure consciousness. The cause of this condition of the centres is supposed to be the same as that of the torpidity of all the other organs in sleep, namely, the r.e.t.a.r.dation of the circulation. But, though there is no doubt as to this, the question of the proximate physiological conditions of sleep is still far from being settled. Whether during sleep the blood-vessels of the brain are fuller or less full than during waking, is still a moot point. Also the qualitative condition of the blood in the cerebral vessels is still a matter of discussion.[72]
Since the effect of sleep is to lower central activity, the question naturally occurs whether the nervous centres are ever rendered inactive to such an extent as to interrupt the continuity of our conscious life.
This question has been discussed from the point of view of the metaphysician, of the psychologist, and of the physiologist, and in no case is perfect unanimity to be found. The metaphysical question, whether the soul as a spiritual substance is capable of being wholly inactive, or whether it is not in what seem the moments of profoundest unconsciousness partially awake--the question so warmly discussed by the Cartesians, Leibnitz, etc.--need not detain us here.
Of more interest to us are the psychological and the physiological discussions. The former seeks to settle the question by help of introspection and memory. On the one side, it is urged against the theory of unbroken mental activity, that we remember so little of the lowered consciousness of sleep.[73] To this it is replied that our forgetfulness of the contents of dream-consciousness, even if this were unbroken, would be fully accounted for by the great dissimilarity between dreaming and waking mental life. It is urged, moreover, on this side that a sudden rousing of a man from sleep always discovers him in the act of dreaming, and that this goes to prove the uniform connection of dreaming and sleeping. This argument, again, may be met by the a.s.sertion that our sense of the duration of our dreams is found to be grossly erroneous; that, owing to the rapid succession of the images, the _realization_ of which would involve a long duration, we enormously exaggerate the length of dreams in retrospection.[74] From this it is argued that the dream which is recalled on our being suddenly awakened may have had its whole course during the transition state of waking.
Again, the fact that a man may resolve, on going to sleep, to wake at a certain hour, has often been cited in proof of the persistence of a degree of mental activity even in perfectly sound sleep. The force of this consideration, however, has been explained away by saying that the antic.i.p.ation of rising at an unusual hour necessarily produces a slight amount of mental disquietude, which is quite sufficient to prevent sound sleep, and therefore to expose the sleeper to the rousing action of faint external stimuli.
While the purely psychological method is thus wholly inadequate to solve the question, physiological reasoning appears also to be not perfectly conclusive. Many physiologists, not unnaturally desirous of upsetting what they regard as a gratuitous metaphysical hypothesis, have p.r.o.nounced in favour of an absolutely dreamless or unconscious sleep.
From the physiological point of view, there is no mystery in a totally suspended mental activity. On the other hand, there is much to be said on the opposite side, and perhaps it may be contended that the purely physiological evidence rather points to the conclusion that central activity, however diminished during sleep, always retains a minimum degree of intensity. At least, one would be disposed to argue in this way from the a.n.a.logy of the condition of the other functions of the organism during sleep. Possibly this modic.u.m of positive evidence may more than outweigh any slight presumption against the doctrine of unbroken mental activity drawn from the negative circ.u.mstance that we remember so little of our dream-life.[75]
Such being the state of physiological knowledge respecting the immediate conditions of sleep, we cannot look for any certain information on the nature of that residual mode of cerebral activity which manifests itself subjectively in dreams. It is evident, indeed, that this question can only be fully answered when the condition of the brain as a whole during sleep is understood. Meanwhile we must be content with vague hypotheses.
It may be said, for one thing, that during sleep the nervous substance as a whole is less irritable than during waking hours. That is to say, a greater amount of stimulus is needed to produce any conscious result.[76] This appears plainly enough in the case of the peripheral sense-organs. Although these are not, as it is often supposed, wholly inactive during sleep, they certainly require a more potent external stimulus to rouse them to action. And what applies to the peripheral regions applies to the centres. In truth, it is clearly impossible to distinguish between the diminished irritability of the peripheral and that of the central structures.
At first sight it seems contradictory to the above to say that stimuli which have little effect on the centres of consciousness during waking life produce an appreciable result in sleep. Nevertheless, it will be found that this is the case. Thus organic processes which scarcely make themselves known to the mind in a waking state, may be shown to be the originators of many of our dreams. This fact can only be explained on the physical side by saying that the special cerebral activities engaged in an act of attention are greatly liberated during sleep by the comparative quiescence of the external senses. These activities, by co-operating with the faint results of the stimuli coming from the internal organs, serve very materially to increase their effect.
Finally, it is to be observed that, while the centres thus respond with diminished energy to peripheral stimuli, external and internal, they undergo a direct, or "automatic," mode of excitation, being roused into activity independently of an incoming nervous impulse. This automatic stimulation has been plausibly referred to the action of the products of decomposition acc.u.mulating in the cerebral blood-vessels.[77] It is possible that there is something in the nature of this stimulation to account for the force and vividness of its conscious results, that is to say, of dreams.
_The Dream State._
Let us now turn to the psychic side of these conditions, that is to say, to the general character of the mental states known as dreams. It is plain that the closing of the avenues of the external senses, which is the accompaniment of sleep, will make an immense difference in the mental events of the time. Instead of drawing its knowledge from without, noting its bearings in relation to the environment, the mind will now be given over to the play of internal imagination. The activity of fancy will, it is plain, be unrestricted by collision with external fact. The internal mental life will expand in free picturesque movement.
To say that in sleep the mind is given over to its own imaginings, is to say that the mental life in these circ.u.mstances will reflect the individual temperament and mental history. For the play of imagination at any time follows the lines of our past experience more closely than would at first appear, and being coloured with emotion, will reflect the predominant emotional impulses of the individual mind. Hence the saying of Herac.l.i.tus, that, while in waking we all have a common world, in sleep we have each a world of our own.
This play of imagination in sleep is furthered by the peculiar att.i.tude of attention. When asleep the voluntary guidance of attention ceases; its direction is to a large extent determined by the contents of the mind at the moment. Instead of holding the images and ideas, and combining them according to some rational end, the attention relaxes its energies and succ.u.mbs to the force of imagination. And thus, in sleep, just as in the condition of reverie or day-dreaming, there is an abandonment of the fancy to its own wild ways.
It follows that the dream-state will not appear to the mind as one of fancy, but as one of actual perception, and of contact with present reality. Dreams are clearly illusory, and, unlike the illusions of waking life, are complete and persistent.[78] And the reason of this ought now to be clear. First of all, the mind during sleep wants what M.
Taine calls the corrective of a present sensation. When awake under ordinary circ.u.mstances, any momentary illusion is at once set right by a new act of orientation. The superior vividness of the external impression cannot leave us in any doubt, when calm and self-possessed, whether our mental images answer to present realities or not. On the other hand, when asleep, this reference to a fixed objective standard is clearly impossible. Secondly, we may fairly argue that the mental images of sleep approximate in character to external impressions. This they do to some extent in point of intensity, for, in spite of the diminished excitability of the centres, the mode of stimulation which occurs in sleep may, as I have hinted, involve an energetic cerebral action. And, however this be, it is plain that the image will gain a preternatural force through the greatly narrowed range of attention. When the mind of the sleeper is wholly possessed by an image or group of images, and the attention kept tied down to these, there is a maximum reinforcement of the images. But this is not all. When the attention is thus held captive by the image, it approximates in character to an external impression in another way. In our waking state, when our powers of volition are intact, the external impression is characterized by its fixity or its obdurate resistance to our wishes. On the other hand, the mental image is fluent, accommodating, and disappears and reappears according to the direction of our volitions. In sleep, through the suspension of the higher voluntary power of attention, the mental image seems to lord it over our minds just as the actual impression of waking life.
This much may suffice, perhaps, by way of a general description of the sleeping and dreaming state. Other points will make themselves known after we have studied the contents and structure of dreams in detail.
Dreams are commonly cla.s.sified (_e.g._ by Wundt) with hallucinations, and this rightly, since, as their common appellation of "vision"
suggests, they are for the most part the semblance of percepts in the absence of external impressions. At the same time, recent research goes to show that in many dreams something answering to the "external impression" in waking perception is the starting-point. Consequently, in order to be as accurate as possible, I shall divide dreams into illusions (in the narrow sense) and hallucinations.
_Dream-Illusions._
By dream-illusions I mean those dreams which set out from some peripheral nervous stimulation, internal or external. That the organic processes of digestion, respiration, etc., act as stimuli to the centres in sleep is well known. Thus, David Hartley a.s.signs as the second great source of dreams "states of the body."[79] But it is not so well known to what an extent our dreams may be influenced by stimuli acting on the exterior sense-organs. Let us first glance at the action of such external stimuli.
_Action of External Stimuli._
During sleep the eyes are closed, and consequently the action of external light on the retina impeded. Yet it is found that even under these circ.u.mstances any very bright light suddenly introduced is capable of stimulating the optic fibres, and of affecting consciousness. The most common form of this is the effect of bright moonlight, and of the early sun"s rays. Krauss tells a funny story of his having once, when twenty-six years old, caught himself, on waking, in the act of stretching out his arms towards what his dream-fancy had pictured as the image of his mistress. When fully awake, this image resolved itself into the full moon.[80] It is not improbable, as Radestock remarks, that the rays of the sun or moon are answerable for many of the dreams of celestial glory which persons of a highly religious temperament are said to experience.
External sounds, when not sufficient to rouse the sleeper, easily incorporate themselves into his dreams. The ticking of a watch, the stroke of a clock, the hum of an insect, the song of a bird, the patter of rain, are common stimuli to the dream-phantasy. M. Alf. Maury tells us, in his interesting account of the series of experiments to which he submitted himself in order to ascertain the result of external stimulation on the mind during sleep, that when a pair of tweezers was made to vibrate near his ear, he dreamt of bells, the tocsin, and the events of June, 1848.[81] Most of us, probably, have gone through the experience of impolitely falling asleep when some one was reading to us, and of having dream-images suggested by the sounds that were still indistinctly heard. Scherner gives an amusing case of a youth who was permitted to whisper his name into the ear of his obdurate mistress, the consequence of which was that the lady contracted a habit of dreaming about him, which led to a felicitous change of feeling on her part.[82]
The two lower senses, smell and taste, seem to play a less-important part in the production of dream-illusions. Radestock says that the odour of flowers in a room easily leads to visual images of hot-houses, perfumery shops, and so on; and it is probable that the contents of the mouth may occasionally act as a stimulus to the organ of taste, and so give rise to corresponding dreams. As Radestock observes, these lower sensations do not commonly make known their quality to the sleeper"s mind. They become transformed at once into visual, instead of into olfactory or gustatory percepts. That is to say, the dreamer does not imagine himself smelling or tasting, but seeing an object.
The contact of objects with the tactual organ is one of the best recognized causes of dreams. M. Maury found that when his lips were tickled, his dream-fancy interpreted the impression as of a pitch plaster being torn off his face. An unusual pressure on any part of the body, as, for example, from contact with a fellow-sleeper, is known to give rise to a well-marked variety of dream. Our own limbs may even appear as foreign bodies to our dream-imagination, when through pressure they become partly paralyzed. Thus, on one occasion, I awoke from a miserable dream, in which I felt sure I was grasping somebody"s hand in bed, and I was racked by terrifying conjectures as to who it might be.
When fully awake, I discovered that I had been lying on my right side, and clasping the wrist of the right arm (which had been rendered insensible by the pressure of the body) with the left hand.
In close connection with these stimuli of pressure are those of muscular movement, whether unimpeded or impeded. We need not enter into the difficult question how far the "muscular sense" is connected with the activity of the motor nerves, and how far with sensory fibres attached to the muscular or the adjacent tissues. Suffice it to say that an actual movement, a resistance to an attempted movement, or a mere disposition to movement, whether consequent on a surplus of motor energy or on a sensation of discomfort or fatigue in the part to be moved, somehow or other makes itself known to our minds, even when we are deprived of the a.s.sistance of vision. And these feelings of movement, impeded or unimpeded, are common initial impulses in our dream-experiences. It is quite a mistake to suppose that dreams are built up out of the purely pa.s.sive sensations of sight and hearing. A close observation will show that in nearly every dream we imagine ourselves either moving among the objects we perceive or striving to move when some weighty obstacle obstructs us. All of us are familiar with the common forms of nightmare, in which we strive hopelessly to flee from some menacing evil, and this dream-experience, it may be presumed, frequently comes from a feeling of strain in the muscles, due to an awkward disposition of the limbs during sleep. The common dream-illusion of falling down a vast abyss is plausibly referred by Wundt to an involuntary extension of the foot of the sleeper.
_Action of Internal Stimuli._
Let us now pa.s.s from the action of stimuli lying outside the organism, to that of stimuli lying within the peripheral regions of the sense-organs. I have already spoken of the influence of subjective sensations of sight, hearing, etc., on the illusions of waking life, and it is now to be added that these sensations play an important part in our dream-life. Johannes Muller lays great prominence on the part taken by ocular spectra in the production of dreams. As he observes, the apparent rays of light, light-patches, mists of light, and so on, due to changes of blood-pressure in the retina, only manifest themselves clearly when the eyes are closed and the more powerful effect of the external stimulus cut off. These subjective spectra come into prominence in the sleepy condition, giving rise to what M. Maury calls "hallucinations hypnagogiques," and which he regards (after Gruithuisen) as the chaos out of which the dream-cosmos is evolved.[83] They are pretty certainly the starting-point in those picturesque dreams in which figure a number of bright objects, such as beautiful birds, b.u.t.terflies, flowers, or angels.
That the visual images of our sleep do often involve the peripheral regions of the organ of sight, seems to be proved by the singular fact that they sometimes persist after waking. Spinoza and Jean Paul Richter both experienced this survival of dream-images. Still more pertinent is the fact that the effects of retinal fatigue are producible by dream-images. The physiologist Gruithuisen had a dream, in which the princ.i.p.al feature was a violet flame, and which left behind it, _after waking_, for an appreciable duration, a complementary image of a yellow spot.[84]
Subjective auditory sensations appear to be much less frequent causes of dream-illusions than corresponding visual sensations. Yet the rushing, roaring sound caused by the circulation of the blood in the ear is, probably, a not uncommon starting-point in dreams. With respect to subjective sensations of smell and taste, there is little to be said. On the other hand, subjective sensations due to varying conditions in the skin are a very frequent exciting cause of dreams. Variations in the state of tension of the skin, brought about by alteration of position, changes in the character of the circulation, the irradiation of heat to the skin or the loss of the same, chemical changes,--these are known to give rise to a number of familiar sensations, including those of tickling, itching, burning, creeping, and so on; and the effects of these sensations are distinctly traceable in our dreams. For example, the exposure of a part of the body through a loss of the bed-clothes is a frequent excitant of distressing dreams. A cold foot suggests that the sleeper is walking over snow or ice. On the other hand, if the cold foot happens to touch a warm part of the body, the dream-fancy constructs images of walking on burning lava, and so on.
These sensations of the skin naturally conduct us to the organic sensations as a whole; that is to say, the feelings connected with the varying condition of the bodily organs. These include the feelings which arise in connection with the processes of digestion, respiration, and circulation, and the condition of various organs according to their state of nutrition, etc. During our waking life these organic feelings coalesce for the most part, forming as the "vital sense" an obscure background for our clear discriminative consciousness, and only come forward into this region when very exceptional in character, as when respiration or digestion is impeded, or when we make a special effort of attention to single them out.[85] When we are asleep, however, and the avenues of external perception are closed, they a.s.sume greater prominence and distinctness. The centres, no longer called upon to react on stimuli coming from without the organism, are free to react on stimuli coming from its hidden recesses. So important a part, indeed, do these organic feelings take in the dream-drama, that some writers are disposed to regard them as the great, if not the exclusive, cause of dreams. Thus, Schopenhauer held that the excitants of dreams are impressions received from the internal regions of the organism through the sympathetic nervous system.[86]
It is hardly necessary, perhaps, to give many ill.u.s.trations of the effect of such organic sensations on our dreams. Among the most common provocatives of dreams are sensations connected with a difficulty in breathing, due to the closeness of the air or to the pressure of the bed-clothes on the mouth. J. Borner investigated the influence of these circ.u.mstances by covering with the bed-clothes the mouth and a part of the nostrils of persons who were sound asleep. This was followed by a protraction of the act of breathing, a reddening of the face, efforts to throw off the clothes, etc. On being roused, the sleeper testified that he had experienced a nightmare, in which a horrid animal seemed to be weighing him down.[87] Irregularity of the heart"s action is also a frequent cause of dreams. It is not improbable that the familiar dream-experience of flying arises from disturbances of the respiratory and circulatory movements.
Again, the effects of indigestion, and more particularly stomachic derangement, on dreams are too well known to require ill.u.s.tration. It may be enough to allude to the famous dream which Hood traces to an excessive indulgence at supper. It is known that the varying condition of the organs of secretion influences our dream-fancy in a number of ways.
Finally, it is to be observed that an injury done to any part of the organism is apt to give rise to appropriate dream-images. In this way, very slight disturbances which would hardly affect waking consciousness may make themselves felt during sleep. Thus, for example, an incipient toothache has been known to suggest that the teeth are being extracted.[88]
It is worth observing that the interpretation of these various orders of sensations by the imagination of the dreamer takes very different forms according to the person"s character, previous experience, ruling emotions, and so on. This is what is meant by saying that during sleep every man has a world of his own, whereas, when awake, he shares in the common world of perception.
_Dream-Exaggeration._
It is to be noticed, further, that this interpretation of sensation during sleep is uniformly a process of exaggeration.[89] The exciting causes of the feeling of discomfort, for example, are always absurdly magnified. The reason of this seems to be that, owing to the condition of the mind during sleep, the nature of the sensation is not clearly recognizable. Even in the case of familiar external impressions, such as the sound of the striking of a clock, there appears to be wanting that simple process of reaction by which, in a waking condition of the attention, a sense-impression is instantly discriminated and cla.s.sed. In sleep, as in the artificially induced hypnotic condition, the slighter differences of quality among sensations are not clearly recognized. The activity of the higher centres, which are concerned in the finer processes of discrimination and cla.s.sification, being greatly reduced, the impression may be said to come before consciousness as something novel and unfamiliar. And just as we saw that in waking life novel sensations agitate the mind, and so lead to an exaggerated mode of interpretation; so here we see that what is unfamiliar disturbs the mind, rendering it incapable of calm attention and just interpretation.
This failure to recognize the real nature of an impression is seen most conspicuously in the case of the organic sensations. As I have remarked, these const.i.tute for the most part, in waking life, an undiscriminated ma.s.s of obscure feeling, of which we are only conscious as the mental tone of the hour. And in the few instances in which we do attend to them separately, whether through their exceptional intensity or in consequence of an extraordinary effort of discriminative attention, we can only be said to perceive them, that is, recognize their local origin, very vaguely. Hence, when asleep, these sensations get very oddly misinterpreted.
The localization of a bodily sensation in waking life means the combination of a tactual and a visual image with the sensation. Thus, my recognition of a twinge of toothache as coming from a certain tooth, involves representations of the active and pa.s.sive sensations which touching and looking at the tooth would yield me. That is to say, the feeling instantly calls up a compound mental image exactly answering to a visual percept. This holds good in dream-interpretation too; the interpretation is effected by means of a visual image. But since the feeling is only very vaguely recognized, this visual image does not answer to the bodily part concerned. Instead of this, the fancy of the dreamer constructs some visual image which bears a vague resemblance to the proper one, and is generally, if not always, an exaggeration of this in point of extensive magnitude, etc. For example, a sensation arising from pressure on the bladder, being dimly connected with the presence of a fluid, calls up an image of a flood, and so on.
This mode of dream-interpretation has by some writers been erected into the typical mode, under the name of dream-symbolism. Thus Scherner, in his interesting though somewhat fanciful work, _Das Leben des Traumes_, contends that the various regions of the body regularly disclose themselves to the dream-fancy under the symbol of a building or group of buildings; a pain in the head calling up, for example, the image of spiders on the ceiling, intestinal sensations exciting an image of a narrow alley, and so on. Such theories are clearly an exaggeration of the fact that the localization of our bodily sensations during sleep is necessarily imperfect.[90]
In many cases the image called up bears on its objective side no discoverable resemblance to that of the bodily region or the exciting cause of the sensation. Here the explanation must be looked for in the subjective side of the sensation and mental image, that is to say, in their emotional quality, as pleasurable or painful, distressing, quieting, etc. It is to be observed, indeed, that in natural sleep, as in the condition known as hypnotism, while differences of specific quality in the sense-impressions are lost, the broad difference of the pleasurable and the painful is never lost. It is, in fact, the subjective emotional side of the sensation that uniformly forces itself into consciousness. This being so, it follows that, speaking generally, the sensations of sleep, both external and internal, or organic, will be interpreted by what G.H. Lewes has called "an a.n.a.logy of feeling;" that is to say, by means of a mental image having some kindred emotional character or colouring.
Now, the a.n.a.logy between the higher emotional and the bodily states is a very close one. A sensation of obstruction in breathing has its exact a.n.a.logue in a state of mental embarra.s.sment, a sensation of itching its counterpart in mental impatience, and so on. And since these emotional experiences are deeper and fuller than the sensations, the tendency to exaggerate the nature and causes of these last would naturally lead to an interpretation of them by help of these experiences. In addition to this, the predominance of visual imagery in sleep would aid this transformation of a bodily sensation into an emotional experience, since visual perceptions have, as their accompaniments of pleasure and pain, not sensations, but emotions.[91]