The second quality, however, is peculiar to the dream as distinguished from the day dream, namely, that the presentation content is not thought, but changed into perceptible images to which we give credence and which we believe we experience. Let us add, however, that not all dreams show this transformation of presentation into perceptible images. There are dreams which consist solely of thoughts to which we cannot, however, on that account deny the substantiality of dreams. My dream “Autodidasker—the waking phantasy with Professor N.”—is of that nature; it contains hardly more perceptible elements than if I had thought its content during the day. Moreover, every long dream contains elements which have not experienced the transformation into the perceptible, and which are simply thought or known as we are wont to think or know in our waking state. We may also recall here that such transformation of ideas into perceptible images does not occur in dreams only but also in hallucinations and visions which perhaps appear spontaneously in health or as symptoms in the psychoneuroses. In brief, the relation which we are investigating here is in no way an exclusive one; the fact remains, however, that where this character of the dream occurs, it appears to us as the most noteworthy, so that we cannot think of it apart from the dream life. Its explanation, however, requires a very detailed discussion.
Among all the observations on the theory of dreams to be found in authorities on the subject, I should like to lay stress upon one as being worth mentioning. The great G. T. Fechner[[35]] expresses his belief (Psychophysik, Part II., p. 520), in connection with some discussion devoted to the dream, that the seat of the dream is elsewhere than in the waking ideation. No other theory enables us to conceive the special qualities of the dream life.
The idea which is placed at our disposal is one of psychic locality. We shall entirely ignore the fact that the psychic apparatus with which we are here dealing is also familiar to us as an anatomical specimen, and we shall carefully avoid the temptation to determine the psychic locality in any way anatomically. We shall remain on psychological ground, and we shall think ourselves called upon only to conceive the instrument which serves the psychic activities somewhat after the manner of a compound microscope, a photographic or other similar apparatus. The psychic locality, then, corresponds to a place within such an apparatus in which one of the primary elements of the picture comes into existence. As is well known, there are in the microscope and telescope partly fanciful locations or regions in which no tangible portion of the apparatus is located. I think it superfluous to apologise for the imperfections of this and all similar figures. These comparisons are designed only to assist us in our attempt to make clear the complication of the psychic activity by breaking up this activity and referring the single activities to the single component parts of the apparatus. No one, so far as I know, has ever ventured to attempt to discover the composition of the psychic instrument through such analysis. I see no harm in such an attempt. I believe that we may give free rein to our assumptions provided we at the same time preserve our cool judgment and do not take the scaffolding for the building. As we need nothing except auxiliary ideas for the first approach to any unknown subject, we shall prefer the crudest and most tangible hypothesis to all others.
We therefore conceive the psychic apparatus as a compound instrument, the component parts of which let us call instances, or, for the sake of clearness, systems. We then entertain the expectation that these systems perhaps maintain a constant spatial relationship to each other like the different systems of lenses of the telescope, one behind another. Strictly speaking, there is no need of assuming a real spatial arrangement of the psychic system. It will serve our purpose if a firm sequence be established through the fact that in certain psychological occurrences the system will be traversed by the excitement in a definite chronological order. This sequence may experience an alteration in other processes; such possibility may be left open. For the sake of brevity, we shall henceforth speak of the component parts of the apparatus as “Ψ-systems.”
The first thing that strikes us is the fact that the apparatus composed of Ψ-systems has a direction. All our psychic activities proceed from (inner or outer) stimuli and terminate in innervations. We thus ascribe to the apparatus a sensible and a motor end; at the sensible end we find a system which receives the perceptions, and at the motor end another which opens the locks of motility. The psychic process generally takes its course from the perception end to the motility end. The most common scheme of the psychic apparatus has therefore the following appearance:
Fig. 1.
But this is only in compliance with the demand long familiar to us, that the psychic apparatus must be constructed like a reflex apparatus. The reflex act remains the model for every psychic activity.
We have now reason to admit a first differentiation at the sensible end. The perceptions that come to us leave a trace in our psychic apparatus which we may call a “Memory trace.” The function which relates to this memory trace we call the memory. If we hold seriously to our resolution to connect the psychic processes into systems, the memory trace can then consist only of lasting changes in the elements of the systems. But, as has already been shown in other places, obvious difficulties arise if one and the same system faithfully preserves changes in its elements and still remains fresh and capable of admitting new motives for change. Following the principle which directs our undertaking, we shall distribute these two activities among two different systems. We assume that a first system of the apparatus takes up the stimuli of perception, but retains nothing from them—that is, it has no memory; and that behind this there lies a second system which transforms the momentary excitement of the first into lasting traces. This would then be a diagram of our psychic apparatus:
