Psychology: an elementary text-book

by Hermann Ebbinghaus

70. Illustrate sensitiveness to change and movement.

71. How is the chief difference in the behavior of chickens and bats to be explained?

§ [5]. Imagination

Mind is influenced not only by that which is present, but also by the past and—one may say—the future, and by that which exists at another place. Consciousness of this kind is called imagery. I imagine a lion and recognize that he looks different from a horse. I recall the room in a hotel where I have recently spent a night and see that it differs from my study.

Imagery does not differ in content from percepts. There are as many kinds of images as there are sensations, and their attributes are the same. Imagination differs from perception only through its independence of external conditions in the formation of new combinations out of the sensory elements which have previously been experienced. Although the kinds of content of imagery do not differ from those of perception, imagery differs from perception, as a rule, in such a characteristic manner that in ordinary life we are not likely to mistake an image for a percept or a percept for an image. The imagined sun lacks brilliancy. Its imagined heat does not burn. A glowing match, perceived, surpasses those images. Only in childhood, in dreams, and in particular individuals (artists, for example), and under particular circumstances (like the imaginative supplementing of that of which only parts have stimulated the sense organ) can imagery come near being compared and confused with percepts. Generally the difference in vividness remains great. A second difference is the lack of details of images. As a rule only a few parts of a rich complex of sensations reappear when an image takes the place of the original percept. And the selection of these details is usually most grotesque. A third characteristic of images is their instability, fleetingness. Compared with the persistence of a percept, an image can scarcely be said to have any definite make-up since its composition changes from moment to moment. Images come and go in spite of our desire to keep them. They change like kaleidoscopic figures.

All this has its disadvantages; but also its great advantages. Being at once pictures and mere abbreviations or symbols of things, images aid effectively in our handling of things. If they were exactly like percepts, they would deceive us, as hallucinations do. Their very lack of details and their fleetingness enable our mind to grasp a greater multitude of things, to adjust itself more quickly and more comprehensively to its surroundings.

Independence of external causes and frequent recurrence from internal causes give to our imagery the character of a permanent possession of the mind. Not every part of this imagery is actually made use of, since these parts are too numerous, but every part is always available for use. This leads to the question as to the nature of the images while mind is not conscious of them, particularly the nature of their nervous correlate. Ever since the discovery of ganglion cells and nerve fibers the naïve conception has readily offered itself that every idea has its residence in a little group of cells, the idea of a dog in one, the idea of a tree in another, and so on. Some have calculated the number of cortical cells which would be necessary in order to provide a sufficient number of residences for all the ideas acquired by a human being during a long life. They have found that the cortical cells are numerous enough.

But the matter is not quite so simple. Our ideas, being made up of many mental elements, overlap. If the idea of a dog has its residence here, the idea of a lion its residence there, where, then, do we find the idea of a carnivore, the idea of another kind of dog, the ideas of the individual dogs known by me, the ideas of other carnivora, the idea of a mammal, of a vertebrate, of an animal in general? These ideas are interwoven in such manifold ways that it is difficult to assume that each should have its separate residence in the brain. It is still more difficult to apply this theory to the idea of barking, which can be imitated by man, being natural to a dog; or to the idea of white, which belongs to some dogs, but also to the clouds, the snow, the lily.

There are also anatomical difficulties. I look first at a dog, then at a goat. The elements of the retina which are stimulated are largely the same in both cases. This makes it difficult to understand why the nervous processes in the former case should all concentrate in one point of the cortex and in the latter case in an entirely different point. Or I hear the word boxwood and later the word woodbox. The anatomical difficulty is the same.

The nervous correlates of ideas are obviously much more complicated than the theory of location in cell groups assumes. There can be no doubt that the nervous correlate of an idea, even of an elementary image, is a process going on in a large number of connecting neurons in the higher nerve centers, often widely distributed, like the meshes of a net. The individual neurons in question do not belong exclusively to this one idea, but, entering into numerous other combinations with other neurons, belong to numerous ideas. The nervous correlate of a latent idea, which is not conscious but ready to enter consciousness at any time, is not a material substance stored away somewhere, but a disposition on the part of neurons which have previously functioned together, to function again in the same order and connection.