(F) Imagination or Ideation (cont.)
Connection of Impressions and Ideas
But, distinct as they are, impressions and images are still closely connected. In the first place, there are two or three well-marked intermediate stages, so that, though we cannot observe it, we seem justified in assuming a steady transition from the one to the other. As the first of such intermediate stages, it is usual to reckon what are often, and – so far as psychology goes – inaccurately, styled after-images. They would be better described as after-sensations, except perhaps when the sense of sight is specially in question, inasmuch as they are due either (1) to the persistence of the original peripheral excitation after the stimulus is withdrawn, or (2) to the effects of the exhaustion of the repair that immediately follows this excitation. In the former case they are qualitatively identical with the original sensation and are called "positive," in the latter they are complementary to it and are called "negative" (see EYE, vol. viii., p. 823). These last, then, of which we have clear instances only in connexion with sight, are obviously in no sort re-presentations of the original impression, but a sequent presentation of diametrically opposite quality; while positive after-sensations are psychologically regarded, nothing but the original sensations is a state of evanescence. It is this continuance and gradual waning after the physical stimulus has completely ceased that give after-sensations their chide title to a place in the transition from impression to image. There is, however, another point of resemblance; after-sensations are less affected by movement. If we turn away our eyes we cease to see the flame at which we have been looking, but the after-image remains and is projected upon the wall, and continues still localized in the dark field of sight even if we close our eyes altogether. But the fact that movement affects their localization, though it does not exclude them, and the fact also that we are distinctly aware of our sense-organs being concerned in their presentations, both serve to mark them off as primary and not secondary presentations. The after-sensation is in reality more elementary then either the preceding percept or its image. In both these, in the case of sight, objects appear in space of three dimensions, i.e., with all the marks of solidity and perspective; [Footnote 59-2] But the so-called after-image lacks all these. Still further removed form normal sensation (i.e., sensations determined by the stimuli appropriate to the sense-organ) are the "recurrent sensations" often unnoticed but probably experienced more or less frequently by everybody – cases, that is, in which sights or sounds, usually such as at the time were engrossing and impressive, suddenly reappear several hours or even days after the physical stimuli, as well as their effects on the terminal sense-organ, seem entirely to have ceased. Thus workers with the microscope often see objects which have examined during the day stand out clearly before them in the dark; it was indeed precisely such an experience that led the anatomist Henle first to call attention to these facts. But he and others have wrongly referred them to what he called a "sense-memory"; all that we know is against the supposition that the eye or the ear has any power to retain and reproduce percepts. "Recurrent sensations" have all the marks of percepts which after-images lack; they only differ from what are more strictly called "hallucinations" in being, as regards form and quality, exact reproductions of the original impression and in being independent of all subjective suggestion determined by emotion or mental derangement.
In what Fechner has called the "memory-after-image," or primary memory-image, as it is better termed, we have the ordinary image in its earliest form. As an instance of what is meant may be cited the familiar experience that a knock at the door, the hour struck on the clock, the face of a friend whom we have passed unnoticed, may sometimes be recognized a few moments later by means of the persisting image, although the actual impression was entirely disregarded. But the primary memory-image can always be obtained, and is obtained to most advantages, by looking intently at some object for an instant and then closing the eyes or turning away. The object is then imaged for a moment very vividly and distinctly, and can be so recovered several times in succession by an effort of attention. Such reinstatement is materially helped by rapidly opening and closing the eyes, or by suddenly moving them in any way. In this respect a primary memory-image resembles an after-sensation, which can be repeatedly revived in this manner when it would otherwise have disappeared. But in other respects the two are very different: the after-sensation is necessarily presented if the intensity and direction of the original excitation suffice for its production, and cannot be presented, however mush we attend, if they do not. Moreover, the after-sensation is only for a moment positive, and then passes into the negative or complementary phase, when, so far from even contributing towards the continuance of the original percept, it directly hinders it. Primary memory-images, on the other hand, and indeed all images, depend mainly upon the attention given to the impression; provided that was sufficient the faintest impression may be long retained, and without it very intense ones will soon leave no trace. The primary memory-image retains so much of its original definiteness and intensity as to make it possible with great accuracy to compare two physical phenomena, one of which is in this way remembered while the other is really present; for the most part this is indeed a more accurate procedure than that of dealing with both together. But this is only possible for a very short time. From Weber’s experiments with weights and lines [Footnote 59-3] it would appear that even after 10 seconds a considerable waning has taken place, and after 100 seconds all that is distinctive of the primary image has probably ceased.
On the whole, then, it appears that the ordinary memory-image is a joint effect; it is not the mere residuum of changes in the presentation-continuum, but an effect of these only when there has been some concentration of attention upon them. It has the form of a percept, but is not constituted of "revived impressions," for the essential marks of impressions are absent; there is no localization or projection, neither is there the motor adaptation, nor the tone of feeling, incident to the reception of impressions. Ideas do not reproduce the intensity of these original constituents, but only their quality and complication. What we call the vividness of an idea is of the nature of intensity, but it is an intensity very partially and indirectly determined by that of the original impression; it depends much more upon the state of the memory-continuum and the attention the idea receives. The range of vividness in ideas is probably comparatively small; what are called variations in vividness are often really variations in distinctness and completeness.1 Where we have great intensity, as in hallucinations, primary presentations may be reasonably supposed to enter into the complex.
It is manifest that the memory-continuum has been in some way formed out of or differentiated from the presentation-continuum by the movements of attention, but the precise connexion of the two continua is still very difficult to determine. We see perhaps the first distinct step of this evolution in the primary memory-image: here there has been no cessation in presentation and yet the characteristic marks of the impression are gone, so much so, indeed, that superposition without "fusion" with an exactly similar impression is possible. In this manner we seem to have several primary images in the field of consciousness together, as when we count up the strokes of the clock after it has ceased striking. But, though the image thus first arises in the field of consciousness as a sort of GREEK or emanation from the presentation-continuum, its return (as which stage it first becomes a proper re-presentation) is never determined directly and solely by a second presentation like that which first gave it being. Its "revival" is nor another birth. With a second impression exactly like the first we should have assimilation or simple recognition – and identity of the indiscernible which preludes the individual distinctness required in representation. But how, then, was this distinctness in the first instance possible in the series of primary images just referred to as being due to the repetition of the same presentation? Seemingly to differences in the rest of that field of consciousness in which each in turn occurred and to some persistence of these differences. If the whole field which the second impression entered had been just like the field of the first it is hard to see what ground for distinctness there would have been. When such second impression does not occur till after the primary memory-image has ceased, a representation is still possible provided the new impression can reinstate sufficient of the mental framing of the old to give the image individual distinctness. This is really what happens in what is ordinarily called "association by similarity," – similarity, that is, in the midst of some diversity. Our inquiry into the connexion between presentations and representations has thus brought us to the general consideration of mental association.
Footnotes
59-2 The following scant quotation form Fechner, one of the best observers in this department, must suffice in illustration. "Lying awake in the early morning after daybreak, with my eyes motionless though open, there usually appears, when I chance to close them for a moment, the black after-image of the white bed immediately before me and the white after-image of the black stove-pipe some distance away against the opposite wall… Both [after-images] appear as if they were in juxtaposition in the same place; and, though – when my eyes are open – I seem to see the white bed in its entire length, the after-image – when my eyes are shut – presents instead only a narrow black stripe owing to the fact that the bed is seen considerably foreshorthened. But the memory-image of the other hand completely reproduced the pictorial illusion as it appears when the eyes are open" (Elemente der Psychophysik, ii. p. 473).
59-3 Die Lehre vom Tastsinne, &c., p. 86 sq.
60-1 As we have seen that there is a steady transition from percept to image, so, if space allowed, the study of hallucinations might make clear an opposite and abnormal process -- the passage, that is to say, of images into percepts, for such, to all intents and purposes, are hallucinations of perceptions, psychologically regarded.
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