Positional signs. this point of view we may say that more partial presentations | arises from movement. In a balloon drifting steadily in a are concerned in the sensation corresponding to two stamps than fog we should have no more experience of change of position in that corresponding to one. The fact that these partial than if it hung becalmed and still, presentations, though identical in quality and intensity, on the We may now consider the part which movement plays in one hand are not wholly identical, and on the other are presented elaborating the presentations of this dimensionless continuum only as a quantity and not as a plurality, is explained by the into percepts of space. In so doing we must distinctness along with the continuity of their local signs. bear in mind that while this continuum implies the Assuming that to every distinguishable part of the body there incopresentability of two impressions having the corresponds a local sign, we may allow that at any moment only same local sign, it allows not only of the presentation of a certain portion of this continuum is definitely within the field sensations of varying massiveness, but also of a sensation of consciousness; but no one will maintain that a part of one involving the whole continuum simultaneously, as in Bain's hand is ever felt as continuous with part of the other or with classic example of the warm bath. As regards the motor part of the face. Local signs have thus an invariable relation element itself, the first point of importance is the incopreto each other: two continuous signs are not one day coincident sentability and invariability of a successive series of auxilioand the next widely separate. This last fact is only implied in motor or kinaesthetic presentations, P1, P2, P3, P. P the mere massiveness of a sensation in so far as this admits of cannot be presented along with P2, and from P, it is imposdifferentiation into local signs. We have, then, when the differ-sible to reach P, again save through Ps and P2. Such a entiation is accomplished, a plurality of presentations constitut- series, taken alone, could afford us, it is evident, nothing ing an extensive continuum, presented simultaneously, and but the knowledge of an invariable sequence of impressions having certain fixed and invariable relations to each other. Of which it was in our own power to produce. Calling the series such experience the typical case is that of passive touch, though of P's "positional signs," the contrast between them and local the other senses exemplify it. It must be allowed that our signs is obvious. Both are invariable, but succession characterconcept of space in like manner involves a fixed continuity of izes the one, simultaneity the other; the one yields potential positions; but then it involves, further, the possibility of move-position without place, the other potential place (Toros) without ment. Now in the continuum of local signs there is nothing position; hence we call them both merely signs. But in the whatever of this; we might call this continuum an implicit course of the movements necessary to the exploration of the plenum. It only becomes the presentation of occupied space body-probably our earliest lesson in spatial perception-these after its several local signs are complicated in an orderly way with positional signs receive a new significance from the active and active touches, when in fact we have experienced the contrast passive touches that accompany them, just as they impart to of movements with contact and movements without, i.e. in these last a significance they could never have alone. vacuo. It is quite true that we cannot now think of this plenum It is only in the resulting complex that we have the presentaexcept as a space, because we cannot divest ourselves of these tions of actual position and of spatial magnitude. For space, motor experiences by which we have explored it. We can, how-though conceived as a coexistent continuum, excludes the notion ever, form some idea of the difference between the perception of space and this one element in the perception by contrasting massive internal sensations with massive superficial ones, or the general sensation of the body as "an animated organism" with our perception of it as extended. Or we may express the difference by remarking that extension implies the distinction of here and there, while extensity rather suggests ubiquity. It must seem strange, if this conception of extensity is essential to a psychological theory of space, that it has escaped notice so long. The reason may be that in investigations into the origin of our knowledge of space it was always the concept of space and not our concrete space percepts that came up for examination. Now in space as we conceive it one position is distinguishable from another solely by its co-ordinates, i.e. by the magnitude and signs of certain lines and angles, as referred to a certain datum, position or origin; and these elements our motor experiences seem fully to explain. But on reflection we ought, surely, to be puzzled by the question, how these coexistent positions could be known before those movements were made which constitute them different positions. The link we thus suspect to be missing is supplied by the more concrete experiences we obtain from our own body, in which two positions have a qualitative difference or "local colour" independently of movement. True, such positions would not be known as spatial without movement; but neither would the movement be known as spatial had those positions no other difference than such as the nerve-endings but in the variety of the underlying parts--in one place bone, in another fatty tissue, in others tendons or muscles variously arranged-we find ample ground for diversity in "the local colouring" of sensations. And comparative zoology helps us to see how such diversity has been developed as external impressions and the answering movements have gradually differentiated an organism originally almost homogeneous and symmetrical. Between one point and another on the surface of a sphere there is no ground of difference; but this is no longer true if the sphere revolves round a fixed axis, still less if it also runs in one direction along its axis. The improvements in the sensibility of our spatial sense sequent on practice, its variations under the action of drugs, &c., are obviously no real contradiction to this; on the contrary, such facts are all in favour of making extensity a distinct factor in our space experience and one more fundamental than that of movement. con of omnipresence or ubiquity; two positions and must coexist, but they are not strictly distinct positions so long as we conceive ourselves present in the same sense in both. But, if F, and F, are, e.g. two impressions produced by compass points touching two different spots as I and I, on the hand or arm, and we place a finger upon la and move it to , experiencing thereby the series P1, P2, P3, P4, this series constitutes 1 and 1, into positions and also invests F. and F, with a relation not of mere distinctness as Too but of definite distance. The resulting complex perhaps admits of symbolization as follows:-. Here the first line represents a portion of the tactual continuum, F, and F, being distinct "feels," if we may so say, or passive touches presented along with the fainter sensations of the continuum as a whole, which the general "body-sense" involves; T stands for the active touch of the exploring finger and P, for the corresponding kinaesthetic sensation regarded as "posi tional sign"; the rest of the succession, as not actually present at this stage but capable of revival from past explorations, is symbolized by the ttt and papap When the series of movements is accompanied by active touches without passive there arises the distinction between one's own body and foreign bodies; when the initial movement of a series is accompanied by both active and passive touches, the final movement by active touches only, and the intermediate movements are unaccompanied by either, we get the further presentation of empty space lying between us and them-but only when by frequent experience of contacts along with those intermediate movements we have come to know all movement as not only succession but change of position. Thus active touches come at length to be projected, passive touches But in actual alone being localized in the stricter sense. fact, of course, the localization of one impression is not perfected before that of another is begun, and we must take care lest our necessarily meagre exposition give rise to the mistaken notion Thus a place may be known topographically without its position being known geographically, and vice versa. that localizing an impression consists wholly and solely in performing or imaging the particular movements necessary to add active touches to a group of passive impressions. That this cannot suffice is evident merely from the consideration that a single position out of relation to all other positions is a contradiction. Localization, though it depends on many special experiences of the kind described, is not like an artificial product which is completed a part at a time, but is essentially a growth, its several constituents advancing together in definiteness and interconnexion. So far has this development advanced that we do not even imagine the special movements which the localization of an impression implies, that is to say, they are no longer distinctly represented as they would be if we definitely intended to make them: the past experiences are "retained," but too much blended in the mere perception to be appropriately spoken of as remembered or imaged. A propos of this almost instinctive character of even our earliest spatial percepts it will be appropriate to animadvert on a misleading implication in the current use of such terms as "localization," projection," ," "bodily reference," "spatial reference" and the like. The implication is that external space, or the body as extended, is in some sort presented or supposed apart from the localization, projection or reference of impressions to such space. That it may be possible to put a book in its place on a shell there must be (1) the book, and (2), distinct and apart from it, the place on the shelf. But in the evolution of our spatial experience impressions and positions are not thus presented apart. We can have, or at least we can suppose, an impression which is recognized without being localized as has been already said; but if it is localized this means that a more complex presentation is formed by the addition of new elements, not that a second distinct object is presented and some indescribable connexion established between the impression and it, still less that the impression is referred to something not strictly presented at all. The truth is that the body as extended is from the psychological point of view not perceived at all apart from localized impressions. In like manner impressions projected (or the absence of impressions projected) constitute all that is perceived as the occupied (or unoccupied) space beyond. It is not till a much later stage, after many varying experiences of different impressions similarly localized or projected, that even the mere materials are present for the formation of such an abstract concept of space as spatial reference" implies. Psychologists, being themselves at this later stage, are apt to commit the oversight of introducing it into the earlier stage which they have to expound. 20. In a complex percept, such as that of an orange or a piece of wax, may be distinguished the following points concerning which psychology may be expected to give an Intuition of Things. account: (a) the object's reality, (b) its solidity or occupation of space, (c) its unity and complexity, (d) its permanence, or rather its continuity in time and (e) its substantiality and the connexion of its attributes and powers. Though, in fact, these items are most intimately blended, our exposition will be clearer if we consider each for a moment apart. Reality. a. The terms actuality and reality have each more than one meaning. Thus what is real, in the sense of material, is opposed to what is mental; as the existent or actual it is Actuality or opposed to the non-existent; and again, what is actual is distinguished from what is possible or necessary. But here both terms, with a certain shade of difference, in so far as actual is more appropriate to movements and events, are used, in antithesis to whatever is ideal or represented, for what is sense-given or presented. This seems at least their primary psychological meaning; and it is the one most in vogue in English philosophy at any rate, over-tinged as that is with psychology. Any examination of this characteristic will be best deferred till we come to deal with ideation generally (see § 21 below). Meanwhile it may suffice to remark that reality or actuality is not a single distinct element added to the others which enter into the complex presentation we call a thing, Cf. on this point Poincaré, La Science et l'hypothèse, pp. 74 sqq. Thus Locke says, "Our simple ideas [i.e. presentations or impressions, as we should now say] are all real...and not fictions at pleasure; for the mind.. can make to itself no simple idea more than what it has received" (Essay, ii. 30, 2). And Berkeley says, The ideas imprinted on the senses by the Author of Nature are called real things; and those excited in the imagination, being less regular, vivid and constant, are more properly termed ideas or images of things, which they copy or represent (Prin. of Hum. Know, pt. i. § 33). as colour or solidity may be. Neither is it a special relation among these elements, like that of substance and attribute, for example. In these respects the real and the ideal, the actual and the possible, are alike; all the elements or qualities within the complex, and all the relations of those elements to each other, are the same in the rose represented as in the presented rose. The difference turns not upon what these elements are, regarded as qualities or relations presented or represented, but upon whatever it is that distinguishes the presentation from the representation of any given qualities or relations. Now this distinction, as we shall see, depends partly upon the relation of such complex presentation to other presentations in consciousness with it, partly upon its relation as a presentation to the subject whose presentation it is. In this respect we find a difference, not only between the simple qualities, such as cold, hard, red and sweet in strawberry ice, e.g. as presented and as represented, but also, though less conspicuously, in the spatial, and even the temporal, relations which enter into our intuition as distinct from our imagination of it. So then, reality or actuality is not strictly an item by itself, but a characteristic of all the items that follow. b. In the so-called physical solidity or impenetrability of things our properly motor presentations or "feelings of effort or innervation come specially into play. They Impenetra are not entirely absent in those movements of bility. exploration by which we attain a knowledge of space; but it is when these movements are definitely resisted, or are only possible by increased effort, that we reach the full meaning of body as that which occupies space. Heat and cold, light and sound, the natural man regards as real, and by and by perhaps as due to the powers of things known or unknown, but not as themselves things. At the outset things are all corporeal like his own body, the first and archetypal thing, that is to say: things are intuited only when touch is accompanied by pressure; and, though at a later stage passive touch without pressure may suffice, this is only because pressures depending on a subjective initiative, i.e. on voluntary muscular exertion, have been previously experienced. It is of more than psychological interest to remark how the primordial factor in materiality is thus due to the projection of a subjectively determined reaction to that action of a not-self of which sense-impressions consist-an action of the not-self which, of course, is not known as such till this projection of the subjective reaction has taken place. Still we must remember that accompanying sense-impressions are a condition of its projection; muscular effort without simultaneous sensations of contact would not yield the distinct presentation of something resistant occupying the space into which we have moved and would move again. Nay more, it is in the highest degree an essential circumstance in this experience that muscular effort, though subjectively initiated, is still only possible when there is contact with something that, as it seems, is making an effort the counterpart of our own. But this something is so far no more than thing-stuff; without the elements next to be considered our psychological individual would fall short of the complete intuition of distinct things. Unity and c. The remaining important factors in the psychological constitution of things might be described in general terms as the time-relations of their components. Such rela-, tions are themselves in no way psychologically deter-Complexity. mined; impressions recur with a certain order or want of order quite independently of the subject's interest or of any psychological principles of synthesis or association whatever. It is essential that impressions should recur, and recur as they have previously occurred, if knowledge is ever to begin; out of a continual chaos of sensation, all matter and no form, such as some philosophers describe, nothing but chaos could result. But a flux of impressions having this real or sense-given order will not suffice; there must be also attention to and retention of the order, and these indispensable processes at least are psychological. But for its familiarity we snould marvel at the fact that out of the variety of impressions simultaneously presented we do e. So far we have been concerned only with the combination of sensory and motor presentations into groups and with the differentiation of group from group; the relations to Substantieach other of the constituents of each group still ality. for the most part remain. To these relations in the main must be referred the correlative concepts of substance and attribute, the distinction in substances of qualities and powers, of primary qualities and secondary, and the like.1 not instantly group together all the sounds and all the colours, | we look at it, whether as part of a larger thing or as itself comall the touches and all the smells; but, dividing what is given pounded of such parts-which has had one beginning in time. together, single out a certain sound or smell as belonging But what is it that has thus a beginning and continues together with a certain colour and feel, similarly singled out indefinitely? This leads to our last point. from the rest, to what we call one thing. We might wonder, too -those at least who have made so much of association by similarity ought to wonder-that, say, the white of snow calls up directly, not other shades of white or other colours, but the expectation of cold or of powdery softness. The first step in this process has been the simultaneous projection into the same occupied space of the several impressions which we thus come to regard as the qualities of the body filling it. Yet such simultaneous and coincident projection would avail but little unless the constituent impressions were again and again repeated in like order so as to prompt anew the same grouping, and unless, further, this constancy in the one group was present along with changes in other groups and in the general field. There is nothing in its first experience to tell the infant that the song of the bird does not inhere in the hawthorn whence the notes proceed, but that the fragrance of the mayflower does. It is only where a group, as a whole, has been found to change its position relatively to other groups, and-apart from casual relations | to be independent of changes of position among them, that such complexes can become distinct unities and yield a world of things. Again, because things are so often a world within themselves, their several parts or members not only having distinguishing qualities but moving and changing with more or less independence of the rest, it comes about that what is from one point of view one thing becomes from another point of view several like a tree with its separable branches and fruits, for example. Wherein then, more precisely, does the unity of a thing consist? This question, so far as it here admits of answer, carries us over to temporal continuity. d. Amidst all the change above described there is one thing comparatively fixed: our own body is both constant as a group and a constant item in every field of groups; and not Temporal only so, but it is beyond all other things an object Continuity. of continual and peculiar interest, inasmuch as our earliest pleasures and pains depend solely upon it and what affects it. The body becomes, in fact, the earliest form of self, the first datum for our later conceptions of permanence and individuality. A continuity like that of self is then transferred to other bodies which resemble our own, so far as our direct experience goes, in passing continuously from place to place and undergoing only partial and gradual changes of form and quality. As we have existed-or, more exactly, as the body has been continuously presented-during the interval between two encounters with some other recognized body, so this is regarded as having continuously existed during its absence from us. However permanent we suppose the conscious subject to be, it is hard to see how, without the continuous presentation to it of such a group as the bodily self, we should ever be prompted to resolve the discontinuous presentations of external things into a continuity of existence. It might be said: Since the second presentation of a particular group would, by the mere workings of psychical laws, coalesce with the image of the first, this coalescence would suffice to " generate "the concept of continued existence. But such assimilation is only the ground of an intellectual identification and furnishes no motive, one way or the other, for real identification: between a second presentation of A and the presentation at different times of two A's there is so far no difference. Real identity no more involves exact similarity than exact similarity involves sameness of things; on the contrary, we are wont to find the same thing alter with time, so that exact similarity after an interval, so far from suggesting one thing, is often the surest proof that there are two concerned. Of such real identity, then, it would seem we must have direct experience; and we have it in the continuous presentation of the bodily self; apart from this it could not be "generated" by association among changing presentations. Other bodies being in the first instance personified, that then is regarded as one thing-from whatever point of view Of all the constituents of things only one is universally present, that above described as physical solidity, which presents itself according to circumstances as impenetrability, resistance or weight. Things differing in temperature, colour, taste and smell agree in resisting compression, in filling space. Because of this quality we regard the wind as a thing, though it has neither shape nor colour, while a shadow, though it has both but not resistance, is the very type of nothingness. This constituent is invariable, while other qualities are either absent or changeform altering, colour disappearing with light, sound and smells intermitting. Many of the other qualities-colour, temperature, sound, smell-increase in intensity if we advance till we touch a body occupying space; with the same movement too its visual magnitude varies. At the moment of contact an unvarying tactual magnitude is ascertained, while the other qualities and the visual magnitude reach a fixed maximum; then first it becomes possible by effort to change or attempt to change the position and form of what we apprehend. This tangible plenum we thenceforth regard as the seat and source of all the qualities we project into it. In other words, that which occupies space is psychologically the substantial; the other real constituents are but its properties or attributes, the marks or manifestations which lead us to expect its presence. Imagination or Ideation." 21. Before the intuition of things has reached a stage so complete and definite as that just described, imagination or ideation as distinct from perception has well begun. In Impressions passing to the consideration of this higher form of and Ideas. mental life we must endeavour first of all analytically to distinguish the two as precisely as may be and then to trace the gradual development of the higher. To begin, it is very questionable whether Hume was right in applying Locke's distinction of simple and complex to ideas · in the narrower sense as well as to impressions. "That idea of red," says Hume, "which we form in the dark and that impression which strikes our eyes in the sunshine differ only in degree, not in nature.' ." But what he seems to have overlooked is that, whereas we may have a mere sensation red, we can only have an image or representation of a red thing or a red form, i.e of red in some way ideally projected or intuited. In other words, there are no ideas-though there are concepts-answering to simple or isolated impressions. The synthesis which has taken place in the evolution of the percept can only partially fail in the idea, and never so far as to leave us with a chaotic "manifold" of mere sensational remnants. On the contrary, we find that in "constructive imagination " a new kind of effort is often requisite in order partially to dissociate these representational complexes as a preliminary to new combinations. But it is doubtful whether the results of such an analysis are ever the ultimate elements of the percept, that is, merely isolated impressions in a fainter form. We may now try to ascertain further the characteristic marks which distinguish what is imaged from what is perceived. The distinction between the thing and its properties is one that Ideation a word of my own coining," says James Mill. marks-of which more presently-by which they may be referred to what is past or future; but as imaged they are present, and, as we have just observed, are regarded as actual whenever there are no correcting impressions. We cannot at once see the sky red and blue; how is it we can imagine it the one while perceiving it to be the other? When we attempt to make the field of sight at once red and blue, as in looking through red glass with one eye and through blue glass with the other, either the colours merge and we see a purple sky or we see the sky first of the one colour and then of the other in irregular alternation. That this docs not happen between impression and image shows that, whatever their connexion, images as a whole are distinct from the presentation-continuum and cannot with strict propriety be spoken of as revived or reproduced impressions. This difference is manifest in another respect, viz. when we compare the effects of diffusion in the two cases. An increase in the intensity of a sensation of touch entails an increase in the extensity; an increase of muscular innervation entails irradiation to adjacent muscles; but when a particular idea becomes clearer and more distinct, there rises into consciousness an associated idca qualitatively related probably to impressions of quite another class, as when the smell of tar calls up memories of the sea-beach and fishingboats. Since images are thus distinct from impressions, and yet so far continuous with each other as to form a train in itself unbroken, we should be justified, if it were convenient, in speaking of images as changes in a new continuum; and later on we may see that this is convenient. The most obvious difference is that which Hume called | is past or future. The images, it is true, have certain temporal "the force or liveliness " of primary presentations as compared Character with secondary presentations. But what exactly istics of are we to understand by this somewhat figurative Ideas. language? A simple difference of intensity cannot be all that is meant, for-though we may be momentarily confused-we can perfectly well distinguish the faintest impression from an image; moreover, we can reproduce such faintest impressions in idea. The whole subject of the intensity of representations awaits investigation. Between moonlight and sunlight or between midday and dawn we can discriminate many grades of intensity; but it does not appear that there is any corresponding variation of intensity between them when they are not seen but imagined. Many persons suppose they can imagine a waxing or a waning sound or the gradual abatement of an intense pain; but what really happens in such cases is probably not a rise and fall in the intensity of a single representation, but a change in the complex represented. In the primary presentation there has been a change of quality along with change of intensity, and not only so, but most frequently a change in the muscular adaptations of the sense-organs too, to say nothing of organic sensations accompanying these changes. | A representation of some or all of these attendants is perhaps what takes place when variations of intensity are supposed to be reproduced. Again, hallucinations are often described as abnormally intense images which simply, by reason of their intensity, are mistaken for percepts. But such statement, though supported by very high authority, is almost certainly false, and would probably never have been made if physiological and epistemological considerations had been excluded as they ought to have been. Hallucinations, when carefully examined, seem just as much as percepts to contain among their constituents some primary presentation-cither a so-called subjective sensation of sight and hearing or some organic sensation due to deranged circulation or secretion. Intensity alone, then, will not suffice to discriminate between impressions and images. What we may call superior steadiness is perhaps a more constant and not less striking characteristic of percepts. Ideas are not only in a continual flux, but even when we attempt forcibly to detain one it varies continually in clearness and completeness, reminding one of nothing so much as of the illuminated devices made of gas jets, common at fêtes, when the wind sweeps across them, momentarily obliterating one part and at the same time intensifying another. There is not this perpetual flow and flicker in what we perceive. The impressions entering consciousness at any one moment are psychologically independent of each other; they are equally independent of the impressions and images presented the moment before-independent, i.e. as regards their order and character, not, of course, as regards the share of attention they secure. Attention to be concentrated in one direction must be withdrawn from another, and images may absorb it to the exclusion of impressions as readily as a first impression to the exclusion of a second. But, when attention is secured, a faint impression has a fixity and definiteness lacking in the case of even vivid ideas. One ground for this definiteness and independence lies in the localization or projection which accompanies all perception. But why, if so, it might be asked, do we not confound percept and image when what we imagine is imagined as definitely localized and projected? Because we have a contrary percept to give the image the lie; where this fails, as in dreams, or where, as in hallucination, the image obtains in other ways the fixity characteristic of impressions, such confusion does in fact result. But in normal waking life we have the whole presentation-continuum, as it were, occupied and in operation: we are distinctly conscious of being embodied and having our senses about us. But how is this contrariety between impression and image possible? With eyes wide open, and while clearly aware of the actual field of sight and its filling, one can recall or imagine a wholly different scene: lying warm in bed one can imagine oneself out walking in the cold. It is useless to say the times are different, that what is perceived is present and what is imaged Impressions then-unlike ideas-have no associates to whose presence their own is accommodated and on whose intensity their own depends. Each bids independently for attention, so that often a state of distraction ensues, such as the train of ideas left to itself never occasions. The better to hear we listen; the better to see we look; to smell better we dilate the nostrils and sniff; and so with all the special senses: each sensory impression sets up nascent movements for its better reception. In like manner there is also a characteristic adjustment for images which can be distinguished from sensory adjustments almost as readily as these are distinguished from each other. We become most aware of this as, mulalis mulandis, we do of them, when we voluntarily concentrate attention upon particular ideas instead of remaining mere passive spectators, as it were, of the general procession. To this ideational adjustment may be referred most of the strain and “head-splitting" connected with recollecting, reflecting and all that people call headwork; and the "absent look" of one intently thinking or absorbed in reverie seems directly due to the absence of sensory adjustment that accompanies the concentration of attention upon ideas. 22. 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 connexion cannot directly observe it, we seem justified in assum- of Impres ing a steady transition from the one to the other. As sions and Images. the first of such intermediate stages, it is usual to reckon what are often, and so far as psychology goesinaccurately, styled after-images. They would be better described as after-sensations, 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 or 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 VISION). These last, then, of which we have clear instances only in connexion with sight, are obviously in no past or future psychologically presupposes the contrast of impression Moreover, as we shall see, the distinction between present and and image. Organic sensations, though distinguishable from images by their definite though often anatomically inaccurate localization, furnish no clear evidence of such adaptations. But in another respect they are still more clearly marked off from images, viz. by the pleasure or pain they directly occasion. sort re-presentations of the original impression, but a sequent | owes its vivacity in part to a positive after-sensation, at any rate presentation of diametrically opposite quality; while positive it proves that it is in some way still sense-sustained. But after-sensations are, psychologically regarded, nothing but the original sensations in a state of evanescence. It is this continuance and gradual waning after the physical stimulus has completely ceased that give after-sensations their chief title to a place in the transition from impression to image. There is, however, another point: after-sensations are less affected by movement than impressions are. If we turn away our eyes we cease to see the flame at which we have been looking, but the after-image remains still projected before us and continues localized in the dark field of sight, even if we close our eyes altogether. This fact that movements do not suppress them, and the fact that yet we are distinctly aware of our sense-organs being concerned in their presentation, serve to mark off after-sensations as intermediate between primary and secondary presentations. The after-sensation is in reality more elementary than 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; but the so-called after-image lacks all these. Still further removed from normal sensations (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 they 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-sensations lack; they only differ from what are more strictly called " hallucinations" in being independent of all subjective suggestion determined by emotion or mental derangement. In what Fechner has called the " memory after-image" or the primary memory-image, as it is better termed, we have the image proper 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 minutes later by means of the persisting image, although-apparentlythe actual impression was entirely disregarded. But in vision the primary memory-image can always be obtained, and is obtained to most advantage, by looking intently at some object for an instant and then closing the eyes or turning them away. The image of the object will appear 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 memoryimage resembles an after-sensation, which can be repeatedly revived in this manner when it would otherwise have disappeared. This seems to show that the primary memory-image in such cases The following scant quotation from 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 plane; 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 foreshortened. But the memory-image on the other hand completely reproduces the pictorial illusion as it appears when the eyes are open (Elemente der Psychophysik, ii. 473). in other respects the two are very different: the after-sensation is necessarily presented if the intensity of the original excitation suffices for its production, and cannot be presented otherwise, however much we attend. 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 it is only possible for a very short time From Weber's experiments with weights and lines' 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 memoryimage 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 in, or projection into, external space, 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 what we shall call 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. 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 someway formed out of or differentiated from the presentation continuum by the movements of attention, but the precise con nexion 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. We have now to inquire into the genesis and development of ideation. Genesis and Development of Ideation. tions, as when tracing, for example, the meanderings of an ant; 23. We find ourselves sometimes engrossed in present percepat other times we may be equally absorbed in reminiscences; or, again, in pure reverie and "castle-building." Here are three well-marked forms of conscious life: the first being concerned with what is, the second with what has been, and the third with the merely possible. Again, the first involves definite spatial and temporal order, though the temporal order, as just said. is in the main restricted to the "sensible present "; the second involves only definite time-order; and the last neither in a definite way. Thus, analytically regarded, perception, memory, imagination, show a steady advance. In infancy the first. ? Die Lehre vom Tastsinne, &c., pp. 86 seq. 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 perception, psychologically regarded. |
