Page:Encyclopædia Britannica, Ninth Edition, v. 20.djvu/70

58 PSYCHOLOGY plexes 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. Charac- The most obvious, if not the most invariable, difference teristics j s that which, as we have seen, Hume calls the superior ideas. f orce or liveliness of primary presentations as compared with secondary presentations. But what exactly are we to understand by this somewhat figurative language ? A simple difference of intensity cannqt be all that is meant, for, though we may be momentarily confused, we can per- fectly well distinguish the faintest impression from an image, and yet can hardly suppose the faintest impression to be intenser than the most lively image. Moreover, we can reproduce such faintest impressions in idea, so that, if everything depended on intensity, we should be committed to the gratuitous supposition that secondary presentations can secure attention with a less intensity than is required for primary presentations. The whole subject of the in- tensity of representations awaits investigation. Between moonlight and sunlight or between midday and dawn we could 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 ima- gined. 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 representa- tion, 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 either a so- called subjective sensation of sight and hearing or some organic sensation due to deranged circulation or secretion. Now we have noticed already incidentally in a preced- ing paragraph that primary presentations reinstate and maintain the representational constituents of a percept in a manner very different from that in which what are unmis- takably ideas reproduce each other. The intensity and steadiness of the impressional elements are, as it were, shared by the ideational elements in a complex containing both. Intensity alone, then, will not suffice to discrimi- nate, neither will extremes of intensity alone lead us to confuse, impressions and images. The superior steadiness just mentioned is perhaps a more constant and not less striking characteristic of per- cepts. Ideas are not only in a continual flux, but even when we attempt forcibly to detain one it varies continu- ally in clearness and completeness, reminding one of nothing so much as of the illuminated devices made of gas jets, common at fetes, 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 ; for this, unlike the train of ideas, has at the outset neither a logical nor a psychological continuity. The impressions entering con- sciousness at any one moment are psychologically inde- pendent 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 definite- ness and independence lies in the localization or projec- tion 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 con- fusion does in fact result. But in normal waking life we have the whole presentation-continuum, as it were, occu- pied and in operation : we are distinctly conscious of being embodied and having our senses about us. This contrariety between impression and image suggests, however, a deeper question : we may ask, not how it is resolved, but IIOAV it is 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 terms are different, that what is perceived is present and what is imaged is past or future. 1 The images, it is true, have certain temporal marks of which more presently by which they may be referred to past or future ; but as imaged they are present, and, as we have just observed, are regarded as both actual and present in the absence of correcting im- pressions. 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 1 ? 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 does not happen between impres- sion and image shows that, whatever their connexion, images altogether are distinct from the presentation-con- tinuum 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 idea qualitatively related prob- ably to impressions of quite another class, as when the smell of tar calls up memories of the sea-beach and fish- ing-boats. Since images are thus distinct from impres- sions, 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 repre- sentation- or memory-continuum ; and later on we may see that this is convenient. Impressions, then, have no associates to whose presence their own is accommodated and on whose intensity their own depends. Each bids independently for attention, so 1 Moreover, as we shall see, the distinction between present and past or future psychologically presupposes the contrast of impression and image.