(F) Imagination or Ideation (cont.)
Characteristics of Ideas
The most obvious, if not the most invariable, difference is that which, as we have seen, Hume calls the superior force of 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 cannot be all that is meant, for, though we may be momentarily confused, we can perfectly 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 each faintest impression 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 intensity 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 imagined. Many persons suppose they can imagine a waxing or a waning sound or the gradual abatement of the 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 in quality along with change of intensity, and not only so, but most frequently a change in muscular adaptations of the sense-organs too, to say nothing of organic sensations accompanying these changes. A representation of some of all of these attendants in 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 and would probably never been made if physiological and epistemological considerations had been excluded as they ought to have been. Hallucinations, when carefully examined, see just as much as percepts to contains among their constituents of a percept in a manner very different from that in which what are unmistakable 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 discriminate, 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 percepts. Ideas are not only in a continual flux, but even when we attempt forcibly to detain one it varies continunally 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 ; for this, unlike the train of ideas, has at the outset neither a logical nor a psychological continuity. 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 beforeindependent, i.e., as regards their order and character, not of course, as regards is the share of attention they secure. Attention to be concerned 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 cases 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 images 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.
This contrariety between impression and image suggests, however, a deeper question : we may ask, not how it is resolved but how it is possible. With eyes wide open, and while clearly aware o the actual field of sight and its filling, one can recall or imagine a wholly different scene : lying warms 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. [Footnote 58-1] The images, it is true, have certain temporal marksof which more presentlyby 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 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 does not happen between impression and image shows that, whatever their connexion, images altogether 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 ; an increase of muscular innervation entails irradiation to adjacent muscles ; but when a particular idea becomes clearer and more distinct there rises into consciousness a associated idea qualitatively related probably to impressions of quite another class as when the smell of tar calls up memories of the sea-beach and fishing-boats. Since images are thus distinct from impressions, and yet so far continuous with each other as to form train in itself unbroken, we should be justified, if it were convenient, in speaking of image as changes in a representation-or memory-continuum ; and later on we may see that this is convenient.
Impression, then, have no associate 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. [Footnote 59-1] In like manner there is also an adjustments almost as readily as these are distinguished from each other. We become most aware of this , as, mutatis mutandis, 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 adjustment that accompanies the concentration of attention upon ideas.
58-1 Moreover, as we shall see, the distinction between present and past or future psychologically presupposes the contrast of impression and image.
59-1 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.
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