42 PSYCHOLOGY objective intensity in that higher form of attention called voluntary we are aware (1) that concentration of atten- tion increases or its abstraction diminishes the intensity of a presentation in circumstances where physically and physiologically there is nothing to prevent the intensity of the presentation from continuing uniform. Again, (2) in circumstances when psychologically we are aware of no previous change in the distribution of attention, we find the intensity of a presentation increased or diminished if certain physical concomitants of the presentation (e.g., stimulus, nervous process, &c.) are increased or diminished. Thus, though this is a point we .could hardly establish without the aid of psychophysics, we may conclude that the intensity of a presentation may be altered from two sides ; that it depends, in other words, partly upon what we may perhaps call its physical intensity and partly on the amount of attention it receives. Some further exposition of the connexion between subjective attention and objective intensity is perhaps desirable here, where we are seeking to get a general view of the essential facts of mind and their relations, rather than later on, when we shall be more concerned with details. We are aware in ordinary life that the intensity of any given sensation depends upon certain physical quantities, varying directly in some proportion as these vary. Hence, since our habitual standpoint is the physical not the psy- chological, we conceive sensory objects as having an intensity per se apart from the attention that their presentation secures. From the physical standpoint indeed it is manifest that no other conception is compatible with a scientific treatment of phenomena. Subjective sources of variation are supposed to be eliminated : the general mind to which, according to the physicist's conception of a pheno- menon, that phenomenon is implicitly supposed to be presented is a mind in which there is no feeling to produce variations of atten- tion, or to favour aesthetic combinations of objects. Attention is thus assumed to be constant, and all variations in intensity to be objectively determined. But psychologically we cannot assume this. In any given presentation there is, it must be admitted, no immediate evidence that the intensity of the object is a function of two variables, (1) what we have called its physical or absolute intensity and (2) the intensity of attention. Still there are facts which justify this conclusion. That the intensity of the presenta- tion varies with the absolute intensity of the object, attention remaining constant, is a proposition not likely to be challenged. "What has to be shown is that the intensity of presentations varies with the attention, all else remaining constant. Assuming that voluntary and non-voluntary attention are fundamentally the same, this amounts to showing (1) that concentration of attention upon some objects diminishes the intensity of presentation of others in the same field, whether the concentration be voluntary or non- voluntary, i.e., due to a shock ; and (2) that, even though only within narrow limits, increasing attention voluntarily has the same effect on the presentation as increasing the objective intensity from the physical side. The narrowness of these limits practically an all-important fact is theoretically no objection. It would not be difficult psychologically to account for our inability to concentrate attention indefinitely : that we can concentrate it at all is enough to show that there is a subjective as well as an objective factor in the intensity of a presentation. Any fuller consideration of the connexion between attention and presentations may be deferred. The inter-objective relations of presentations, on which their second characteristic, that of revivability and asso- ciability depends, though of the first importance in them- selves, hardly call for examination in a general analysis like the present. But there is one point still more funda- mental that we cannot wholly pass by : it is in part at any rate what is commonly termed the unity or con- tinuity of consciousness. From the physical standpoint and in ordinary life we can talk of objects that are isolated and independent and in all respects distinct individuals. The screech of the owl, for example, has physically nothing to do with the brightness of the moon : either may come or go without changing the order of things to which the other belongs. But psychologically, for the individual percipient, they are parts of one whole : special attention to one diminishes the intensity of presentation of the other and the recurrence of the one will afterwards entail the re-presentation of the other also. Not only are they still parts of one whole, but such distinctness as they have at present is the result of a gradual differentiation. It is quite impossible for us now to imagine the effects of years of experience removed, or to picture the character of our infantile presentations before our interests had led us habitually to concentrate attention on some, and to ignore others, whose intensity thus diminished as that of the former increased. In place of the many things which we can now see and hear, not merely would there then be a confused presentation of the whole field of vision and of a mass of undistinguished sounds, but even the difference between sights and sounds themselves would be without its present distinctness. Thus the further we go back the nearer we approach to a total presentation having the character of one general continuum in which differences are latent. There is, then, in psychology, as in biology, what may be called a principle of " progressive differen- tiation or specialization " ; and this, as well as the facts of reproduction and association, forcibly suggests the con- ception of a certain objective continuum forming the background or basis to the several relatively distinct pre- sentations that are elaborated out of it the equivalent, in fact, of that unity and continuity of consciousness which has been supposed to supersede the need for a conscious subject. There is one class of objects of special interest even in Motor a general survey, viz., movements or motor presentations, presenta- These, like sensory presentations, admit of association and toons, reproduction, and seem to attain to such distinctness as they possess in adult human experience by a gradual differ- entiation out of an original diffused mobility which is little besides emotional expression. Of this, however, more presently. It is primarily to such dependence upon feel- ing that movements owe their distinctive character, the possession, that is, under normal circumstances, of definite and assignable psychical antecedents, in contrast to sensory presentations, which enter the field of consciousness ex abrupto. We cannot psychologically explain the order in which particular sights and sounds occur ; but the move- ments that follow them, on the other hand, can be ade- quately explained only by psychology. The twilight that sends the hens to roost sets the fox to prowl, and the lion's roar which gathers the jackals scatters the sheep. Such Subjec diversity in the movements, although the sensory presenta- i y e se tions are similar, is due, in fact, to what we might call the Ion ' principle of " subjective or hedonic selection " that, out of all the manifold changes of sensory presentation which a given individual experiences, only a few are the occasion of such decided feeling as to become objects of possible appetite (or aversion). The representation of what in- terests us comes to be associated with the representation of such movements as will secure its realization, so that although no concentration of attention will secure the requisite intensity to a pleasurable object present only in idea we can by what is strangely like a concentration of attention convert the idea of a movement into the fact, and by means of the movement attain the coveted reality. And this has brought us round naturally to what is per- Cor haps the easiest way of approaching the question : What toon- is a conation or actionl In ordinary voluntary move- ment we have first of all an idea or re-presentation of the movement, and last of all the actual movement itself, a new presentation which may for the present be described as the filling out of the re-presentation, 1 which thereby attains that intensity, distinctness, and embodiment we call reality. How does this change come about ? The attempt has often been made to explain it by a reference to the more uniform, and apparently simpler, case of reflex 1 On the connexion of presentations and re-presentations, see p. 59 below.
