Perception: Mental Synthesis or Integration.
In treating apart of the differentiation of our sensory and motor continua, as resulting merely in a number of distinguishable sensations and movements, we have been compelled by the exigencies of exposition to leave out of sight another process which really advances pari passu with this differentiation, viz., the integration or synthesis of these proximately elementary presentations into those complex presentations which are called perceptions, intuitions, sensori-motor reactions, and the like. It is, of course, not to be supposed that in the evolution of mind any creature attained to such variety of distinct sensations and movements as a human being processes without making even the first step towards building up this material into the most rudimentary knowledge and action. On the contrary, there is every reason to think, as has been said already incidentally, that further differentiation was helped by previous integration, that perception prepared the way for distincter sensations, and purposive action for more various movements. This process of synthesis, which is in the truest sense a psychical process, deserves some general consideration before we proceed to the several complexes that result fromit. Most complexes, certainly the most important important, are consequences of that principle of subjective selection whereby interesting sensations lead through the intervention of feeling to movements ; and the movements that turn out to subserve such interest come to have a share in it. In this waywhich we need not stay to examine more closely nowit happens that, in the alteration of sensory and motor phases which is common to all psychical life, a certain sensation, comparatively intense, and a certain movement, definite enough to control that sensation, engage attention in immediate succession, to the more or less complete exclusion from attention of the other less intense sensations an more diffused movements that accompany them. Apart from this intervention of controlling movements, the presentation-continuum, however much differentiated, would be for all purposes of knowledge little better than disconnected manifold for which Kant took it. At the same time it is to be remembered that the subject command of particular movements because such movements prove on occurrence adapted to control certain sensations. Before experience, and apart from heredity, there seems not only no scientific warrant for assuming any sort of practical prescience but also none for the hypothesis of a priori forms of knowledge. Of a pre-established harmony between the active and passive phases of consciousness we need none, orit may be safer to sayat least indefinitely little. A sentient creature moves first of all because it feels, not because it intends. A long process, in which natural selection probably played the chief part of the outsetsubjective becoming more prominent as the process advancedmust have been necessarily to secure as much purposive movement as even a lobster displays. It seems impossible to except from this process the movements of the special sense-organs which are essential to our perception of external things. Here too subjective interest will explain, so far as psychological explanation is possible, those syntheses of motor and sensory presentations which we call spatial perceptions and intuitions of material things. For examples, some of the earliest lessons of this kind seem to be acquired, as we may presently see, in the process of exploring the body by means of the limbs,a process for which grounds in subjective interest can obviously never be wanting.
The mere process of "association"whereby we may suppose the synthesis of presentations to be effected so that presentation originally in no way connected tend to move in consciousness togetherwill confront us with its own problems later on. We need for the present only to bear in mind that the conjunction or continuity upon which the association primarily depends is one determined by the movements of attention, which movements in turn depend very largely upon the pleasure or pain that presentations occasion. To some extent, however, there is no doubt that attention may pass non-voluntarily from one indifferent presentation to another, each being sufficiently intense to give what has been called a "shock of surprise," but not so intense as to awaken feeling to move for their detention or dismissal. But throughout of mental development, where are concerned with what is new, the range of such indifference is probably small : indifferent presentations there will be, but the does not matter while there are others that are to take the lead.
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