PSYCHOLO-GY 53 Assimi- impressions is wide : between the simplest mental process lation of they may be supposed to denote and the most complex there is a great difference. The penguin that watched unmoved the first landing of man upon its lonely rock becomes as wild and wary as more civilized fowl after two or three visits from its molester : it then recognizes that featherless biped. His friends at home also recognize him though altered by years of peril and exposure. In the latter case some trick of his voice or manner, some " strik- ing " feature, calls up and sustains a crowd of memories of the traveller in the past, events leading on to the present scene. The two recognitions are widely different, and it is from state's of mind more like the latter than the former that psychologists have usually drawn their descrip- tion of perception. At the outset, they say, we have a primary presentation or impression P, and after sundry repetitions there remains a mass or a series of P residua, 2hP'2Ps ' ') perception ensues when, sooner or later, P n " calls up " and associates itself with these re-presentations or ideas. Much of our later perception, and especially Avhen we are at all interested, awakens, no doubt, both distinct memories and distinct expectations ; but, since these imply previous perceptions, it is obvious that the earliest form of recognition, or, as we might better call it, assimilation, must be free from such complications, can have nothing in it answering to the overt judgment, P n is a P. Assimilation involves retentiveness and differentia- tion, as we have seen, and prepares the way for re-presenta- tion ; but in itself there is no confronting the new with the old, no determination of likeness, and no subsequent classification. The pure sensation we may regard as a psychological myth ; and the simple image, or such sensa- tion revived, seems equally mythical, as we may see later on. The nth sensation is not like the first : it is a change in a presentation-continuum that has itself been changed by those preceding ; and it cannot with any propriety be said to reproduce these past sensations, for they never had the individuality which such reproduction implies. Nor does it associate with images like itself, since where there is association there must first have been distinctness, and what can be associated can also, for some good time at least, be dissociated.
- ocaliza- To treat of the localization of impressions is really to give
ion of an account of the steps by which the psychological indi- vidual comes to a knowledge of space. At the outset of such an inquiry it seems desirable first of all to make plain what lies within our purview, and what does not, lest we disturb the peace of those who, confounding philosophy and psychology, are ever eager to fight for or against the a priori character of this element of knowledge. That space is a priori in the epistemological sense it is no concern of the psychologist either to assert or to deny. Psychologically a priori or original in such sense that it has been either actually or potentially an element in all presentation from the very beginning it certainly is not. It will help to make this matter clearer if we distinguish what philosophers frequently confuse, viz., the concrete spatial experiences, constituting actual localization for the individual, and the abstract conception of space, generalized from what is found to be common in such experiences. A gannet's mind "possessed of" a philosopher, if such a conceit may be allowed, would certainly afford its tenant very different spatial experiences from those he might share if he took up bis quarters in a mole. So, any one who has revisited in after years a place from which he had been absent since childhood knows how largely a " personal equation," as it were, enters into his spatial perceptions. Or the same truth may be brought home to him if, walking with a friend more athletic than himself, they come upon a ditch, which both know to be twelve feet wide, but which the one feels he can clear by a jump and the other feels he cannot. In the concrete " up " is much more than a different direc- tion from "along." The hen-harrier, which cannot soar, is indifferent to a quarry a hundred feet above it to which the peregrine, built for soaring, would at once give chase but is on the alert as soon as it descries prey of the same apparent magnitude, but upon the ground. Similarly, in the concrete, the body is the origin or datum to which all posi- tions are referred, and such positions differ not merely quantitatively but qualitatively. Moreover, our various bodily movements and their combinations constitute a net- work of co-ordinates, qualitatively distinguishable but geo- metrically, so to put it, both redundant and incomplete. It is a long way from these facts of perception, which the brutes share with us, to that scientific conception of space as having three dimensions and no qualitative differences which we have elaborated by the aid of thought and lan- guage, and which reason may see to be the logical presup- position of what in the order of mental development has chronologically preceded it. That the experience of space is not psychologically original seems obvious quite apart from any successful explanation of its origin from the mere consideration of its complexity. Thus we must have a plurality of objects A out of B, B beside C, distant from D, and so on ; and these relations of externality, juxtapo- sition, and size or distance imply further specialization ; for with a mere plurality of objects we have not straight- way spatial differences. Juxtaposition, e.g., is only possible when the related objects form a continuum ; but, again, not any continuity is extensive. Now how has this com- plexity come about 1 The first condition of spatial experience seems to lie Exten- in what has been noted above (p. 46) as the extensity of sensation. This much we may allow is original ; for the longer we reflect the more clearly we see that no combina- tion or association of sensations varying only in intensity and quality, not even if motor presentations are added, will account for the space-element in our perceptions. A series of touches a, b, c, d may be combined with a series of movements m v m 2 , m z , ra 4 ; both series may be reversed ; and finally the touches may be presented simultaneously. In this way we can attain the knowledge of the coexistence of objects that have a certain quasi-distance between them, and such experience is an important element in our per- ception of space ; but it is not the whole of it. For, as has been already remarked by critics of the associationist psychology, we have an experience very similar to this in singing and hearing musical notes or the chromatic scale. The most elaborate attempt to get extensity out of succes- sion and coexistence is that of Mr Herbert Spencer. He has done, perhaps, all that can be done, and only to make it the more plain that the entire procedure is a va-repov TrpoTfpov. We do not first experience a succession of touches or of retinal excitations by means of movements, and then, when these impressions are simultaneously pre- sented, regard them as extensive, because they are asso- ciated with or symbolize the original series of movements ; but, before and apart from movement altogether, we ex- perience that massiveness or extensity of impressions in which movements enable us to find positions, and also to measure. 1 But it will be objected, perhaps not without 1 We are ever in danger of exaggerating the competence of a new discovery ; and the associationists seem to have fallen into this mistake, not only in the use they have made of the conception of asso- ciation in psychology in general, but in the stress they have laid upon the fact of movement when explaining our space-perceptions in particular. Indeed, both ideas have here conspired against them, association in keeping up the notion that we have only to deal with a plurality of discrete impressions, and movement in keeping to the front the idea of sequence. Mill's Examination of Hamilton (3d ed., p. 266 sq.) surely ought to convince us that, unless we are prepared to
