Further, the exactness of the assimilative process throughout waits on the advance of differentiation. Thus the child begins, as we have seen, by roughly classing different varieties of red as red long before it more exactly classes a particular variety, as scarlet or plum-colour, as such. Assimilation thus becomes close and exact in the measure in which distinction is introduced.1

This consideration helps us to understand what is meant by saying that assimilation (likeness) precedes discrimination (difference) in the development of the child. Crude assimilation progresses in advance of discrimination. Witness the daring of childish classification, as when it calls all males "dada," a rabbit "ba lamb," and so forth, a matter to be dealt with more fully by-and-by. On the other hand, assimilation as a precise process follows, or at least involves, discrimination. Tastes, odours, colours, etc., become carefully assimilated or classed in proportion as their several kinds are distinctively apprehended.

While, however, differentiation thus circumscribes the area of exact assimilation, assimilation reacts upon differentiation. It is, as already pointed out, through the interest awakened by the recurrence of partially old and familiar impressions that attention comes to be directed to these, and so the differentiating process to be carried a step further. If I did not recognise something familiar in this colour-group, this voice, and so forth, that is, partially assimilate it, I should not scrutinise it and so grow aware of its finer points of difference. As we shall see by-and-by, when we take up the subject of analysis of complexes, the singling out of a particular constituent, that is, the discriminative apprehension of it, is greatly aided by the

1 This dependence of assimilation on differentiation is illustrated in some experimental inquiries of Lehmann on "Recognition" (" Ueber Wiedererkennen "). He found that when a subject is required to refer a gray to a well-discriminated and separately named shade as a class, e.g., dark, middle, or neutral, the decision is much more certain than when he is asked to class a shade of gray under one of a series of arbitrarily selected six or nine gradations, which are not commonly distinguished and named. But oddly enough Lehmann (here following German psychologists generally in their inadequate recognition of the function of discrimination) does not connect his results with the variation of the discriminative factor in the case. (See Wundt's Phil. Studien, v. p. 135 ff.) The point insisted on is further illustrated in the effect of repetition in increasing precision, for this (as Lehmann himself seems to recognise) involves improved discrimination (pp. 148, 149).

CONNEXION OF DIFFERENTIATION AND ASSIMILATION.

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circumstance that we have met with its like before, and so have our attention specially drawn to it by a process of assimilation, or, as the Herbartians would say, "apperception".

Finally, it is to be remarked that the higher forms of each, conscious apprehension of difference and of likeness, involve one another. We can only consciously compare two sensationcomplexes as like when we distinguish these as two, and so in a manner at least different.1 On the other hand, we cannot discriminate things exactly, save when we recognise a common aspect under which we can compare them. To say that two things differ is to say that they differ in respect of a common attribute, as size, colour, local complexion.

(c) ASSOCIATION.

$9. General Nature of Associative Process. In addition to the two processes, differentiation and assimilation, there is a third process involved in mental elaboration known as Association. By this is meant that process of psychical combination or integration which binds together presentative elements occurring together or in immediate succession. Thus, for example, the several sensations that a child receives together from one and the same object, as those of warmth, softness, and smoothness from the mother's breast, become conjoined, tied together, or integrated into one complex. Similarly, the succession or chain of visual and other impressions received in watching the preparation of its food, or undergoing the operations of dressing, bathing, etc., become conjoined or integrated into a series. It may be added that such integration has for its main condition, in addition to the co-presentation of two sensational elements, either together or in close succession, a mental reaction on these, either in the shape of a simultaneous grasp. of them by attention, or of a movement of attention from the one to the other.2

This weaving together of the elements of experience (which is necessary to the very idea of experience as a system of con

1 That is, at least, differing in their local or temporal character, if not in their qualitative aspect.

2 Cf. above, pp. 160. Wundt, following Herbart, marks off Association from Assimilation under the head "Complication" (op. cit., ii. p. 369).

nected parts) begins from the earliest moment, and runs on pari passu with the other processes just dealt with. At the same time, the effect of this process of associative integration only becomes clearly manifest when mental development has reached the point where reproduction of sensations grows distinct. When we say that a mass of sensation-elements has been integrated we imply that when next we experience a part of the aggregate this will tend to recall, that is, revive under a representative form, the rest of the aggregate. Thus we know that the sight and taste of the infant's food have become integrated when the former manifestly calls up a representation (expectation) of the latter. Psychical binding together, or association, always has reference to a subsequent process of mental reproduction.

And here we reach a point of our exposition at which it becomes necessary to say something more about the psychological nature of retentiveness, and the closely-related process of reproduction.

§ 10. Retentiveness. By retention as a psychological phenomenon is meant in general the fact that a sensation tends to persist, or to be followed by some analogous after-effect when the process of stimulation has ceased. In its simplest form it shows itself in the temporary survival of a sensation in the shape of an after-sensation,' when the stimulus ceases to act, as when we retain an after-image of a bright object, say the sun's disc, some seconds after looking away from this. Here we suppose that the process of central excitation after having been started by the peripheral stimulation is capable of being prolonged, just as a tight string will go on vibrating after the withdrawal of the force which originated the movement.1

A much higher degree of retentiveness is shown where a sensation is not simply prolonged, but recalled after a considerable interval, as when a hungry child recalls the sensations of feeding. Here it is evident retentiveness means something different from what it meant in the case of the temporarily prolonged or surviving sensation. The sensation recalled is

1 Cf. above, p. 97.

2 There is an intermediate case between the after-sensation and the revival after a considerable interval; but we need not consider this yet.

not supposed to have persisted, at least as a conscious sensation, during the interval. How then are we to conceive of the retention of it during this period? Two answers at once present themselves. (1) It has persisted as a true psychical phenomenon, but, having fallen below the threshold of consciousness, it has failed to make its existence known. (2) It has not existed at all as a psychical phenomenon, but the 'retention' is referrible exclusively to the persistence of certain changes, changes variously spoken of as physiological 'traces' or 'dispositions' in the nervous centres. In other words, it has been retained 'potentially' in the sense that its nervous conditions or substratum have been rendered permanent.

The determination of this point is, as already hinted, one of the 'cruces' of psychology. That sensations persist as psychical phenomena seems a necessity of thought to those who, like Leibniz and the Herbartians, conceive of the mind as a distinct spiritual substance. It follows from this view that all spiritual activity is indestructible, like the energy of the physical world. According to this way of envisaging the matter, it is not retention but loss or forgetfulness that requires to be accounted for. On the other hand, it has been urged that psychological retentiveness is only a special case of a general biological function; and that all organs preserve either as an ingrained change of structure, or, at least, as a permanently acquired physiological disposition, the traces or residua of their previous activity. On this view, psychological retention is merely the subjective correlative of a physiological process, viz., the cerebral organisation of the traces of past functional activity.2

How far this second view will help us to understand all that is meant by the conscious processes of memory and recollection cannot be discussed as yet. It may be as well to point out, however, even at this stage, that there is no greater difficulty in understanding how a persistent cerebral action or disposition should secure the revival of a sensation than how the original peripherally-induced cerebral excitation occasioned the sensation itself. The transition from physiological conditions to psychological results is just as difficult in the one case as in the other.

§ 11. Process of Reproduction: Immediate and Mediate Revival. The process of reproduction is something added to mere retention, since it implies the reappearance "in consciousness" of

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1 See Hamilton, Lectures on Metaphysics, ii. lect. xxx.; and Ward, article Psychology," p. 47.

2 It seems to be a question whether such a physiological disposition involves a prolongation of the functional activity in a weakened or nascent form. (See Wundt, op. cit., ii. 381; cf. article "Memory," by Dr. Burnham, in American Journal of Psychology, vol. ii. p. 571, etc.)

the impression, no longer indeed as a sensation, but under a new representative form.1

This reproduction, as already hinted, appears in a crude or nascent form in automatic assimilation. When a new sensation or sensation-complex is recognised as something familiar it is because of the revival and coalescence with the presentation of representative residua of past sensations. Here, however, as pointed out above, the revival is in most cases nascent and incomplete. The new sensation has its character altered by the consciousness of familiarity, that is, of having had a like sensation before, but there is no distinct representation of this past sensation. It is only in exceptional cases, as when one particular experience of an odour, of a musical impression, and so forth, is retained with special distinctness, standing out clearly from among other retentions of the like, that a new similar experience at once recalls this particular member of the series of experiences. This partial reproduction, being due directly to the stimulus of the new like sensation and independent of any other stimulus, has been called Immediate Reproduction.

The other and more perfect form of revival of a presentation involves the absence of a like presentation at the moment. We cannot recall a colour and see a perfectly similar colour at the same moment, just because a presentation and its corresponding representation, being qualitatively indistinguishable, irresistibly coalesce. Perfect revival can only take place in a free form, through the rousing action of some other, that is, unlike stimulus. Such a stimulus is supplied by some connected or associated presentation. Hence this fuller form of revival is known as Associative Revival or Suggestion. Since, in this case, the revival is brought about indirectly by some disparate associated element, the process is spoken of as Mediate Reproduction.

This distinction of immediate and mediate reproduction is common among the Herbartians. It is possible to give the distinction a psycho-physical meaning by supposing, as is commonly done, that immediate revival involves a nervous process restricted to certain cortical elements answering to sensation and idea alike,

1 The exact relation of this to the original presentation-form can be more profitably discussed later on.