FUSION (Lat. fusio, fusion, from fundere, to pour). A concept which has played a large part in recent psychological discussion, but the mean ing of which cannot be said to be finally and pre cisely settled. It denotes a connection of sense elements of an extremely intimate kind—a con nection so close that the resultant compound process seems rather to be a fusion or weld than a mere association of elements. The best instance of a fusion is the sound of a musical note or clang in which a number of tonal elements are blended to give a single resultant perception which, in certain cases, may counterfeit the sim plicity of sensation itself. See CLANG-TINT.
Fusion, as thus defined, might be nothing more than a limiting form of simultaneous associa tion (q.v.). Wundt accordingly classifies simul taneous associations as: (1) Fusions (intensive, e.g. tones, and extensive, e.g. sights and touches) ; (2) assimilations, including discrimination and recognition; and (3) complications, connections of elements from different sense departments (e.g. of visual impressions and the organic sen sations accompanying bodily movement). As thus understood, fusion does not necessarily im ply any change in the connected sensations. We may suppose that they are intimately associated, owing to their habitual and constant concur rence; some one of them dominates the group, forcing the others into obscurity, so that the whole is apprehended as a whole, and not as a sum; but still analysis is possible, and when it takes place the obscure components may turn out to be the same in all respects as they would be if given in isolation. Fusion, in other words, might be merely a modern name for James Mill's indissoluble association. In point of fact, the question is more complicated.
(1) We must, in the first place, take account of Wundt's law of psychical resultants. This law declares that "every mental complex shows attributes which may, indeed, be understood from the attributes of its elements, when these elements have been once presented, but which are by no means to be regarded as the mere sum of the attributes of these elements." Thus the musical note or chord has attributes, on its perceptival and affective sides, which do not attach to the com ponent simple tones. So, too, spatial and tem
poral arrangement—extension, duration, order in space or time-4 conditioned upon a certain col location of sense elements; but neither space nor time is an intrinsic attribute of any sensation. It follows, then, that for Wundt both the inten sive and the extensive fusions are, in reality, something more than indissoluble associations; the fusion is not only a whole, but a new whole, something that can be understood but not predi cated from the nature of its elemental constitu ents. The law of psychical resultants has been much criticised, on the ground that it involves a belief in 'mental chemistry' for which the facts give no warrant; on the ground, more particu larly, that it is impossible to derive space from the non-spatial and time from the non-temporal. Nevertheless, many psychologists of high stand ing accept the doctrine of 'consolidated contents' or 'consolidated attributes'; the doctrine, i.e. that associated complexes contain processes or show attributes which are set up by the associa tion as such, and are not discoverable when the elements are separately examined; and this doc trine is but a variant of Wundt's law.
(2) The laws of tonal fusion have been worked out in great detail by Stumpf. This author is very far from accepting a principle of mental chemistry; but, at the same time, he differenti ates fusion from simple association. According to Stumpf, there is in a collocation of tones, after all other hindrances to analysis have been removed, a tendency to fusion, or to a resultant oneness of impression, due to the character of the sense material itself. When full allowance is made for habitual association, for misdirection or distraction of attention, for lack of practice, and what not, this 'sense phenomenon' of being fused still remains. It is not that a new process or attribute is set up; it is simply that, just as visual extents, owing to their intrinsic nature, associate, so do tonal qualities, owing to their nature as tones, fuse or blend. This position has recently been disputed; but the evidence for it is too strong to be lightly overthrown.