OF ASSOCIATION, HABIT, IMITATION, Ste.
WE have frequently had occasion to refer to the effects of association, and it will therefore be proper to give some account of its origin and mode of operation. When two impressions of any kind have been made upon the nervous system, and repeated together for a sufficient number of times, if one of them be afterwards excited, the idea of the other necessarily succeeds. Although this principle was not overlooked by the ancients, Locke appears to have been the first who clearly saw the full extent of its operations, and arranged them in a systematic form. A still more minute attention was afterwards paid to it by Hartley, who made it the basis of his system, and extended it to all parts of the animal economy, both physical and intellectual. It is, indeed, generally admitted that he carried his favourite doctrine to an unreasonable tength ; yet we are disposed to admit that its influence is very extensive, and of almost constant occurrence. Our object, in this place, is, to con sider association so far only as it relates to physiology ; and, proceeding upon this ground, we may point out the follow ing varieties, or modes, in which this principle operates. Perceptions may be associated with other perceptions; they may also be associated with ideas, and ideas may be associated with each other. Perceptions may likewise be associated with mechanical actions, mechanical actions with ideas, and with other mechanical actions ; the combi nation which is the most connected with our subject, is the association of muscular motions, either with each other, or with some affection of the nerves.
With respect to the associated muscular motions, it has been laid down as a general rule by Darwin, " that all ani mal motions which have occurred at the same tune, or in immediate succession, become so connected, that when one is reproduced, the other has a tendency to accompany or succeed it." Many of the ordinary actions of life are composed of a number of individual operations, which, in the first instance, had no necessary connexion with each other ; but yet, if the conjunction be sufficiently repeated, an indissoluble association is produced. On this account
it becomes extremely difficult to determine, in many cases, whether any particular train of actions is connected toge ther by association, or by some natural law of the consti tution. This difficulty may sometimes be removed by as certaining how these complex actions are acquired. In the case of progressive motion, as in walking, ‘ve employ a number of muscles in different parts of the body, which individually serve very different purposes ; we alternately contract the muscles of the lower extremities ; by an efliort of the loins we throw the weight of the body, first to one side, and then to the other, while we move the upper ex tremities in order to assist in preserving the body in a per pendicular position. The act of walking, which consists of this complicated train of actions, we know can only be acquired by long practice ; and we may affirm, that a per son born without legsovho should afterwards be furnished with them, would be no more able to walk without instruc tion, than to play upon a musical instrument. Yet these motions become so firmly associated together, that it re quires a powerful effort of the will to perform them in a different order ; and they proceed with almost as much re gularity as the motion of the heart, or any other function over which the will has no control.
There are, on the contrary, some actions strictly volun tary, and which also require the co-operation of many muscles, but which seem to have a necessary connexion with each other. In the act of swallowing, the muscles of the mouth, lips, cheeks, tongue, neck, and gullet, are all concerned, and they act in such a manner, and in such an order with respect to each other, as all to contribute to produce the desired effect in the most appropriate manner. Yet we find that the newly-born infant, immediately after birth, swallows the mother's milk as readily as at any sub sequent period : this cannot, therefore, be the effect of as sociation.