EXPRESSION, EXPRESSIVE MOVE MENTS. That bodily movements may serve as indexes of mental states is a matter of daily ob servation. The smiling face, the bright eye. the animated gestures characteristic of joy and pleas antness, contrast sharply with the attitude of dejection which sorrow and grief entail. Experi mental methods have shown that even the sim plest modes of affective experience, the pleasure of an agreeable odor, the unpleasantness of a dis cord, are accompanied by distinct and specific alterations of certain physiological functions. When we are pleased the pulse is strong. we breathe more deeply, the blood flows more freely into the peripheral blood-vessels, and we are mus cularly stronger. But it is naturally in the more complex and far-reaching nervous disturb ante of the emotion (q.v.) that bodily expres sion becomes so well marked as to be accessible to external observation.
One of the peculiar features of emotional ex pression is the seemingly useless and even posi tively disadvantageous nature of certain of the bodily disturbances. Why should we curl our lip in scorn? Why should we clap our hands for joy, or blush for shame, or tremble for fear? It is in answer to such questions that Various authori ties have deduced what arc called 'the principles of expression.' with the aim at once of classifying and of explaining the genesis of the expressive movements. The best-known and most important contributions to this subject are those of Darwin, \Vundt, and James.
In 1873 Darwin brought forward three prin ciples, by which he hoped to account for most, if not all, of the expressive gestures involuntarily used by man and the lower animals tinder the in fluence of the emotions. Darwin's principles are as follows: (1) The principle of as sociated habits. Many complicated movements which under certain circumstances were of direct or indirect use are retained when their use is no longer apparent, in consequence of the general laws of association, habit, and inheritance. Thus the cat executes peculiar 'pawing' movements with the fore feet when it is pleased. These move ments are the relic of the purposeful use of the same movements to start or increase the flow of milk from the mammary glands of the mother. The movements became thereby associated with a pleasurable and satisfied consciousness, and tend to recur whenever such a consciousness re curs. \Vundt considers that this principle is but
a special case of Darwin's third, the direct action of the nervous system; for the overflow of ner vous energy takes those paths which are habitual and most frequently used. (2) The principle of antithesis. As Darwin explains it. 'every move ment which we have voluntarily performed throughout our lives has reimired the action of certain muscles; and when we have performed a directly opposite movement, an opposite set of muscles has been habitually brought into play. . . . So when actions of one kind have become firmly associated with any sensation or emotion, it appears natural that actions of a directly opposite kind, though of no use, should be un consciously performed through habit and associa tion under the influence of a directly opposite sensation or emotion." Thus impotence is ex pressed by raised eyebrows, shrugged shoulders, and open palms; since these are the antithesis of the frowning brow, the thrown-baek shoulders. and the •lenched fists, symbolic of rage :Ind power. .lames says in comment: "No doubt a certain number of movements can be formulated under this law; but whether it expresses a causal principle is more doubtful. It has been by most erities considered the least successful of Darwin's speculations on this subject." (3) The principle of the direct artion of the ner tem : or of actions due to the constitution of the nervous system. independent from the first. of the will, and independent to a certain extent of habit. The sinhlon,release of large quantities of nervous energy demands unusual outlet from the central nervons system. This takes place ae eording to the preformed conneetions of the nervous elements. Its results are visible in the general distnrbanee of organic function due to the exciting or inhibitory effects of these irradiations of energy from the central nervous system. On this principle are explained such phenomena as the muscular tremors of fear or of great joy; the increased glandular activity of the liver, kidneys, and mamma.; the alterations in cardiac and vaso motor functions ; and such movements as the clapping of the hands for joy. It is admitted by James, and is practically identical with the first principle of Wundt.