§ 2. The Special Sensations.—We now turn to consider the special sensations of sight, sound, smell, taste, touch, and temperature. The feeling-tone of these sensations varies, first, with their intensity, secondly, with their duration, and thirdly, with their quality.

(1) Many of them in a low grade of intensity appear to be virtually neutral. All of them acquire appreciable feeling-tone as their intensity is increased. Some of them are unpleasant even when they are weak. All of them become unpleasant when intensified beyond a certain point. Before reaching this point they nearly all have an agreeable phase; after reaching this point they continue to bo more and more disagreeable as intensity increases. It is a matter of dispute whether there is any sensation which is constantly disagreeable in whatever phase of intensity it appears. It is always possible to urge that though a sensation is generally disagreeable, it might be agreeable if it could be made weak enough. As an example of a pleasant phase of an experience which everybody would regard as absolutely disagreeable from its very quality, we may quote the following from Mr. H. R. Marshall: "I remember well once having been aroused from serious thought in a railway carriage by a delicious odour, and the words ' What a delightful perfume!' were actually formed in thought. Almost immediately the smell changed to disagreeableness with growing intensity, and there appeared evident the intensely disagreeable smell emitted by a polecat which had been killed by the train."* We may formulate the general rule for the relation of intensity and feeling-tone as follows. A sensation must reach a certain minimum of intensity in order to have an appreciable feeling-tone. Further rise in intensity of sensation is accompanied by a rise in intensity of feeling-tone. If the sensation is initially unpleasant, its unpleasantness continues to increase as the sensation is intensified. If it is initially pleasant, the pleasantness increases to a certain maximum, at which it remains roughly constant until the intensity of the sensation is increased beyond a certain limit. When this limit is passed, the pleasantness decreases, and finally passes into unpleasantness.+

* Pain, Pleasure, and Aesthetics, p. 288.

+See A. Lehmann, Die Hauptgesetze des menschlichen Gefiihlslebens, p. 181.

The nature of the transition from pleasantness to unpleasantness requires further elucidation. An unpleasant element appears to enter into the experience even while the original sensation continues to be in itself agreeable. This is sometimes distinctly traceable to other definitely assignable sensations, which are superadded to the primary one. Thus, at a certain pitch of intensity, warmth may continue to be still agreeable in itself, although it is accompanied by a distinctly disagreeable sensation of a prickly or pungent character, probably due to stimulation of pressurepoints in the part of the skin affected. So a bright light may continue to give pleasure when it is so intense that the effort to accommodate the eye to it is unpleasant. But there are other cases in which it is much more difficult to assign definitely the source of the collateral unpleasantness. However intense sweetness may be, it scarcely seems to become in its own intrinsic nature disagreeable. At the same time, it may excite strong disgust, which seems to be connected with accompanying organic sensations not easy to analyse or describe.

(2) The dependence of feeling-tone on duration varies in nature according as the sensation is continuously maintained or repeated intermittently.

There appears to be no appreciable interval of time between the emergence of a sensation of given intensity and the corresponding feeling-tone. Apparent exceptions can be explained away. If we touch a disagreeably hot object, the heat is felt before the unpleasantness; but this is because the stimulus requires a certain time before it can take full effect. On its first application the sensation is not intense enough to be disagreeable.

The following is the general formula for variations of feeling-tone with the continuous persistence of the sensation in time. The feeling-tone increases in intensity to a maximum. If the sensation is pleasant, it continues for some time at this maximum, and then gradually becomes less agreeable, and in the end distinctly disagreeable. If the sensation is initially unpleasant, the maximum persists for a much longer period than in the case of agreeable sensations. After this, the unpleasantness may become fainter, but it never passes into pleasantness, and it is always liable to reappear at intervals in more intense phases.

The same remarks which, we made about the transition from pleasantness to unpleasantness with rise in intensity, apply to the same transition as dependent on continuous persistence in time. Here also collateral elements of a disagreeable kind are introduced into the experience before the primary sensation becomes in itself unpleasant. The illustrations of the bright colour and of the sweet taste may be transferred, mutatis mutandis, to the case of duration. A boy eating sugarplums, if he continues to indulge himself beyond a certain point, has disagreeable sensations distinctly traceable to the stomach and other internal organs, while the sweetness itself remains sufficiently agreeable to tempt him to go on eating. But even apart from such definitely assignable collateral accompaniments, there may be a surfeit of sweetness, though sweetness remains in itself an agreeable taste. Doubtless this is due to some general organic effect hard to define by introspective analysis. Sometimes the disagreeableness is simply due to tedium; if we gaze at a bright colour too long we feel bored because of the suspension of other activities, although the colour continues to be pleasing.

The case in which the sensation is repeated intermittently is in many ways analogous to that in which it persists continuously. If the repetition is too frequent, a pleasant sensation tends to become less pleasant, and often becomes unpleasant. Unpleasant sensations by frequent repetition often, but by no means always, become less unpleasant. They may even become virtually neutral or even actually pleasant. Perhaps the best instance of a disagreeable sensation becoming agreeable by repetition is the "acquired taste" for olives.

When a pleasant sensation by repetition does not lose its pleasantness and become disgusting, and when an initially unpleasant sensation has become more or less pleasant by repetition, its absence from consciousness will at certain moments give rise to a craving for it. The craving of the smoker for tobacco, of the oliveeater for olives, or of the drinker for his bitter beer, are cases in point. Certainly, the effect is most marked when originally unpleasant sensations have become pleasant by repetition. The nervous system has adapted itself to certain modes of excitation returning at certain intervals, and their absence produces a disturbance of neural equilibrium. If a person is in the habit of using tobacco only at fixed times in the day, the craving is apt to arise exclusively at these times. The omission of a customary early morning pipe may trouble the smoker in the early morning, but the craving may pass away and not recur during the day.

(3) We have seen that there are probably some sensations which are disagreeable in all phases of intensity. Others become disagreeable at a very low intensity. In the case of others, such as sweetness, it is not quite certain that they ever become intrinsically disagreeable, even when they are most intense. It follows that quality of sensation is a most important factor in determining feeling-tone. We can do little to explain why one quality is predominantly agreeable and another predominantly disagreeable. The nearest approach to an explanation is found in the special case of complex sound-sensations. The disagreeableness of dissonance is due to the presence of beats which interrupt the uniform course of the periodic stimulation of the organ of hearing. The central nervous matter has adapted itself to a certain rhythm of excitation, and this rhythm is disturbed by the beats. We have no similar reasons to assign whycertain combinations of odours and tastes are agreeable, and others disagreeable.