by natural evolution.1 Given a certain physical stimulus and a certain feeling follows.

Acquired Connections.-At first thought this seems to be the end of the matter; but, as was briefly stated in Chapter II, § 8, the stimulus itself is not the sole cause of the mental state. To the question, "What determines what things anyone feels at any moment?" common sense gives the ready answer, "That which is there to be sensed, -to be seen, heard or touched." But common sense is only partly right. The physical stimulus affecting the sense organs is one, but only one, of the causes which determine what the percept shall be. For (1) we may feel different things, have different percepts, from the same stimulus; moreover (2) we may have the same percept from different stimuli; and in the third place (3) we may feel a thing when there is no physical stimulus corresponding to it.

Thus (1) the same cup of coffee tastes sweet after quinine and bitter after honey; the same light is bright by night and dim by day; the same gray looks reddish on a green background and greenish on a red background. The same air waves which make me feel a vague tumult of sound, make the musician feel the tones of five distinct instruments combined in a harmony; the same mass of colors is a blur to me and a definite group of micro-organisms to the trained microscopist.

Thus (2) patches of quite different shades may all be

1 There is no absolute necessity that the connections should be as they are. Man might conceivably have been such a creature that sound waves of 50-100 vibrations would make him feel cold and those of 20000-40000 vibrations make him feel warm. There might conceivably exist connections between the presence of the Xrays and feelings of some sort unlike any we now possess. Or we might lack, as the fishes apparently and as some lower animals certainly do, any conections between sound waves and mental states. The existing connections represent only one of many possible arrangements.

felt as the same green (e.g., grass in the sunshine and in the shade); the table top is felt to be a rectangle, though seen as a sharp rhombus; in a brief glance at the letters 'bad oratory,' half an audience saw the same word as when the letters presented were 'laboratory;' so also with 'peneil' and 'pencil.'

Thus (3) occasionally in waking hours, and customarily in dreams, we see and hear and smell and taste things though neither they nor anything like them is present.

Not only the outside stimulus, but also the inner constitution of the individual's mental life, decides what thing shall be felt. There is more to perception than passive impressibility by external forces. Every act of perception is really an act of association. What is felt depends not only upon how the afferent neurones are stimulated, but also upon what neurones they in turn arouse; not only upon what the external object is, but also upon (A) the past experiences and (B) the present tendencies of the individual who perceives it.

(A) The musician feels the sounds made by the string quintette differently from the untrained person, because he has in the past attended to musical sounds and learned to discriminate the parts of a harmony; the audience saw peneil as pencil because the pen il had so often connected with the thought pencil in their previous reading. (B) The coffee tastes now sweet, now bitter, the light is now bright, now dim, according to the backgrounds of taste and illumination accompanying them; the 'bad oratory' was felt as 'laboratory' because in the minds of the audience (a class seated in a laboratory where they had been doing laboratory work for the month past) the thought of laboratory was especially ready to be aroused, was in a line of little resistance. If 'labora

tory' had been shown for a fraction of a second to an audience accustomed to listening to and thinking about speeches, many of them would have seen it as 'bad oratory.'

843. The Law of Association in the Case of Connections of Impression

In General.-What one feels at any given sense stimulus depends then upon what one has felt and upon what one is feeling at the time. Not only the mere capacities for responding to certain events in the physical world by feelings of certain qualities, but also the development of these capacities by training and their dependence upon the particular circumstances attending each case of response, must be taken into account in a study of the connections between sense stimuli and mental states. Nurture modifies nature even in the case of feelings from the senses. The connections between sense stimuli and mental states are partly instinctive and partly learned. Perception involves the influence of training and is explained by the law of association as surely as is the formation of habits; there are habits of perceiving as truly as there are habits of thought and conduct. The incoming stimulus from any set of afferent neurones may discharge into any one of several cell groups; which one it will arouse depends upon the general laws of association and assimilation deciding which connection is strongest.

In Detail. Other things being equal the strongest connection will be (1) that favored by inborn structure, (2) that most frequently made, (3) that most recently made, (4) that with the most easily excitable mental state and (5) that most in harmony with the general set of the

mind at the time. Illustrations of the influence of each of these factors may be found in anyone's daily experience. (1) is of course illustrated in every minute of perceptual experience. The trained nurse reading ‘abominable' as 'abdominal' illustrates (2); the householder who, after a burglary at his house, heard every noise as a fumbling at the door illustrates a combination of (3) and (4). The psychology class who saw 'psychogaly' as 'psychology' illustrates (5) combined with (2) and (3). The author's name was heard by various people to whom he was introduced at the time of the discovery of gold in Alaska, as Klondike; and an old lady in a country town once greeted him as Mr. Corn-doctor.

One consequence of the laws of association and assimilation in the case of connections of impression is that any sense stimulus tends to be felt as some definite 'thing.' The incoming nerve currents have by the law of diffusion to go somewhere and the connections which have been made in the past are largely with cell actions corresponding to feelings of 'things.' So ink blots made at random often strike the observer as pictures of real objects; the clouds take on animal forms; there is a man in the moon ; the wind in the trees is heard as a 'sighing.'

The Influence of the General Set of the Mind.— Three special forms of the influence of the general set of the mind, of the mental context in which the percept is felt, are so important as to deserve formulation as special laws. The first and most general is the Law of Relativity, that any stimulus will be felt, not as it would be if by itself alone, but in comparison with the sensations and percepts which accompany or precede it. Thus a gray on a black background will look whiter than when on a white background; a one-pound weight added to a pound will be felt as an increase, but will not when added to a

hundred pounds. The second and third laws refer to special cases of the law of relativity. The Law of Diminishing Returns from increases in the amount of a stimulus (Weber's law) is that the same stimulus will produce a more intense sensation when added to a weak stimulus than when added to a strong one. Under this law belongs the case of the pound weight. Similarly an inch more makes 2 inches perceptibly longer, but adds little feeling of length to ten feet; it is easy to distinguish a three candle power lamp from a two candle power lamp, but between a two hundred and three and a two hundred and two candle power lamp practically no difference can be felt. The Law of Contrast is that one sensation or percept felt with or after another tends to take on the quality opposite to or complementary to that other. When the other is felt with it, we have Simultaneous Contrast; when the other is felt before it, we have Successive Contrast. Thus the gray on a black looks whiter and on a white blacker than it would by itself; a candle light looks brighter in the dark than in daylight; a tone seems lower after a high than after a low one; lemonade tastes sweeter after vinegar than after honey; a gray on red looks greenish; on blue, yellowish; and on green, reddish.

Percepts, Illusions and Hallucinations. It follows from the facts so far stated that the same general process causes percepts, illusions and hallucinations. When the word beautiful is spoken and heard, hearing it is called a percept; when dutiful is spoken but beautiful heard, hearing it is called an illusion; when nothing is spoken (as in a dream) but beautiful is heard, hearing it is called an hallucination. In all three cases the same final brain process was aroused, the difference being that in the first case one afferent process excited it, in the second a slightly different process, and in the third no afferent process at all