From the point of view of physiology, the process of habit-formation consists in securing a particular nerve coupling, establishing a particular nerve path, so that a definite form of stimulation will bring about a definite form of response. A nerve tendency is simply the likelihood that a stimulus will take a certain course rather than any other. This likelihood is brought about by getting the stimulus to take the desired route through the nervous system to a group of muscles and to continue following this route. The more times it passes the same way, the greater is the probability that at any given time the stimulus will take the accustomed route and bring about the usual response. At first any sort of action is possible. A nerve stimulus can take any one of the many routes to the different muscles. By chance or by conscious direction, the stimulus takes a certain path, and by repetition we fix and make permanent this particular route. This constitutes a nerve tendency or habit.
Plasticity. Our discussion should have made it clear that habit is acquired nature, while instinct is inherited nature. Habit is acquired tendency while instinct is inherited tendency. The possibility of acquiring habits is peculiarly a human characteristic. While inanimate things have a definite nature, a definite way of reacting to forces which act upon them, they have little, if any, possibility of varying their way of acting. Water might be said to have habits. If one cools water, it turns to ice. If we heat it, it turns to steam. But it invariably does this. We cannot teach it any different way of acting. Under the same conditions it always does the same thing.
Plants are very much like inanimate things. Plants have definite ways of acting. A vine turns around a support. A leaf turns its upper surface to the light. But one cannot teach plants different ways of acting. The lower forms of animals are somewhat like plants and inanimate objects. But to a very slight extent they are variable and can form habits. Among the higher animals, such as dogs and other domestic animals, there is a greater possibility of forming habits. In man there are the greatest possibilities of habit-formation. In man the learned acts or habits are many as compared to the unlearned acts or instincts; while among the lower animals the opposite is the case—their instincts are many as compared to their habits.
We may call this possibility of forming habits plasticity. Inanimate objects such as iron, rocks, sulphur, oxygen, etc., have no plasticity. Plants have very little possibility of forming habits. Lower animals have somewhat more, and higher animals still more, while man has the greatest possibility of forming habits. This great possibility of forming habits is one of the main characteristics of man. Let us illustrate the contrast between man and inanimate objects by an example. If sulphur is put into a test tube and heated, it at first melts and becomes quite thin like water. If it is heated still more, it becomes thick and will not run out of the tube. It also becomes dark. Sulphur always does this when so treated. It cannot be taught to act differently. Now the action of sulphur when heated is like the action of a man when he turns to the right upon meeting a person in the street. But the man has to acquire this habit, while the sulphur does not have to learn its way of acting. Sulphur always acted in this way, while man did not perform his act at first, but had to learn it by slow repetition.
Everything in the world has its own peculiar nature, but man is unique in that his nature can be very much changed. To a large extent, a man is made, his nature is acquired. After we become men and women, we have hundreds and thousands of tendencies to action, definite forms of action, that we did not have when young. Man’s nature might be said to consist in his tendencies to action. Some of these tendencies he inherits; these are his instincts. Some of these he acquires; these are his habits.
What Habits Do for Us. We have found out what habits are like; let us now see what they do for us. What good do they accomplish for us? How are we different after forming a habit from what we were before? We can best answer these questions by a consideration of concrete cases. Typewriting will serve very well the purpose of illustration. We shall give the result of an actual experiment in which ten university students took part. During their first half hour of practice, they wrote an average of 120 words. At the end of forty-five hours of practice, they were writing an average of 680 words in a half hour. This was an increase of speed of 560 per cent. An expert typist can write about 3000 words in a half hour. Such a speed requires much more than forty-five hours practice, and is attained by the best operators only.
Figure III.—Learning Curves
The upper graph shows the improvement in speed of a group of students working two half hours a day. The lower curve shows the improvement of a group working ten half-hours a day.