This interweaving of the instinctive reactions of the body with conscious life is of the greatest practical significance. However well adapted the inherited reflexes may be to the purpose of keeping the young animal alive, they are very insufficient in meeting the ever growing complications of life. And they are not perfect even in the beginning. A reflex is the response to a present and direct impression upon the organism; but very similar impressions may come from things of different properties. Poisonous substances often look and taste like articles of food. The enemy assumes the attitude of a friend welcoming you. Reflex action is powerless to give the organism the protection needed in such cases. Instinct is easily deceived. But as soon as the harmful consequences impress themselves upon the organism, the instinct is modified, and in the future these consequences will be avoided. The instincts are ready-made institutions intended to be applied to average conditions. Their readiness and completeness is in so far of inestimable advantage to the organism. If it had to learn everything necessary for life, it could not survive. But for the manifold deviations of the external world from the average no provision can be made in this manner.
The variation of the organism’s response is made possible by the existence of higher nerve centers, that is, of connecting neurons of a higher order, more remote from the sensory and motor points of the body. Let us imagine the proverbial reaction of a child to the sight of a flame, and discuss the successive stages of development by the help of figure 15. (1) The visual stimulation starts a nervous process from s1, which passes through the bulb and spinal cord into the muscles of the arm at m1. A small part of the current may branch off at a and, instead of passing down towards b, take the direction of v. But the resistance in this direction is for the present so high that only an insignificant part of the process can take this way, and so no corresponding motor response is noticeable.
(2) While all this is still going on and the child’s arm is still moving forward, the heat of the flame acts as a pain stimulus at s2. The nervous process produced passes over c and d to the muscles at m2, whose contraction results in the arm’s being pulled back. This results in a third stimulation at s3, which we need not trace farther here. But not the whole of the nervous process passes from c down to d. A part of it, of considerable absolute magnitude because of the intensity of stimulation, passes from c up to p and thence over k down to d and finally also into m2. This process going from p to k, according to a general law of nervous activity, tends to attract other, weaker nervous processes, if the neuron connections make this possible. Consequently the nervous process from s1 to a is now turned mostly into the path a-v-p and only an insignificant part of it continues to go from a towards b. The consequence is that the resistance of the path a-v-p-k-d is soon reduced to less than the resistance of the path a-b. The great significance of this fact becomes clear in the third stage of development.
(3) At some later time the flame again acts as a visual stimulus. But now, because of the change of resistance just explained, the nervous process takes for the most part the path over a-v-p-k-d, and the reaction follows at m2 instead of at m1. The child has learned to avoid the flame. The child, when seeing the flame, is conscious of the pain, as imagery, without having to receive the actual stimulation at s2.
Thus the inflexible regularity of reaction gives place to another type of reaction, an adaptation, not only to those conditions which at the time make their impression upon the organism, but also to those conditions which are mere future possibilities. The experience of the past guides the organism into the future.
QUESTIONS
117. What is the twofold connection into which instinctive movement enters with consciousness?
118. Why is the movement of a billiard ball often accompanied by movements of the players or spectators?