of the central nervous system it is almost impossible to state. All the different parts of the cortex seem to be involved in everything that happens. All the stimuli that reach the brain are reflected into all parts of the brain, and yet we do get a unitary action. There remains, then, a problem which is by no means definitely solved: the unity of the action of the central nervous system. Wundt undertook to find certain centers which would be responsible for this sort of unity, but there is nothing in the structure of the brain itself which isolated any parts of the brain as those which direct conduct as a whole. The unity is a unity of integration, though just how this integration takes place in detail we cannot say.
What I wanted to bring out is that the approach to psychological theory from the standpoint of the organism must inevitably be through an emphasis upon conduct, upon the dynamic rather than the static. It is, of course, possible to work in the other direction, that is, to look at experience from the point of view of the psychologist and to draw conclusions as to what must go on in the central nervous system. It is possible to recognize, for example, that we are not simply at the mercy of the different stimuli that play in the central nervous system – the natural view of the physiologist. We can see these organs adjust themselves to different types of stimuli. When air waves come in they affect the particular organs of the ear; when tastes and odors come in the stimuli get to tracts in the proper organs that respond. There may seem to be merely a response of the organism to the stimuli. This position is taken over into the psychology of Spencer, who accepted the Darwinian principle of evolution. The influence of environment is exercised over the form, and the adaptation of the form results from the influences of the environment on it. Spencer conceived of the central nervous system as being continually played upon by stimuli which set up certain paths, so that it was the environment which was fashioning the form.
The phenomena of attention, however, give a different picture of conduct. The human animal is an attentive animal, and his attention may be given to stimuli that are relatively faint. One can pick out sounds at a distance. Our whole intelligent process seems to lie in the attention which is selective of certain types of stimuli. Other stimuli which are bombarding the system are in some fashion shunted off. We give our attention to one particular thing. Not only do we open the door to certain stimuli and close it to others, but our attention is an organizing process as well as a selective process. When giving attention to what we are going to do we are picking out the whole group of stimuli which represent successive activity. Our attention enables us to organize the field in which we are going to act. Here we have the organism as acting and determining its environment. It is not simply a set of passive senses played upon by the stimuli that come from without. The organism goes out and determines what it is going to respond to, and organizes that world. One organism picks out one thing and another picks out a different one, since it is going to act in a different way. Such is an approach to what goes on in the central nervous system which comes to the physiologist from the psychologist.
The physiology of attention is a field which is still a dark continent. The organism itself fits itself to certain types of conduct, and this is of considerable importance in determining what the animal will do. There also lie back in the organism responses, such as those of escape from danger, that represent a peculiar sensitivity. A sound in some other direction would not have the same effect. The eye is very sensitive to motions that lie outside of the field of central vision, even though this area of the retina of the eye is not so sensitive to form and distinctions of color. You look for a book in a library and you carry a sort of mental image of the back of the book; you render yourself sensitive to a certain image of a friend you are going to meet. We can sensitize ourselves to certain types of stimuli and we can build up the sort of action we are going to take. In a chain set of responses the form carries out one instinctive response and then finds itself in the presence of another stimulus, and so forth; but as intelligent beings we build up such organized reactions ourselves. The field of attention is one in which there must be a mechanism in which we can organize the different stimuli with reference to others so that certain responses can take place. The description of this is something we can reach through a study of our own conduct, and at present that is the most that we can say.
Parallelism in psychology was very largely under the control of the study of the central nervous system, and that led on inevitably to functional, motor, voluntaristic, and finally behavioristic psychology. The more one could state of the processes of the individual in terms of the central nervous system, the more one would use the pattern which one found in the central nervous system to interpret conduct. What I am insisting upon is that the patterns which one finds in the central nervous system are patterns of action – not of contemplation, not of appreciation as such, but patterns of action. On the other hand I want to point out that one is able to approach the central nervous system from the psychologist's point of view and set certain problems to the physiologist. How is the physiologist to explain attention? When the physiologist attempts that he is bound to do so in terms of the various paths. If he is going to explain why one path is selected rather than another he must go back to these terms of paths and actions. You cannot set up in the central nervous system a selective principle which can be generally applied throughout; you cannot say there is a specific something in the central nervous system that is related to attention; you cannot say that there is a general power of attention. You have to state it specifically, so that even when you are directing your study of the central nervous system from the point of view of psychology, the type of explanation that you are going to get will have to be in terms of paths which represent action.
Such, in brief, is the history of the appearance of physiological psychology in its parallelistic form, a psychology which had moved to the next stage beyond that of associationalism. Attention is ordinarily stressed in tracing this transition, but the emphasis on attention is one which is derived largely from the study of the organism as such, and it accordingly should be seen in the larger context we have presented.
5. PARALLELISM AND THE AMBIGUITY OF »CONSCIOUSNESS«
»Consciousness« is a very ambiguous term. One often identifies consciousness with a certain something that is there under certain conditions and is not there under other conditions. One approaches this most naturally by assuming that it is something that happens under certain conditions of the organism, something, then, that can be conceived of as running parallel with certain phenomena in the nervous system, but not parallel with others. There seems to be no consciousness that answers to the motor processes as such; the consciousness we have of our action is that which is sensory in type and which answers to the current which comes from the sensory nerves which are affected by the contraction of the muscles. We are not conscious of the actual motor pocesses, but we have a sensory process that runs parallel to it. This is the situation out of which parallelistic psychology arises. It implies on the one side an organism which is a going concern, that seemingly can run without consciousness. A person continues to live when he is under a general anesthetic. Consciousness leaves and consciousness returns, but the organism itself runs on. And the more completely one is able to state the psychological processes in terms of the central nervous system the less important does this consciousness become.
The extreme statement of that sort was given by Hugo Münsterberg. He assumed the organism itself simply ran on, but that answering to certain nervous changes there were conscious states. If one said that he did something, what that amounted to was a consciousness of the movement of the muscles of his body in doing it; the consciousness of the beginning of the act is that which he interpreted as his own volition to act. There is only a consciousness of certain processes that are going on. Parallelism in this extreme form, however, left out of account just such processes as those of attention and the selective character of consciousness. If the physiologist had been able to point out the mechanism of the central nervous system by which we organize our action, there might be still dominant such a statement in terms of this extreme parallelism which would regard the individual as simply conscious of the selection which the organism made. But the process of selection itself is so complex that it becomes almost impossible to state it, especially in such terms. Consciousness as such is peculiarly selective, and the processes of selection, of sensitizing the organ to stimuli, are something very difficult to isolate in the central nervous system. William James points out that the amount of difference which you have to give to a certain stimulus to make it dominant is very slight,