Margaret Floy Washburn
Vassar College
The construction of an hypothesis can never give the same repose and satisfaction to the scientific conscience as does the discovery of even a moderately significant fact. And hypothesis-building brings with it the less sense of solid accomplishment, the more its results are removed from the actual test of fact. Hence the person who tries to erect a theory as to what occurs in the nervous system, in connection with any processes less amenable to experimental conditions than scratch reflexes, is not likely to feel a gratification proportionate to his pains. And yet a consistent theory of the physiological processes underlying the higher mental processes would be of some practical value, even though it could not be tested by physiological experiment. For a coherent presentation of the facts demands some principle of explanation, and the laws of learning, which lie at the bottom of the complexer processes of mind, suggest certain physiological assumptions which logically demand to be followed out and elaborated into a complete physiological theory.
The present paper aims to suggest an hypothesis regarding the nature of some essential features in the nervous process underlying the production of a mental image, a revived or centrally excited mental process. Since the leading part in such processes, according to this theory, is played by the initiation of movements that are not fully carried out, it may be termed the theory of incipient motor processes. As a preliminary to consideration of the image, we may discuss the physiological nature of the associative processes in general.
There are grounds for thinking that to that form of association which has traditionally been called the association of ideas, the association of movements is preliminary. In the so-called association of ideas we have called into consciousness
( 377) the image of a past experience. If stimulus A and stimulus B have at some former time been experienced together, the occurrence of A `makes us think of B; that is, calls up a mental image or centrally excited sensation of B. There are two reasons, at least, for believing that a more primitive process than this is to be found in the type of association whereby, stimulus A comes to produce the movement which formerly resulted from stimulus B, rather than an image of stimulus B. These two reasons are as follows. First, among the lower animals we have constant proof that one stimulus may through being repeatedly experienced in connection with another, come to assume the motor tendencies of the other; but we have very limited evidence of the occurrence in the animal mind of the associative production of images. Secondly, in the human mind, the association of images rests absolutely upon attention. Not the fact that the stimuli A and B occur together gives to A the power of calling up an image of B, but the fact that the two are attended to together. And whatever else attention may mean, the fact is reasonably certain that simultaneous attention to two things means a simultaneous motor response to them. The dependence of association upon attention, an essentially motor phenomenon, becomes comprehensible if we think of association as being itself primitively an association of movements.
Let us then first consider the processes by which stimuli come to be associated with new movements. We shall use in this consideration four fundamental physiological assumptions, all of which have some warrant from the facts discovered in experiments on simple reflexes.