Learning is continuous with growth

While we are accustomed to distinguish rather sharply between those reactions of the organism which are due to organic growth and maturation and those which are due to environmental experience and learning, this is, of course, an artificial dichotomy. The developmental growth of organisms in embryo is not a mere unfolding from within of potentially contained characteristics. It takes place under the conjoint action of external and internal agencies. There is no sharp break in these developmental mechanics at birth, but in the wider environment to which the organism is now exposed external agencies exert a greater influence in modifying the course of development than heretofore. If we wish to refer to the later modifications as learning, we must be clear, at the very outset, with regard to their essential continuity with growth. Development is a process of functional construction; that is, beginning with a given structure and function, continuance of function modifies the structural substratum, and this in turn modifies further function, and so on. Growth (in so far as it produces structuro-functional development in distinction to mere increase in the size of a structure) and learning seem, therefore, to be one and the same process. It is merely for convenience that we set apart the later phases of this process and refer to them as learning. The physiological problem involved has as its ultimate basis a further understanding and extension of principles which will account for the modifications of neural tissue in embryo.

To affirm that learning is continuous with growth does not, of course, constitute either a physiological or a psychological description of the complex modifications in behavior brought about largely by external stimulation. But it does give us a degree of confidence in dealing with these modifications systematically. Because so much has been said and written of the learning process, one sometimes gets the impression that it is the central, almost the only, problem of psychology. As a result of such undue emphasis innumerable "theories of learning" have been built upon special details of behavior, without recognition of a common thread. Each of these theories was first presented as a description of modifications produced in a special type of learning experiment and then was developed as an explanation of all learning. This transfer from description to explanation naturally led to hypothetical principles, and the pages of our scientific journals are filled with the arguments of the counter schools; for instance, the trial and error theory is contrasted with the conditioned reflex theory and with the configural theory.

To consider the merits and defects of such formulations is part of our problem, but a resume of the nature of learning and of the organic changes involved is first indicated. Experiments on the problems of learning can be conveniently grouped into a few major types. There are: (1) studies of the general characteristics of learned response and (2) studies of the conditions under which learning occurs. These provide the bulk of the material upon which theories of learning are usually based. Equally important from the physiological standpoint, however, are: (3) studies of the relation of learning to neural structure, including those on localization of the engram, (4) studies of changes in the pattern of the postural substrate which accompany learning, and (5) studies in the transfer of learning. After taking up these several problems in order, we shall consider the major theories of learning, especially as they apply to the nervous system.