Before proceeding to discuss the process of trial and error learning, however, we should consider certain other mechanisms of neural impression, real or alleged. We have seen in the preceding chapter that the cerebral cortex is presumably able to receive and to retain impressions of exact patterns of afferent nerve excitation without linking these impressions or excitations with any particular motor innervations or reactions. The simplest kind of learning would seem to consist in the mere recording of such patterned impressions upon the cortex. Such learning does not involve the formation of habits and, in itself, cannot be detected by purely behavioristic observations. A large part of what passes for education consists in the laying down of purely afferent records of this sort, which never express themselves in the behavior of the individual. Their failure to gain such expression results from the fact that they have no natural relationship to the principles of motor control. In order for such "expression" to appear, an arbitrary association must be established between the afferent patterns and particular efferent ones. The means by which such connections are made constitute our most interesting problem. The laying down of afferent records in the cerebral cortex may be attributed to the principle of exercise or the opening up of a certain pathway as a consequence of the mere incidence of nervous energy.
The conception of learning which predominates both in common sense discussion and in psychological research is that of the process by which particular kinds of motor reaction become connected with specific stimuli. There is one case in which this can apparently be accomplished by the mere formation of an afferent excitation record. This is the case of the generation of a conditioned reflex. We assume in the beginning that there is an hereditary connection between a certain stimulus and a particular reaction. Then a purely afferent process can lay down a patterned record in the cerebral cortex which simultaneously involves or includes as parts, first, the innately operating stimulus in question and, second, certain other stimulus factors. The pattern which is thus formed makes it possible for the new afferent or sensory component to set off the efferent reaction because it has become associated with an afferent element which already has this specific motor connection. In this process, it is unnecessary to form any new liaison between the afferent and efferent sides. Learning in accordance with this principle plays a very important part in the development of response in the individual.
Another aspect of learning which is emphasized in popular thought seems to have a purely efferent character: the acquisition of skill. Such acquisition involves the perfection of incito-motor mechanisms and their accessories. However, it is to be doubted whether this process is ever exclusively efferent in nature. Certain kinds of skill very obviously involve the evolution of a close coördination between sensory and motor factors as, for example, in marksmanship. In other cases, as in playing a musical instrument, --without reference to a score--the mechanism may seem to be exclusively motor, but closer examination shows that it actually involves proprioceptive and tactual afferent nerve currents, in an intimate manner. When these afferent impulses are eliminated, the reactions become impossible. The skill of a white rat in running a maze is independent of visual, auditory or olfactory stimuli, but is believed by Watson to rest upon proprioceptive or kinaesthetic impressions; and in such case, is not an exclusively motor acquisition.
In the case of human beings, there are certain supposed methods of establishing specific response, or particular connections between stimuli and motor reactions which do not seem to follow the plan of trial and error learning, as observed in animal experimentation. One of the commonest methods of attempting to establish habits in children is that of verbal instruction, command, or "telling them what to do." The principle of this form of teaching appears to be as follows. First, certain words must be associated with the stimulus and with the reaction, respectively, so that the individual "knows the meanings of the words." Second, a sentence in the form of an admonition or command, is presented to the "pupil," which links together the name of the stimulus with that of the reaction. There must, also, as a rule, be a name for the individual who is being instructed and this must be included in the instructions. Ordinarily this name is "you."
Sometimes this verbal method of establishing a reaction appears to be very effective. Its effectiveness may be a measure of what we call the "suggestibility" of the individual, that is his tendency to be governed in his behavior by verbal formulae. However, in the case of children-and, particularly, very young children--the method is singularly ineffective. It obviously cannot be applied to infants or those who are incapable of appreciating the significance of words, because they have never successfully associated them with objects, situations, or the like. But, even when the instructions are "understood," it is ordinarily necessary to add further verbal formulae, which usually take the form of promises or threats, representing some sort of reward or punishment. Even with these accompaniments, the instructional method may fail entirely.
It is evident that the basis of this most commonly accepted method of human control is rather complicated and depends upon the establishment of a considerable amount of "experience," in the form of associations, before it can become at all effective. Consequently, we shall be justified in postponing a detailed analysis of this scheme until we have arrived at a satisfactory explanation of a means for teaching which will apply to infants or to animals.
Another somewhat more primitive device, which has been used somewhat successfully with animals, but with considerable less success in the case of children, is that of forcibly putting the organism through the movements, which it is desired to have executed, while in the presence of the appropriate stimuli. Thus, we may endeavor to teach an animal how to get out of a problem box, by dragging it or leading it to the right part of the box and then manipulating its limbs so that it operates the latch or other releasing device. As a rule, this scheme is not very effective, because the associations which it establishes in the animal or child are quite different from those which are desired by the instructor. The difficulty is that we may not be able to secure active motor innervations through the cortical centers, corresponding to the forced postures or movements. Even the proprioceptive currents which arrive at the cortex will not be the same as those which would be generated if the movements were active, instead of being passive. Nevertheless, there may be some degree of similarity between the proprioceptive impulses in the two cases, which will serve to aid in the establishment of the desired interconnections between afferent and efferent activities.
This leads us to consider the interesting relationship which necessarily exists between proprioceptive and the corresponding efferent nerve currents. On account of the nature and location of the proprioceptors, they must be set off in patterns of excitation which correspond with the form of the given motor innervation. These proprioceptive configurations arrive, in most cases, at the cortex while the motor innervations are still operative. Consequently, an association will inevitably be established between each specific form of motor incitation and the corresponding proprioceptive, afferent pattern. It is, undoubtedly, for this reason that the proprioceptive configurations become the keys to the selection of particular kinds of movements, from the afferent side. Just as soon as the organism begins to experiment with its motor apparatus, it starts to lay down proprioceptive or kinaesthetic records in the cortex, which may be presumed to have afferent-efferent connections with the corresponding motor incitations. Thus, it has ready for use by the more advanced forms of learning, a repertory of afferent cortical neurograms which are in dynamic correspondence with an equal number of motor control systems.
Two other methods of learning or teaching which are commonly employed in human education are those of imitation and reasoning, respectively. Imitation involves the duplication of movements which are seen or otherwise represented in a non-motor fashion (possibly only by verbal description), and therefore requires a relatively direct translation of afferent patterns to efferent ones. This may possibly take place through the intermediation of proprioceptive or kinaesthetic factors. Learning in this manner has been noted among the lower animals as well as in men. It is particularly frequent in the case of apes, and evidently plays a part in the fixation of characteristic songs in birds. Like the other popularly considered methods of instruction, the neurological basis is complex and consequently we must postpone its detailed consideration. Learning by reasoning is the most complex of all of the methods by which we perfect our forms of response. This method seems to be a peculiarly human device, which is probably due to the fact that it depends essentially upon language or symbolism. We shall consider some details of the process at the appropriate point in our argument.