Instinct and the Unconscious. W.H.R.Rivers
expression is given by Fechner's formula that the sensation is proportional to the logarithm of the stimulus. Any such exact relation is wholly absent in the case of protopathic sensibility, in the reactions of the "extensor-thrust" or the mass-reflex, and similarly, there is no such exact relation between the conditions setting an instinctive or emotional reaction into being and the strength of the reaction, at any rate in the child, or in the adult human being whose emotions have not been brought well under control by long training and practice.
The Fechner formula has been supposed to hold good of one affective state. It has been pointed out that the amount of pleasure derived from an accession of fortune stands in a definite relation to the fortune we already possess. A gift of half-a-crown will have a very different effect on a beggar and on a millionaire, and it has been supposed that this relation is subject to logarithmic expression; that equal increment of good fortune produce steadily decreasing increments of pleasure. Even if this law could be shown to apply with any degree of exactness, it conceals a highly-developed aspect of the affective life, one in which the crude emotional basis has been elaborated by the addition of highly complex intellectual factors. The states of pleasure and displeasure, at any rate in their more customary forms, are definitely graded. From the point of view here put forward, they must be regarded as states in which the crude emotional basis has undergone great development under the influence of individual experience. The nature of pleasure and displeasure, as well as the relation between what have been called physical and moral fortune, show a certain amount of definiteness of relation between stimulus and affect. This definite and even quantitative relation is not true of the cruder [p. 48] passions which I connect with the instinctive behaviour of the man, and still less is it true of the passions of the child. Here there is not even an approach to any exact proportionality between the fear or other emotion and the condition or conditions by which the emotion has been produced.
I have chosen the "all-or-none " principle and the absence of the relation expressed by Fechner's formula as my examples of the kinds of character by which we may distinguish different forms of instinctive behaviour, because they furnish differences which are capable of exactness of expression and even of measurement. Another character, common to emotive reactions, to protopathic sensibility and to the forms of reflex action I have considered, is their immediate, and as it were unreflective, character. It is characteristic of emotion that it flares up at once and leads immediately to the behaviour characteristic of it. When, on the other hand, the crude affective tendencies which I associate with instinct have been brought under control, and even brief reflexion becomes possible, the emotion will only come into being if the conditions tending to produce it have such force as to sweep before them with their flood the obstacles interposed by intelligence. Similarly, it is characteristic of the reactions of protopathic sensibility that they tend immediately to result in movements approaching in nature those of reflex action, and are quite beyond the control which we normally exert over our more reasoned movements. One of the first signs of the return of the later epicritic sensibility is that this urgency goes, so that stimulation is followed by movements which are adapted to the nature of the stimulus.
I propose, therefore, to adopt as the distinguishing marks of one class of instincts: firstly, the absence of exactness of discrimination, of appreciation and of graduation of response; secondly, the character of reacting to conditions with all the energy available; and thirdly, the immediate and uncontrolled character of the response. It is interesting to note that Head and Gordon Holmes have found these characters to hold good in large measure of the activity of the optic thalamus, the essential nucleus of which they have shown to be the central [p. 49] representative of the protopathic aspect of peripheral sensibility and the central basis of emotive reactions. As I have already pointed out, it is clear that in this case we have to do with a structure which has come down from an early stage of the development of the nervous system. The optic thalamus is now hidden sway in the interior of the brain, overlaid and buried by the vast development of the cerebral cortex. Just as I have supposed that emotive and instinctive reactions are buried within the unconscious, hidden from consciousness by the vast development of those reactions which are associated with intelligence, so do we find that the organ of the emotions and instinctive reactions has been buried under the overwhelming mass of the nervous structure we know to be pre-eminently associated with consciousness.
It is interesting to note that the line of argument which I have followed has brought us to the view of Lloyd Morgan that instinct is the product of subcortical activity, but with the very important difference that I regard such structures as the thalamus as the organs only of certain forms of instinct, and have attempted to distinguish these forms of instinct by means of definite characters of the mental processes involved, and of the behaviour by which the instinct becomes manifest.
It must be remembered that this attempt to mark off one kind of instinctive behaviour by its psychological character has been based almost entirely on the study of human behaviour. It is now necessary to consider briefly how far these distinctions apply to the behaviour of those animals we have come to regard as our patterns of the instinctive. It is quite clear that the characters which I have taken as the special marks of certain instinctive aspects of human behaviour do not apply to those actions which are universally regarded as characteristic forms of the instinctive behaviour of the insect. It is certain that the "all-or-none" principle does not hold good of the activity of the bee when constructing the cells of the honeycomb, nor even the cruder art of such an animal as the grub of the Capricorn beetle which I have cited as a typical example of innate behaviour. The actions of these animals, certainly those of the [p. 50] bee, require in large measure the fine discrimination and delicacy of adjustment which remind us of epicritic rather than of protopathic sensibility. The way in which an insect will often carry out a set of activities dependent on its inherited tendencies when the external conditions are different from the ordinary, thus depriving these activities of all value, may perhaps be regarded as a sign that the insect is subject in some measure to the working of the "all-or-none" principle, but this is something different from the nature of the reactions themselves.
If we were to take the characters I have considered as marks of certain forms of instinct, it is evident that the behaviour of the insect could not be thus explained, but that some other principle must be in action, giving to its behaviour the power of discrimination and graduation of response. The lines taken by the development which has conferred this power are probably widely different from those which have been followed in the case of the vertebrata. The vast difference between the nervous system of an insect and that of a vertebrate animal would lead us to expect a correspondingly wide difference in the nature of the controlling and graduating mechanisms of the two kinds of animal. If the views here put forward seem worthy of adoption as a working hypothesis by students of insect-behaviour, it will become their business to seek out the nature of the controlling and graduating mechanism by which the originally crude modes of response of the insect have been modified and regulated.
I have in this chapter attempted to show that it is possible to distinguish two kinds of instinctive behaviour according as they do or do not exhibit certain characters. The characters which I have used as a means of distinguishing the instincts which are especially obvious in the innate behaviour of Man resemble in many respects the characters of protopathic sensibility, of a person who is dependent on the activity of the thalamus or of the isolated spinal cord, and in the domain of pure physiology the characters of the isolated nerve and of the heart. The discriminative and graduated activity of the more elaborate instinct of the insect, and also of certain forms of innate behaviour in Man, resemble in its general nature the [p. 51] epicritic sensibility of the skin and the activities of the body generally when fully under the influence of the cerebral cortex. It will be convenient to have terms for these two different kinds of instinct and instinctive behaviour, and I propose that they shall be named after the two kinds of characters which, through the work of Head, can be recognised in cutaneous sensibility. I shall, therefore, in this book, speak of instinctive behaviour as protopathic or epicritic according as it is or is not subject to the "all-or-none" principle, and according as it is not or is capable of graduation in relation to the conditions which call it forth.
Footnotes