An Introduction to Comparative Psychology
Chapter 2: The Physiological Conditions of Consciousness
C. Lloyd Morgan
IT is now a matter of familiar knowledge that the living body contains, and is largely composed of, a complex substance or, group of substances called protoplasm, which is found in all the tissues, such as muscle, bone, or nerve. The protoplasm is found in minute particles of various shapes, termed cells ; and of these -cells or their products all parts of the body are formed. Within the cells, during life, chemical changes of a special and complicated nature take place; and associated with these chemical changes there are transformations of energy, of great delicacy and complexity. But notwithstanding the special nature of the protoplasmic substance, and the complicated character of the -ceaseless transformations of energy, it nevertheless remains true that, so far as the body is concerned, all that it does or suffers belongs to the category of occurrences in the material world, -the world with which physical and physiological science have to deal. From the physical point of view life is an orderly, or perhaps we had better say co-ordinated, sequence of transformations of energy. In the living body a particular kind of matter is thrilling with a peculiar and complex series of molecular changes. The special conditions under which a living organism continues to perform its proper activities are sometimes spoken of as the conditions of vitality.
When the body dies nothing material is taken from it, but the orderly sequence of transformations of energy ceases. The co-ordinated chemical and physical changes which are
(25) characteristic of life stop ; the movements are no longer seen, the conditions of vitality no longer obtain. For a while the substance seems to undergo no obvious change, but then decay sets in ; the elaborate chemical materials undergo decomposition, and the body moulders away. The products of this decomposition are still material ; and' the mouldering of the body neither adds anything to, nor takes anything from, the world's store of matter. And though the orderly sequence of transformations of energy ceases at death, and gives place ere long to the new series of changes which accompany decay, nothing is abstracted from the world's store of energy, nothing annihilated. The death of the body is a change of state or condition of its substance, and its decay is a further change of state or condition of its constituent molecules. Thus the living body, so far as its matter and its energy is concerned, belongs to the physical world.
Accompanying some of the transformations of energy, or molecular changes in the body or some part of it, there are states of consciousness. These must be carefully distinguished from occurrences in the physical series of events. Imagination and fancy, love and hate, shame and remorse, admiration and pity, judgment and inference,--these are psychical states, not physical events. Each of us experiences them for himself. However convinced I may be that my neighbour experiences states of consciousness similar to those of which I am myself aware, I have no direct and immediate acquaintance with any consciousness but my own. It is with such states of consciousness that psychology has to deal. Rut inasmuch as these psychical states are associated with a physical organism, comparative psychology must pay attention to the nature and conditions of the association.
Grouping together sequent states of consciousness under a comprehensive term antithetical to " the body,'' we fre-
(26) -quently speak of them as pertaining to " the mind." What is this mind ? The answer of empirical psychology to this question is : The wave of consciousness constitutes the mind. From other standpoints this answer may be imperfect or incomplete, but for descriptive or empirical psychology it is sufficient. All that we have direct experience of is the psychical wave in the moment of consciousness. When once it has passed, any particular phase of the psychical wave has no more existence than last year's roses, or than the air waves started by my voice five minutes since. Its effects may remain, but itself has ceased to exist.
Of course, in reflection on my own past life, and on the lives of those around me, I apply the term " mind " not merely to the psychical wave at any moment of consciousness, but to the wave of consciousness in its totality. I thus speak of the products of Shakespeare's mind, the development of my children's minds, the depravity of Nero's mind, and so forth. There is nothing in this usage, however, at variance with the view that the wave Of consciousness constitutes the mind, and that when the moment of consciousness has passed, the particular phase of the psychical wave which constituted the. mind at that moment has no longer any existence, though its effects may remain.
We sometimes speak of ideas being retained in or by the mind. But it is clear that on the psychological view here put forward, this is not an accurate mode of expression, though it suffices for the needs of practical intercourse. Ideas cannot be retained in or by phases of the wave that have ceased to exist. Nor assuredly are there retained in any existing phase all the ideas of all pre-existing phases. Were this so, the wave would soon reach a state of complexity which would not only be hopelessly bewildering in the moment of consciousness, but would assuredly defy any attempt at psychological analysis. Instead of this, we have to" recall to mind" the ideas which characterised
(27) pre-existing phases. This phrase "recall to mind," seems to imply that the ideas which are thus brought to mind in remembrance have to be fetched from somewhere outside the mind. But ideas are states of consciousness. How then can they exist outside the mind ? But do they so exist outside the mind? The negative answer which we must give to this question seems a first sight to increase our difficulties, but in reality paves the way for their removal.
I said just now that when once it has passed, any phase of the psychical wave no more continues to exist, as such a phase, than last year's roses, or than the tones of my voice which made the air vibrate five minutes ago. But if the rose-tree which bore the roses shall continue to live and to flourish, fresh roses may bloom next summer; and if I and my vocal chords remain, the tones of my voice may again disturb the air. We do not say that last year's roses are retained in the rose-bush to bloom again next year; but we say that so long as the tree lives and is healthy, roses will be reproduced under appropriate conditions. So too in the case of reproduction of ideas. So long as I live and am healthy, ideas may be reproduced under appropriate conditions. In a word, we seem to be thrown back upon organic conditions as the most probable basis for an explanation of the so-called retention of ideas. The ideas as such have ceased to exist ; but the organic structure has been modified in such a way that under the needful conditions similar ideas will be again produced. The reproduction of ideas is thus, or) this hypothesis, associated with an organic process : and hence we may say that one of the conditions of the orderly manifestations of consciousness is the maintenance of the integrity of the bodily organization.
There can be little question that in man and mammal the brain, or some part of it, is the specialized seat of consciousness From all parts of the surface of the body, from eye, ear, nose, and palate, from the muscles, joints, and internal
(28) viscera, there run nerves--ingoing or afferent nerves-which eventually are in communication with the brain. These nerves are the channels along which I waves of molecular change (impulses) may be transmitted to the nerve-centres. At their outer ends there are special cells which are so delicately constituted that their molecular equilibrium is readily upset. In the retina of the eye there are cells which thrill to the impact of waves of light; in the ear are cells which respond to the sound-vibrations of the air ; in the nose and mouth are cells which have their equilibrium disturbed by the vibrations which we interpret as smells and tastes ; in the skin are cells which respond to the contact of solid or fluid bodies, and others which thrill to the stimulation of heat or cold. When any of these are stimulated, impulses are propagated along the nerves with which these cells are connected, and thus disturbances are set up in the nerve-centres of the brain. As the result of these disturbances, other impulses are transmitted down other nerves-outgoing or efferent nerves-to muscles which are thus stimulated to contraction, or to glands which are stimulated to secretion.
It is generally believed, 'as the result of many observations and experiments, that no consciousness accompanies the transmission of impulses along the nerves ; but that when the molecular thrill reaches the brain, or some part of it (probably the cerebral hemispheres), there consciousness emerges. One of the conditions of consciousness, therefore, seems to be the occurrence of certain molecular vibrations or disturbances in certain specialised nerve-centres within the cerebral hemispheres. The fact that it takes an appreciable and measureable time for impulses to be transmitted, is prettily illustrated by a series of instantaneous photographs, in Mr Muybridge's collection, of a girl pouring ice-cold water over another girl sitting in a bath. In the first photograph, the girl stands with the bucket, and is just beginning to pour. In the second photograph she has emptied the
(29) bucket. The girl in the bath is quite surrounded and covered with ice-cold water. But she has not moved a muscle. She is sitting in exactly the same attitude as in the first photograph. The ice-cold water has stimulated the nerve-ends but no contraction impulse has yet reached the muscles. In a third photograph the girl is leaping from the bath. Her face appears to be the index of somewhat forcible states of consciousness, the iced water being somewhat unexpected.
The rate of transmission of the nervous impulse has been the subject of much careful measurement. It travels along a nerve at the rate of about 100 feet in a second. But if it has to pass through the brain the rate is slower; and if there is choice involved, much slower still.
What may be the nature of the connection between the molecular changes in these nerve-centres and the states of consciousness which accompany them is a problem which has been eagerly discussed. According to the view which is. most commonly held, and which is taught to most of us in childhood, before we are at all capable of understanding the nature of the problem, the mind and the body are quite different and eventually separable existences. The body is the mere machine in and by means of which the mind works. The mind, therefore, animates the body, and plays the part of engineer to the organic engine. But during life the nature of the connection is such that the mind, though it uses and must use the body as its instrument, is constantly hampered by its association with gross matter and death at last sets free the mind or soul from the restrictions of the flesh. Now it i's not my province here to deal with this matter from any other point of view than that of empirical psychology. From this point of view the molecular changes in the nerve-centres are merely the concomitants or physiological conditions of the' mental processes. Thus in common parlance the mind is said to act upon the body
(30) through the nerve-centres, and the body to react on the mind through the same instrumentality. And if it be held that, during life, all mental processes have their physiological concomitants, it is clear that these physiological concomitants, namely the molecular changes in nerve-centres, would, if completely ascertained, afford an accurate index. of the mental processes. For psychology, then, this dualistic solution of the problem comes to this, that physiological and psychical processes are distinct and separate modes of existence, but that during life every change of the one is the strictly parallel concomitant of a change of the other.
According to another, the monistic, solution of the problem, the physiological and psychical processes, though distinguishable, are indivisible. They are not separate existences temporarily associated during life, but different ways of regarding the same natural occurrences. Whereas according to empirical dualism, the curve by means of which we might represent any given state of consciousness is precisely similar to a second curve by which we might represent those concomitant brain-changes, whatever they may be, which are assumed to be the invariable accompaniments of the state. of consciousness ; -according to monism there is but one curve, which, regarded from one aspect, is psychical, and regarded from the other aspect is physiological. It is clear that, as a matter of psychological interpretation, the differences between these two solutions, which are symbolized diagrammatically in Fig. q, are not worth quarrelling about, however important they may be as a matter of general philosophy.
Adopting this hypothesis, then, the curve which represents a state of consciousness may also be taken to represent
(31) a co-existent state of physiological change which exists coincidently in the brain. Let us however be quite clear as to what is meant by such a curve.
At any moment of our waking life there are pouring in upon the nerve-centres of the brain afferent impulses, transmitted from all the sensitive parts of the body through the ingoing nerve-channels. When these impulses reach the lower nerve-centres they are co-ordinated, and their net results are, or may be, handed on to the cerebral hemispheres, where they give rise to molecular disturbances, some of which are conscious or are accompanied by consciousness. Tile nature of these molecular disturbances, as such, it is not necessary that we should here discuss. They may be complex vibrations, unaccompanied by chemical change; more probably they involve changes of chemical state with associated transformations of energy. I shall therefore speak of these as molecular disturbances, or as transformations of
(32) energy, without attempting further to particularize their nature. One characteristic of physiological response to stimulus may however be noticed, since it serves to illustrate the physiological aspect of the wave of consciousness. It has recently been very beautifully demonstrated in the electrical discharge of the torpedo-fish, but holds good in many other cases. The result of a particular stimulus is an effect which is not instantaneous, but lasts 'an appreciable and measureable time. During this appreciable time it is not uniform in intensity, but at first rapidly increases to a maximum, and then more slowly diminishes. In other words, a graphical representation of the physiological effects of a stimulus is quite similar in general principle to the curve that I gave in Fig. I, as a longitudinal section of the wave of consciousness.
Now the mass of nerve-centres in the brain is very considerable, even if we exclude all but the highest centres of the cerebral hemispheres;. and during waking life the' amount of molecular disturbance arising from the impulses coming in through a great number of afferent nerves, which are stimulated in different degrees, must be very great. Moreover, owing to the different degrees of stimulation, and the different sensitiveness of the various parts stimulated, the molecular disturbances in the cerebral hemispheres must vary in intensity. - The higher brain-centres may be likened to a piano, in which a number of stretched wires may be set in vibration with different intensities. The keys are the sensitive ends of the afferent nerves, on which the objects round us play, now in one way and now in another. The character of the musical chords evoked will depend inpart upon which strings are set in Vitiation, and in part upon the relative intensities of the vibrations so caused; so
(33) too the character of the states of consciousness evoked ,through molecular disturbance, will depend in part upon what areas of the nerve-centres are disturbed, and in part on the relative intensities of the disturbances due to afferent impulses.
If then we could represent graphically these relative intensities of molecular disturbance in the cerebral hemispheres, we should obtain a curve of molecular disturbance, which, on the hypothesis of scientific monism, would be identical with the curve of consciousness; or, on the hypothesis of empirical dualism, would accurately correspond to that curve. The dominant disturbances would be those which are fully conscious or focal, and at a lower level on the curve would be the subdominant disturbances which are subconscious or marginal.
But it is exceedingly probable that there are disturbances in the cerebral hemispheres which, though they are of the me order as those which are conscious or subconscious, re of intensity too low to enable them to enter consciousess at all. These we may term infra-dominant. They lie in the region below the threshold of consciousness. On the hypothesis of empirical dualism, the curve of consciousness, which runs parallel with the curve of molecular disturbance down to the threshold of consciousness, there abruptly eases. But what shall we say of this infra-dominant part the curve on the hypothesis of scientific monism, according to which the curve of molecular disturbance and that of consciousness are identical, are in fact the same curve regarded from different aspects ? If we say that in this region below the threshold there is a form of consciousness which is not even marginally subconscious, we seem 'guilty of a contradiction in terms; for then we must speak of unconscious consciousness. I shall endeavour to avoid the difficulty, and to leave the matter open for future consideration, by restricting the word consciousness to that
(34) which lies above the threshold, and by speaking of that which lies below the threshold as infra-conscious. This infra-consciousness is, in my view, not merely negative,' but something positive and existent,-what, for want of better terms, we may call the not-yet or the not-quite conscious; too low in intensity or in kind to become even marginally subconscious, and yet of the same order of existence as that which lies above the threshold. But although this is my own view with regard to the infra-conscious part of the curve, the word I employ does not necessarily imply such positive existence, and may be read by those who so prefer as simply below the level at which consciousness comes into existence.
We are now in a position to give in graphic form the curve of molecular disturbance which is assumed to be identical with the curve of consciousness. At the upper
(35) part of the' curve we have the dominant molecular disturbances, which are psychically fully conscious or focal; beneath this are the sub-dominant disturbances, which are psychically subconscious or marginal ; and beneath this again are the infra-dominant disturbances which lie below the threshold of consciousness in the infra-conscious or, extra-marginal region.
Clear, full, or focal consciousness is thus, on the view here taken, the concomitant of dominant cerebral change. And now the further question arises: -What are the determining conditions of 'dominance? Obviously this question must be answered separately from the physiological and the psychological aspects. The conditions of dominance of cerebral changes, as such, is a matter of nerve-physiology, and cannot here be discussed. The conditions' of dominance of focal states of consciousness-impressions or ideas-is a matter of psychology, the discussion of which we shall take up in the fourth chapter.
Any adequate discussion of the physiological conditions of consciousness is impossible without metaphysical implications. According to current idealistic doctrine, matter is phenomenal -merely an appearance in and to consciousness. Physiological changes in the brain being thus merely phenomena], it seems ridiculous to assert that they are the conditions of consciousness. It must be remembered, however, that in the Prolegomena the strictly co-ordinate reality for experience and knowledge of the objective and subjective aspects-both phenomenal-is a cardinal tenet of the monistic view I accept. Both are equally real for practical purposes of empirical discussion. In considering the question from the physiological aspect, the practical objective reality is taken as a basis. Front the strictly metaphysical point of view the true underlying reality is tile "thing-in-itself" of which physiological and psychological happenings are the phenomenal manifestations.