Can Unconscious Cerebration be proved? By WILLIAM W. IRELAND, M.D., Edin., Medical Superintendent of the Scottish National Institution for the Education of Imbecile Children, Larbert, Stirlingshire.

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Unconscious cerebration is regarded as so important a discovery that two well-known scientific men have contended for the priority of its publication, and while some people are anxious to give it fresh applications and illustrations, others proclaim it to the public as a new demonstration of science, accepted by physiologists, and stable enough to uphold new theories founded upon it. After having carefully considered the evidence upon which the theory of unconscious cerebration is supposed to rest, I am disposed to think that the facts, or assumed facts, may be explained in a simpler manner, and that the theory itself is superfluous and unproved. For an exposition of what is understood by unconscious cerebration, and on what grounds it is believed to exist, I have used a work called, "The Principles of Mental Physiology," by Dr. Carpenter, the well known physiologist, who claims to have worked out the theory in his own mind, without knowing that any other had preceded him, and whose recognised reputation is a sufficient guarantee that the argument, in his hands, is sure of being well stated. The term itself seems far from being a happy one. Dr. Carpenter tells us that it has been found readily intelligible; he objects to "unconscious reasoning" as a contradiction in terms, and yet his own description seems either to imply unconscious reasoning, or unfelt feeling; and the difficulty of finding an appropriate term for this class of operations, is really owing to the difficulty of conceiving what these operations really are. In fact, to state them clearly, is to render the theory incredible. To call thought cerebration, may show the desire of a writer to assign thought as the product of brain action; but it is neither warranted by true philosophy, nor by the popular and scientific uses of speech. When the liver secretes bile, one does not say that it hepatates; or when a man breathes, we do not say he pulmonates.

Dr. Carpenter tells us that he was led into the train of thinking which brought him to formulate his theory by what he calls automatic motion; and it was by doubting

I have also used Dr. Carpenter's "Principles of Human Physiology." Fourth Edition, London, 1853.

the correctness of Dr. Carpenter's explanation of automatic motion that I was led to disbelieve in unconscious cerebration. This explanation may be given in his own words-as Paley says: "A child learning to walk is the greatest posture master in the world." Yet, when this co-ordination has been once established, the ordinary movements of locomotion, though involving the combined action of almost every muscle in the body, are performed automatically, the Will being only concerned in starting, directing, or checking them. Of this we have familiar experience in the continuance of the act of walking whilst the attention is occupied by some "train of thought" which completely and continuously engrosses it. Though we set out with the intention of proceeding in a certain direction, after a few minutes we may lose all consciousness of where we are, or of whither our legs are carrying us; yet we continue to walk on steadily, and may unexpectedly find ourselves at the end of our journey before we are aware of having done more than commence it. Each individual movement here suggests the succeeding one, and the repetition continues, until, the attention having been recalled, the automatic impulse is superseded by the control of the will. Further, the direction of the movement is given by the sense of sight, which so guides the motions of our legs that we do not jostle our fellow passengers, or run up against lampposts; and the same sense directs also their general course along the line that habit has rendered most familiar, although at the commencement of our walk we may have intended to take some other." It seems to me that a man who walks along a crowded street must always exercise a certain amount of attention; if he is accustomed to do so like a thoroughbred citizen, he can thread his way with much less attention than a man used to walk along quiet country roads, and consequently he is able to divert his thoughts to other subjects as he goes along, to converse with a friend, or to meditate over some difficult problem; but if the attention to the problem be too profound, the minimum of attention necessary to guide the footsteps is withdrawn, so that he will go on in a straight line without turning round the proper corner, or if the distraction be further increased, he will strike against the passers by, or perhaps stand still till his attention is again directed to the necessity of attending to his steps. We can understand how a man might perform some simple motion such as flexing or extending his legs by reflex or automatic action; but that he should walk from one part of a crowded

city to another without any exertion of conscious intelligence seems altogether unproved and unproveable.

In what we call absence of mind, the attention is so concentrated upon a single subject, or train of thought, that one loses the sense of his present situation which accompanies less intense mental action. Consciousness runs only in one channel, and we wake up as it were from a dream, when the concentration is relaxed. The amount of concentration of mind determines the amount and complexity of the physical actions which can be at the same time carried on. The concentration may be so great that the individual can execute no motion whatever; he is wrapped in a reverie, like Socrates, who stood for a whole day and night in the camp before Potidæa motionless, with his attention completely engrossed with some subject of meditation. In a lesser degree of mental attention the walk becomes slower, or more awkward than usual, or there may be even a double action of the mind; a train of thought is diligently pursued, while the motions are regulated by a loose association of ideas. Thus, there is a story told of a learned clergyman, very much given to absence of mind, who went up stairs to change his dress, previous to going out to dinner. After a while, his wife went up to see what had become of him, and found that he had taken off all his clothes, and gone to bed. In this case there were obviously two trains of thought going on in the mind; one the subject of learned contemplation, and the other the association of ideas which connected the taking off his upper garments with that of going to bed.

Dr. Carpenter talks of a man walking by reflex action "being sustained by the successive contacts of our feet with the ground, each exciting the next action;" but it is clear that, without the picture of the street or road present to the conscious mind, walking to any purpose cannot go on, the mere absence of light being sufficient to put an end to it, save in the case of blind persons, who, however, do not walk by reflex action, but depend upon the increased activity and exercise of their other senses. It is difficult to perceive what Dr. Carpenter means by the sense of light guiding the motion of our legs; for indeed sensation can be no guide. It transmits information to the mind, which makes use of it for our guidance, and if the functions of the hemispheres were suspended, and no information transmitted to the mind as to the state of the external world, the process of walking would soon cease, though all true reflex action might continue.

Here it may be noticed that the advocates of unconscious cerebration seem to ground a great many of their arguments upon the assumption that the mind can only attend to one subject at once, and if this be doubted, many of their arguments must appear inconclusive. It is generally admitted by metaphysicians, however, that the mind can attend to more than a single object at once. Sir William Hamilton's opinion, which ought to be acceptable to Dr. Carpenter,* is thus given : "You will recollect that I formerly stated that the greater the number of objects among which the attention of the mind is distributed, the feebler and less distinct will be its cognisance of each-Pluribus intentus, minor est ad singula sensus."

"Consciousness will thus be at its maximum of intensity when attention is concentrated on a single object; and the question comes to be, how many several objects can the mind simultaneously survey, not with vivacity, but without absolute confusion. I find this problem stated, and differently answered by different philosophers, and apparently without a knowledge of each other. By Charles Bonnet the mind is allowed to have a distinct notion of six objects at once; by Abraham Tucker the number is limited to four; while Destutt Tracy again amplifies it to six. The opinion of the first and last of these philosophers appears to me correct."

A man can attend to two simultanecus processes all the more easily if they are different in kind; for example, one can direct a bodily action with a purely intellectual operation more readily than he can attend to two intellectual operations. The human mind requires less attention to intellectual or muscular operations to which it is accustomed, than to those which are new, and therefore difficult, and as the effort is much smaller, the amount of attention or directed consciousness is much less; but to attempt to transmute this diminution of attention into a proof that no attention whatever is required, seems to me precisely the fallacy which underlies the whole of Dr. Carpenter's argument. We know that when a thing is once done it is easier done over again; the oftener we do it the easier; and this is true both of purely mental and of voluntary muscular operations. The easier a thing is done the more ready is the mind to forget the efforts it has made to do it; and again, great rapidity of conscious impressions is accompanied with a very faint memory of these impressions; and thoughts and volition resulting in actions

* See Sir William Hamilton's "Lectures on Metaphysics," Lecture XIV., vol. i., p. 254.

are much less readily remembered than thoughts ending in speech. To such an extent indeed is this true, that some people have actually argued that we cannot think without words. But take for example a man fencing with another. He watches his opponent's point, and his opponent's eye, and executes a series of most complicated and rapid movements of parry and thrust every instant in a different order. He interprets his opponent's thrusts or feints, parries them, and then makes lounges and feints himself. All this requires quick apprehension and thought, yet it is not translated into words. The fencer is conscious, though he is not conscious of being conscious; that is, he has no time for introspection or retrospection, and although he would be conscious of each pass, if he only made one, or stopped, or rested his consciousness on the last one which he made, he is totally unable to recall the series of motions which he has gone through; and nothing remains in his memory but one or two of the most striking incidents in the fencing, such as that he has hit his opponent several times, or has been hit himself.

The large field of wordless thought is a subject well worthy of consideration. Not only are there thoughts which die away without being translated into words, there are also thoughts which we habitually confound with sensations,* and thoughts which pass into motions without ever being expressed by symbols. These are extremely numerous, especially in the fields of technical art and action; but to follow up the subject at present would lead us into a digression. It is one of our besetting mental fallacies not only to imagine that thoughts are inseparable from words, but that where there are no words, there are also no thoughts. One thing is certain, that words add much to the clearness of our conceptions.

* Those who have not already studied the question will find examples of the play of comparison, association, ideal anticipation, judgment and inference in the use of the senses, in the "Westminster Review" for July, 1872, in an article entitled, "Recent Experiments with the Senses," and in the works there quoted, especially "Helmholtz's Handbuch der Physiologischen Optik." It requires a careful study of optics to learn how much of the mental action enters into our vision of the phenomenal world. As the Reviewer remarks, "If a part of an impression, however elementary it may seem, is sometimes overcome and changed into its opposite, by a mere element of inference or effect of experience, it is clear that it is not the pure result of the nervous stimulation, but depends, in part at least, on further and cerebral processes. In this way, for example, we know that a person's recognition of a colour is in part an act of inference. The science of optics is full of the most startling illustrations of the displacement of inferences, so rapid and mechanical that they easily appear intuitions to persons ignorant of these facts."