# Popular Science Monthly/Volume 81/July 1912/The Physiological Basis of Esthetics

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* THE PHYSIOLOGICAL BASIS OF ESTHETICS
By HENRY SEWALL, Ph.D., M.D.
PROFESSOR OP MEDICINE, UNIVERSITY OF COLORADO
IN its very etymology the word esthetics denotes perception of sense impressions and implies a physiological reaction between a sense organ and objective stimuli. The significance of the term has become modified to indicate rather the feelings produced by the sense perceptions than the mental picture itself. Certain of such are pleasing in their effect and the mind inevitably occupies itself in analyzing the factors giving rise to pleasing impressions and attempts to recombine them in relations the results of which will be still more agreeable.
Reason irresistibly seeks to formulate laws which may be used to construct ideals, or concepts of perfect beauty, and we thus have the origin of the fine arts. By general consensus of opinion there is drawn a more or less well defined line of separation between those pleasurable emotions which do and those which do not involve the intellect. The latter are indispensable to the vegetative life, subserving especially the functions of procreation and nutrition.
The former we intuitively apprehend as higher in their nature, leading us to conceptions of perfection, to ideals which lift us above the sordid struggle of selfish existence.
The fundamental query as to the nature and conditions of beauty has engaged the minds of philosophers from the earliest times. Why is one object or group of sensations beautiful, another ugly, another indifferent? "Why we receive pleasure from some forms and colors and not from others," says Professor Ruskin, "is no more to be asked than why we like sugar and dislike wormwood." From Socrates to Herbert Spencer abstract thinkers have devoted their best energies to elucidating the origin and conditions of the Ideals that make up the apotheosis of life.
It would add little to the conception unfolded in the present essay to review the voluminous literature of esthetics; indeed, such a task is far beyond the powers of the writer. A comprehensive synoptical survey of the subject is given by Sully.
The first writer to have attempted to coordinate the development of esthetics with the evolution of physiologic function seems to have been Herbert Spencer. Grant Allen sought to give physiologic basis to the ​whole esthetic field. Parts of the work of Marshall are especially helpful.
The various conceptions of beauty entertained by any man or race of men strictly conform to the grade of general culture of that individual or that race. Therefore we find the ideals of beauty among different peoples to vary directly with their grade of development in intellect and feeling. Each one of us can trace an evolution of his ideals corresponding with the phases of his mental development.
It would seem, therefore, that an absolute ideal of beauty, whether in morals, in form, in sound or in vision, is not to be found; that the tom-tom of the savage and the violin of the master of symphony are of equal excellence because each expresses most adequately the emotional activity of its respective player.
But psychology remained much like a tractless chaos until students bent themselves to the investigation of laws and functions of the nervous system; and the rich accessions contributed thereby to the knowledge of the mind gives reasonable hope that perception of the beautiful may find in the sense apparatus, which is in general its physical basis, an orderly explanation of facts which otherwise seem without law. If it can be shown that certain esthetic states are dependent for their development upon the specific structure and mode of action of the body in its reaction to external stimuli, it is evidence that the resulting conceptions of beauty are not ephemeral but are founded on the laws of nature which do not operate by chance.
The proof that all esthetic pleasure depends upon a certain harmony between objective stimuli and the structure and operation of the sense apparatus would demand a number of concrete demonstrations correlative with the ideas of beauty.
Nevertheless our main thesis may be firmly founded on a single group of facts if it can be shown that the esthetic attributes of a sense organ arise out of an anatomical or physiological peculiarity of the apparatus which is not concerned in or is even opposed to its prime utilitarian function. Our knowledge of biology appears to be too meager to support a generalization in this field, but certain known facts as to the reactions of the visual apparatus establish that certain of its idiosyncrasies which would condemn it as an optical instrument lend themselves to the development of ideals of visual beauty.
The astonishing revelation appears that when in the evolution of our visual organs under operation of the Law of Usefulness the structure has taken on characters which are inherently subversive of its utilitarian functions, nature has, as it were, circumvented the tendency of these defects; and out of them arise interpretations of the external ​world which lose nothing in exactness but gain something altogether new—esthetic feeling.
Vision is the sense which provides the mind with an overwhelming preponderance of the sensations which lie at the basis of esthetic conceptions. If it can be demonstrated that esthetic visual ideas are founded upon reactions which are dependent upon anatomical peculiarities of the sense organ, the main purpose of this argument will have been accomplished. The evidence follows:
The globe of the eye is admittedly the analogue of a photographic camera, but it is marked by mechanical imperfections that would completely unfit it for the projection of a sharp image upon the sensitive plate. For the eye lets in light not only through the pupil, which corresponds with the aperture in the photographic diaphragm, but the sidewall of the globe—the sclerotic coat and its underlying choroid coat—are penetrable to the light. Consequently, the whole retina must be bathed in a dim light which has entered through the wall of the eyeball. This light is diffuse, and since it has traversed many blood streams it must have acquired a reddish color.
Under ordinary conditions of vision then, there is thrown upon the center of the retina a more or less sharply defined image of objects the light from which has entered the pupil. In addition, the whole of the retina is illuminated by a diffuse reddish glow, due to light leaking through the white of the eye, a condition the parallel of which would completely subvert the efficiency of an artificial camera. Apparency, then, evolution has produced for us an optical instrument which is hopelessly defective. But the sensitive film of the eye is alive and the impressions formed on it are interpreted through the aid of living structures. It is conceivable that what seem to be mechanical deficiencies in the eye may be compensated or even turned into actual benefits through physiological agency.
It is a familiar law of chromatics that whenever an objective color falls upon the retina, the affected area becomes fatigued for that color and refreshed for its complementary. The complementary color of red is green. Under the conditions named, then, the irritability of the retina for green is continually maintained through the influence of light leaking through the sclerotic coat. So long as this side light penetrates the globe of the eye, and such is the habitual condition in daylight, the perception for green is automatically refreshed and this color, therefore, excels all its companions of the spectrum in its ability to play upon the sensorium without inducing fatigue.
Now the characteristic tint of vegetation is green. A tree clothed with verdure never wearies the color sense. But look at this same tree through an opaque mask having eye-holes admitting light only ​through the pupils, and very soon the foliage takes on a rusty hue, the esthetic charm of the creation departs and the onlooker feels a sense of depression; all because the sidelight entering the white of the eye has been cut off. Such may be the physical basis of that droop in spirits which every one is apt to feel on a summer's day when a cloud suddenly obscures the sun.
Such is one indication that the universal esthetic joy of the open, as far as dependent on the color sense, is specifically subserved by the physiological reactions of the eye, reactions which would seem to impair the efficiency of the organ as a mere optical apparatus. A mechanical defect is translated by physiological intervention into a psychic triumph.
In the foregoing it has been shown that esthetic feelings may be founded directly upon anatomical and physiological peculiarities of the eye. Now I will proceed in the converse manner and attempt to account for some intuitively perceived esthetic qualities by reference to idiosyncrasies of the visual instrument. It is doubtful whether ideals of beauty can ever be embodied by the conscious mathematical synthesis of their elements as a mechanic constructs a building by laying stone on stone.
I imagine that the creation of the artist at first appears to him as an intuition, of a quality determined by his race culture, and that he uses his techniuqe to put together objective materials to represent it. But such a work is its own justification; it is accepted and graded at its face value by a general consensus of cultured opinion, according as it is fit and pleasing, irrespective of the laws of physics and physiology. If it is beautiful it may claim place as a model of taste, needing no defense. Now if beauty of whatever sort is but the outcome of certain correlations of physiological and anatomical characters, it should be possible to point out the biological substratum on which depends the excellence of any work of art.
But few works of art appeal to all men as approaching objective perfection. Possibly one such structure in architecture is represented by a ruin—the Parthenon at Athens. Many themes have been written in admiring description of this building; much has been debated the secret of its charm. With great diffidence I venture to dwell upon certain reported peculiarities of construction of the Parthenon as they appear to me related to known facts of binocular vision, and to suggest that from this interdependence springs at least part of the esthetic satisfaction aroused by the structure.
Competent observers describe one physical detail in the construction of the Parthenon which has aroused much curious comment.
No line and no form in the composition of the temple are exactly what they appear to be: . . . No horizontal line is really horizontal, and no vertical line really vertical, . . . every huge and massive feature is changed and almost imperceptibly deflected from the appearance it bears.
The free edges, namely, of the edifice instead of being straight, as in a modern architectural design, are all curved gently in the arcs of large circles. The edges and vertical faces of the steps leading to the portico thus have a gentle convexity outward. The surface of the platform itself has the form of a very flat vault. The columns do not stand exactly vertical, but slant inward and their outlines are curved so that their actual thickness is greatest about one third the distance from the base. So great is the radius of curvature that to the casual glance there is no departure from straightness in the outlines.
Such being the objective mechanical facts, let us see what relation they may have to the visual physiology of the onlooker.
The physiological conditions may be made clear by means of a simple experiment. Let a cross formed of two strips of colored paper which intersect at right angles be fastened against a neutral tinted wall at the level of the eyes of the observer who stands at a distance of, say, ten feet. The gaze is fixed intently for some seconds upon the center of the cross. The image of the latter is thus impressed upon the retina, so that when the glance is directed elsewhere upon the wall a "negative after-image" of the cross is projected with startling distinctness upon the surface. When the eyes move so that the optic axes run along either the horizontal or vertical lines extending from the center of the cross the limbs of the latter maintain their true directions in the afterimage. But when the optic axes are directed obliquely upward or downward, the cross seems to be inclined upon the wall, the vertical limb leaning at a greater angle than the horizontal. When the orbital movement is upward and to the right, the vertical part of the cross inclines to the right, it may be as much as fifteen degrees; the horizontal limb inclines downward to the right as much as five degrees. When the oblique movement of the optic axes is upward to the left the inclination of the cross is to the left. Oblique downward movements give complementary results. The amount of angular inclination of the after-image is proportional to the range of oblique movement. The physiological explanation of this phenomenon is not here important; the results are such as would occur if the eyeball in its oblique motions rotated slightly like a wheel about its visual axis.
As an observer stands before an architectural structure, his gaze roving over its lines and surfaces, the extremely complex nerve-muscle ​mechanism of ocular fixation must carry out its movements with an ease or effort determined by the external configuration brought into attention. It has been shown that in oblique movements of the eyes there is a definite rotatory movement of the globes, so that in following any line departing obliquely from the prime axis of vision it seems obvious that the fixation mechanism would suffer less fatigue when this line is curved objectively to correspond with the normal rotation round the visual axis. In following oblique lines which are objectively straight the fixation mechanism must be continually harrassed by the voluntary effort to maintain the contemplated line in the horopter.
No homily is needed to convince the modern physician of the paramount psychological importance of the motor sensations arising from the coordinations of the external eye muscles. As sensory disasters from eyestrain often result in muscular unbalance, it is not difficult to believe, conversely, that peculiar advantages may spring from unobtrusive objective aids to the action of the intricate machinery of fixation whereby the eye is enabled to rove over a picture without conscious effort. According to this view, then, the curved lines of the Parthenon are psychologically straight to the onlooker in so far as they parallel the normal inclination of the after-image in oblique vision. It is easy to believe that the physiological result of such relations is rest, absence' of fatigue. But kind nature repays subconscious physiological coordination in a rich and peculiar way; the thing so seen and understood without effort arouses a new class of ideas—an esthetic feeling—beauty.
It may be objected to the foregoing argument that, though the outline of one side of a column may by reason of its curve allow the eye to glance along it without the effort of fixation, that of the opposite side, forming a reciprocal arc, must simultaneously offer an equally exaggerated impediment to ease of vision. I answer that the percipient mind tends to neglect all sensory impressions which interfere with the homogeneity of a mental picture. The infinite details of a landscape impressed upon the outskirts of the retina? give rise for the most part to mental double images, but these in no wise disturb the acuteness of vision for an object projected on the retinal foveæ. Moreover, it is not intended here to imply that the idea elaborated above contains the whole physiologic basis of the esthetic charm of the Parthenon. Indeed, the author of the admirable paper which has been quoted, whose thesis, by the way, ascribes the preeminence of Greek art to its foundation on physiological principles, himself gives other interpretations to the psychic impression produced by the temple. These explanations, however, do not displace, but rather complement that detailed above.
In the foregoing discussion evidence has been offered along two ​different lines that structural or functional properties of the eye which, considered from the purely physical point of view, would seem to impair the efficiency of the organ as a registrar and transmitter of objective visual facts, not only do not confuse the recipient sensory nerve centers, but, on the contrary, the psychical apprehension of objective phenomena is distinctly modified by the reaction to such instrumental defects in a manner which leads to the generation in consciousness of a state or an atmosphere of feeling—esthetic feeling. It is as if the stone rejected of the builders were made the chief of the corner.
In pursuance of this line of thought I will offer one additional illustration of the direct dependence of psychic perception upon what may be termed the structural aberration of the visual apparatus.
When external objects are viewed with one eye, held at rest, the image upon the retina is exactly similar to that upon the sensitive plate of the camera, it has length and breadth, but no depth, and it has no power of directly arousing in the mind a perception of the third dimension—projection.
It is inconceivable, indeed, that an anatomical apparatus should be capable of directly presenting to its sensory center an impression of depth. Such a perception is of purely psychological construction from simpler data derived from retinal impulses. By an exceedingly familiar line of evidence it can be shown that the direct visual perception of depth is dependent upon idiosyncrasies of binocular vision. It is a physiological law that an object viewed by the two eyes appears to be single only when the images which it casts upon the retinas fall upon "corresponding points" of the two surfaces. It is obviously of paramount importance to the instrumental efficiency of the eyes that there should be a horopter in which objective and subjective facts must coincide. It is well known that the fixation of objects by means of which their images are retained upon corresponding retinal areas invokes activity of most complex nerve-muscle machinery. Now when a small solid object is viewed with both eyes, it is clear that the right eye must see more of the right side of the object and the left eye more of the left side. Therefore it is certain that the images on the two retinas can not be identical and therefore can not exactly "correspond."
Some extra-mundane theorists summing up these facts would naturally reach the conclusion that distinct binocular vision is in its nature impossible. Nevertheless we know that the mental picture of external objects loses nothing essential in focal sharpness through binocular vision but, on the other hand, the two unlike retinal pictures combine, as it were, in the mind to form a new idea—the concept of depth.
Of all esthetic perceptions that of projection is the highest, the most purely psychic. Through it the universe is instantly converted from a ​flat surface of two dimensions into an infinity reaching in all directions. If the unlikeness of the retinal images as seen simultaneously with the two eyes is really the physical basis of our visual perception of the third dimension of space it would naturally be suspected that the depth perception must become more lively the greater the unlikeness of the two images, up to a certain point. Manifestly the binocular images must depart from similarity in proportion as the eyes are further apart.
Pursuing this idea, Helmholtz contrived a most ingenious instrument the "telestereoscope," by which the distance between the eyes of an observer can be virtually increased to any extent. In its simplest original form the telestereoscope may be reproduced by joining at right angles the edges of two small squares of silvered glass which are then set into the middle of a strip of board having a length of, say, three feet. When the eyes are brought close to this rectangular mirror so that its edge is parallel with the bridge of the nose, it is evident that the right eye sees only the reflection of objects to the right of the field of view and the left eye those in the corresponding area on the left. At each free extremity of the board another, larger mirror is placed, so fastened by hinges that one mirror shall be movable round a vertical and the other round a horizontal axis. These terminal mirrors have their reflecting surfaces turned outwards, away from the observer.
In using the instrument the experimenter brings his eyes close to the fixed rectangular mirror so that they look into either reflecting surface. Now the terminal mirrors are focused on some distant object, as a tree, and it is easy to bring the reflections of the two images on "corresponding points" of the retinas and the distant object appears single but as if viewed by a pair of eyes separated by a distance of three feet. No one can realize, without having experienced its influence, the startling stereoscopic effect of such a view. For the first time in his experience the observer becomes enthralled with a perception of depth as a specific factor in objective impressions. It seems to the writer worth recording, as a suggestion in esthetic pedagogics, that after continued experimentation with this apparatus for some weeks, during which all manner of solid objects occupying the landscape was studied, there insensibly grew up in him an esthetic appreciation of depth, per se, which gave to all solid objects, viewed with the unaided eyes, a charm which immensely enhanced the pleasing combination of their natural attributes. The beauty in nature called more insistently from all her creatures. To sum up, in brief, the very dissimilarity of the retinal images which would seem to subvert the acuity of binocular vision is not only without disadvantage thereto but forms the physical substratum of a new psychic realm.
​To the writer these facts and reflections seem very strong evidence that the principles of esthetics, like those of the psychology from which they spring, are fundamentally an outgrowth of physiological and anatomical factors and phenomena. The belief seems to prevail among psychologists that the general states of pleasure and pain are referable to functional nutritive metabolisms of the sensory apparatus which, on the one hand, tend to restore and, on the other, to destroy it.
There is experimental evidence that the emotion of fear and the sensations of pain, at least the sensations resulting from trauma, have a physical basis, manifested by histological alterations in the nerve cells of the brain. It might be plausibly argued that the scheme of usefulness which is the basis of organic evolution accounts for the origin and development of an esthetic sense.
But the peculiar mechanical substratum of the esthetic faculty as far as it is related to the visual apparatus seems to be seated in idiosyncrasies of the sense organ which have, at first view, no important relation to its usefulness as a physical instrument; which, on the contrary, would seem to be impediments to the perfection of its main function. This is suggestive of the thought of Herbert Spencer that the distinguishing mark of esthetic sentiments is their separableness from life-serving functions.
Curious it is, and still stranger if a matter of chance, that where the utility of a sense organ ends its glory may begin.
* ↑ Quoted by Grant Allen, infra.
* ↑ Article "Æsthetics," Encycl. Britannica, 9th Ed.
* ↑ "Psychology," 2d Ed.
* ↑ "Physiological Æsthetics," 1877.
* ↑ "Pain, Pleasure and Æsthetics," 1894.
* ↑ Cf. Brücke, Pogg. Annalen, Bd. LXXXIV., S. 418.
* ↑ Sewall, "On the Physiological Effects of Light which Enters the Eye through the Sclerotic Coat," Journ. of Physiology, 1883, V., p. 132.
* ↑ "Greek Art and Modern Craftsmanship," Edinburgh Review, October, 1906, Vol. 204, p. 430.
* ↑ Le Conte, "Sight," p. 164. Internat. Scientific Series, 1881.
* ↑ Edinburgh Review, loc. cit.
* ↑ Geo. W. Crile, "Phylogenetic Association in Relation to Certain Medical Problems," Ether Day address, Mass. Genl. Hosp., October 15, 1910.