The ancient theory of human vision, based on the soul, is confirmed by Leonardo.

by Robert L. Gallagher

eonardo da Vinci's advances in the science of perspective developed from his penetrating investiga-

tions into optics and human vision. In Leonardo's Ital-ian, prospettiva, usually translated today as perspective, simply means optics, and by Leonardo's definition, optics or prospettiva "is nothing else than a thorough knowledge of the function of the eye." [A. 3a; Richter 50]'

The theory of vision Leonardo adheres to and elaborates is very different from the modernist theory with which the reader may be familiar. Leonardo's prospettiva cannot be grasped unless it is approached from the theory of vision that guides his work.

From ancient times through the Renaissance, most thinkers held that perception is the result of an act of the soul outwards, to form the image seen or the sound heard out of a sensory continuum.? The eye is conceived of as an instrument of the soul, not a passive receiver of images.

These views flow from the perspective that the soul is ontologically prior to all bodies that subsist in discrete time and space. While all things change with different temporal and spatial conditions, the soul undergoes change only in time, and because of that is prior to all bodies, writes St. Augustine his De Musica: "The form changeable only in time is prior to that changeable both in time and place." [6,14,44]°

This Augustinian view of vision is part of the Renaissance culture that produces Leonardo and guides the work of his predecessors in optics, for example, John Pecham, whom he studied.

all the senses meet; and this is called senso commune. . . . The senso commune is the seat of the soul, and the memory is its ammunition [munitione] and the imprensiva is its standard of reference, since the sense waits on the soul and not the soul on the sense [W. An. IV 202a (B); Richter 838].

In contrast, the modernist theory of vision rejects the Christian view that the metaphysical nature of the soul is

By this view the visual image is not formed passively on

the basis of human vision. The modernists assume that the retina but rather is synthesized by the human judgment-objects imprint their images on the mind as though it were a al faculty, which Leonardo situates in a specific ventricle of blank slate, a Lockean tabula rasa. They make no distinction the brain. between sensation and perception, and deny there is a

The two views of perception, classical and modern, ex-

need for a judgmental process of the human mind to form press fundamentally divergent attitudes toward aesthetics. complete images out of raw sense data. For the modernists,

The important question is: Do the harmonies we experi-

focused images arrive already formed on the surface of the ence through the fine arts have their origin in the physical retina by virtue of the optical characteristics of the atmo- art object itself, that is, the painting seen, or the music sphere and of the eye. The retina serves only as a passive heard, or do they have their origin in the soul of the viewer viewing screen for the brain, as in a camera obscura.

or hearer?

The modernists posit a point-for-point correspondence

If sensory data act directly upon the mind, with no judg-

between images on the surface of the retina and the visual mental process intervening, we would be forced to con-field, with the brain analyzing this digital image as a com- clude that the harmonies we experience originate in the art puter would. By this theory, the human mind and soul are itself as an object or sense datum in discrete time and space. at best mere epiphenomena of the mechanics of sensory

But sense datalare ephemeral and have no lasting existence.

stimulus and motor response.

They could beviewed as characterized by arbitrariness rath-

The modernist view appeals to naive prejudice: We "see" er than harmoniousness. Under these conditions, how only complete images; we are not conscious of a judgment- could art inspire us with any appreciation of the lawful al process. Vision appears self-evident. It seems plausible nature of the universe? How would art even be possible? that images are formed on the retina and that we simply

Augustine raises this in De musica and resolves this prob-

observe them.

lem by stating that although the world itself is fundamental-

Reflecting the modernist theory that the eye is a passively harmonic, we can know this only by reference to a stan-viewing instrument, M.H. Pirenne, one-time lecturer in dard of judgment that our souls receive from God. From physiology at the University of Oxford, writes in his Vision this standpoint, Leonardo embarks on a thorough investi-and the Eye: "The human eye acts like a camera obscura, gation of optics and vision and establishes anew a scientific an image of the objects outside being formed on the retina basis for the relation of that sense to human knowledge. by the transparent refracting media of the eye. The essential principle is the same as a photographic camera. . . ."

On the Action of Light in the 'Luminous Atmosphere'

Pirenne's beliefs lead him to hypothesize a completely

Leonardo's work on optics may be divided into several

"objective" art, dissociated from human vision and the hu- progressive levels of investigation: (1) how light acts in the man mind. He concludes that "the perspective drawing atmosphere to produce the optical substrata required for made for a fly's eye will be the same as that for a man's eye." vision: (2) how passive optical instruments like the camera A completely different attitude toward vision and the obscura, lenses, and mirrors function; (3) how the eye func-senses is expressed by the thinkers who played the greatest tions; (4) Leonardo's prospettiva naturale; (5) Leonardo's role in shaping the Renaissance, of which Leonardo's work prospettiva divina; and (6) his aesthetics. In the course of is the most advanced expression in science. St. Augustine, elaborating his prospettiva, Leonardo develops his critique for example, argues convincingly that hearing or vision of linear perspective. These headings are usually consid-could not exist without the judgmental processes of the ered distinct subjects treated by Leonardo, but as this inves-soul." Leonardo elaborates this viewpoint, contending that tigation shows, and like his work in anatomy and physiol-images are not presented to the mind preformed on the ogy, these are not self-standing "sciences" but rather sub-retina and that judgment is a necessary function of the ordinate parts of his prospettiva. human mind. In his "Treatise on the Eye" he writes:

In the first part of his investigations Leonardo asks the question: Do objects themselves produce the images that

From this surface [of the retinal . . . the species are taken by the imprensiva and transmitted to the senso commune where they are judged [D. 2b; Strong 9].

The soul seems to reside in the judgment, and the judgment would seem to be seated in that part where we see with the eye? To the contrary, Leonardo says that images are produced by the action of light in the atmo-sphere. He begins by describing the optical activity continually taking place in the atmosphere, and he emphasizes that light is continuously interacting upon the surfaces of bodies around us. The same light by which you see this

Source: D3b; Keele 206

A drawing from Leonardo's manuscripts of an experiment with a model of the human eye.

printed page scatters elsewhere in the room where you are sitting, interacts on other surfaces, and conveys, for example, an image of a picture on the wall.