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Some Important Issues in Philosophy |
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Critical Presentative Realism A Critique and a Defense by Celestine N. Bittle, O.F.M.Cap.
Sight: Scotopic and Photopic Vision There are two kinds of receptors in the retina, rods and cones, forming a double apparatus of sight. Physiologists have determined that the cones are the organ of high intensity or photopic vision, while the rods are the organ of low intensity or scotopic vision. The cones are adapted for brightness and the rods for twilight and darkness. The central portion of the human retina is covered with cones, and here direct vision and color perception take place; the peripheral portion of the retina is covered with rods, and here oblique vision and "rod-white" perception occur. The cones, therefore, translate the light stimuli into colors, and the rods into "rod-white" luminosity devoid of color. Nocturnal animals, like mice, bats, and hedgehogs, possess no cones in their retina; they are colorblind, because color vision would be of little use to them at night. For the same reason nocturnal birds have the cones developed in much smaller quantity than diurnal birds. Here, then, we have a double apparatus, natural and normal in every respect, designed in a most marvelous manner for functioning in brightness and in relative darkness, one for color vision and the other for neutral luminosity vision. Each operates in its own way, producing its own particular subjective effect in the perceiver. A simple experiment will show the double effect of the same light rays. Place three electric lamps (preferably with carbon filaments) in a row, connected together in one circuit and standing about a yard apart. Decrease the current until the filaments barely glow. Stand in such a position that only the center bulk is seen in the line of direct vision, while the two outer bulbs are seen by oblique vision only. In a darkened room the center bulb will now appear with a red glow, while the two outer bulks will show the "rod-white" neutral luminosity. No matter how quickly you shift your gaze from one lamp to the other, only the one directly viewed will be red; the other two will immediately change to "rod-white." You perceive the lamp as "red" when its rays fall upon the cones, and as "rod-white" when its rays enter the eyes obliquely and fall upon the rods. Although the lamps do not change color, the position of your eyes and their rod-and-cone construction produce in your retina a continuous change of color. Color, then, is subjective, dependent on the organ of perception for its existence. There are numerous phenomena within the eye itself which are impossible to explain according to the theory of objectivity. Thus, the "rays" which are such characteristic features of stars, or other bright points in the visual field, are attributable not to the physical luminaries, but to the striated structures of the eye lenses. Halos, surrounding such bright points, are due to the scattering or diffraction of light by cells in the cornea. The "muscae volitantes," which may move across a white paper or open sky area, are representations of tissue fragments floating between the vitreous humor and the retina. Darting and sparkling points, seen against bright backgrounds, correspond with the blood corpuscles which pulse through the retinal capillaries. Under violet illumination, the complex branching formation of the retinal blood vessels become clearly visible. These and many other "entopic phenomena" demonstrate that changes in ray patterns within the eye can bring about corresponding modifications of consciousness. Such facts strengthen our belief that the consciousness is adequately determined by the retinal images, without references to preceding stages of the response. Certain phenomena of binocular vision also contribute to this conviction. If one of the eyes is pressed out of its normal position, the visual pattern in experience is doubled. A similar effect is noticeable in the case of objects upon which the eyes do not properly converge. In these instances, the stimulus conditions external to the eyes are essentially unmodified, but the normal interrelations of the two retinal images are disturbed. In cases of retinal detachment, the visual objects in experience are correspondingly distorted; and may even be doubled or tripled where the receptor layer is folded over upon itself. However, we can go further than this and show that the excitation of the retina, by means other than light, yields corresponding results in the visual-experience field. Thus, pressure produces patches of brilliance, electrical currents yield color patterns, and an alternating magnetic field generates a luminous haze. When absolutely all light is excluded from the eyes, as in a totally dark room, the resulting sensation is not that of an ideal black, but of a deep gray. This is sometimes called idio-retinal light, produced by the self-activity of the retinal elements. Afterimages also show the subjectivity of visual perception. If we keep our eyes fixed on a colored object placed on a black ground, we will notice after a time that the color gradually loses something of its luster. Then, if the eye is suddenly shifted to a white surface, we see an image of the same shape and form with the original object, but of a color complementary to the other. An original red object will thus appear as a green image, and vice versa; yellow will appear as violet and blue as orange, and vice versa. The same effect can be produced, if the eyes, after viewing the object for a time, are closed and a handkerchief or other opaque thing is pressed tight against the eyes, so as to shut out all light. In this total darkness and within the closed eyes an afterimage of the original object will appear in perfect outline and colored with the complementary color. If, in the above experiment, the eyes are kept closed, but the handkerchief be taken away, so that light can shine through the lids, this image immediately changes into an accidental image of the reverse color. Thus, a bright window in daylight will have dark sashes and light panes, when all light is excluded from the eyes; they will appear as light sashes and dark panes, when light is allowed to enter the eyes through the tissues of the eyelids. This phenomenon brings out a very important fact. The change of color here takes place absolutely within the closed eyes. Where, then, is this color which is so vividly perceived? Not in any object, but in the eye itself. But if this color is subjective, the original color must be in the eye as subjective also. Any other explanation would mean playing fast and loose with the facts. The "cause" of the color is assuredly external and objective; but the "effect" (the formal color) is internal and subjective. Sight: Image Projection and Perspective Image projection is another fact which proves that vision is subjective. To say that visual images are projected or "externalized" seems opposed to all experience; it is apparently evident that we behold distant objects at a distance. However, consider the implications of the following experiment. While in a dark room hold a burning taper about two inches away from one eye, a little in front and at the side, so as to insure oblique vision. Keeping the other eye closed, the field of vision will gradually become red. If the taper is moved slowly up and down, while the eye gazes steadily at the wall opposite, an arborescent figure of a dark color on a red field will appear on the wall. This is the "choroid figure," a shadow picture of the retinal arteries and veins upon the seat of vision. Apparently, this choroid figure is on the wall, and we do not seem to perceive it as present in the eye, although that is the only place where it exists and can be perceived to be. There is no "objective" red on the wall, nor an arborescent figure; both are "subjective" perception images within the eye. Is there, then, a process of real "externalization" or projection? Evidently not; the perception takes place within the eye and stays there. Then how can the red field and the shadow figure be perceived as "external" on the external wall? Because the perception of the wall itself is not external but internal. In fact, all visual perception is but retinal imaging consciously apprehended as present. The same explanation accounts for perception of objects in perspective. Parallel tracks seem to converge; highways vanish to a point in the distance; all objects appear proportionately smaller the farther they are away; a near object looks larger than a distant object of the same size. If we accept the view that we perceive a consciously apprehended retinal image, everything is explained, because light must naturally strike the retinal field according to the angles and laws of perspective. This will also explain the apparent shifting of the countryside when we ride in a car or train or airplane, and the apparent position of the stars in a place where they no longer exist. All of which shows that we do not see the objects themselves; visual perception consists in consciously apprehended retinal imaging. Such, then, is the case of critical presentative realism. If these facts force us to the conclusion that the secondary qualities are subjective in character and not objectively present in nature, independent of, and antecedent to, the act of perception, then rigid perceptionism must be abandoned and critical perceptionism accepted. Whether the facts as presented are convincing, is a matter for the individual to decide. Is Critical Perceptionism Disguised Idealism? Rigid perceptionists claim claim that this theory destroys the truth-value of all sense-perception; it is a compromise between idealism and realism and as such has the difficulties of both without the merits of either. They are convinced that critical perceptionism must be a wrong theory, because it is against the natural evidence of the senses; the senses tell us plainly that secondary qualities are "objective." The answer to this objection is simple. The senses tell us nothing about the objectivity or subjectivity of the secondary qualities; they merely report the presence of these qualities in our perception. The senses cannot judge about objects and qualities. It is the intellect alone which interprets the data furnished by the senses and gives us a reasoned certitude as to whether these things are internal or external, subjective or objective. If rigid realists are convinced of the objectivity of all qualities, they obtain this conviction through reason, not through the mere sense presentation of the organs of perception. Hence, if reason comes to the conclusion that the secondary qualities are not objective, it does not go contrary to the testimony of the senses, provided the senses themselves furnish the facts which warrant this conclusion. Rigid realists claim that critical perceptionism leads to idealism: if the secondary qualities are subjective, then the primary qualities must also be considered subjective, because we would never be able to know which particular causes produce the particular secondary qualities as effects. Critical perceptionists answer that the matter is not so desperate as this. The intellect has a very simple way of discovering which bodies are the particular causes of particular effects in our sense-organs. This way: My body is an integral part of my Ego; I am identified with it, and I perceive it is "mine." It is an extended reality, possessing triple dimensions; it possesses extended parts and members, and these I also perceive as "mine." This is evidenced by my immediate consciousness, and I cannot doubt this testimony. We know of the real existence of extra-mental reality. Independent of all sight-perception, through the direct contact of my body with "other" bodies, I can prove that extended bodies, other than my own, also exist. If my body is real, they are real; if they are not real, mine is not real. I do not need sight or color or sound to prove the real existence and the real extension of extra-Ego bodies. Hence, even if all sight-perceptions be shown to be subjective, I would still have a reasoned certitude of extension and extended bodies other than my own, through the direct and immediate contact of my own body. From this to the localization of the causes of the secondary qualities of color, sound, flavor, odor, and temperature, is an easy step. I see a lamp and touch it; I turn on the light with my hand, and it burns; I extinguish the light, and it is dark. It is clear to me that the lamp is the "cause" of the sensation of light. I see a colored apple; I place my hand over it, and the color is gone; I remove my hand, and the color appears again. My intellect rightly concludes that this particular object, the apple, produced the sensation of color in me. I put a piece of candy in my mouth, and the taste is sweet; I hold a rose to my nose, and the odor is pleasant. If I remove them, the sensation ceases. I hold a hell in my hand, shake it, and I hear a sound; I stop it, and I no longer hear the tone. All this happens as long as I repeat the procedure. I thus know with certitude just what particular bodies are the particular causes of the secondary qualities which I perceive. Nothing more is needed for the intellect for its causal knowledge of the bodies and of the secondary sense-qualities. Rigid realists, therefore, are wrong when they assert that the denial of the objectivity of these secondary qualities would destroy our certainty of the existence of the external world. Idealism does not follow from critical perceptionism. Again, rigid perceptionists claim that man experiences a natural compulsion in considering the secondary qualities to be objective; if they are subjective, man must be said to suffer from an unavoidable illusion. Critical perceptionists admit that, if there were a real mental compulsion here, the question would be settled in favor of the objectivity of the secondary qualities. Such, however, is not the case; it is only an apparent mental compulsion. A real mental compulsion exists in analytical judgments like "2 plus two equals 4"; or in a principle which states that "everything must have a sufficient reason for its existence and being"; also in facts perceived in a direct act of consciousness, like the fact that I am writing at this very moment. We cannot doubt the immediate evidence of our reason or of consciousness; to do so would destroy the essential reliability of our powers of knowledge. But when things are not self-evident, one cannot speak of a "necessary" compulsion of our intellectual judgment. The rigid realists themselves admit that the intellect can and does commit errors, in its judgment concerning the objectivity of some qualities. They lay down certain rules and conditions which the intellect must follow in order to guard itself against rash judgments and errors. But this shows plainly that the objectivity of secondary qualities is not self-evident; consequently there can be no necessary compulsion on the part of the intellect to judge these qualities to be objective. At best there may be an apparent mental compulsion; in that case, though, even a prolonged misjudgment on the part of unreflecting mankind will not justify the conclusion that a revision of our judgment would imply necessary illusion in normal perception. We see this clearly in the case of the judgment of mankind regarding the apparent movement of the sun around the earth. It is only in the last few hundred years that people have realized that the earth moves and not the sun. This revision of our judgment was due to science; our eyes still se difference between the movement of the sun and the moon. But if science can correct an erroneous judgment prevalent from the dawn of the human race without destroying the validity of sense-perception and of human knowledge in this case, there is no reason why it cannot do the same with regard to the objectivity of secondary qualities. Here, too, we have merely an apparent mental compulsion of our intellectual judgment. Critical perceptionism, therefore, does not lead to idealism nor does it destroy the essential validity of sense-perception. |
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