• To introduce the students to some of the fundamentals about vision that will increase their understanding of the visual world;
• To use many visual aids demonstrating sight, light, and projects by artists related to these areas (the teacher should have some on display in class, and use slides and movies when possible);
• To have the students carry out a brief research project with a short oral or written report in an area of this unit that interests them;
• To point out areas where the science of vision relates to art;
• To demonstrate some scientific experiments for the visual impact of the experience (the students will remember the principles more if they participate in the experiments);
• To carry out an experimental art project as individuals, groups, or a class, that is related to this unit (such a project will reinforce the principles learned during lectures).

Physics of Light

The teacher should review some informative and helpful principles about the nature and behavior of light. Begin by asking the students what they have learned or remember about light. Cover such topics as the following (see Resource Material at the end of this unit for more information on the nature of light):

VOCABULARY The teacher should discuss with the students the following vocabulary words associated with light. These words are important to describe the visual world and many are used in art.

Ø ABSORPTION: light taken in by a substance.
Ø DIFFRACTION: rays that spread outward after passing through a narrow space.
Ø LUMINOUS: something that gives off its own light.
Ø OPAQUE: substance that does not allow light to pass through it.
Ø REFLECTION: the bounding of light (black reflects little light, a mirror reflects almost all).
Ø REFRACTION: the bending of light rays on passing from one medium to another which slows them down, such as air into water.
Ø TRANSPARENT: substances that allow light to pass through them such as cellophane or Plexiglas.
___________________________

* The principles marked with an asterisk (*) can be demonstrated by experiments in class (see Resource Material for possible experiments). Or, the teacher might have students do experiments at home associated with these phenomena of light and write about their procedure and results for extra credit.

REPORTS The teacher should have the students carry out a brief research project with a short oral or written report in an area of light and light art that interests them. Following are some possible topics:

o Cameras (the image and the role of light)
o Electromagnetic Spectrum (visible light, infrared)
o Fibre Optics
o Laser Light
o Mirror Reflections (good for geometry-angles of incidence and reflection)
o Motion Pictures
o Polarization of Light
o Telescopes and Lenses (the path of light through them)

APPLICATION The teacher should have the students think of ways that the properties of light they have studied are relevant to what they see everyday, and how the properties of light might be important for an artist to know and understand. For example, have the students noticed that their shadow appears a different size and shape at different times of the day? From the experiment with shadows, do they understand why? Why would an artist need to know how a light source affects cast shadows? Have any of the students ever pointed a flashlight up into the night sky? Did the light disappear? If there were clouds could they see the light beam? Does an artist need to know how light affects a realistic scene? Can an artist create the effect of a fantasy scene by varying light from a realistic effect? Does an artist need to know how light will reflect from and affect a three-dimensional project? Does the color of light affect the appearance of objects? Should that be considered when designing an interior with artificial lighting, or buying something to be used in sunlight?

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THE EYE

LECTURE The teacher will present the following lecture to the students:

Introduction

Sight is what takes place in the eyes when nerves respond to light stimulus. Vision occurs when messages triggered by light go to the brain and are properly interpreted.
Vision is man's primary sense and occurs without any conscious awareness of the process. We are so accustomed to normal vision that we don't recognize the incredible capacity we have to collect and store visual information. How does all this occur?

Folklore and Superstition

The ability of the eye to see has been a source of amazement to man throughout the ages. Ancient cultures credited the eye with supernatural powers. Seafaring people painted eyes on the prow of their ships to help them see through the storms and dangers of sailing.
Poets have described the eyes as the "windows of the soul." The tradition that you can see a man's character through his eyes is still present in modern society. A "shifty" eyed person is someone who may be dishonest. Throughout history, people who squinted due to shortsightedness or farsightedness sight have been targets for character misinterpretation. And of course, we all know that someone who looks you straight in the eye is honest and has a clear conscience. Or is it possible that the best liar is the one that has learned to look you straight in the eye while telling a lie?

Art and other records of ancient civilizations give us an indication of the importance of the eye in their culture and beliefs. For example, a stele from ancient Egypt shows the eyes of the god Horus watching over the King and Queen (figure 2.6). A similar effect is portrayed centuries later in a painting from India dominated by the eyes of the Hindu god Shiva (figure 2.7).
Figure 2.8 illustrates the hundred-eyed monster, Argus, of Greek mythology. Appropriately, Argus was a watchman. When he was killed, Hera, queen of the gods, adorned the peacock's tail with Argus' eyes. Among the warrior tribesmen of New Zealand, the eyes of the chief were eaten when he was slain because divinity rested in them.

Our modern vocabulary still reflects one ancient superstition: "the evil eye." Folklore abounds with references to the evil eye. Even the New Testament talks of it. A Roman mosaic from the second century portrays the veil eye (figure 2.9). This superstition carried forward to the Elizabethan age. Shakespeare's poetry mentioned a plague caught from another's eyes.
The folklore persisted and was so prevalent that in the nineteenth century, the Russian Academy of Science decided to test the superstition of the evil eye. A condemned prisoner was starved for three days while he could see but not touch a loaf of bread. Analysis of the bread afterward found that it contained a "poisonous substance."

History

Ancient peoples achieved great skill in medicine, including eye maladies. Some of the remedies for eye diseases were documented in the Papyrus Ebers which was found between the legs of a mummy buried near the city of Thebes in Egypt. Written about 1500 B.C., the papyrus contained a collection of medical writings copied from earlier records indicating that some of the remedies had been passed down through the centuries, possibly from as early as 4000 B.C. The Egyptians cured eye inflammations among other problems, and cured a cataract by pushing the clouded lens aside (called couching) rather than removing it as is done today.

Hammurabi was the ruler of the Babylonian Empire about 1900 B.C. The code of Hammurabi established laws, including the regulation of the practice of medicine, and established set fees to be paid for particular services. The code discussed operations with a knife to open abscesses in the eye. If the operation was successful and the eye was saved, 10 shekels of silver were to be paid. However, the code called for the loss of hands for someone who opened the eye of a freeman with a brass needle and destroyed it.

Although the ancients treated eye diseases, there has not been found from before the fifth century B.C. any recorded speculation on the way the eye sees. At that time, the Greek Democritus argues that objects shed indivisible particles called atoms into space. When atoms struck the eye they were intercepted by the soul and thus perceived.
A contemporary of Democritus, Empedocles, formally stated a rival theory that the eyes cast rays toward objects and so created sight. Around 430 B.C., Plato converted this to the visual ray theory. Plato believed that the eyes' rays coalesced with daylight and intercepted rays from objects. The interaction of daylight and rays produced vision. However, Plato's pupil, Aristotle, rejected the theory on the premise that if it were true we would see in the dark. Aristotle devised his own complex theory that amounted to the space between the viewer and the object conveying the visual image. Yet, the prestige of Plato sustained his theory through the middle ages. Later, the mathematician Euclid embraced the ray theory and applied geometry to it (Wertenbaker, 1981).

In the Arab world, from the ninth to the eleventh centuries several philosophers studied vision based on the writings of the Greeks. One of the first, Arab al-Kindi, defended Euclid's visual ray theory, however he felt that the eyes projected a single, continuous stream rather than a series of individual rays (Euclid) which would cause spotted vision. The Islamic philosopher and theorist of the eye, Avicenna (figure 2.10), followed Aristotle's ideas. In the eleventh century, the greatest Islamic investigator of the eye, Alhazen of Basra, a physician, studied the anatomy of the eye and published a work entitled, "On Otics." Alhazen rejected previous theories and declared that visual rays came from objects. He recognized that light affects the eye (anyone staring at the sun feels pain) and color affects the eye (when the gaze is shifted from a brightly colored object a colored after image or lingering impression is seen). He concluded that light and color issue along straight lines from each point of every colored body illuminated by light. Alhazen also experimented with magnifying glasses and some medical historians credit him with contributing to the development of eyeglasses (Seeman, 1968).

Other than the invention of eyeglasses in the late 1200's (Wertenbaker, 1981), the Middle Ages saw no new progress and Europe's universities were dominated by the theories of Aristotle. Then, based on Arab knowledge, scientists of the Renaissance further explored the nature of sight. The theories of Alhazen influenced Leonardo da Vinci. Leonardo noted that the pupil shrunk and grew according to brightness. He also deduced that the eye operated like a camera obscura (a pinhole lets a stream of light into a darkened room, producing an inverted image on the wall, figure 2.11).

At the turn of the seventeenth century, the Imperial Mathematician to the Holy Roman Empire, Johannes Kepler, declared that the retina was the part of the eye most responsible for vision. Kepler realized that the eye lens focused light on the retina and that a blurred image was due to improper focusing. Kepler also realized that the eye worked like camera obscura, the pupil functioning s the pinhole where light enters. The proof came in 1625 when a Jesuit priest, Christoph Scheier, cut away the coating fo the back of the eye of an ox, exposing an inverted image on the retina (Wertenbaker, 1981).

Building on the theory of the retina, the French philosopher and scientist, Rene Descartes, named the most sensitive part of the retina s the "fovea." Descartes also recognized that the light impulses ere transmitted to the brain via the optic nerve (Seeman, 1968).
In 1672, Isaac Newton published his Light and Color Theory which completely struck down the visual ray theory. Based on experiments with a prism, Newton postulated that light was minute articles of different sizes which corresponded to different colors. The particles emanated in straight rays from illuminated objects. This theory was rivaled by Dutch physicist, Christiaan Huygens. In 1690 Huygens published his Treatise on Light which presented his theory that light travels in waves. These two theories competed until the twentieth century when scientists learned that light has properties of both particles and waves.
The eighteenth century began the modern era of studies in color vision with the work of the English physician Dr. Thomas Young. Young measured light waves and found that the colors had different frequencies. Young also recognized that color was only a sensation created by a limited number of receptors in the eye that responded to the different frequencies. Young first named three receptors of red, yellow, and blue. He later changed his theory to the colors of red, green, and violet (Gregory, 1978).

Fifty years later, in Germany, the physiologist and physicist, Hermann von Helmholtz, developed the othalmoscope which made it possible to look directly into the eye. Helmgotz also developed a trichromatic color theory of vision. Like Young, Helmholtz believed that the eye had three primary color receptors that could recreate any color of the rainbow. A contemporary German physiologist, Edward hering, insisted that four primary colors were the basis for all color sensation. Hering proposed that the hues were arranged in opposite pairs which did not readily mix, such as red and green and blue and yellow. In the eye, coders caused on color to block another (this is the opponent-process theory): red inhibits green, and blue suppresses yellow. In 1873, the Scottish physicist James Clerk Maxwell published his "Treatise on Electricity and Magnetism." In this work Maxwell theorized that light was electromagnetic radiation consisting of oscillating electric and magnetic fields (Morris, 1979).
Now, let us discuss the bodily organ which is our "eye to the world" according to the findings of the twentieth century science.

Physiology of the Eye

Retina. An image before the eye is seen because of stimulation on the nerve cells which line the back of the eyeball in an area called the retina. The retina, composed of rods and cones, produces signals or impulses when light shines on the nerve cells.

Fovea. At the center back of the eye is an area called the fovea which has only cones. The fovea has the most accurate vision in bright light. The eye is constantly shifting to focus to the fovea. Sharp focus decreases toward the outside of the retina.

Rods and Cones. The rods see shades of gray and the cones see color. The cones are sensitive to re, green, and blue, and are most responsive to the yellowish-green part fo the color spectrum. Impulses transmitted by the red cones tend to inhibit the brain's ability to see green, as suggested by Hering's opponent-process theory.

The rods are used to see at night and respond best to the blue-green wavelengths. As a result, at night a red flower will look almost black and a blue flower will seem brighter than the red. In moonlight we see the world in shades of gray.

Pupil. The pupil is the darkened surface of the lens. Its name is derived from the Greek work for "doll" because of the miniature reflection of oneself seen when looking closely in another's eye. The reflection shows how dramatically the image is reduced. In the same way a camera can control the amount of light which enters, the eye can control the amount of light which enters, the eye can control the amount of light passing through the pupil. A ring of muscle called the iris can change the size of the pupil. The pupil constricts to block bright light and expands when more light is needed.

Lens. The eye has a crystalline lens made of a clear rubbery material which is moved by tiny muscles. The lens adjusts for clear focus. Unlike a camera which moves its lens nearer to an object or farther away from it in order to focus, the eye changes the shape of the lens in order to focus. When looking at distant objects the lens thins and becomes flatter and the objects appear small. The lens thickens and is more curved when looking at close objects and they appear large. With age, the lens hardens and "accommodation" (flattening or curving) stops, causing a fixed distant focal point. Then the eyes need the help of glasses to see within or beyond this range.

The eye lens acts as a filter. It is tinted slightly yellow and blocks out all light beyond the violet end of the visible spectrum. With age the yellow tint darkens, decreasing the violet and blue colors of normal vision. This may explain why some painters late in their careers shy away from purples and blues.

Saccades. There is another reason our eyes are constantly moving. If an image were held stationary on the retina, the photoreceptors would fatigue and the image would fade. The quick involuntary movements our eyes make as they change points of fixation are called "saccades." This movement is important to recognize in art because saccades move the eyes from point to point along the lines of the composition. Our eyes typically scan from the top to the bottom and from left to right. (Here's a topic for students to think about or research: Do orientals, who read from right to left, have a different scanning pattern?) Advertisers use the normal patterns of eye movement, or scanning, to direct the viewer's gaze to the important parts of an advertisement.

Depth. All the images reaching our eyes compete for recognition until our mind can give them meaning. Our brain transforms the two-dimensional signals from our eyes into three-dimensional conscious experience by drawing deductions from the visual clues it ha received. These clues give information about depth or distance of objects and movement. For example, information about distance of an object is transmitted by the sense organs in response to the accommodation of the lens shape. The full experience of depth is provided by both eyes. Stereoscopic vision is the fusion of two images viewed from slightly different angles.
Some of the everyday visual cues interpreted by the brain are also used to create a three-dimensional illusion in a two-dimensional artwork:

Movement. We know when something in our world is moving because our eyes detect the movement of objects in two ways: when the eyes are still and an image sweeps across the retina, the message sent to the brain is interpreted as movement; or, when our eyes track a moving object, the action of the eye muscles informs the brain of motion. A cue to the distance of moving objects is provided by "motion parallax." Nearby objects pass the viewer more rapidly than distant ones.

The constant movement of our eyes also creates some visual illusions of movement. For example, a small motionless point o flight in a darkened room, such as a cigarette on an ashtray, will appear to "tremor," or hover unsteadily. This phenomenon may account for some UFO reports, such as when a cabin light shining high on a mountain is too far away to distinguish the shape of the mountain and cabin in the dark (Wertenbaker, 1981). A point of light may appear to move slowly off center as we gaze at it. This is called "drift." A "flick" occurs when a light appears to jump or throw itself back on center.

Adaptation. Our eyes must be able to adapt to differences in light received. In order to see at night, the eyes must adjust to the dark. The pupil size changes to admit more light and the photo receptors of the retina must supply more visual pigment, called rhodopsin. The rhodopsin increases the eyes' sensitivity, but acuity in space and time decreases in the dark.
In the same way a camera needs a longer exposure in dim light, our brain is delayed in reaction time in the dark. The delay is caused by a lag in the time it takes the receptors to respond, affecting the length of time required to receive messages. This can be demonstrated by the Pulfrich Pendulum (Gregory, 1978). Tie a bob to a one meter long string and swing it in a normal arc in front of the eyes. Cover one eye with a dark filter such as a lens from sunglasses. The bob will appear to move in an ellipse. The dark lens makes one eye see the bob slightly in the past, causing a shift of the moving image and creating stereo depth (figure 2.12, p. 51). Three-dimensional movies create stereo depth when the viewer wears special glasses with one darkened lens.

Reaction time of drivers is lengthened in dim light. It is also more difficult to precisely locate moving objects, making tennis and ball games more difficult in poor light. The delay due to dark adaptation is also why we see a comet tail following moving fireworks at night. Night vision serves mainly to help in orientation and motion detection because the rods do not focus images very distinctly.

Abnormalities. Because vision takes place in the brain, sever brain injury can blind a person although the eyes still function normally (Mueller, 1966). The author of this visual literacy curriculum had a dog whose head was injured ina fight. Although the eyes were not physically damaged, the dog lost its sight.

Humans are subject to disease and abnormalities of the eyes. Some of these abnormalities are interesting to note for the way they affect our vision of the world. Myopia or short-sightedness can increase attention to detail. A short-sighted artist may use a lot of detail in paintings, and have less detail later in life when sight is failing. An astigmatism may cause one to see figures as if they were taller. An artist with an astigmatism may elongate and thin figures in an artwork. Cataracts can change the color of the world one sees. An artist with a red cataract may choose a different color palette than another artist, or a different palette than before the cataract occurred.

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RESOURCE MATERIAL

THE NATURE OF LIGHT

Following are some miscellaneous scientific facts regarding light:

· Any material heated to sufficiently high temperature radiates energy into space. This energy travels in straight lines at high velocity (speed so great that it may be considered to arrive at the eye simultaneously with departure from the object-except for astronomical distances). When an object is encountered by the energy it is either absorbed, transmitted, or reflected.

· Light is an electromagnetic wave which carries radiant energy.
· Photons are particles of light waves.
· The speed of light in fee space (a Vacuum) is 186,282 miles/second.
· Electromagnetic light waves vary in frequency (the number of waves per second) and length (wavelength). The higher the frequency the shorter the wavelength.
· Frequency times wavelength equals the speed of the wave.
· Light rays are invisible unless they are reflected.
· VISIBLE LIGHT is that portion of the electromagnetic spectrum that stimulates the sense of sight.
· Ultraviolet rays are produced by the sun and special lamps. They are not detected by the eye, though they affect photographic film and cause suntan. Ordinary glass does not transmit much ultraviolet. Ultraviolet wavelengths are longer than X-rays but shorter than light.
· Infrared radiation has longer waves than light. It is sensed as heat.
· Gamma rays and X-rays are penetrating radiations that are absorbed very little in passing through solid matter. The amount of absorption depends on the density of the material so they are used for shadowgrams (X-rays) of the denser parts of an object.
· White light (colorless light) is a mixture of all the visible wavelengths (sunlight). An object that equally reflects all the wavelengths appears white to our eyes.
· The index of refraction (vending of light) is the ratio of the speed of light in air to the speed of light in some medium.
· The sun's light is reflected in the earth's atmosphere by dust and water particles giving color to the sky and clouds. Light rays are made visible by dust and moisture.
· The scattering of sunlight by the atmosphere is greater for short (blue) waves than for long (red) ones. The sun overhead at noon appears yellow and the scattered light is blue due to the relatively short atmospheric path. At sunset, more blue rays are scattered in the longer path and the sun appears red. The reflection of this red light from the clouds makes the sky pink.
· Colors on soap bubbles are caused by reflections inside and outside of the bubble. The bubble wall has an uneven thickness producing an irregular rainbow effect.
· Shadows have fuzzy edges because as the rays diffract they can interfere and cancel one another.
· Polarizaton of light occurs when the light is forced by molecular structure to one plane of movement (horizontal): when the same molecular structure is placed behind it and is turned, the waves are reduced until they are completely blocked when the molecular structure is at a 90 degree angle (vertical).

LIGHT EXPERIMENTS

The following experiments can be done by dividing the class into groups. Have each group demonstrate and report on their experiment to the rest of the class.

Bending light: Place a ruler in a deep bowl. Where does the ruler appear to bend? Add more water. What happens? Put a jar in front of a book: what happens to the print? Fill the jar with water and observe. Move the jar away from the book and observe (Catherall, 1981).

Light rays are invisible: Paint the inside of a box black and the inside of 2 cardboard tubes. Cut holes in the box and insert the tubes at each short end. Tape in place. Tape the lid on the box. Cut a window in one long side and cover with transparent plastic (figure 2.14). In a dark room, shine a flashlight through the tubes onto a white piece of paper at the end. Looking into the box you will see blackness (Jollands, 1984).

Light travels in straight lines: Make holes in the center of three cards. Use clay or something to stand them upright. Shine a flashlight through the holes. What happens if the holes are not in a straight line (Catherall, 1981)?

Shadows: Stand a white card upright (use clay or something to hold it up). Shine a flashlight on the card. Stand a pencil between them. What do you see on the card? Move the pencil. How can you make the shadow get smaller? Move the flashlight. What happens to the shadow? What happens if you use two flashlights? You can make a shadow theater with firugres fastened to the pencil or a straw to move them around (Catherall, p. 25).

Separating light wavelengths: cover the widows of the room except for one hole that allows the light through. Hold an optical device such as a prism or a diffraction grating in the path of the white light beam. This will spread out the energies in the light along a wavelength axis making each wavelength separate. This band of light is called the "spectrum" and varies in color from the shortest visible wavelength violet, through blue, green, yellow, and orange to the longest visible wavelength, red. The color dies out at both end where the response of the eye fails.

Pinhole camera: Make a hole in the bottom of a can (with a hammer and nail). Cover the hole with aluminum foil (tape it on). Cover the hole with aluminum foil in line with the hole in the can. Cover the other end with waxed paper and rubberband it in place. Darken the room then put the pinhole toward the window. What do you see? What happens if you slightly enlarge the pinhole (Catherall, 1981)?

Magnification: Make a small hole in a piece of aluminum foil. Fold the foil to make a bridge. Place a drop of water to rest on the hole and place something under the foil bridge. Look down through the drop of water. Does it magnify? What shape is the water drop? What happens if you make a larger hole in the foil?

Mirrors: Stand two mirrors upright facing each other with a coin between them. How many coins do you see? Place the mirrors at right angles with a coin between. How many coins can be seen? Move the mirrors towards each other as if closing a book. What happens? Form a triangle with the addition of a third mirror. Drop colored paper in the center and watch the kaleidoscope pattern (Catherall, 1981)

Look into the bowl of a spoon and the back of a spoon. Move the spoon closer and farther away. What do you see? Can you explain why the image in the bowl of the spoon is upside-down? Why are mirrors on cars curved? Why are mirrors placed in supermarkets and other stores? Where are they placed and which way are they curved (Catherall, 1981)?

THE NATURE OF SIGHT

Following are some miscellaneous scientific facts regarding sight:

· The cornea transmits nearly 100 percent of the visible rays that strike it, and bends rays so they converge on the retina.
· The cornea does most of the refraction of light to the retina because of the difference between the density of air and the cornea.
· The pupil not only controls light, but shrinks to sharpen near vision.
· The rods have a purple pigment called rhodopsin (visual purple) that provides the "seeing" ability-discovered in 1876 by a German professor of physiology, Franz C. Boll.
· The cones have three different pigments for color vision. Incoming light is absorbed by the visual pigment which goes through a chemical change in shape which triggers an electrical change and amplification-this sets off the signal impulses to the optic nerve.
· Everyone has a blindspot where the optic nerve cord leaves the eye because there are no nerve cells to register an image. With both eyes, one will make up for the blindspot in the other.
·"Adaptation" is the phasing in and out of daylight and night vision. When a lighting change occurs too rapidly the visual system temporarily breaks down. Thus, moving quickly from a dark room in to the daylight can be blinding and painful.
· "Vergence" is the eye movement that turns the eyes inward toward close objects.
· The iris color is determined by the amount of melanin (skin pigment). Blue has the least melanin. At birth, the pigment is hidden down in the folds of the iris making all babies' eyes blue. Within a few months the melanin travels upward taking its place on the iris's surface to determine lifelong eye color.
· A decrease in the blood's oxygen due to exercise can dilate the pupil. Anger, fear, pleasure can be read in the eyes (pupil/iris). For centuries merchants have known to watch the eyes of customers-they dilate with desire.
· Dead cells occasionally invade the vitreous humor casting vague shadows that float in the eye.
· When the eyes are open the central nervous system is exposed. This happens nowhere else in the body. To defend from vulnerability, the eyes will slam shut from any sudden movement near the face, a flash of blinding light, or a loud noise. The nerve cells I which eyelashes are rooted are so sensitive that a particle caught b one lash will automatically close the eyes.
· Emotional tears contain a protein that may be related to chemical changes in the blood stream due to stress. Tears may help filter out the body's stressful chemicals.

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UNIT 3 PERCEPTION

The eye is blind to what the mind does not see.
- Arab Proverb

OBJECTIVES Unit 3 is designed to achieve specific objectives which are:
· to increase understanding of how our minds are able to perceive and comprehend the visual world;
· to increase comprehension of images, symbols, and other visual communication;
· to increase understanding of perceptual illusions;
· to increase perceptual acuity;
· to improve self-expression through visual communications to others;
· to explain practical applications of this information; and
· to relate this information to art and design.

THEORIES OF PERCEPTION

LECTURE The teacher will direct the following lecture to the students:

Seeing is more than receiving stimuli in the eye. It is the result of becoming aware of them. Perception is a matter of how one responds to what the eye receives. A modern camera may be able to produce a more accurate image than the human eye, but in humans, sight is connected with the brain. The brain adds memory, imagination, and emotion to the image in the eye.

Right after birth one begins the process to learn and remember how things look. It takes a baby a short time to figure out what the images are that are before his/her eyes. Soon, the baby will recognize people and remember mom and dad. After a while the baby won't have to keep figuring out what he/she is seeing because the brain has stored enough information to instantaneously recognize familiar features and objects.

ACTIVITY The teacher will direct the following activity. Begin by instructing the students to close their eyes, then continue with the discussion as follows:

With your eyes closed, think of all the people you have known. Consider friends, family, entertainers, and political figures that you could recognize if you saw their pictures. Can you "see" their face in your "mind's eye"? Does it amaze you how many people you would be able to recognize?

Visualize in your mind something you have seen before. For example, can you count the windows in the house you grew up in? Can you do it while focusing on an object in front of you, or do you have to focus in your mind? Can you see the whole house and count all the windows at once? Do you have to "look" at each room?

LECTURE The teacher will continue by directing the following lecture to the students:
How does the visual system recognize different facial features and sort out one person from another? How is it that we can recognize the scene inside a room as separate from what we see outside a window? Through the help of science we can unravel some of the mysteries of perception. We can understand somewhat about how we recognize one shape from another, different textures, three-dimensionality, solidity of objects, distance, and motion.

Information processing. Visual perception requires an information processing system, the brain. An enormous amount of material pours constantly into the brain through the senses and this must be organized and utilized. Because of the magnitude of information available, the senses and brain must also be able to eliminate unnecessary information.

When we look at an object or scene, we depend on our visual perception to give us cues about it. Then our intelligence and mind's problem-solving capabilities must go to work. Our mind gathers the information available from what meets our eye, then searches for an appropriate category or grouping to identify objects perceived. Such categorization is based on knowledge gained from previous experience (which probably includes other senses).

Gathering information. Visual information is built up by glances directly at scenes and objects. Our scrutiny progresses from the general to the particular. We do not consciously notice or remember details unless we look right at those details. A quick glance at a scene or object will only provide general information. Looking at a friend two or three feet away, we can quickly recognize him, but we see only in general what he is wearing. We must "look him all over" to know more specifically what he is wearing and to see more detail. have you ever seen a friend and felt that something was different about her, without being able to put your finger on what it was? That probably means you have not been very perceptive or observant of details. Perhaps she just had a haircut, but all you have is a feeling that something is different. Details that we note about clothing, furniture, decorations, or whatever, are retained in mind for as long as wanted then as quickly erased.

Filling in. The mind interprets and reacts to as much information as is presented to it and fills in missing parts to make a "whole" that makes sense to us. In other words, on a dark night in our bedroom, our mind does not ignore the small amount of information it receives from our eyes about the shadowy outlines we see. Instead, it takes that information, matches it with previously learned information about our bedroom and its contents, and fills in the missing information so that we are able to recognize our surroundings and furniture. However, when less sensory data is presented to us, there is a decrease in the reliability of our recognition. At some point there is a break between actually "perceiving" an object and "guessing" at it.
When processed correctly, the information received by the eye, together with the interpretation by the brain, results in an accurate perception of an object or scene. All of this happens so quickly that we take it for granted.

Let's discuss in more detail some of the theories about the perceptual skills that make us capable of seeing such things as shapes, objects, and action in our world.

Perceptual Skills

In the eye, the pattern stimulus on the retina is continuous, yet we see separate objects. In the same way, our ears receive sound in one continuous stream, yet we hear words distinctly. Physically, the words run into each other just the same as objects do on the retina. Our mind must be able to take the mass of features we see and determine what regions go together and form a structure. yet, if the retina stimulus is continuous, how is it that we identify one object from another and from its surroundings?

One phenomenon that aids in the recognition of separate objects in space is stereoscopic vision. Our two eyes work together to synthesize two somewhat different images into a single perception of solid objects lying in three-dimensional space. We see three dimensions because the distance between our eyes allows us to see some of the sides of an object along with the front, thus pulling it forward from its background (see more about stereoscopic vision under Illusions.) However, stereo vision does not solve all the problems of object perception.

Recognizing forms as separate from the background, part of perceptual organizing, begins when the mind interprets the patterns that are stimulated on the retina. the mind makes interpretations of a scene based on various cues such as color changes which signal edges, foreground and background relationships, and grouping of objects.

The mind almost always interprets one part of a visual field as standing out from the rest. This is the figure-ground relationship. That is, the objects or figures are distinguishable or separated from the background. People who have never seen a picture or a photograph must "learn" how to see the objects (that is, to discern the foreground from the background) in that two-dimensional scene. Life would be very confusing if the scenes before our eyes were like modern paintings that flatten space, tilt and distort objects, and project background space into the foreground, such as in a painting by Matisse (slide 3.1). Imagine trying to walk through one of the realistic appearing but absurdly impossible buildings created by the artist Escher (figure 3.1).

Borders and outlines are very important in form perception. Scientists speculate that the eyes see objects only by discerning edges. Large areas of constant intensity provide no information to the brain. Instead, they seem to be inferred from signaling borders, while the central nervous system makes up the missing signals to save information processing in the brain (Gregory, 1978). Note in figure 3.2 how the white shapes appear as background figures that form the edges of convex and concave sided squares. In actual fact, the squares do not exist, but our perception has defined them be creating illusory contours. We also perceive form by assigning to any situation a top, bottom and sides (Freese, 1977).

Following are some of the visual cues that help our mind recognize figure (object) and ground relationships:
- Small areas enclosed in larger areas are taken as figures.
- Repeated patterns can be figure or ground, but not both.
- Straight lines are attributed to figures.
- Emotionally-toned shapes are attributed to figures and make them dominant.

Principles of grouping also aid in the process of determining organization of a scene. Similar shapes, similar sizes, features in proximity, features with continuity, and features with closure are generally grouped together.

The well known, and also debated, Gestalt theory in art indicates that elements with good form, or forming a "good figure," will be perceived together. Note how easily the left and right parenthesis lines are distinguished in figure 3.3a. The same parenthesis lines are hard to picture independently in figure 3.3b where they have been connected, forming closed figures. Some shapes with closure are superior to others according to the Gestalt theory. A good figure is symmetrical, completed and composed of straight or curved lines. For example, circles are better forms than ellipses. (Some artists might agree that some shapes are superior to others, but the theory is debatable.) We also perceive similar shapes and other elements as belonging together. In figure 3.4 the pattern is perceived as dots and squares in rows.

According to the Gestalt theory, elements close to one another are more likely to be grouped by the eye than those farther apart. Figure 3.5a shows how points placed in proximity are grouped. Rather than seeing a line, we tend to see the pattern as pairs of dots.

The law of proximity says that if a group of dots is spaced more closely horizontally, the dots will be perceived as horizontal line groups or rows (figure 3.5b). Dots spaced more closely vertically will be perceived as vertical columns (figure 3.5c). Equally spaced dots allow the perception of both rows and columns with equal ease (figure 3.5d).

However, the complexity of perceptual grouping is revealed in figure 3.5e, where a column of vertical dots is met by an oblique line of dots. Dot "C" of the oblique line is closer to dots "A" and "B" of the vertical column than dots "A" and "B" are to each other. Yet dot "C" is not perceptually grouped with dots "A" and "B." The figure demonstrates that the tendency to group features that follow along and link (continuity), is stronger than perceptual grouping by proximity.

The summation of the Gestalt theory of perception is that "the perceptual whole is more than the sum of its parts" (Frisby, 1980, p. 10). In other words, in a complete composition or scene, the parts seen together create a perceptual experience that has more impact than if you just looked at each part individually.

Perception of Size. An image on the retina is not the true size of the object. Our mind perceives size according to the principle of constancy. The memory stores information that a person does not change in size as he moves away from you. The image on the retina does get smaller as the person moves away, yet we do not see him as smaller in relation to his surroundings. If we know the size of an object from experience, such as a book, it will be perceived as the size we know it to be whether we hold it in our hand or see it across the room. When an object is unfamiliar, depth cues must be used to judge its size if it is at a distance.
Size constancy works only if one is familiar with the sizes of the objects involved. A picture of a fish by itself gives no size clues (figure 3.6a). Next to a large picture of a pencil it appears to be a minnow (figure 3.6b). Next to a small picture of a man the fish looks huge (figure 3.6c).

Does the picture in figure 3.7 [not shown here] of the doll house with the disproportionately large shell inside cause some visual confusion? Normally, we judge the size of an object by relating it to its surroundings. The artwork "Personal Values" by Rene Magritte (figure 3.8) [not shown here] shows an unusual combination of familiar objects in unnatural relative scales.

Shape Constancy. Shape constancy comes from our knowledge of the position of parts of the object, not in accordance with the picture in the eye. Distance has an effect on shape which we generally ignore because we know from experience what the shape is like. However, an artist must learn how shapes change with distance in order to create a scene that convinces the eye that it is seeing things as if they get farther away.

Lighting, or lack of it, can affect the shape we perceive an object to be. For example, a suspended cube seen silhouetted (figure 3.9a) appears flat and has a strange contour (not a square). When lighting reveals its 3-D form (figure 3.9b), the outline shape is subtly changed in the mind although the cube has not moved. The perceptual change possibly happens because shape constancy, initiated by information of the three-dimensional form, modifies the silhouette in the brain (Gregory, 1973 p. 49).

 

Perception of Depth. Put an 8 X 10 paper on a table and close one eye. Put a pencil, the eraser end down, at the bottom left and right corners. Holding the pencils vertically, align them with the edges of the paper. Open both eyes and see how the pencils tilt toward each other. This is the same effect as linear perspective, the convergence of lines at a distant point, a trick that artists use to create the sense of distance in a picture.

Try these experiments to experience how both your eyes work together in distance perception. (1) Roll a piece of paper into a tube and look through the eleven inch length toward an object two or three feet away. At the same time, put your other hand (palm toward your eyes ) against the side of the tube about three inches from your eyes. It will appear as if you are viewing the object through a hole in your hand (you may have to adjust the position of the paper or your hand to create the illusion). The visual cortex has combined the two images from each of your eyes. When you close either eye the illusion will disappear. (2) Hold one finger in front of your eyes at a distance of two feet. When you look directly at it you will see one finger. Now look beyond it (across the street) and focus on the distant scene. Two fingers will be visible. (You may have to experiment with the point your eyes are focusing on to experience the illusion.)

You can expect distortions to occur when a perceived distance is incorrect and when there are misleading depth cues.

Perception of Motion. Why does the world remain stable when we move our eyes? Whenever there is movement the brain has to decide what is moving and what is stable. There are two neural systems that signal movement: the image on the retina and our eye/head movement. When we move, our body cues signal such information and the brain knows that other things are stationary. When we are still the images changing on the retina provide the sensations of motion. L A gunnery uses the same two means as our eyes to detect movement of a target: 1) when stationary, a moving image fires receptors across the retinal wall; or 2) when tracking, the movment of the eye and/or head is signaled.

We use visual motion perception to judge when to swing in baseball, or in tennis while we are running. The whole process takes place without conscious thought or effort. The impulses from our joints, muscles, skin and inner ear provide information about our own motion. We rely on our brain to correctly synthesize this information with that received by our eyes, along with timing learned through experience and practice so that we perform a complex task effortlessly.

Information from other senses is overridden by visual perception when it conflicts with the visual sense. For example, scientifically and intellectually we know that the earth rotates around the sun. This does not change our visual perception that makes it appear as if the sun moves across the sky. The moon and stars appear to move with your car when you are traveling (possibly because the angle of the car to them remains unchanged as it moves). Imagine a football, the same size as the moon appears to be, several hundred feet from your car. When you drive past it, it is rapidly left behind. But the moon does not get left behind. The perceptual system may try to reconcile this by interpreting it as an object moving with the car. In a plane it may be a toss-up whether we perceive ourselves or the ground as moving so pilots must rely on mechanical instruments.

The effect of movement can be induced by artificial means. A spiral projected and rotated on a large cinema screen will cause the observer to feel that he is moving forward or away from it. Large screen projections can sweep an observer from his seat with moving images. (You can experience this at Disneyland's 360 degree theatre.) This effect is caused because the entire retina seldom receives systematic movement except when the observer is moving. For this reason, flight simulators need large displays to be effective.

We generally perceive smaller objects as moving and larger objects as stationary. If a spot of light is projected on a large mobile screen, when the screen is moved, the spot will be perceived as moving. This effect can be important when driving a car: is that person over there moving or is the emergency brake of your car off? The author experienced this sensation when parked on a the slight hill of a drive-in theater. The car began moving backward and the sound speaker hooked to the window was almost yanked off the cord before the author realized that it was her own car that was moving not the one next to it.

At times the senses can be confused. The world can swing round us when we are overly fatigued or under the influence of alcohol. This is possibly caused by errors in the nervous system which under normal conditions would be rejected by the brain. Hallucinations are internal visual distortions when information from the eyes and other senses is low but activity of the brain cells is high causing images originating in the brain to be perceived as coming from outside the senses.

Perception of Brightness. Seeing brightness is an experience. It is also a function of the intensity of light being received by the eye in combination with the light the eye has been subject to in the recent past. In low level light the eyes grow more sensitive and a given light will look brighter.

Brightness is also affected by the intensity of surrounding areas. Weber's Law states that the smallest difference in intensity which can be detected is directly proportional to the background intensity (Gregory, 1978). In other words, an area looks brighter if its surroundings are dark. Slide 3.2 shows how four gray triangles of the same brightness appear to have different intensities on each of four backgrounds which vary from white to black.

The affect of surrounding light can also be demonstrated by lighting a candle in a bright room. You will notice that the effect of one candle in a bright room is not very noticeable. In a dim room, one candle makes a distinct difference.

The brightness of color is also affected by surroundings. Colors look more intense when surrounded by their complementary color (see Color for more detail).

Inborn Perceptual Skills. Scientists are still trying to discover what perceptual skills humans are born with and which are acquired through learning and environment. Blind people have been found to have an intuitive sense of perspective and can depict shape and motion in drawings without having been taught to draw. A person blind in one eye can learn to judge distance to drive a car or pilot a plane.

A person blinded at ten months of age, received his sight again much later in life at age 52. He quickly learned to recognize things he had touched and asked many questions about, such a time on a clock, and animals. However, he never did learn to judge depth or distance or recognize facial expressions. In fact, this man became depressed about the visual world, quit turning on lights, and died within three years of regaining his sight (Froman, 1970).

From Images to Meaning

Imagery. An image is a representation or likeness of an actual object or figure. Seeing is dependent on the creation of images in the eye and mind, because an object itself certainly cannot be inside the head. Images are part of thinking, dreaming, remembering, and imagining. Perceiving and thinking are not independent: "I see what you mean" is not a pun but indicates a real connection. We can see something in our mind's eye. We can remember faces when we have forgotten names. We imagine by picturing something in the mind. Inventions are created when someone looks at something and sees in the "mind's eye" a creativge use for it.

The brain responds to visual images on one or more of the following levels: identifying patterns of color, interpreting meaning; and determining expressive content.

Identification. On the first level, identification, when we see a table we don't touch it before setting something on it to see if it is actually a solid object rather than a brown patch on the retina. Through experience, we have stored more than the visual information about the table. The mind quickly links appropriate information, giving meaning to the visual stimuli.

Interpretation. Again, experience provides the basis for perceptual interpretation. For example, after you identify a visual stimulus as the figure of a person across the street with a hand in the air, your perceptual interpretation leads to the conclusion that it is a friend waving a greeting.

Problems in perceptual interpretation arise when a perceiver lacks appropriate categories for classification of visual stimuli. For example, a foreigner may be unaware of the hand signals used by a traffic policeman. Seeing the hand of a policeman raised to stop traffic, the foreigner may interpret the raised hand as a sign of friendship rather than as a signal to stop.

The process of perception is an aid to adjust quickly and smoothly to events. However, when objects perceived are not easily categorized, adjustment and readiness to the situation may slow down. A banal environment can result in a narrower set of classification categories, causing difficulty in identification and interpretation when the environment changes or something unexpected arises.

The visual cues we receive can sometimes create interesting effects if our mind has reached an interpretation (perceptual theory) that proves to be incorrect. This can happen because perception has a tendency to "run ahead of the evidence." For example, when we look at a box that appears heavy, our muscles will tense and put forth the expected energy required to lift its weight. If it is lighter than expected, it will practically fly into the air when our muscles strain to lift it.

Although perceptions that run ahead of the evidence can lead to incorrect interpretation, it is sometimes essential to our survival that our mind be able to interpret stimuli and leap to quick conclusions from a small amount of information provided by the senses. Imagine how long it would take you to react if you had to consciously go through the process of figuring out that a screech of wheels and moving object in front of you was a car that ran a red light. We can react quickly because our perception process tends to ignore redundant and familiar information, focusing instead on changes in stimulation which can signal a need for alertness.

Expressive content. Returning to the example of a friend waving, we take cues from the hand gesture, facial expression, and body posture to determine whether the friend is feeling happy, angry, or indifferent. This is the expressive content. At this point in the perceptual process we have received a message (greeting) from a friend and identified accompanying emotions and feelings. Familiarity and sensitivity are required to correctly understand the significance of the friend's hand gesture and how that gesture reflects his/her personality.

Long before infants can understand formal language or read written words, they learn to read and respond to facial expressions, voice tones, and body movements. Sometimes survival can depend on reading the expressive character of others, whether they are threatening, friendly, or indifferent. Our perceptual skills are exercised everyday as we interpret nonverbal cues and voice tones to determine a person's attitude towards ourselves. We can tell if someone sitting nearby is comfortable, upset, or angry. We find meaning in smiles, as well as lack of a smile.

ACTIVITY The teacher might enlist the aid of some drama students or students from the class to demonstrate expressive content of body language. Choose a mood or emotion to be acted out through facial expression and body movement and have the class guess at the interpretation. Verbal sounds can be included if appropriate, but avoid actual words.

To be continued...

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