HOW WE SEE OUR WORLD
OPTICAL ILLUSIONS HOW WE SEE OUR WORLD
CONTENTS
07 1 2 Ch 20 C apt h e Ch apte r 1 : ap r 2 P R ter O : 3 : VIS PER V I UA T I EW L ES IN PER OF G TH CEP LIG H T E W ION T A OR ND LD TH
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OPTICAL ILLUSIONS | HOW WE SEE OUR WORLD
Chapter 1
Properties of light and the Human Eye
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Electromagnetic waves exist with an enormous range of frequencies. This continuous range of frequencies is known as the electromagnetic spectrum. The entire range of the spectrum is often broken into specific regions. The subdividing of the entire spectrum into smaller spectra is done mostly on the basis of how each region of electromagnetic waves interacts with matter. The diagram below depicts the electromagnetic spectrum and its various regions. The longer wavelength, lower frequency regions are located on the far left of the spectrum and the shorter wavelength, higher frequency regions are on the far right. Two very narrow regions within the spectrum are the visible light region and the X-ray region. You are undoubtedly familiar with some of the other regions of the electromagnetic spectrum. The very narrow band of wavelengths located to the right of the infrared region and to the left of the ultraviolet region. Though electromagnetic waves exist in a vast range of wavelengths, our eyes are sensitive to only a very narrow band. Since this narrow band of wavelengths is the means by which humans see, we refer to it as the visible light spectrum. Normally when we use the term “light,� we are refer-
ring to a type of electromagnetic wave that stimulates the retina of our eyes. In this sense, we are referring to visible light, a small spectrum from the enormous range of frequencies of electromagnetic radiation. This visible light region consists of a spectrum of wavelengths that range from approximately 700 nanometers (abbreviated nm) to approximately 400 nm. Expressed in more familiar units, the range of wavelengths extends from 7 x 10-7 meter to 4 x 10-7 meter. This narrow band of visible light is affectionately known as ROYGBIV. Each individual wavelength within the spectrum of visible light wavelengths is representative of a particular color. That is, when light of that particular wavelength strikes the retina of our eye, we perceive that specific color sensation. Isaac Newton showed that light shining through a prism will be separated into its different wavelengths and will thus show the various colors that visible light is comprised of. The separation of visible light into its different colors is known as dispersion. Each color is characteristic of a distinct wavelength; and different wavelengths of light waves will bend varying amounts upon passage through a prism. For
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How Our See Color
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Color can be thought of as a psychological and physiological response to light waves of a specific frequency or set of frequencies impinging upon the eye. An understanding of the human response to color demands that one understand the biology of the eye. Light that enters the eye through the pupil ultimately strikes the inside surface of the eye known as the retina. The retina is lined with a variety of light sensing cells known as rods and cones. While the rods on the retina are sensitive to the intensity of light, they cannot distinguish between lights of different wavelengths. On the other hand, the cones are the color-sensing cells of the retina. When light of a given wavelength enters the eye and strikes the cones of the retina, a chemical reaction is activated that results in an electrical impulse being sent
along nerves to the brain. It is believed that there are three k inds o f cones, each s ensitive to i ts own range of wavelengths within the visible light spectrum. These three kinds of cones are referred to as red cones, green cones, and blue cones because of their respective sensitivity to the wavelengths of light that are associated with red, green and blue. Since the red cone is sensitive to a range of wavelengths, it is not only activated by wavelengths of red light, but a lso (to a lesser extent) by wavelengths of orange light, yellow light and even green light. In the same manner, the green cone is most sensitive t o wavelengths of light associated with t he color green. Yet the green cone can also be activated by wavelengths of light associated with the colors yellow and blue.
Chapter 2
Visual Perception
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OPTICAL ILLUSIONS | HOW WE SEE OUR WORLD
VISUAL PERCEPTION
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Visual perception is t he ability to i nterpret the surrounding environment by processing information that is contained i n visible light. The resulting perception is a lso known as eyesight, sight, o r vision ( adjectival form: visual, optical, or o cular). The various physiological components involved in vision are referred to collectively as the visual system, and are the focus of much research in psychology, cognitive science, neuroscience, and molecular biology, collectively referred to as vision science. The m ajor problem i n visual perception i s that w hat people see is not simply a translation of retinal stimuli (i.e., the image on the retina). Thus people interested in perception have long struggled to explain what visual processing does to create what is actually seen. Hermann von Helmholtz is often credited with the first study of visual perception in modern times. Helmholtz examined t he human eye a nd concluded t hat i t was, optically, rather p oor. The p oor-quality information gathered via the eye seemed to him to make vision impossible. He therefore concluded that vision could only be the result of some form of unconscious inferences: a matter of making assumptions and conclusions from incomplete data, based on previous experiences. Inference requires prior experience of the world.
Examples of well-known assumptions, based on visual experience, are: • light comes from above • objects are normally not viewed from below • faces are seen (and recognized) upright. • closer objects can block the view of more distant objects, but not vice versa The study of v isual illusions ( cases w hen t he i nference process goes wrong) has yielded much insight into w hat s ort of assumptions the v isual system makes.
Various visual cues such as color and shape are telling our brains that there is a cube in the center of the feild.
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WHICH TWO DOTS
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To beter understand perception, we can play a game, And to win this game, all you have to do is see the reality that’s in front of you as it really is, all right? So we have two panels here, of colored dots. And one of those dots is the same in the two panels. Can you tell which one?
ARE THE SAME?
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If you lift the black square it becomes much more clear which dot is the same. This is pretty amazing. Because nearly every living system has evolved the ability to detect light in one way or another. So for us, seeing color is one of the simplest things the brain does. And yet, even at this most fundamental level, context is everything. What I’m going to talk about is not that context is everything, but why context is everything. Because it’s answering that question that tells us not only why we see what we do, but who we are as individuals, and who we are as a society.
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HOW BEES SEE
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And now, in this experiment they get a reward if they go to the blue flowers. They land on the flower, stick their tongue in there, called a proboscis, and drink sugar water. She’s drinking a glass of water that’s about that big to you and I, will do that about three times, then fly. And sometimes they learn not to go to the blue, but to go where the other bees go. So they copy each other. They can count to five. They can recognize faces. And here she comes down the ladder. And she’ll come into the hive, find an empty honey pot, and throw up, and that’s honey.
Now remember, she’s supposed to be going to the blue flowers, but what are these bees doing in the upper right corner? It looks like they’re going to green flowers. Now, are they getting it wrong? And the answer to the question is no. Those are actually blue flowers. But those are blue flowers under green light. So they’re using the relationships between the colors to solve the puzzle, which is exactly what we do.
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OPTICAL ILLUSIONS | HOW WE SEE OUR WORLD
Humans are interesting creatures. We look at the world with some of the most advanced eyes and minds, but often fail to realize that others see the world differently than we do. While this idea is often put forward when talking about the way other people experience the world, in this case I’m literally talking about vision. In the vast electromagnetic spectrum of wavelengths (extending from below the long wavelengths used for radio, to the short wavelengths of gamma radiation) we humans see only a miniscule fraction that we call visible light. This small sliver, spanning the distance between violet and red is the way we perceive the world around us with our eyes. However bees and other insects have a different view of the world. Their whole range of light is shifted further towards the violet end of the spectrum and further from the red. This means that, while they can’t perceive red, they see colors we simply cannot see – what we call ultra-violet. This also means is that bees see a world literally hidden before our eyes. Snakes do not see colors, but their eyes are equipped with a combination of light receptors: rods that provide low-light but fuzzy vision, and cones that produce clear images. The complexity of the eyes varies among species because of their different lifestyles. For instance, snakes that live primarily underground have smaller eyes that only process light and dark, but snakes that live above ground and hunt by sight have crystal-clear vision and good depth perception. Some species, specifically boas and pythons, have a second visual tool: Pit organs on their heads see heat sources in their surroundings like infrared goggles -- an effective ability for nocturnal hunters of warm-blooded animals.
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OPTICAL ILLUSIONS | HOW WE SEE OUR WORLD
CONCLUSION
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OPTICAL ILLUSIONS | HOW WE SEE OUR WORLD
So, illusions are often used, especially in art, in the words of a more contemporary artist, “to demonstrate the fragility of our senses.” Okay, this is complete rubbish. The senses aren’t fragile. And if they were, we wouldn’t be here. Instead, color tells us something completely different, that the brain didn’t actually evolve to see the world the way it is. We can’t. Instead, the brain evolved to see the world the way it was useful to see in the past. And how we see is by continually redefining normality. So, how can we take this incredible capacity of plasticity of the brain and get people to experience their world differently? Well, one of the ways we do it in my lab and studio is we translate the light into sound, and we enable people to hear their visual world. And they can navigate the world using their ears. Now, what does all this mean? What this suggests is that no one is an outside observer of nature, okay? We’re not defined by our central properties, by the bits that make us up. We’re defined by our environment and our interaction with that environment, by our ecology. And that ecology is necessarily relative, historical and empirical. So, what I’d like to finish with is this over here. Because what I’ve been trying to do is really celebrate uncertainty. Because I think only through uncertainty is there potential for understanding.
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This Book was designed, printed, and bound by Tyler Balogh Fall 2015 Visual Systems 1 Programs Printer Paper
Megumi Kiyama_Instructor Adobe CC Indesign and Illustrator Epson Artisan 1430 Moab Lasil, Bright White