{"id":156,"date":"2015-02-06T23:15:46","date_gmt":"2015-02-06T23:15:46","guid":{"rendered":"https:\/\/courses.candelalearning.com\/ospsych\/?post_type=chapter&#038;p=156"},"modified":"2024-07-19T15:15:20","modified_gmt":"2024-07-19T15:15:20","slug":"vision","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/waymaker-psychology\/chapter\/vision\/","title":{"raw":"How We See","rendered":"How We See"},"content":{"raw":"<section data-depth=\"1\">\r\n<div class=\"textbox learning-objectives\">\r\n<h3>Learning Objectives<\/h3>\r\n<ul>\r\n \t<li>Describe the basic anatomy of the visual system<\/li>\r\n \t<li>Describe how light waves enable vision<\/li>\r\n<\/ul>\r\n<\/div>\r\n<h2>Anatomy of the Visual System<\/h2>\r\n<div class=\"ab-test-alternative\">\r\n\r\nThe eye is the major sensory organ involved in\u00a0<strong>vision<\/strong> (Figure 1). There are several parts of the eye from the front to the back side, including the cornea, pupil, iris, lens, retina, fovea, and optic nerve. The cornea, pupil, iris, and lens are situated toward the front of the eye. At the back are the retina, fovea, and optic nerve. The slideshow (in Figure 1) below shows those parts, one at a time, along with a brief description. You will get to practice at the end of the slide.\r\n\r\n<strong>Figure 1.<\/strong>\u00a0The anatomy of the eye is illustrated in this activity.\r\n\r\n<iframe src=\"https:\/\/lumenlearning.h5p.com\/content\/1291637308837611378\/embed\" width=\"1088\" height=\"637\" frameborder=\"0\" allowfullscreen=\"allowfullscreen\" aria-label=\"Anatomy of the Visual System v2\"><\/iframe><script src=\"https:\/\/lumenlearning.h5p.com\/js\/h5p-resizer.js\" charset=\"UTF-8\"><\/script>\r\n\r\nNow let us dive into each of the parts in detail.\r\n<h3>Cornea<\/h3>\r\nThe <strong>cornea<\/strong> is the transparent covering over the eye. It serves as a barrier between the inner eye and the outside world, and it is involved in focusing light waves that enter the eye. Light waves are transmitted across the cornea and enter the eye through the pupil.\r\n<h3>Pupil<\/h3>\r\nThe\u00a0<strong>pupil<\/strong>\u00a0is the small opening in the eye through which light passes, and the size of the pupil can change as a function of light levels as well as emotional arousal. When light levels are low, the pupil will become dilated, or expanded, to allow more light to enter the eye. When light levels are high, the pupil will constrict, or become smaller, to reduce the amount of light that enters the eye.\r\n<h3>Iris<\/h3>\r\nThe <strong>iris<\/strong> is the colored portion of the eye. It is connected to the muscles that control the pupil\u2019s size.\r\n<h3>Lens<\/h3>\r\nThe <strong>lens<\/strong> is a curved, transparent structure that serves to provide additional focus for light entering the eye. Light crosses the lens after passing through the pupil. The lens is attached to muscles that can change its shape to aid in focusing light that is reflected from near or far objects.\r\n<h3>Retina<\/h3>\r\nThe <strong>retina<\/strong> is the light-sensitive lining of the eye located at the back of the eye.\r\n<h3>Fovea<\/h3>\r\nThe <strong>fovea<\/strong>, which is part of the retina, is a small indentation in the back of the eye. In a normal-sighted individual, the lens will focus images perfectly on fovea. The fovea contains densely packed specialized <strong>photoreceptor<\/strong> cells, known as <strong>cones<\/strong>, which are light-detecting cells. Another type of photoreceptor is rods. See Figure 2.\r\n<figure>\r\n\r\n[caption id=\"attachment_6756\" align=\"aligncenter\" width=\"468\"]<a href=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/855\/2015\/02\/29194236\/7092854136b856409f1dbe9f76d123492b979928.jpeg\"><img class=\" wp-image-6756\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/855\/2015\/02\/29194236\/7092854136b856409f1dbe9f76d123492b979928-300x262.jpeg\" alt=\"This illustration shows light reaching the optic nerve, beneath which are Ganglion cells, and then rods and cones.\" width=\"468\" height=\"409\" \/><\/a> <strong>Figure 2<\/strong>. The two types of photoreceptors are shown in this image. Cones are colored green and rods are blue.[\/caption]<\/figure>\r\nThe cones are specialized types of photoreceptors that work best in bright light conditions. Cones are very sensitive to acute detail and provide tremendous spatial resolution. They also are directly involved in our ability to perceive color.\r\n\r\nWhile cones are concentrated in the fovea, where images tend to be focused, rods, another type of photoreceptor, are located throughout the remainder of the retina. <strong>Rods<\/strong> are specialized photoreceptors that work well in low light conditions, and while they lack the spatial resolution and color function of the cones, they are involved in our vision in dimly lit environments as well as in our perception of movement on the periphery of our visual field.\r\n\r\nWe have all experienced the different sensitivities of rods and cones when making the transition from a brightly lit environment to a dimly lit environment. Imagine going to see a blockbuster movie on a clear summer day. As you walk from the brightly lit lobby into the dark theater, you notice that you immediately have difficulty seeing much of anything. After a few minutes, you begin to adjust to the darkness and can see the interior of the theater. In the bright environment, your vision was dominated primarily by cone activity. As you move to the dark environment, rod activity dominates, but there is a delay in transitioning between the phases. If your rods do not transform light into nerve impulses as easily and efficiently as they should, you will have difficulty seeing in dim light, a condition known as night blindness.\r\n\r\nRods and cones are connected (via several interneurons) to retinal ganglion cells. Axons from the retinal ganglion cells converge and exit through the back of the eye to form the optic nerve.\r\n<h3>Optic Nerve<\/h3>\r\nRods and cones are connected (via several interneurons) to retinal ganglion cells (see Figure 2 again). Axons from the retinal ganglion cells converge and exit through the back of the eye to form the optic nerve. The\u00a0<strong>optic nerve<\/strong>\u00a0carries visual information from the retina to the brain. There is a point in the visual field called the\u00a0blind spot (not shown in Figure 1): Even when light from a small object is focused on the blind spot, we do not see it. We are not consciously aware of our blind spots for two reasons: First, each eye gets a slightly different view of the visual field; therefore, the blind spots do not overlap. Second, our visual system fills in the blind spot so that although we cannot respond to visual information that occurs in that portion of the visual field, we are also not aware that information is missing.\r\n\r\n<\/div>\r\n<div class=\"ab-test-original\">\r\n\r\nThe eye is the major sensory organ involved in <strong>vision<\/strong> (Figure 1). Light waves are transmitted across the cornea and enter the eye through the pupil. The <strong>cornea<\/strong> is the transparent covering over the eye. It serves as a barrier between the inner eye and the outside world, and it is involved in focusing light waves that enter the eye. The <strong>pupil<\/strong> is the small opening in the eye through which light passes, and the size of the pupil can change as a function of light levels as well as emotional arousal. When light levels are low, the pupil will become dilated, or expanded, to allow more light to enter the eye. When light levels are high, the pupil will constrict, or become smaller, to reduce the amount of light that enters the eye. The pupil\u2019s size is controlled by muscles that are connected to the <strong>iris<\/strong>, which is the colored portion of the eye.\r\n<figure>\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"586\"]<img class=\"\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/902\/2015\/02\/23224718\/CNX_Psych_05_03_Eye.jpg\" alt=\"Different parts of the eye are labeled in this illustration. The cornea, pupil, iris, and lens are situated toward the front of the eye, and at the back are the optic nerve, fovea, and retina.\" width=\"586\" height=\"416\" data-media-type=\"image\/jpg\" \/> <strong>Figure 1<\/strong>. The anatomy of the eye is illustrated in this diagram.[\/caption]<\/figure>\r\nAfter passing through the pupil, light crosses the <strong>lens<\/strong>, a curved, transparent structure that serves to provide additional focus. The lens is attached to muscles that can change its shape to aid in focusing light that is reflected from near or far objects. In a normal-sighted individual, the lens will focus images perfectly on a small indentation in the back of the eye known as the <strong>fovea<\/strong>, which is part of the <strong>retina<\/strong>, the light-sensitive lining of the eye. The fovea contains densely packed specialized photoreceptor cells (Figure 2). These <strong>photoreceptor<\/strong> cells, known as <strong>cones<\/strong>, are light-detecting cells. The cones are specialized types of photoreceptors that work best in bright light conditions. Cones are very sensitive to acute detail and provide tremendous spatial resolution. They also are directly involved in our ability to perceive color.\r\n\r\nWhile cones are concentrated in the fovea, where images tend to be focused, rods, another type of photoreceptor, are located throughout the remainder of the retina. <strong>Rods<\/strong> are specialized photoreceptors that work well in low light conditions, and while they lack the spatial resolution and color function of the cones, they are involved in our vision in dimly lit environments as well as in our perception of movement on the periphery of our visual field.\r\n<figure>\r\n\r\n[caption id=\"attachment_6756\" align=\"aligncenter\" width=\"468\"]<a href=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/855\/2015\/02\/29194236\/7092854136b856409f1dbe9f76d123492b979928.jpeg\"><img class=\" wp-image-6756\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/855\/2015\/02\/29194236\/7092854136b856409f1dbe9f76d123492b979928-300x262.jpeg\" alt=\"This illustration shows light reaching the optic nerve, beneath which are Ganglion cells, and then rods and cones.\" width=\"468\" height=\"409\" \/><\/a> <strong>Figure 2<\/strong>. The two types of photoreceptors are shown in this image. Cones are colored green and rods are blue.[\/caption]<\/figure>\r\nWe have all experienced the different sensitivities of rods and cones when making the transition from a brightly lit environment to a dimly lit environment. Imagine going to see a blockbuster movie on a clear summer day. As you walk from the brightly lit lobby into the dark theater, you notice that you immediately have difficulty seeing much of anything. After a few minutes, you begin to adjust to the darkness and can see the interior of the theater. In the bright environment, your vision was dominated primarily by cone activity. As you move to the dark environment, rod activity dominates, but there is a delay in transitioning between the phases. If your rods do not transform light into nerve impulses as easily and efficiently as they should, you will have difficulty seeing in dim light, a condition known as night blindness.\r\n\r\nRods and cones are connected (via several interneurons) to retinal ganglion cells. Axons from the retinal ganglion cells converge and exit through the back of the eye to form the optic nerve. The <strong>optic nerve<\/strong> carries visual information from the retina to the brain. There is a point in the visual field called the <strong>blind spot<\/strong>: Even when light from a small object is focused on the blind spot, we do not see it. We are not consciously aware of our blind spots for two reasons: First, each eye gets a slightly different view of the visual field; therefore, the blind spots do not overlap. Second, our visual system fills in the blind spot so that although we cannot respond to visual information that occurs in that portion of the visual field, we are also not aware that information is missing.\r\n\r\n<\/div>\r\n<div class=\"textbox tryit\">\r\n<h3>Try It<\/h3>\r\nhttps:\/\/assess.lumenlearning.com\/practice\/e78d435f-f8f2-4257-8213-ec8557fa7cc5\r\n\r\n<\/div>\r\nThe optic nerve from each eye merges just below the brain at a point called the <strong>optic chiasm<\/strong>. As Figure 3 shows, the optic chiasm is an X-shaped structure that sits just below the cerebral cortex at the front of the brain. At the point of the optic chiasm, information from the right visual field (which comes from both eyes) is sent to the left side of the brain, and information from the left visual field is sent to the right side of the brain.\r\n<figure>\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"573\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/902\/2015\/02\/23224723\/CNX_Psych_05_03_OpticChias.jpg\" alt=\"Visual stimuli enter the eyes, pass through the optic nerve and into the optic chiasm, then back to the occipital lobe at the back of the brain.\" width=\"573\" height=\"412\" data-media-type=\"image\/jpg\" \/> <strong>Figure 3<\/strong>. This illustration shows the optic chiasm at the front of the brain and the pathways to the occipital lobe at the back of the brain, where visual sensations are processed into meaningful perceptions.[\/caption]<\/figure>\r\nOnce inside the brain, visual information is sent via a number of structures to the occipital lobe at the back of the brain for processing. Visual information might be processed in parallel pathways which can generally be described as the \u201cwhat pathway\u201d (the ventral pathway) and the \u201cwhere\/how\u201d pathway (the dorsal pathway). The \u201cwhat pathway\u201d is involved in object recognition and identification, while the \u201cwhere\/how pathway\u201d is involved with location in space and how one might interact with a particular visual stimulus (Milner &amp; Goodale, 2008; Ungerleider &amp; Haxby, 1994). For example, when you see a ball rolling down the street, the \u201cwhat pathway\u201d identifies what the object is, and the \u201cwhere\/how pathway\u201d identifies its location or movement in space.\r\n\r\n<\/section>&nbsp;\r\n\r\n[caption id=\"attachment_2153\" align=\"aligncenter\" width=\"524\"]<a href=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/855\/2016\/10\/26200309\/visualpathways.png\"><img class=\"wp-image-2153\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/855\/2016\/10\/26200309\/visualpathways.png\" alt=\"Areas of the brain showing the ventral pathway, along the side of the brain closer to the temporal lobes, and the dorsal pathway in the back of the brain. It also shows the visual cortex areas at the back of the brain: V1\/V2, V3, V3A, and V4 (associated with color), and the faces and object recognition areas (next to V4).\" width=\"524\" height=\"264\" \/><\/a> <strong>Figure 4<\/strong>. Visual areas in the brain.[\/caption]\r\n\r\n<div class=\"textbox exercises\">\r\n<h3>what do you think?<\/h3>\r\n<h2><strong>The Ethics of Research Using Animals<\/strong><\/h2>\r\nDavid Hubel and Torsten Wiesel were awarded the Nobel Prize in Medicine in 1981 for their research on the visual system. They collaborated for more than twenty years and made significant discoveries about the neurology of visual perception (Hubel &amp; Wiesel, 1959, 1962, 1963, 1970; Wiesel &amp; Hubel, 1963). They studied animals, mostly cats and monkeys. Although they used several techniques, they did considerable single-unit recordings, during which tiny electrodes were inserted in the animal\u2019s brain to determine when a single cell was activated. Among their many discoveries, they found that specific brain cells respond to lines with specific orientations (called ocular dominance), and they mapped the way those cells are arranged in areas of the visual cortex known as columns and hypercolumns.\r\n\r\nIn some of their research, they sutured one eye of newborn kittens closed and followed the development of the kittens' vision. They discovered there was a critical period of development for vision. If kittens were deprived of input from one eye, other areas of their visual cortex filled in the area that was normally used by the eye that was sewn closed. In other words, neural connections that exist at birth can be lost if they are deprived of sensory input.\r\n\r\nWhat do you think about sewing a kitten's eye closed for research? To many animal advocates, this would seem brutal, abusive, and unethical. What if you could do research that would help ensure babies and children born with certain conditions could develop normal vision instead of becoming blind? Would you want that research done? Would you conduct that research, even if it meant causing some harm to cats? Would you think the same way if you were the parent of such a child? What if you worked at the animal shelter?\r\n\r\nLike virtually every other industrialized nation, the United States permits medical experimentation on animals, with few limitations (assuming sufficient scientific justification). The goal of any laws that exist is not to ban such tests but rather to limit unnecessary animal suffering by establishing standards for the humane treatment and housing of animals in laboratories.\r\n\r\nAs explained by Stephen Latham, the director of the Interdisciplinary Center for Bioethics at Yale (2012), possible legal and regulatory approaches to animal testing vary on a continuum from strong government regulation and monitoring of all experimentation at one end, to a self-regulated approach that depends on the ethics of the researchers at the other end. The United Kingdom has the most significant regulatory scheme, whereas Japan uses the self-regulation approach. The U.S. approach is somewhere in the middle, the result of a gradual blending of the two approaches.\r\n\r\nThere is no question that medical research is a valuable and important practice. The question is whether the use of animals is a necessary or even best practice for producing the most reliable results. Alternatives include the use of patient-drug databases, virtual drug trials, computer models and simulations, and noninvasive imaging techniques such as magnetic resonance imaging and computed tomography scans (\u201cAnimals in Science\/Alternatives,\u201d n.d.). Other techniques, such as microdosing, use humans not as test animals but as a means to improve the accuracy and reliability of test results. In vitro methods based on human cell and tissue cultures, stem cells, and genetic testing methods are also increasingly available.\r\n\r\nToday, at the local level, any facility that uses animals and receives federal funding must have an Institutional Animal Care and Use Committee (IACUC) that ensures that the NIH guidelines are being followed. The IACUC must include researchers, administrators, a veterinarian, and at least one person with no ties to the institution: that is, a concerned citizen. This committee also performs inspections of laboratories and protocols.\r\n\r\n<\/div>\r\n<section data-depth=\"1\">\r\n<div class=\"textbox tryit\">\r\n<h3>Try It<\/h3>\r\nhttps:\/\/assess.lumenlearning.com\/practice\/dfbc15d0-5cc0-4286-b96c-4edc4de0f870\r\n\r\nhttps:\/\/assess.lumenlearning.com\/practice\/bad360e6-94d0-4411-b3ee-c82de47df204\r\n\r\nhttps:\/\/assess.lumenlearning.com\/practice\/0b5a82cc-cd64-471d-b838-3282551b4be3\r\n\r\nhttps:\/\/assess.lumenlearning.com\/practice\/f2c40907-189e-42da-95e3-5c40a19a7390\r\n\r\n<\/div>\r\n<h2>Amplitude and Wavelength<\/h2>\r\nAs mentioned above, light enters your eyes as a wave. It is important to understand some basic properties of waves to see how they impact what we see. Two physical characteristics of a wave are <strong>amplitude<\/strong> and wavelength (Figure 5). The amplitude of a wave is the height of a wave as measured from the highest point on the <strong>wave<\/strong> (<strong>peak<\/strong> or <strong>crest<\/strong>) to the lowest point on the wave (trough). <strong>Wavelength<\/strong> refers to the length of a wave from one peak to the next.\r\n<figure>\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"649\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/902\/2015\/02\/23224709\/CNX_Psych_05_02_Wave.jpg\" alt=\"A diagram illustrates the basic parts of a wave. Moving from left to right, the wavelength line begins above a straight horizontal line and falls and rises equally above and below that line. One of the areas where the wavelength line reaches its highest point is labeled \u201cPeak.\u201d A horizontal bracket, labeled \u201cWavelength,\u201d extends from this area to the next peak. One of the areas where the wavelength reaches its lowest point is labeled \u201cTrough.\u201d A vertical bracket, labeled \u201cAmplitude,\u201d extends from a \u201cPeak\u201d to a \u201cTrough.\u201d\" width=\"649\" height=\"229\" data-media-type=\"image\/jpg\" \/> <strong>Figure 5<\/strong>. The amplitude or height of a wave is measured from the peak to the trough. The wavelength is measured from peak to peak.[\/caption]<\/figure>\r\nWavelength is directly related to the frequency of a given waveform. <strong>Frequency<\/strong> refers to the number of waves that pass a given point in a given time period and is often expressed in terms of <strong>hertz (Hz<\/strong>), or cycles per second. Longer wavelengths will have lower frequencies, and shorter wavelengths will have higher frequencies (Figure 6).\r\n<figure>\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"510\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/902\/2015\/02\/23224710\/CNX_Psych_05_02_Frequencies.jpg\" alt=\"Stacked vertically are 5 waves of different colors and wavelengths. The top wave is red with a long wavelengths, which indicate a low frequency. Moving downward, the color of each wave is different: orange, yellow, green, and blue. Also moving downward, the wavelengths become shorter as the frequencies increase.\" width=\"510\" height=\"171\" data-media-type=\"image\/jpg\" \/> <strong>Figure 6<\/strong>. This figure illustrates waves of differing wavelengths\/frequencies. At the top of the figure, the red wave has a long wavelength\/short frequency. Moving from top to bottom, the wavelengths decrease and frequencies increase.[\/caption]<\/figure>\r\n<\/section><section data-depth=\"1\">\r\n<h2>Light Waves<\/h2>\r\nThe <strong>visible spectrum<\/strong> is the portion of the larger electromagnetic spectrum that we can see. As Figure 7 shows, the <strong>electromagnetic spectrum<\/strong> encompasses all of the electromagnetic radiation that occurs in our environment and includes gamma rays, x-rays, ultraviolet light, visible light, infrared light, microwaves, and radio waves. The visible spectrum in humans is associated with wavelengths that range from 380 to 740 nm\u2014a very small distance since a nanometer (nm) is one-billionth of a meter. Other species can detect other portions of the electromagnetic spectrum. For instance, honeybees can see light in the ultraviolet range (Wakakuwa, Stavenga, &amp; Arikawa, 2007), and some snakes can detect infrared radiation in addition to more traditional visual light cues (Chen, Deng, Brauth, Ding, &amp; Tang, 2012; Hartline, Kass, &amp; Loop, 1978).\r\n<figure>\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"975\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/902\/2015\/02\/23224712\/CNX_Psych_05_02_Spectrum.jpg\" alt=\"This illustration shows the wavelength, frequency, and size of objects across the electromagnetic spectrum.. At the top, various wavelengths are given in sequence from small to large, with a parallel illustration of a wave with increasing frequency. These are the provided wavelengths, measured in meters: \u201cGamma ray 10 to the negative twelfth power,\u201d \u201cx-ray 10 to the negative tenth power,\u201d ultraviolet 10 to the negative eighth power,\u201d \u201cvisible .5 times 10 to the negative sixth power,\u201d \u201cinfrared 10 to the negative fifth power,\u201d microwave 10 to the negative second power,\u201d and \u201cradio 10 cubed.\u201dAnother section is labeled \u201cAbout the size of\u201d and lists from left to right: \u201cAtomic nuclei,\u201d \u201cAtoms,\u201d \u201cMolecules,\u201d \u201cProtozoans,\u201d \u201cPinpoints,\u201d \u201cHoneybees,\u201d \u201cHumans,\u201d and \u201cBuildings\u201d with an illustration of each . At the bottom is a line labeled \u201cFrequency\u201d with the following measurements in hertz: 10 to the powers of 20, 18, 16, 15, 12, 8, and 4. From left to right the line changes in color from purple to red with the remaining colors of the visible spectrum in between, occurring roughly between 10 to the power of 15 and 10 to the power of 12.\" width=\"975\" height=\"404\" data-media-type=\"image\/jpg\" \/> <strong>Figure 7<\/strong>. Light that is visible to humans makes up only a small portion of the electromagnetic spectrum.[\/caption]<\/figure>\r\nIn humans, light wavelength is associated with perception of color (Figure 8). Within the visible spectrum, our experience of red is associated with longer wavelengths, greens are intermediate, and blues and violets are shorter in wavelength. (An easy way to remember this is the mnemonic ROYGBIV: <strong>r<\/strong>ed, <strong>o<\/strong>range, <strong>y<\/strong>ellow, <strong>g<\/strong>reen, <strong>b<\/strong>lue, <strong>i<\/strong>ndigo, <strong>v<\/strong>iolet.) The amplitude of light waves is associated with our experience of brightness or intensity of color, with larger amplitudes appearing brighter.\r\n<figure>\r\n\r\n[caption id=\"\" align=\"alignnone\" width=\"975\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/902\/2015\/02\/23224713\/CNX_Psych_05_02_VisSpec.jpg\" alt=\"Wavelengths from low to high as measured in nanometers. Below the visible spectrum, in increasing order, are \u201cCosmic radiation,\u201d \u201cGamma rays,\u201d \u201cX-rays,\u201d and \u201cUltraviolet,\u201d. The visible wavelengths of light are between 400 and 700 nanometers. Wavelengths above the visible spectrum, in increasing order, are \u201cInfrared,\u201d \u201cTerahertz radiation,\u201d \u201cRadar,\u201d \u201cTelevision and radio broadcasting,\u201d and \u201cAC circuits.\u201d\" width=\"975\" height=\"186\" data-media-type=\"image\/jpg\" \/> <strong>Figure 8<\/strong>. Different wavelengths of light are associated with our perception of different colors. (credit: modification of work by Johannes Ahlmann)[\/caption]<\/figure>\r\n<div class=\"textbox tryit\">\r\n<h3>Try It<\/h3>\r\nhttps:\/\/assess.lumenlearning.com\/practice\/930c39a8-f512-4590-8552-44c950861781\r\n\r\nhttps:\/\/assess.lumenlearning.com\/practice\/c10cbbbc-3696-49d6-960f-0fe48543e2cb\r\n\r\nhttps:\/\/assess.lumenlearning.com\/practice\/fd1301de-4197-4207-9ce9-dffdd24fa9d7\r\n\r\nhttps:\/\/assess.lumenlearning.com\/practice\/e88c73f0-78be-49ec-bcb9-f65318876734\r\n\r\nhttps:\/\/assess.lumenlearning.com\/practice\/ca761c4c-ca04-4a87-9a5b-cdcb053353ec\r\n\r\nhttps:\/\/assess.lumenlearning.com\/practice\/97269cab-3902-4252-aff1-ceb5f435a07b\r\n\r\n<\/div>\r\n<\/section><section data-depth=\"1\"><section>\r\n<div class=\"textbox key-takeaways\">\r\n<h3>Glossary<\/h3>\r\n<div data-type=\"definition\"><strong>amplitude:\u00a0<\/strong>height of a wave<\/div>\r\n<div data-type=\"definition\"><strong>blind spot:\u00a0<\/strong>point where we cannot respond to visual information in that portion of the visual field<\/div>\r\n<div data-type=\"definition\"><strong>cone:\u00a0<\/strong>specialized photoreceptor that works best in bright light conditions and detects color<\/div>\r\n<div data-type=\"definition\"><strong>cornea:\u00a0<\/strong>transparent covering over the eye<\/div>\r\n<div data-type=\"definition\"><strong>electromagnetic spectrum:<\/strong> all the electromagnetic radiation that occurs in our environment<\/div>\r\n<div data-type=\"definition\"><strong>fovea:\u00a0<\/strong>small indentation in the retina that contains cones<\/div>\r\n<div data-type=\"definition\"><strong>frequency:\u00a0<\/strong>number of waves that pass a given point in a given time period<\/div>\r\n<div data-type=\"definition\"><strong>hertz (Hz):\u00a0<\/strong>cycles per second; measure of frequency<\/div>\r\n<div data-type=\"definition\"><strong>iris:\u00a0<\/strong>colored portion of the eye<\/div>\r\n<div data-type=\"definition\"><strong>lens:\u00a0<\/strong>curved, transparent structure that provides additional focus for light entering the eye<\/div>\r\n<div data-type=\"definition\"><strong>optic chiasm:\u00a0<\/strong>X-shaped structure that sits just below the brain\u2019s ventral surface; represents the merging of the optic nerves from the two eyes and the separation of information from the two sides of the visual field to the opposite side of the brain<\/div>\r\n<div data-type=\"definition\"><strong>optic nerve:\u00a0<\/strong>carries visual information from the retina to the brain<\/div>\r\n<div data-type=\"definition\"><strong>peak:\u00a0<\/strong>(also, crest) highest point of a wave<\/div>\r\n<div data-type=\"definition\"><strong>photoreceptor:\u00a0<\/strong>light-detecting cell<\/div>\r\n<div data-type=\"definition\"><strong>pupil:\u00a0<\/strong>small opening in the eye through which light passes<\/div>\r\n<div data-type=\"definition\"><strong>retina:\u00a0<\/strong>light-sensitive lining of the eye<\/div>\r\n<div data-type=\"definition\"><strong>rod:\u00a0<\/strong>specialized photoreceptor that works well in low light conditions<\/div>\r\n<div data-type=\"definition\"><strong>trough:\u00a0<\/strong>lowest point of a wave<\/div>\r\n<div data-type=\"definition\">\r\n<div data-type=\"definition\"><strong>visible spectrum:\u00a0<\/strong>portion of the electromagnetic spectrum that we can see<\/div>\r\n<div data-type=\"definition\"><strong>wavelength:\u00a0<\/strong>length of a wave from one peak to the next peak<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/section><\/section>","rendered":"<section data-depth=\"1\">\n<div class=\"textbox learning-objectives\">\n<h3>Learning Objectives<\/h3>\n<ul>\n<li>Describe the basic anatomy of the visual system<\/li>\n<li>Describe how light waves enable vision<\/li>\n<\/ul>\n<\/div>\n<h2>Anatomy of the Visual System<\/h2>\n<div class=\"ab-test-alternative\">\n<p>The eye is the major sensory organ involved in\u00a0<strong>vision<\/strong> (Figure 1). There are several parts of the eye from the front to the back side, including the cornea, pupil, iris, lens, retina, fovea, and optic nerve. The cornea, pupil, iris, and lens are situated toward the front of the eye. At the back are the retina, fovea, and optic nerve. The slideshow (in Figure 1) below shows those parts, one at a time, along with a brief description. You will get to practice at the end of the slide.<\/p>\n<p><strong>Figure 1.<\/strong>\u00a0The anatomy of the eye is illustrated in this activity.<\/p>\n<p><iframe loading=\"lazy\" src=\"https:\/\/lumenlearning.h5p.com\/content\/1291637308837611378\/embed\" width=\"1088\" height=\"637\" frameborder=\"0\" allowfullscreen=\"allowfullscreen\" aria-label=\"Anatomy of the Visual System v2\"><\/iframe><script src=\"https:\/\/lumenlearning.h5p.com\/js\/h5p-resizer.js\" charset=\"UTF-8\"><\/script><\/p>\n<p>Now let us dive into each of the parts in detail.<\/p>\n<h3>Cornea<\/h3>\n<p>The <strong>cornea<\/strong> is the transparent covering over the eye. It serves as a barrier between the inner eye and the outside world, and it is involved in focusing light waves that enter the eye. Light waves are transmitted across the cornea and enter the eye through the pupil.<\/p>\n<h3>Pupil<\/h3>\n<p>The\u00a0<strong>pupil<\/strong>\u00a0is the small opening in the eye through which light passes, and the size of the pupil can change as a function of light levels as well as emotional arousal. When light levels are low, the pupil will become dilated, or expanded, to allow more light to enter the eye. When light levels are high, the pupil will constrict, or become smaller, to reduce the amount of light that enters the eye.<\/p>\n<h3>Iris<\/h3>\n<p>The <strong>iris<\/strong> is the colored portion of the eye. It is connected to the muscles that control the pupil\u2019s size.<\/p>\n<h3>Lens<\/h3>\n<p>The <strong>lens<\/strong> is a curved, transparent structure that serves to provide additional focus for light entering the eye. Light crosses the lens after passing through the pupil. The lens is attached to muscles that can change its shape to aid in focusing light that is reflected from near or far objects.<\/p>\n<h3>Retina<\/h3>\n<p>The <strong>retina<\/strong> is the light-sensitive lining of the eye located at the back of the eye.<\/p>\n<h3>Fovea<\/h3>\n<p>The <strong>fovea<\/strong>, which is part of the retina, is a small indentation in the back of the eye. In a normal-sighted individual, the lens will focus images perfectly on fovea. The fovea contains densely packed specialized <strong>photoreceptor<\/strong> cells, known as <strong>cones<\/strong>, which are light-detecting cells. Another type of photoreceptor is rods. See Figure 2.<\/p>\n<figure>\n<div id=\"attachment_6756\" style=\"width: 478px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/855\/2015\/02\/29194236\/7092854136b856409f1dbe9f76d123492b979928.jpeg\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-6756\" class=\"wp-image-6756\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/855\/2015\/02\/29194236\/7092854136b856409f1dbe9f76d123492b979928-300x262.jpeg\" alt=\"This illustration shows light reaching the optic nerve, beneath which are Ganglion cells, and then rods and cones.\" width=\"468\" height=\"409\" \/><\/a><\/p>\n<p id=\"caption-attachment-6756\" class=\"wp-caption-text\"><strong>Figure 2<\/strong>. The two types of photoreceptors are shown in this image. Cones are colored green and rods are blue.<\/p>\n<\/div>\n<\/figure>\n<p>The cones are specialized types of photoreceptors that work best in bright light conditions. Cones are very sensitive to acute detail and provide tremendous spatial resolution. They also are directly involved in our ability to perceive color.<\/p>\n<p>While cones are concentrated in the fovea, where images tend to be focused, rods, another type of photoreceptor, are located throughout the remainder of the retina. <strong>Rods<\/strong> are specialized photoreceptors that work well in low light conditions, and while they lack the spatial resolution and color function of the cones, they are involved in our vision in dimly lit environments as well as in our perception of movement on the periphery of our visual field.<\/p>\n<p>We have all experienced the different sensitivities of rods and cones when making the transition from a brightly lit environment to a dimly lit environment. Imagine going to see a blockbuster movie on a clear summer day. As you walk from the brightly lit lobby into the dark theater, you notice that you immediately have difficulty seeing much of anything. After a few minutes, you begin to adjust to the darkness and can see the interior of the theater. In the bright environment, your vision was dominated primarily by cone activity. As you move to the dark environment, rod activity dominates, but there is a delay in transitioning between the phases. If your rods do not transform light into nerve impulses as easily and efficiently as they should, you will have difficulty seeing in dim light, a condition known as night blindness.<\/p>\n<p>Rods and cones are connected (via several interneurons) to retinal ganglion cells. Axons from the retinal ganglion cells converge and exit through the back of the eye to form the optic nerve.<\/p>\n<h3>Optic Nerve<\/h3>\n<p>Rods and cones are connected (via several interneurons) to retinal ganglion cells (see Figure 2 again). Axons from the retinal ganglion cells converge and exit through the back of the eye to form the optic nerve. The\u00a0<strong>optic nerve<\/strong>\u00a0carries visual information from the retina to the brain. There is a point in the visual field called the\u00a0blind spot (not shown in Figure 1): Even when light from a small object is focused on the blind spot, we do not see it. We are not consciously aware of our blind spots for two reasons: First, each eye gets a slightly different view of the visual field; therefore, the blind spots do not overlap. Second, our visual system fills in the blind spot so that although we cannot respond to visual information that occurs in that portion of the visual field, we are also not aware that information is missing.<\/p>\n<\/div>\n<div class=\"ab-test-original\">\n<p>The eye is the major sensory organ involved in <strong>vision<\/strong> (Figure 1). Light waves are transmitted across the cornea and enter the eye through the pupil. The <strong>cornea<\/strong> is the transparent covering over the eye. It serves as a barrier between the inner eye and the outside world, and it is involved in focusing light waves that enter the eye. The <strong>pupil<\/strong> is the small opening in the eye through which light passes, and the size of the pupil can change as a function of light levels as well as emotional arousal. When light levels are low, the pupil will become dilated, or expanded, to allow more light to enter the eye. When light levels are high, the pupil will constrict, or become smaller, to reduce the amount of light that enters the eye. The pupil\u2019s size is controlled by muscles that are connected to the <strong>iris<\/strong>, which is the colored portion of the eye.<\/p>\n<figure>\n<div style=\"width: 596px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" class=\"\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/902\/2015\/02\/23224718\/CNX_Psych_05_03_Eye.jpg\" alt=\"Different parts of the eye are labeled in this illustration. The cornea, pupil, iris, and lens are situated toward the front of the eye, and at the back are the optic nerve, fovea, and retina.\" width=\"586\" height=\"416\" data-media-type=\"image\/jpg\" \/><\/p>\n<p class=\"wp-caption-text\"><strong>Figure 1<\/strong>. The anatomy of the eye is illustrated in this diagram.<\/p>\n<\/div>\n<\/figure>\n<p>After passing through the pupil, light crosses the <strong>lens<\/strong>, a curved, transparent structure that serves to provide additional focus. The lens is attached to muscles that can change its shape to aid in focusing light that is reflected from near or far objects. In a normal-sighted individual, the lens will focus images perfectly on a small indentation in the back of the eye known as the <strong>fovea<\/strong>, which is part of the <strong>retina<\/strong>, the light-sensitive lining of the eye. The fovea contains densely packed specialized photoreceptor cells (Figure 2). These <strong>photoreceptor<\/strong> cells, known as <strong>cones<\/strong>, are light-detecting cells. The cones are specialized types of photoreceptors that work best in bright light conditions. Cones are very sensitive to acute detail and provide tremendous spatial resolution. They also are directly involved in our ability to perceive color.<\/p>\n<p>While cones are concentrated in the fovea, where images tend to be focused, rods, another type of photoreceptor, are located throughout the remainder of the retina. <strong>Rods<\/strong> are specialized photoreceptors that work well in low light conditions, and while they lack the spatial resolution and color function of the cones, they are involved in our vision in dimly lit environments as well as in our perception of movement on the periphery of our visual field.<\/p>\n<figure>\n<div id=\"attachment_6756\" style=\"width: 478px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/855\/2015\/02\/29194236\/7092854136b856409f1dbe9f76d123492b979928.jpeg\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-6756\" class=\"wp-image-6756\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/855\/2015\/02\/29194236\/7092854136b856409f1dbe9f76d123492b979928-300x262.jpeg\" alt=\"This illustration shows light reaching the optic nerve, beneath which are Ganglion cells, and then rods and cones.\" width=\"468\" height=\"409\" \/><\/a><\/p>\n<p id=\"caption-attachment-6756\" class=\"wp-caption-text\"><strong>Figure 2<\/strong>. The two types of photoreceptors are shown in this image. Cones are colored green and rods are blue.<\/p>\n<\/div>\n<\/figure>\n<p>We have all experienced the different sensitivities of rods and cones when making the transition from a brightly lit environment to a dimly lit environment. Imagine going to see a blockbuster movie on a clear summer day. As you walk from the brightly lit lobby into the dark theater, you notice that you immediately have difficulty seeing much of anything. After a few minutes, you begin to adjust to the darkness and can see the interior of the theater. In the bright environment, your vision was dominated primarily by cone activity. As you move to the dark environment, rod activity dominates, but there is a delay in transitioning between the phases. If your rods do not transform light into nerve impulses as easily and efficiently as they should, you will have difficulty seeing in dim light, a condition known as night blindness.<\/p>\n<p>Rods and cones are connected (via several interneurons) to retinal ganglion cells. Axons from the retinal ganglion cells converge and exit through the back of the eye to form the optic nerve. The <strong>optic nerve<\/strong> carries visual information from the retina to the brain. There is a point in the visual field called the <strong>blind spot<\/strong>: Even when light from a small object is focused on the blind spot, we do not see it. We are not consciously aware of our blind spots for two reasons: First, each eye gets a slightly different view of the visual field; therefore, the blind spots do not overlap. Second, our visual system fills in the blind spot so that although we cannot respond to visual information that occurs in that portion of the visual field, we are also not aware that information is missing.<\/p>\n<\/div>\n<div class=\"textbox tryit\">\n<h3>Try It<\/h3>\n<p>\t<iframe id=\"assessment_practice_e78d435f-f8f2-4257-8213-ec8557fa7cc5\" class=\"resizable\" src=\"https:\/\/assess.lumenlearning.com\/practice\/e78d435f-f8f2-4257-8213-ec8557fa7cc5?iframe_resize_id=assessment_practice_id_e78d435f-f8f2-4257-8213-ec8557fa7cc5\" frameborder=\"0\" style=\"border:none;width:100%;height:100%;min-height:300px;\"><br \/>\n\t<\/iframe><\/p>\n<\/div>\n<p>The optic nerve from each eye merges just below the brain at a point called the <strong>optic chiasm<\/strong>. As Figure 3 shows, the optic chiasm is an X-shaped structure that sits just below the cerebral cortex at the front of the brain. At the point of the optic chiasm, information from the right visual field (which comes from both eyes) is sent to the left side of the brain, and information from the left visual field is sent to the right side of the brain.<\/p>\n<figure>\n<div style=\"width: 583px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/902\/2015\/02\/23224723\/CNX_Psych_05_03_OpticChias.jpg\" alt=\"Visual stimuli enter the eyes, pass through the optic nerve and into the optic chiasm, then back to the occipital lobe at the back of the brain.\" width=\"573\" height=\"412\" data-media-type=\"image\/jpg\" \/><\/p>\n<p class=\"wp-caption-text\"><strong>Figure 3<\/strong>. This illustration shows the optic chiasm at the front of the brain and the pathways to the occipital lobe at the back of the brain, where visual sensations are processed into meaningful perceptions.<\/p>\n<\/div>\n<\/figure>\n<p>Once inside the brain, visual information is sent via a number of structures to the occipital lobe at the back of the brain for processing. Visual information might be processed in parallel pathways which can generally be described as the \u201cwhat pathway\u201d (the ventral pathway) and the \u201cwhere\/how\u201d pathway (the dorsal pathway). The \u201cwhat pathway\u201d is involved in object recognition and identification, while the \u201cwhere\/how pathway\u201d is involved with location in space and how one might interact with a particular visual stimulus (Milner &amp; Goodale, 2008; Ungerleider &amp; Haxby, 1994). For example, when you see a ball rolling down the street, the \u201cwhat pathway\u201d identifies what the object is, and the \u201cwhere\/how pathway\u201d identifies its location or movement in space.<\/p>\n<\/section>\n<p>&nbsp;<\/p>\n<div id=\"attachment_2153\" style=\"width: 534px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/855\/2016\/10\/26200309\/visualpathways.png\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2153\" class=\"wp-image-2153\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/855\/2016\/10\/26200309\/visualpathways.png\" alt=\"Areas of the brain showing the ventral pathway, along the side of the brain closer to the temporal lobes, and the dorsal pathway in the back of the brain. It also shows the visual cortex areas at the back of the brain: V1\/V2, V3, V3A, and V4 (associated with color), and the faces and object recognition areas (next to V4).\" width=\"524\" height=\"264\" \/><\/a><\/p>\n<p id=\"caption-attachment-2153\" class=\"wp-caption-text\"><strong>Figure 4<\/strong>. Visual areas in the brain.<\/p>\n<\/div>\n<div class=\"textbox exercises\">\n<h3>what do you think?<\/h3>\n<h2><strong>The Ethics of Research Using Animals<\/strong><\/h2>\n<p>David Hubel and Torsten Wiesel were awarded the Nobel Prize in Medicine in 1981 for their research on the visual system. They collaborated for more than twenty years and made significant discoveries about the neurology of visual perception (Hubel &amp; Wiesel, 1959, 1962, 1963, 1970; Wiesel &amp; Hubel, 1963). They studied animals, mostly cats and monkeys. Although they used several techniques, they did considerable single-unit recordings, during which tiny electrodes were inserted in the animal\u2019s brain to determine when a single cell was activated. Among their many discoveries, they found that specific brain cells respond to lines with specific orientations (called ocular dominance), and they mapped the way those cells are arranged in areas of the visual cortex known as columns and hypercolumns.<\/p>\n<p>In some of their research, they sutured one eye of newborn kittens closed and followed the development of the kittens&#8217; vision. They discovered there was a critical period of development for vision. If kittens were deprived of input from one eye, other areas of their visual cortex filled in the area that was normally used by the eye that was sewn closed. In other words, neural connections that exist at birth can be lost if they are deprived of sensory input.<\/p>\n<p>What do you think about sewing a kitten&#8217;s eye closed for research? To many animal advocates, this would seem brutal, abusive, and unethical. What if you could do research that would help ensure babies and children born with certain conditions could develop normal vision instead of becoming blind? Would you want that research done? Would you conduct that research, even if it meant causing some harm to cats? Would you think the same way if you were the parent of such a child? What if you worked at the animal shelter?<\/p>\n<p>Like virtually every other industrialized nation, the United States permits medical experimentation on animals, with few limitations (assuming sufficient scientific justification). The goal of any laws that exist is not to ban such tests but rather to limit unnecessary animal suffering by establishing standards for the humane treatment and housing of animals in laboratories.<\/p>\n<p>As explained by Stephen Latham, the director of the Interdisciplinary Center for Bioethics at Yale (2012), possible legal and regulatory approaches to animal testing vary on a continuum from strong government regulation and monitoring of all experimentation at one end, to a self-regulated approach that depends on the ethics of the researchers at the other end. The United Kingdom has the most significant regulatory scheme, whereas Japan uses the self-regulation approach. The U.S. approach is somewhere in the middle, the result of a gradual blending of the two approaches.<\/p>\n<p>There is no question that medical research is a valuable and important practice. The question is whether the use of animals is a necessary or even best practice for producing the most reliable results. Alternatives include the use of patient-drug databases, virtual drug trials, computer models and simulations, and noninvasive imaging techniques such as magnetic resonance imaging and computed tomography scans (\u201cAnimals in Science\/Alternatives,\u201d n.d.). Other techniques, such as microdosing, use humans not as test animals but as a means to improve the accuracy and reliability of test results. In vitro methods based on human cell and tissue cultures, stem cells, and genetic testing methods are also increasingly available.<\/p>\n<p>Today, at the local level, any facility that uses animals and receives federal funding must have an Institutional Animal Care and Use Committee (IACUC) that ensures that the NIH guidelines are being followed. The IACUC must include researchers, administrators, a veterinarian, and at least one person with no ties to the institution: that is, a concerned citizen. This committee also performs inspections of laboratories and protocols.<\/p>\n<\/div>\n<section data-depth=\"1\">\n<div class=\"textbox tryit\">\n<h3>Try It<\/h3>\n<p>\t<iframe id=\"assessment_practice_dfbc15d0-5cc0-4286-b96c-4edc4de0f870\" class=\"resizable\" src=\"https:\/\/assess.lumenlearning.com\/practice\/dfbc15d0-5cc0-4286-b96c-4edc4de0f870?iframe_resize_id=assessment_practice_id_dfbc15d0-5cc0-4286-b96c-4edc4de0f870\" frameborder=\"0\" style=\"border:none;width:100%;height:100%;min-height:300px;\"><br \/>\n\t<\/iframe><\/p>\n<p>\t<iframe id=\"assessment_practice_bad360e6-94d0-4411-b3ee-c82de47df204\" class=\"resizable\" src=\"https:\/\/assess.lumenlearning.com\/practice\/bad360e6-94d0-4411-b3ee-c82de47df204?iframe_resize_id=assessment_practice_id_bad360e6-94d0-4411-b3ee-c82de47df204\" frameborder=\"0\" style=\"border:none;width:100%;height:100%;min-height:300px;\"><br \/>\n\t<\/iframe><\/p>\n<p>\t<iframe id=\"assessment_practice_0b5a82cc-cd64-471d-b838-3282551b4be3\" class=\"resizable\" src=\"https:\/\/assess.lumenlearning.com\/practice\/0b5a82cc-cd64-471d-b838-3282551b4be3?iframe_resize_id=assessment_practice_id_0b5a82cc-cd64-471d-b838-3282551b4be3\" frameborder=\"0\" style=\"border:none;width:100%;height:100%;min-height:300px;\"><br \/>\n\t<\/iframe><\/p>\n<p>\t<iframe id=\"assessment_practice_f2c40907-189e-42da-95e3-5c40a19a7390\" class=\"resizable\" src=\"https:\/\/assess.lumenlearning.com\/practice\/f2c40907-189e-42da-95e3-5c40a19a7390?iframe_resize_id=assessment_practice_id_f2c40907-189e-42da-95e3-5c40a19a7390\" frameborder=\"0\" style=\"border:none;width:100%;height:100%;min-height:300px;\"><br \/>\n\t<\/iframe><\/p>\n<\/div>\n<h2>Amplitude and Wavelength<\/h2>\n<p>As mentioned above, light enters your eyes as a wave. It is important to understand some basic properties of waves to see how they impact what we see. Two physical characteristics of a wave are <strong>amplitude<\/strong> and wavelength (Figure 5). The amplitude of a wave is the height of a wave as measured from the highest point on the <strong>wave<\/strong> (<strong>peak<\/strong> or <strong>crest<\/strong>) to the lowest point on the wave (trough). <strong>Wavelength<\/strong> refers to the length of a wave from one peak to the next.<\/p>\n<figure>\n<div style=\"width: 659px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/902\/2015\/02\/23224709\/CNX_Psych_05_02_Wave.jpg\" alt=\"A diagram illustrates the basic parts of a wave. Moving from left to right, the wavelength line begins above a straight horizontal line and falls and rises equally above and below that line. One of the areas where the wavelength line reaches its highest point is labeled \u201cPeak.\u201d A horizontal bracket, labeled \u201cWavelength,\u201d extends from this area to the next peak. One of the areas where the wavelength reaches its lowest point is labeled \u201cTrough.\u201d A vertical bracket, labeled \u201cAmplitude,\u201d extends from a \u201cPeak\u201d to a \u201cTrough.\u201d\" width=\"649\" height=\"229\" data-media-type=\"image\/jpg\" \/><\/p>\n<p class=\"wp-caption-text\"><strong>Figure 5<\/strong>. The amplitude or height of a wave is measured from the peak to the trough. The wavelength is measured from peak to peak.<\/p>\n<\/div>\n<\/figure>\n<p>Wavelength is directly related to the frequency of a given waveform. <strong>Frequency<\/strong> refers to the number of waves that pass a given point in a given time period and is often expressed in terms of <strong>hertz (Hz<\/strong>), or cycles per second. Longer wavelengths will have lower frequencies, and shorter wavelengths will have higher frequencies (Figure 6).<\/p>\n<figure>\n<div style=\"width: 520px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/902\/2015\/02\/23224710\/CNX_Psych_05_02_Frequencies.jpg\" alt=\"Stacked vertically are 5 waves of different colors and wavelengths. The top wave is red with a long wavelengths, which indicate a low frequency. Moving downward, the color of each wave is different: orange, yellow, green, and blue. Also moving downward, the wavelengths become shorter as the frequencies increase.\" width=\"510\" height=\"171\" data-media-type=\"image\/jpg\" \/><\/p>\n<p class=\"wp-caption-text\"><strong>Figure 6<\/strong>. This figure illustrates waves of differing wavelengths\/frequencies. At the top of the figure, the red wave has a long wavelength\/short frequency. Moving from top to bottom, the wavelengths decrease and frequencies increase.<\/p>\n<\/div>\n<\/figure>\n<\/section>\n<section data-depth=\"1\">\n<h2>Light Waves<\/h2>\n<p>The <strong>visible spectrum<\/strong> is the portion of the larger electromagnetic spectrum that we can see. As Figure 7 shows, the <strong>electromagnetic spectrum<\/strong> encompasses all of the electromagnetic radiation that occurs in our environment and includes gamma rays, x-rays, ultraviolet light, visible light, infrared light, microwaves, and radio waves. The visible spectrum in humans is associated with wavelengths that range from 380 to 740 nm\u2014a very small distance since a nanometer (nm) is one-billionth of a meter. Other species can detect other portions of the electromagnetic spectrum. For instance, honeybees can see light in the ultraviolet range (Wakakuwa, Stavenga, &amp; Arikawa, 2007), and some snakes can detect infrared radiation in addition to more traditional visual light cues (Chen, Deng, Brauth, Ding, &amp; Tang, 2012; Hartline, Kass, &amp; Loop, 1978).<\/p>\n<figure>\n<div style=\"width: 985px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/902\/2015\/02\/23224712\/CNX_Psych_05_02_Spectrum.jpg\" alt=\"This illustration shows the wavelength, frequency, and size of objects across the electromagnetic spectrum.. At the top, various wavelengths are given in sequence from small to large, with a parallel illustration of a wave with increasing frequency. These are the provided wavelengths, measured in meters: \u201cGamma ray 10 to the negative twelfth power,\u201d \u201cx-ray 10 to the negative tenth power,\u201d ultraviolet 10 to the negative eighth power,\u201d \u201cvisible .5 times 10 to the negative sixth power,\u201d \u201cinfrared 10 to the negative fifth power,\u201d microwave 10 to the negative second power,\u201d and \u201cradio 10 cubed.\u201dAnother section is labeled \u201cAbout the size of\u201d and lists from left to right: \u201cAtomic nuclei,\u201d \u201cAtoms,\u201d \u201cMolecules,\u201d \u201cProtozoans,\u201d \u201cPinpoints,\u201d \u201cHoneybees,\u201d \u201cHumans,\u201d and \u201cBuildings\u201d with an illustration of each . At the bottom is a line labeled \u201cFrequency\u201d with the following measurements in hertz: 10 to the powers of 20, 18, 16, 15, 12, 8, and 4. From left to right the line changes in color from purple to red with the remaining colors of the visible spectrum in between, occurring roughly between 10 to the power of 15 and 10 to the power of 12.\" width=\"975\" height=\"404\" data-media-type=\"image\/jpg\" \/><\/p>\n<p class=\"wp-caption-text\"><strong>Figure 7<\/strong>. Light that is visible to humans makes up only a small portion of the electromagnetic spectrum.<\/p>\n<\/div>\n<\/figure>\n<p>In humans, light wavelength is associated with perception of color (Figure 8). Within the visible spectrum, our experience of red is associated with longer wavelengths, greens are intermediate, and blues and violets are shorter in wavelength. (An easy way to remember this is the mnemonic ROYGBIV: <strong>r<\/strong>ed, <strong>o<\/strong>range, <strong>y<\/strong>ellow, <strong>g<\/strong>reen, <strong>b<\/strong>lue, <strong>i<\/strong>ndigo, <strong>v<\/strong>iolet.) The amplitude of light waves is associated with our experience of brightness or intensity of color, with larger amplitudes appearing brighter.<\/p>\n<figure>\n<div style=\"width: 985px\" class=\"wp-caption alignnone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/902\/2015\/02\/23224713\/CNX_Psych_05_02_VisSpec.jpg\" alt=\"Wavelengths from low to high as measured in nanometers. Below the visible spectrum, in increasing order, are \u201cCosmic radiation,\u201d \u201cGamma rays,\u201d \u201cX-rays,\u201d and \u201cUltraviolet,\u201d. The visible wavelengths of light are between 400 and 700 nanometers. Wavelengths above the visible spectrum, in increasing order, are \u201cInfrared,\u201d \u201cTerahertz radiation,\u201d \u201cRadar,\u201d \u201cTelevision and radio broadcasting,\u201d and \u201cAC circuits.\u201d\" width=\"975\" height=\"186\" data-media-type=\"image\/jpg\" \/><\/p>\n<p class=\"wp-caption-text\"><strong>Figure 8<\/strong>. Different wavelengths of light are associated with our perception of different colors. (credit: modification of work by Johannes Ahlmann)<\/p>\n<\/div>\n<\/figure>\n<div class=\"textbox tryit\">\n<h3>Try It<\/h3>\n<p>\t<iframe id=\"assessment_practice_930c39a8-f512-4590-8552-44c950861781\" class=\"resizable\" src=\"https:\/\/assess.lumenlearning.com\/practice\/930c39a8-f512-4590-8552-44c950861781?iframe_resize_id=assessment_practice_id_930c39a8-f512-4590-8552-44c950861781\" frameborder=\"0\" style=\"border:none;width:100%;height:100%;min-height:300px;\"><br \/>\n\t<\/iframe><\/p>\n<p>\t<iframe id=\"assessment_practice_c10cbbbc-3696-49d6-960f-0fe48543e2cb\" class=\"resizable\" src=\"https:\/\/assess.lumenlearning.com\/practice\/c10cbbbc-3696-49d6-960f-0fe48543e2cb?iframe_resize_id=assessment_practice_id_c10cbbbc-3696-49d6-960f-0fe48543e2cb\" frameborder=\"0\" style=\"border:none;width:100%;height:100%;min-height:300px;\"><br \/>\n\t<\/iframe><\/p>\n<p>\t<iframe id=\"assessment_practice_fd1301de-4197-4207-9ce9-dffdd24fa9d7\" class=\"resizable\" src=\"https:\/\/assess.lumenlearning.com\/practice\/fd1301de-4197-4207-9ce9-dffdd24fa9d7?iframe_resize_id=assessment_practice_id_fd1301de-4197-4207-9ce9-dffdd24fa9d7\" frameborder=\"0\" style=\"border:none;width:100%;height:100%;min-height:300px;\"><br \/>\n\t<\/iframe><\/p>\n<p>\t<iframe id=\"assessment_practice_e88c73f0-78be-49ec-bcb9-f65318876734\" class=\"resizable\" src=\"https:\/\/assess.lumenlearning.com\/practice\/e88c73f0-78be-49ec-bcb9-f65318876734?iframe_resize_id=assessment_practice_id_e88c73f0-78be-49ec-bcb9-f65318876734\" frameborder=\"0\" style=\"border:none;width:100%;height:100%;min-height:300px;\"><br \/>\n\t<\/iframe><\/p>\n<p>\t<iframe id=\"assessment_practice_ca761c4c-ca04-4a87-9a5b-cdcb053353ec\" class=\"resizable\" src=\"https:\/\/assess.lumenlearning.com\/practice\/ca761c4c-ca04-4a87-9a5b-cdcb053353ec?iframe_resize_id=assessment_practice_id_ca761c4c-ca04-4a87-9a5b-cdcb053353ec\" frameborder=\"0\" style=\"border:none;width:100%;height:100%;min-height:300px;\"><br \/>\n\t<\/iframe><\/p>\n<p>\t<iframe id=\"assessment_practice_97269cab-3902-4252-aff1-ceb5f435a07b\" class=\"resizable\" src=\"https:\/\/assess.lumenlearning.com\/practice\/97269cab-3902-4252-aff1-ceb5f435a07b?iframe_resize_id=assessment_practice_id_97269cab-3902-4252-aff1-ceb5f435a07b\" frameborder=\"0\" style=\"border:none;width:100%;height:100%;min-height:300px;\"><br \/>\n\t<\/iframe><\/p>\n<\/div>\n<\/section>\n<section data-depth=\"1\">\n<section>\n<div class=\"textbox key-takeaways\">\n<h3>Glossary<\/h3>\n<div data-type=\"definition\"><strong>amplitude:\u00a0<\/strong>height of a wave<\/div>\n<div data-type=\"definition\"><strong>blind spot:\u00a0<\/strong>point where we cannot respond to visual information in that portion of the visual field<\/div>\n<div data-type=\"definition\"><strong>cone:\u00a0<\/strong>specialized photoreceptor that works best in bright light conditions and detects color<\/div>\n<div data-type=\"definition\"><strong>cornea:\u00a0<\/strong>transparent covering over the eye<\/div>\n<div data-type=\"definition\"><strong>electromagnetic spectrum:<\/strong> all the electromagnetic radiation that occurs in our environment<\/div>\n<div data-type=\"definition\"><strong>fovea:\u00a0<\/strong>small indentation in the retina that contains cones<\/div>\n<div data-type=\"definition\"><strong>frequency:\u00a0<\/strong>number of waves that pass a given point in a given time period<\/div>\n<div data-type=\"definition\"><strong>hertz (Hz):\u00a0<\/strong>cycles per second; measure of frequency<\/div>\n<div data-type=\"definition\"><strong>iris:\u00a0<\/strong>colored portion of the eye<\/div>\n<div data-type=\"definition\"><strong>lens:\u00a0<\/strong>curved, transparent structure that provides additional focus for light entering the eye<\/div>\n<div data-type=\"definition\"><strong>optic chiasm:\u00a0<\/strong>X-shaped structure that sits just below the brain\u2019s ventral surface; represents the merging of the optic nerves from the two eyes and the separation of information from the two sides of the visual field to the opposite side of the brain<\/div>\n<div data-type=\"definition\"><strong>optic nerve:\u00a0<\/strong>carries visual information from the retina to the brain<\/div>\n<div data-type=\"definition\"><strong>peak:\u00a0<\/strong>(also, crest) highest point of a wave<\/div>\n<div data-type=\"definition\"><strong>photoreceptor:\u00a0<\/strong>light-detecting cell<\/div>\n<div data-type=\"definition\"><strong>pupil:\u00a0<\/strong>small opening in the eye through which light passes<\/div>\n<div data-type=\"definition\"><strong>retina:\u00a0<\/strong>light-sensitive lining of the eye<\/div>\n<div data-type=\"definition\"><strong>rod:\u00a0<\/strong>specialized photoreceptor that works well in low light conditions<\/div>\n<div data-type=\"definition\"><strong>trough:\u00a0<\/strong>lowest point of a wave<\/div>\n<div data-type=\"definition\">\n<div data-type=\"definition\"><strong>visible spectrum:\u00a0<\/strong>portion of the electromagnetic spectrum that we can see<\/div>\n<div data-type=\"definition\"><strong>wavelength:\u00a0<\/strong>length of a wave from one peak to the next peak<\/div>\n<\/div>\n<\/div>\n<\/section>\n<\/section>\n\n\t\t\t <section class=\"citations-section\" role=\"contentinfo\">\n\t\t\t <h3>Candela Citations<\/h3>\n\t\t\t\t\t <div>\n\t\t\t\t\t\t <div id=\"citation-list-156\">\n\t\t\t\t\t\t\t <div class=\"licensing\"><div class=\"license-attribution-dropdown-subheading\">CC licensed content, Shared previously<\/div><ul class=\"citation-list\"><li>Vision, Waves and Wavelengths. <strong>Authored by<\/strong>: OpenStax College. <strong>Located at<\/strong>: <a target=\"_blank\" href=\"https:\/\/openstax.org\/books\/psychology-2e\/pages\/5-3-vision\">https:\/\/openstax.org\/books\/psychology-2e\/pages\/5-3-vision<\/a>. <strong>License<\/strong>: <em><a target=\"_blank\" rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/\">CC BY: Attribution<\/a><\/em>. <strong>License Terms<\/strong>: Download for free at https:\/\/openstax.org\/books\/psychology-2e\/pages\/1-introduction<\/li><li>Vision, information on ventral and dorsal pathways. <strong>Authored by<\/strong>: Simona Buetti and Alejandro Lleras . <strong>Provided by<\/strong>: University of Illinois at Urbana-Champaign. <strong>Located at<\/strong>: <a target=\"_blank\" href=\"http:\/\/nobaproject.com\/modules\/vision\">http:\/\/nobaproject.com\/modules\/vision<\/a>. <strong>License<\/strong>: <em><a target=\"_blank\" rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by-nc-sa\/4.0\/\">CC BY-NC-SA: Attribution-NonCommercial-ShareAlike<\/a><\/em><\/li><li>Waves and Wavelengths. <strong>Authored by<\/strong>: OpenStax College. <strong>Located at<\/strong>: <a target=\"_blank\" href=\"http:\/\/cnx.org\/contents\/Sr8Ev5Og@5.52:1Cicp6CO@8\/Waves-and-Wavelengths\">http:\/\/cnx.org\/contents\/Sr8Ev5Og@5.52:1Cicp6CO@8\/Waves-and-Wavelengths<\/a>. <strong>License<\/strong>: <em><a target=\"_blank\" rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/\">CC BY: Attribution<\/a><\/em>. <strong>License Terms<\/strong>: Download for free at http:\/\/cnx.org\/contents\/4abf04bf-93a0-45c3-9cbc-2cefd46e68cc@5.48<\/li><\/ul><\/div>\n\t\t\t\t\t\t <\/div>\n\t\t\t\t\t <\/div>\n\t\t\t <\/section>","protected":false},"author":5797,"menu_order":6,"template":"","meta":{"_candela_citation":"[{\"type\":\"cc\",\"description\":\"Vision, Waves and Wavelengths\",\"author\":\"OpenStax College\",\"organization\":\"\",\"url\":\"https:\/\/openstax.org\/books\/psychology-2e\/pages\/5-3-vision\",\"project\":\"\",\"license\":\"cc-by\",\"license_terms\":\"Download for free at https:\/\/openstax.org\/books\/psychology-2e\/pages\/1-introduction\"},{\"type\":\"cc\",\"description\":\"Vision, information on ventral and dorsal pathways\",\"author\":\"Simona Buetti and Alejandro Lleras \",\"organization\":\"University of Illinois at 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