{"id":2111,"date":"2016-10-25T20:35:47","date_gmt":"2016-10-25T20:35:47","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/waymaker-psychology\/?post_type=chapter&#038;p=2111"},"modified":"2017-05-20T21:52:58","modified_gmt":"2017-05-20T21:52:58","slug":"outcome-vision","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-fmcc-intropsych\/chapter\/outcome-vision\/","title":{"raw":"Vision","rendered":"Vision"},"content":{"raw":"<h2>What you'll learn to do: explain the process of vision and how people see color and depth<\/h2>\r\n<figure>\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"530\"]<img class=\"\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/902\/2015\/02\/23224717\/CNX_Psych_05_03_Eyes.jpg\" alt=\"Several photographs of peoples\u2019 eyes are shown.\" width=\"530\" height=\"284\" data-media-type=\"image\/jpg\" \/> Our eyes take in sensory information that helps us understand the world around us. (credit \"top left\u201d: modification of work by \"rajkumar1220\"\/Flickr\"; credit \u201ctop right\u201d: modification of work by Thomas Leuthard; credit \u201cmiddle left\u201d: modification of work by Demietrich Baker; credit \u201cmiddle right\u201d: modification of work by \"kaybee07\"\/Flickr; credit \u201cbottom left\u201d: modification of work by \"Isengardt\"\/Flickr; credit \u201cbottom right\u201d: modification of work by Willem Heerbaart)[\/caption]<\/figure>\r\nThe visual system constructs a mental representation of the world around us. This contributes to our ability to successfully navigate through physical space and interact with important individuals and objects in our environments. This section will provide an overview of the basic anatomy and function of the visual system. In addition, you'll\u00a0explore our ability to perceive color and depth.\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 \t<li>Describe the trichromatic theory of color vision and the opponent-process theory<\/li>\r\n \t<li>Describe how monocular and binocular cues are used in the perception of depth<\/li>\r\n<\/ul>\r\n<\/div>\r\n<section data-depth=\"1\">\r\n<h2>Anatomy of the Visual System<\/h2>\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\" \/> Figure 1. 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=\"\" align=\"aligncenter\" width=\"501\"]<img class=\"\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/902\/2015\/02\/23224721\/CNX_Psych_05_03_RodsCones.jpg\" alt=\"This illustration shows light reaching the optic nerve, beneath which are Ganglion cells, and then rods and cones.\" width=\"501\" height=\"437\" data-media-type=\"image\/jpg\" \/> Figure 2. The two types of photoreceptors are shown in this image. Rods are colored green and cones 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<div class=\"textbox tryit\">\r\n<h3>Try It<\/h3>\r\nhttps:\/\/assessments.lumenlearning.com\/assessments\/2837\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 class=\"\" 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=\"An illustration shows the location of the occipital lobe, optic chiasm, optic nerve, and the eyes in relation to their position in the brain and head.\" width=\"573\" height=\"412\" data-media-type=\"image\/jpg\" \/> Figure 3. 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>\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 V1\/V2, V3, V3A, and V4.\" width=\"524\" height=\"264\" \/><\/a> Figure 4. Visual areas in the brain.[\/caption]\r\n\r\n<section data-depth=\"1\">\r\n<div class=\"textbox tryit\">\r\n<h3>Try It<\/h3>\r\nhttps:\/\/assessments.lumenlearning.com\/assessments\/2833\r\n\r\nhttps:\/\/assessments.lumenlearning.com\/assessments\/2834\r\n\r\nhttps:\/\/assessments.lumenlearning.com\/assessments\/2835\r\n\r\nhttps:\/\/assessments.lumenlearning.com\/assessments\/2836\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\" \/> Figure 5. 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 wave form. <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\" \/> Figure 6. 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.\" width=\"975\" height=\"404\" data-media-type=\"image\/jpg\" \/> Figure 7. 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=\"A line provides Wavelength in nanometers for \u201c400,\u201d \u201c500,\u201d \u201c600,\u201d and \u201c700\u201d nanometers. Within this line are all of the colors of the visible spectrum. Below this line, labeled from left to right are \u201cCosmic radiation,\u201d \u201cGamma rays,\u201d \u201cX-rays,\u201d \u201cUltraviolet,\u201d then a small callout area for the line above containing the colors in the visual spectrum, followed by \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\" \/> Figure 8. 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:\/\/assessments.lumenlearning.com\/assessments\/2839\r\n\r\nhttps:\/\/assessments.lumenlearning.com\/assessments\/2840\r\n\r\nhttps:\/\/assessments.lumenlearning.com\/assessments\/2841\r\n\r\nhttps:\/\/assessments.lumenlearning.com\/assessments\/2842\r\n\r\nhttps:\/\/assessments.lumenlearning.com\/assessments\/2843\r\n\r\nhttps:\/\/assessments.lumenlearning.com\/assessments\/4270\r\n\r\n<\/div>\r\n<\/section>We do not see the world in black and white; neither do we see it as two-dimensional (2-D) or flat (just height and width, no depth). Let\u2019s look at how color vision works and how we perceive three dimensions (height, width, and depth).\r\n\r\n<section data-depth=\"1\"><section data-depth=\"2\">\r\n<h2 data-type=\"title\">Color Vision<\/h2>\r\nNormal-sighted individuals have three different types of cones that mediate <strong>color vision<\/strong>. Each of these cone types is maximally sensitive to a slightly different wavelength of light. According to the Young-Helmholtz\u00a0<strong>trichromatic theory of color vision<\/strong>, shown in Figure 9, all colors in the spectrum can be produced by combining red, green, and blue. The three types of cones are each receptive to one of the colors.\r\n<figure>\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"492\"]<img class=\"\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/902\/2015\/02\/23224725\/CNX_Psych_05_03_Trichrom.jpg\" alt=\"A graph is shown with \u201csensitivity\u201d plotted on the y-axis and \u201cWavelength\u201d in nanometers plotted along the x-axis with measurements of 400, 500, 600, and 700. Three lines in different colors move from the base to the peak of the y axis, and back to the base. The blue line begins at 400 nm and hits its peak of sensitivity around 455 nanometers, before the sensitivity drops off at roughly the same rate at which it increased, returning to the lowest sensitivity around 530 nm . The green line begins at 400 nm and reaches its peak of sensitivity around 535 nanometers. Its sensitivity then decreases at roughly the same rate at which it increased, returning to the lowest sensitivity around 650 nm. The red line follows the same pattern as the first two, beginning at 400 nm, increasing and decreasing at the same rate, and it hits its height of sensitivity around 580 nanometers. Below this graph is a horizontal bar showing the colors of the visible spectrum.\" width=\"492\" height=\"409\" data-media-type=\"image\/jpg\" \/> Figure 9. This figure illustrates the different sensitivities for the three cone types found in a normal-sighted individual. (credit: modification of work by Vanessa Ezekowitz)[\/caption]<\/figure>\r\nThe trichromatic theory of color vision is not the only theory\u2014another major theory of color vision is known as the <strong>opponent-process theory<\/strong>. According to this theory, color is coded in opponent pairs: black-white, yellow-blue, and green-red. The basic idea is that some cells of the visual system are excited by one of the opponent colors and inhibited by the other. So, a cell that was excited by wavelengths associated with green would be inhibited by wavelengths associated with red, and vice versa. One of the implications of opponent processing is that we do not experience greenish-reds or yellowish-blues as colors. Another implication is that this leads to the experience of negative afterimages. An <strong>afterimage<\/strong> describes the continuation of a visual sensation after removal of the stimulus. For example, when you stare briefly at the sun and then look away from it, you may still perceive a spot of light although the stimulus (the sun) has been removed. When color is involved in the stimulus, the color pairings identified in the opponent-process theory lead to a negative afterimage. You can test this concept using the flag in Figure 10.\r\n<figure>\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"487\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/902\/2015\/02\/23224727\/CNX_Psych_05_03_Afterimage.jpg\" alt=\"An illustration shows a green flag with a thick, black-bordered yellow lines meeting slightly to the left of the center. A small white dot sits within the yellow space in the exact center of the flag.\" width=\"487\" height=\"352\" data-media-type=\"image\/jpg\" \/> Figure 10. Stare at the white dot for 30\u201360 seconds and then move your eyes to a blank piece of white paper. What do you see? This is known as a negative afterimage, and it provides empirical support for the opponent-process theory of color vision.[\/caption]<\/figure>\r\nBut these two theories\u2014the trichromatic theory of color vision and the opponent-process theory\u2014are not mutually exclusive. Research has shown that they just apply to different levels of the nervous system. For visual processing on the retina, trichromatic theory applies: the cones are responsive to three different wavelengths that represent red, blue, and green. But once the signal moves past the retina on its way to the brain, the cells respond in a way consistent with opponent-process theory (Land, 1959; Kaiser, 1997).\r\n<div class=\"textbox tryit\">\r\n<h3>Try It<\/h3>\r\nhttps:\/\/assessments.lumenlearning.com\/assessments\/2844\r\n\r\nhttps:\/\/assessments.lumenlearning.com\/assessments\/4272\r\n\r\nhttps:\/\/assessments.lumenlearning.com\/assessments\/4273\r\n\r\nhttps:\/\/assessments.lumenlearning.com\/assessments\/2845\r\n\r\n<\/div>\r\n<\/section><section data-depth=\"2\">\r\n<h2 data-type=\"title\">Depth Perception<\/h2>\r\nOur ability to perceive spatial relationships in three-dimensional (3-D) space is known as <strong>depth perception<\/strong>. With depth perception, we can describe things as being in front, behind, above, below, or to the side of other things.\r\n\r\nOur world is three-dimensional, so it makes sense that our mental representation of the world has three-dimensional properties. We use a variety of cues in a visual scene to establish our sense of depth. Some of these are <strong>binocular cues<\/strong>, which means that they rely on the use of both eyes. One example of a binocular depth cue is <strong>binocular disparity<\/strong>, the slightly different view of the world that each of our eyes receives. To experience this slightly different view, do this simple exercise: extend your arm fully and extend one of your fingers and focus on that finger. Now, close your left eye without moving your head, then open your left eye and close your right eye without moving your head. You will notice that your finger seems to shift as you alternate between the two eyes because of the slightly different view each eye has of your finger.\r\n\r\nA 3-D movie works on the same principle: the special glasses you wear allow the two slightly different images projected onto the screen to be seen separately by your left and your right eye. As your brain processes these images, you have the illusion that the leaping animal or running person is coming right toward you.\r\n\r\nAlthough we rely on binocular cues to experience depth in our 3-D world, we can also perceive depth in 2-D arrays. Think about all the paintings and photographs you have seen. Generally, you pick up on depth in these images even though the visual stimulus is 2-D. When we do this, we are relying on a number of <strong>monocular cues<\/strong>, or cues that require only one eye. If you think you can\u2019t see depth with one eye, note that you don\u2019t bump into things when using only one eye while walking\u2014and, in fact, we have more monocular cues than binocular cues. The following video of anamorphic art demonstrates how we rely on these monocular cues to see depth, even when the depth is only imagined.\r\n\r\nhttps:\/\/youtu.be\/tBNHPk-Lnkk?t=14s\r\n\r\nAn example of a monocular cue would be what is known as <strong>linear perspective<\/strong>. Linear perspective refers to the fact that we perceive depth when we see two parallel lines that seem to converge in an image (Figure 11). Some other monocular depth cues are interposition, the partial overlap of objects, the relative size and closeness of images to the horizon, relative size, and the variation between light and shadow.\r\n<figure>\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"529\"]<img class=\"\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images-archive-read-only\/wp-content\/uploads\/sites\/902\/2015\/02\/23224729\/CNX_Psych_05_03_LinPerspec.jpg\" alt=\"A photograph shows an empty road that continues toward the horizon.\" width=\"529\" height=\"318\" data-media-type=\"image\/jpg\" \/> Figure 11. We perceive depth in a two-dimensional figure like this one through the use of monocular cues like linear perspective, like the parallel lines converging as the road narrows in the distance. (credit: Marc Dalmulder)[\/caption]<\/figure>\r\n<div data-type=\"note\" data-label=\"Dig Deeper\">\r\n<div data-type=\"title\">\r\n<div data-type=\"title\">\r\n<div class=\"textbox exercises\">\r\n<h3>Dig Deeper: Stereoblindness<\/h3>\r\nBruce Bridgeman was born with an extreme case of lazy eye that resulted in him being stereoblind, or unable to respond to binocular cues of depth. He relied heavily on monocular depth cues, but he never had a true appreciation of the 3-D nature of the world around him. This all changed one night in 2012 while Bruce was seeing a movie with his wife.\r\n\r\nThe movie the couple was going to see was shot in 3-D, and even though he thought it was a waste of money, Bruce paid for the 3-D glasses when he purchased his ticket. As soon as the film began, Bruce put on the glasses and experienced something completely new. For the first time in his life he appreciated the true depth of the world around him. Remarkably, his ability to perceive depth persisted outside of the movie theater.\r\n\r\nThere are cells in the nervous system that respond to binocular depth cues. Normally, these cells require activation during early development in order to persist, so experts familiar with Bruce\u2019s case (and others like his) assume that at some point in his development, Bruce must have experienced at least a fleeting moment of binocular vision. It was enough to ensure the survival of the cells in the visual system tuned to binocular cues. The mystery now is why it took Bruce nearly 70 years to have these cells activated (Peck, 2012).\r\n\r\n<\/div>\r\n<div class=\"textbox tryit\">\r\n<h3>Try It<\/h3>\r\nhttps:\/\/assessments.lumenlearning.com\/assessments\/2846\r\n\r\nhttps:\/\/assessments.lumenlearning.com\/assessments\/2847\r\n\r\nPhotos in this activity from\u00a0of <a id=\"_i_3\" href=\"http:\/\/www.flickr.com\/photos\/glaciernps\/4454825783\/\" target=\"_blank\" rel=\"noopener noreferrer\">GlacierNPS<\/a>, <a id=\"_i_4\" href=\"http:\/\/www.flickr.com\/photos\/anijdam\/2586190200\/\" target=\"_blank\" rel=\"noopener noreferrer\">Alicia Nijdam<\/a>, <a id=\"_i_5\" href=\"http:\/\/www.flickr.com\/photos\/klipsch_fan\/230712919\/\" target=\"_blank\" rel=\"noopener noreferrer\">KlipschFan<\/a>, <a id=\"_i_6\" href=\"http:\/\/www.flickr.com\/photos\/scillystuff\/1572120541\/\" target=\"_blank\" rel=\"noopener noreferrer\">scillystuff<\/a>, <a id=\"_i_7\" href=\"http:\/\/www.flickr.com\/photos\/rhondawebber\/3699334339\/\" target=\"_blank\" rel=\"noopener noreferrer\">rhondawebber<\/a> (<a id=\"_i_8\" href=\"http:\/\/creativecommons.org\/licenses\/by\/2.0\" target=\"_blank\" rel=\"noopener noreferrer\">CC-BY-2.0<\/a>)\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div data-type=\"title\">\r\n<h2>Integration with Other Modalities<\/h2>\r\nVision is not an encapsulated system. It interacts with and depends on other sensory modalities. For example, when you move your head in one direction, your eyes reflexively move in the opposite direction to compensate, allowing you to maintain your gaze on the object that you are looking at. This reflex is called the <strong>vestibulo-ocular reflex<\/strong>. It is achieved by integrating information from both the visual and the vestibular system (which knows about body motion and position). You can experience this compensation quite simply. First, while you keep your head still and your gaze looking straight ahead, wave your finger in front of you from side to side. Notice how the image of the finger appears blurry. Now, keep your finger steady and look at it while you move your head from side to side. Notice how your eyes reflexively move to compensate the movement of your head and how the image of the finger stays sharp and stable. Vision also interacts with your proprioceptive system, to help you find where all your body parts are, and with your auditory system, to help you understand the sounds people make when they speak. You can learn more about this in the multimodal module.\r\n\r\nFinally, vision is also often implicated in a blending-of-sensations phenomenon known as\u00a0<strong>synesthesia<\/strong>. Synesthesia occurs when one sensory signal gives rise to two or more sensations. The most common type is <em>grapheme-color<\/em> synesthesia. About 1 in 200 individuals experience a sensation of color associated with specific letters, numbers, or words: the number 1 might always be seen as red, the number 2 as orange, etc. But the more fascinating forms of synesthesia blend sensations from entirely different sensory modalities, like taste and color or music and color: the taste of chicken might elicit a sensation of green, for example, and the timbre of violin a deep purple.\r\n<div class=\"textbox examples\">\r\n<h3>Link to Learning<\/h3>\r\nAll of this talk about vision may have you wondering what this has to do with psychology. Remember that sensation is input about the physical world obtained by our sensory receptors, and perception is the process by which the brain selects, organizes, and interprets these sensations. In other words, senses are the physiological basis of perception. Perception of the same senses may vary from one person to another because each person's brain interprets stimuli differently based on that individual's learning, memory, emotions, and expectations. It is for this reason that psychologists study sensation\u2014in order to understand perception, which is clearly a component of behavior and mental processes (the definition of psychology).\r\n\r\nTo see this all in action, visit the BBC website <a href=\"https:\/\/www.bbc.co.uk\/science\/humanbody\/body\/interactives\/senseschallenge\/senses.swf\" target=\"_blank\" rel=\"noopener noreferrer\">HERE<\/a> to participate in the sensation lab. Complete the twenty exercises and click on the \u201cexplanation\u201d after each question to learn about\u00a0how our senses are easily fooled.\r\n\r\n<\/div>\r\n<div class=\"textbox learning-objectives\">\r\n<h3>Think It Over<\/h3>\r\n<section data-depth=\"1\">\r\n<div data-type=\"exercise\">\r\n<div data-type=\"problem\">\r\n\r\nTake a look at a few of your photos or personal works of art. Can you find examples of linear perspective as a potential depth cue?\r\n\r\n<\/div>\r\n<\/div>\r\n<\/section><\/div>\r\n<\/div>\r\n<\/div>\r\n<\/section><\/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>afterimage:\u00a0<\/strong>continuation of a visual sensation after removal of the stimulus<\/div>\r\n<div data-type=\"definition\"><strong>binocular cue:\u00a0<\/strong>cue that relies on the use of both eyes<\/div>\r\n<div data-type=\"definition\"><strong>binocular disparity:\u00a0<\/strong>slightly different view of the world that each eye receives<\/div>\r\n<div data-type=\"definition\">\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>\r\n<div data-type=\"definition\"><strong>depth perception:\u00a0<\/strong>ability to perceive depth<\/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\">\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>\r\n<div data-type=\"definition\"><strong>linear perspective:\u00a0<\/strong>perceive depth in an image when two parallel lines seem to converge<\/div>\r\n<div data-type=\"definition\"><strong>monocular cue:\u00a0<\/strong>cue that requires only one eye<\/div>\r\n<div data-type=\"definition\"><strong>opponent-process theory of color perception:\u00a0<\/strong>color is coded in opponent pairs: black-white, yellow-blue, and red-green<\/div>\r\n<div data-type=\"definition\">\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\">\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>\r\n<\/div>\r\n<div data-type=\"definition\"><strong>synesthesia<\/strong>: the blending of two or more sensory experiences, or the automatic activation of a secondary (indirect) sensory experience due to certain aspects of the primary (direct) sensory stimulation<\/div>\r\n<div data-type=\"definition\"><strong>trichromatic theory of color perception:\u00a0<\/strong>color vision is mediated by the activity across the three groups of cones<\/div>\r\n<div data-type=\"definition\"><strong>trough:\u00a0<\/strong>lowest point of a wave<\/div>\r\n<div data-type=\"definition\"><strong>vestibulo-ocular reflex:<\/strong> coordination of motion information with visual information that allows you to maintain your gaze on an object while you move<\/div>\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\">\r\n<div data-type=\"definition\">\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<\/div>\r\nhttps:\/\/assessments.lumenlearning.com\/assessments\/4824\r\n\r\n<\/section><\/section>","rendered":"<h2>What you&#8217;ll learn to do: explain the process of vision and how people see color and depth<\/h2>\n<figure>\n<div style=\"width: 540px\" 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\/23224717\/CNX_Psych_05_03_Eyes.jpg\" alt=\"Several photographs of peoples\u2019 eyes are shown.\" width=\"530\" height=\"284\" data-media-type=\"image\/jpg\" \/><\/p>\n<p class=\"wp-caption-text\">Our eyes take in sensory information that helps us understand the world around us. (credit &#8220;top left\u201d: modification of work by &#8220;rajkumar1220&#8243;\/Flickr&#8221;; credit \u201ctop right\u201d: modification of work by Thomas Leuthard; credit \u201cmiddle left\u201d: modification of work by Demietrich Baker; credit \u201cmiddle right\u201d: modification of work by &#8220;kaybee07&#8243;\/Flickr; credit \u201cbottom left\u201d: modification of work by &#8220;Isengardt&#8221;\/Flickr; credit \u201cbottom right\u201d: modification of work by Willem Heerbaart)<\/p>\n<\/div>\n<\/figure>\n<p>The visual system constructs a mental representation of the world around us. This contributes to our ability to successfully navigate through physical space and interact with important individuals and objects in our environments. This section will provide an overview of the basic anatomy and function of the visual system. In addition, you&#8217;ll\u00a0explore our ability to perceive color and depth.<\/p>\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<li>Describe the trichromatic theory of color vision and the opponent-process theory<\/li>\n<li>Describe how monocular and binocular cues are used in the perception of depth<\/li>\n<\/ul>\n<\/div>\n<section data-depth=\"1\">\n<h2>Anatomy of the Visual System<\/h2>\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\">Figure 1. 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 style=\"width: 511px\" 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\/23224721\/CNX_Psych_05_03_RodsCones.jpg\" alt=\"This illustration shows light reaching the optic nerve, beneath which are Ganglion cells, and then rods and cones.\" width=\"501\" height=\"437\" data-media-type=\"image\/jpg\" \/><\/p>\n<p class=\"wp-caption-text\">Figure 2. The two types of photoreceptors are shown in this image. Rods are colored green and cones 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 class=\"textbox tryit\">\n<h3>Try It<\/h3>\n<p>\t<iframe id=\"lumen_assessment_2837\" class=\"resizable\" src=\"https:\/\/assessments.lumenlearning.com\/assessments\/load?assessment_id=2837&#38;embed=1&#38;external_user_id=&#38;external_context_id=&#38;iframe_resize_id=lumen_assessment_2837\" frameborder=\"0\" style=\"border:none;width:100%;height:100%;min-height:400px;\"><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\" class=\"\" 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=\"An illustration shows the location of the occipital lobe, optic chiasm, optic nerve, and the eyes in relation to their position in the brain and head.\" width=\"573\" height=\"412\" data-media-type=\"image\/jpg\" \/><\/p>\n<p class=\"wp-caption-text\">Figure 3. 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<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 V1\/V2, V3, V3A, and V4.\" width=\"524\" height=\"264\" \/><\/a><\/p>\n<p id=\"caption-attachment-2153\" class=\"wp-caption-text\">Figure 4. Visual areas in the brain.<\/p>\n<\/div>\n<section data-depth=\"1\">\n<div class=\"textbox tryit\">\n<h3>Try It<\/h3>\n<p>\t<iframe id=\"lumen_assessment_2833\" class=\"resizable\" src=\"https:\/\/assessments.lumenlearning.com\/assessments\/load?assessment_id=2833&#38;embed=1&#38;external_user_id=&#38;external_context_id=&#38;iframe_resize_id=lumen_assessment_2833\" frameborder=\"0\" style=\"border:none;width:100%;height:100%;min-height:400px;\"><br \/>\n\t<\/iframe><\/p>\n<p>\t<iframe id=\"lumen_assessment_2834\" class=\"resizable\" src=\"https:\/\/assessments.lumenlearning.com\/assessments\/load?assessment_id=2834&#38;embed=1&#38;external_user_id=&#38;external_context_id=&#38;iframe_resize_id=lumen_assessment_2834\" frameborder=\"0\" style=\"border:none;width:100%;height:100%;min-height:400px;\"><br \/>\n\t<\/iframe><\/p>\n<p>\t<iframe id=\"lumen_assessment_2835\" class=\"resizable\" src=\"https:\/\/assessments.lumenlearning.com\/assessments\/load?assessment_id=2835&#38;embed=1&#38;external_user_id=&#38;external_context_id=&#38;iframe_resize_id=lumen_assessment_2835\" frameborder=\"0\" style=\"border:none;width:100%;height:100%;min-height:400px;\"><br \/>\n\t<\/iframe><\/p>\n<p>\t<iframe id=\"lumen_assessment_2836\" class=\"resizable\" src=\"https:\/\/assessments.lumenlearning.com\/assessments\/load?assessment_id=2836&#38;embed=1&#38;external_user_id=&#38;external_context_id=&#38;iframe_resize_id=lumen_assessment_2836\" frameborder=\"0\" style=\"border:none;width:100%;height:100%;min-height:400px;\"><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\">Figure 5. 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 wave form. <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\">Figure 6. 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.\" width=\"975\" height=\"404\" data-media-type=\"image\/jpg\" \/><\/p>\n<p class=\"wp-caption-text\">Figure 7. 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=\"A line provides Wavelength in nanometers for \u201c400,\u201d \u201c500,\u201d \u201c600,\u201d and \u201c700\u201d nanometers. Within this line are all of the colors of the visible spectrum. Below this line, labeled from left to right are \u201cCosmic radiation,\u201d \u201cGamma rays,\u201d \u201cX-rays,\u201d \u201cUltraviolet,\u201d then a small callout area for the line above containing the colors in the visual spectrum, followed by \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\">Figure 8. 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=\"lumen_assessment_2839\" class=\"resizable\" src=\"https:\/\/assessments.lumenlearning.com\/assessments\/load?assessment_id=2839&#38;embed=1&#38;external_user_id=&#38;external_context_id=&#38;iframe_resize_id=lumen_assessment_2839\" frameborder=\"0\" style=\"border:none;width:100%;height:100%;min-height:400px;\"><br \/>\n\t<\/iframe><\/p>\n<p>\t<iframe id=\"lumen_assessment_2840\" class=\"resizable\" src=\"https:\/\/assessments.lumenlearning.com\/assessments\/load?assessment_id=2840&#38;embed=1&#38;external_user_id=&#38;external_context_id=&#38;iframe_resize_id=lumen_assessment_2840\" frameborder=\"0\" style=\"border:none;width:100%;height:100%;min-height:400px;\"><br \/>\n\t<\/iframe><\/p>\n<p>\t<iframe id=\"lumen_assessment_2841\" class=\"resizable\" src=\"https:\/\/assessments.lumenlearning.com\/assessments\/load?assessment_id=2841&#38;embed=1&#38;external_user_id=&#38;external_context_id=&#38;iframe_resize_id=lumen_assessment_2841\" frameborder=\"0\" style=\"border:none;width:100%;height:100%;min-height:400px;\"><br \/>\n\t<\/iframe><\/p>\n<p>\t<iframe id=\"lumen_assessment_2842\" class=\"resizable\" src=\"https:\/\/assessments.lumenlearning.com\/assessments\/load?assessment_id=2842&#38;embed=1&#38;external_user_id=&#38;external_context_id=&#38;iframe_resize_id=lumen_assessment_2842\" frameborder=\"0\" style=\"border:none;width:100%;height:100%;min-height:400px;\"><br \/>\n\t<\/iframe><\/p>\n<p>\t<iframe id=\"lumen_assessment_2843\" class=\"resizable\" src=\"https:\/\/assessments.lumenlearning.com\/assessments\/load?assessment_id=2843&#38;embed=1&#38;external_user_id=&#38;external_context_id=&#38;iframe_resize_id=lumen_assessment_2843\" frameborder=\"0\" style=\"border:none;width:100%;height:100%;min-height:400px;\"><br \/>\n\t<\/iframe><\/p>\n<p>\t<iframe id=\"lumen_assessment_4270\" class=\"resizable\" src=\"https:\/\/assessments.lumenlearning.com\/assessments\/load?assessment_id=4270&#38;embed=1&#38;external_user_id=&#38;external_context_id=&#38;iframe_resize_id=lumen_assessment_4270\" frameborder=\"0\" style=\"border:none;width:100%;height:100%;min-height:400px;\"><br \/>\n\t<\/iframe><\/p>\n<\/div>\n<\/section>\n<p>We do not see the world in black and white; neither do we see it as two-dimensional (2-D) or flat (just height and width, no depth). Let\u2019s look at how color vision works and how we perceive three dimensions (height, width, and depth).<\/p>\n<section data-depth=\"1\">\n<section data-depth=\"2\">\n<h2 data-type=\"title\">Color Vision<\/h2>\n<p>Normal-sighted individuals have three different types of cones that mediate <strong>color vision<\/strong>. Each of these cone types is maximally sensitive to a slightly different wavelength of light. According to the Young-Helmholtz\u00a0<strong>trichromatic theory of color vision<\/strong>, shown in Figure 9, all colors in the spectrum can be produced by combining red, green, and blue. The three types of cones are each receptive to one of the colors.<\/p>\n<figure>\n<div style=\"width: 502px\" 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\/23224725\/CNX_Psych_05_03_Trichrom.jpg\" alt=\"A graph is shown with \u201csensitivity\u201d plotted on the y-axis and \u201cWavelength\u201d in nanometers plotted along the x-axis with measurements of 400, 500, 600, and 700. Three lines in different colors move from the base to the peak of the y axis, and back to the base. The blue line begins at 400 nm and hits its peak of sensitivity around 455 nanometers, before the sensitivity drops off at roughly the same rate at which it increased, returning to the lowest sensitivity around 530 nm . The green line begins at 400 nm and reaches its peak of sensitivity around 535 nanometers. Its sensitivity then decreases at roughly the same rate at which it increased, returning to the lowest sensitivity around 650 nm. The red line follows the same pattern as the first two, beginning at 400 nm, increasing and decreasing at the same rate, and it hits its height of sensitivity around 580 nanometers. Below this graph is a horizontal bar showing the colors of the visible spectrum.\" width=\"492\" height=\"409\" data-media-type=\"image\/jpg\" \/><\/p>\n<p class=\"wp-caption-text\">Figure 9. This figure illustrates the different sensitivities for the three cone types found in a normal-sighted individual. (credit: modification of work by Vanessa Ezekowitz)<\/p>\n<\/div>\n<\/figure>\n<p>The trichromatic theory of color vision is not the only theory\u2014another major theory of color vision is known as the <strong>opponent-process theory<\/strong>. According to this theory, color is coded in opponent pairs: black-white, yellow-blue, and green-red. The basic idea is that some cells of the visual system are excited by one of the opponent colors and inhibited by the other. So, a cell that was excited by wavelengths associated with green would be inhibited by wavelengths associated with red, and vice versa. One of the implications of opponent processing is that we do not experience greenish-reds or yellowish-blues as colors. Another implication is that this leads to the experience of negative afterimages. An <strong>afterimage<\/strong> describes the continuation of a visual sensation after removal of the stimulus. For example, when you stare briefly at the sun and then look away from it, you may still perceive a spot of light although the stimulus (the sun) has been removed. When color is involved in the stimulus, the color pairings identified in the opponent-process theory lead to a negative afterimage. You can test this concept using the flag in Figure 10.<\/p>\n<figure>\n<div style=\"width: 497px\" 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\/23224727\/CNX_Psych_05_03_Afterimage.jpg\" alt=\"An illustration shows a green flag with a thick, black-bordered yellow lines meeting slightly to the left of the center. A small white dot sits within the yellow space in the exact center of the flag.\" width=\"487\" height=\"352\" data-media-type=\"image\/jpg\" \/><\/p>\n<p class=\"wp-caption-text\">Figure 10. Stare at the white dot for 30\u201360 seconds and then move your eyes to a blank piece of white paper. What do you see? This is known as a negative afterimage, and it provides empirical support for the opponent-process theory of color vision.<\/p>\n<\/div>\n<\/figure>\n<p>But these two theories\u2014the trichromatic theory of color vision and the opponent-process theory\u2014are not mutually exclusive. Research has shown that they just apply to different levels of the nervous system. For visual processing on the retina, trichromatic theory applies: the cones are responsive to three different wavelengths that represent red, blue, and green. But once the signal moves past the retina on its way to the brain, the cells respond in a way consistent with opponent-process theory (Land, 1959; Kaiser, 1997).<\/p>\n<div class=\"textbox tryit\">\n<h3>Try It<\/h3>\n<p>\t<iframe id=\"lumen_assessment_2844\" class=\"resizable\" src=\"https:\/\/assessments.lumenlearning.com\/assessments\/load?assessment_id=2844&#38;embed=1&#38;external_user_id=&#38;external_context_id=&#38;iframe_resize_id=lumen_assessment_2844\" frameborder=\"0\" style=\"border:none;width:100%;height:100%;min-height:400px;\"><br \/>\n\t<\/iframe><\/p>\n<p>\t<iframe id=\"lumen_assessment_4272\" class=\"resizable\" src=\"https:\/\/assessments.lumenlearning.com\/assessments\/load?assessment_id=4272&#38;embed=1&#38;external_user_id=&#38;external_context_id=&#38;iframe_resize_id=lumen_assessment_4272\" frameborder=\"0\" style=\"border:none;width:100%;height:100%;min-height:400px;\"><br \/>\n\t<\/iframe><\/p>\n<p>\t<iframe id=\"lumen_assessment_4273\" class=\"resizable\" src=\"https:\/\/assessments.lumenlearning.com\/assessments\/load?assessment_id=4273&#38;embed=1&#38;external_user_id=&#38;external_context_id=&#38;iframe_resize_id=lumen_assessment_4273\" frameborder=\"0\" style=\"border:none;width:100%;height:100%;min-height:400px;\"><br \/>\n\t<\/iframe><\/p>\n<p>\t<iframe id=\"lumen_assessment_2845\" class=\"resizable\" src=\"https:\/\/assessments.lumenlearning.com\/assessments\/load?assessment_id=2845&#38;embed=1&#38;external_user_id=&#38;external_context_id=&#38;iframe_resize_id=lumen_assessment_2845\" frameborder=\"0\" style=\"border:none;width:100%;height:100%;min-height:400px;\"><br \/>\n\t<\/iframe><\/p>\n<\/div>\n<\/section>\n<section data-depth=\"2\">\n<h2 data-type=\"title\">Depth Perception<\/h2>\n<p>Our ability to perceive spatial relationships in three-dimensional (3-D) space is known as <strong>depth perception<\/strong>. With depth perception, we can describe things as being in front, behind, above, below, or to the side of other things.<\/p>\n<p>Our world is three-dimensional, so it makes sense that our mental representation of the world has three-dimensional properties. We use a variety of cues in a visual scene to establish our sense of depth. Some of these are <strong>binocular cues<\/strong>, which means that they rely on the use of both eyes. One example of a binocular depth cue is <strong>binocular disparity<\/strong>, the slightly different view of the world that each of our eyes receives. To experience this slightly different view, do this simple exercise: extend your arm fully and extend one of your fingers and focus on that finger. Now, close your left eye without moving your head, then open your left eye and close your right eye without moving your head. You will notice that your finger seems to shift as you alternate between the two eyes because of the slightly different view each eye has of your finger.<\/p>\n<p>A 3-D movie works on the same principle: the special glasses you wear allow the two slightly different images projected onto the screen to be seen separately by your left and your right eye. As your brain processes these images, you have the illusion that the leaping animal or running person is coming right toward you.<\/p>\n<p>Although we rely on binocular cues to experience depth in our 3-D world, we can also perceive depth in 2-D arrays. Think about all the paintings and photographs you have seen. Generally, you pick up on depth in these images even though the visual stimulus is 2-D. When we do this, we are relying on a number of <strong>monocular cues<\/strong>, or cues that require only one eye. If you think you can\u2019t see depth with one eye, note that you don\u2019t bump into things when using only one eye while walking\u2014and, in fact, we have more monocular cues than binocular cues. The following video of anamorphic art demonstrates how we rely on these monocular cues to see depth, even when the depth is only imagined.<\/p>\n<p><iframe loading=\"lazy\" id=\"oembed-1\" title=\"Amazing Anamorphic Illusions!\" width=\"500\" height=\"281\" src=\"https:\/\/www.youtube.com\/embed\/tBNHPk-Lnkk?start=14&#38;feature=oembed\" frameborder=\"0\" allowfullscreen=\"allowfullscreen\"><\/iframe><\/p>\n<p>An example of a monocular cue would be what is known as <strong>linear perspective<\/strong>. Linear perspective refers to the fact that we perceive depth when we see two parallel lines that seem to converge in an image (Figure 11). Some other monocular depth cues are interposition, the partial overlap of objects, the relative size and closeness of images to the horizon, relative size, and the variation between light and shadow.<\/p>\n<figure>\n<div style=\"width: 539px\" 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\/23224729\/CNX_Psych_05_03_LinPerspec.jpg\" alt=\"A photograph shows an empty road that continues toward the horizon.\" width=\"529\" height=\"318\" data-media-type=\"image\/jpg\" \/><\/p>\n<p class=\"wp-caption-text\">Figure 11. We perceive depth in a two-dimensional figure like this one through the use of monocular cues like linear perspective, like the parallel lines converging as the road narrows in the distance. (credit: Marc Dalmulder)<\/p>\n<\/div>\n<\/figure>\n<div data-type=\"note\" data-label=\"Dig Deeper\">\n<div data-type=\"title\">\n<div data-type=\"title\">\n<div class=\"textbox exercises\">\n<h3>Dig Deeper: Stereoblindness<\/h3>\n<p>Bruce Bridgeman was born with an extreme case of lazy eye that resulted in him being stereoblind, or unable to respond to binocular cues of depth. He relied heavily on monocular depth cues, but he never had a true appreciation of the 3-D nature of the world around him. This all changed one night in 2012 while Bruce was seeing a movie with his wife.<\/p>\n<p>The movie the couple was going to see was shot in 3-D, and even though he thought it was a waste of money, Bruce paid for the 3-D glasses when he purchased his ticket. As soon as the film began, Bruce put on the glasses and experienced something completely new. For the first time in his life he appreciated the true depth of the world around him. Remarkably, his ability to perceive depth persisted outside of the movie theater.<\/p>\n<p>There are cells in the nervous system that respond to binocular depth cues. Normally, these cells require activation during early development in order to persist, so experts familiar with Bruce\u2019s case (and others like his) assume that at some point in his development, Bruce must have experienced at least a fleeting moment of binocular vision. It was enough to ensure the survival of the cells in the visual system tuned to binocular cues. The mystery now is why it took Bruce nearly 70 years to have these cells activated (Peck, 2012).<\/p>\n<\/div>\n<div class=\"textbox tryit\">\n<h3>Try It<\/h3>\n<p>\t<iframe id=\"lumen_assessment_2846\" class=\"resizable\" src=\"https:\/\/assessments.lumenlearning.com\/assessments\/load?assessment_id=2846&#38;embed=1&#38;external_user_id=&#38;external_context_id=&#38;iframe_resize_id=lumen_assessment_2846\" frameborder=\"0\" style=\"border:none;width:100%;height:100%;min-height:400px;\"><br \/>\n\t<\/iframe><\/p>\n<p>\t<iframe id=\"lumen_assessment_2847\" class=\"resizable\" src=\"https:\/\/assessments.lumenlearning.com\/assessments\/load?assessment_id=2847&#38;embed=1&#38;external_user_id=&#38;external_context_id=&#38;iframe_resize_id=lumen_assessment_2847\" frameborder=\"0\" style=\"border:none;width:100%;height:100%;min-height:400px;\"><br \/>\n\t<\/iframe><\/p>\n<p>Photos in this activity from\u00a0of <a id=\"_i_3\" href=\"http:\/\/www.flickr.com\/photos\/glaciernps\/4454825783\/\" target=\"_blank\" rel=\"noopener noreferrer\">GlacierNPS<\/a>, <a id=\"_i_4\" href=\"http:\/\/www.flickr.com\/photos\/anijdam\/2586190200\/\" target=\"_blank\" rel=\"noopener noreferrer\">Alicia Nijdam<\/a>, <a id=\"_i_5\" href=\"http:\/\/www.flickr.com\/photos\/klipsch_fan\/230712919\/\" target=\"_blank\" rel=\"noopener noreferrer\">KlipschFan<\/a>, <a id=\"_i_6\" href=\"http:\/\/www.flickr.com\/photos\/scillystuff\/1572120541\/\" target=\"_blank\" rel=\"noopener noreferrer\">scillystuff<\/a>, <a id=\"_i_7\" href=\"http:\/\/www.flickr.com\/photos\/rhondawebber\/3699334339\/\" target=\"_blank\" rel=\"noopener noreferrer\">rhondawebber<\/a> (<a id=\"_i_8\" href=\"http:\/\/creativecommons.org\/licenses\/by\/2.0\" target=\"_blank\" rel=\"noopener noreferrer\">CC-BY-2.0<\/a>)<\/p>\n<\/div>\n<\/div>\n<\/div>\n<div data-type=\"title\">\n<h2>Integration with Other Modalities<\/h2>\n<p>Vision is not an encapsulated system. It interacts with and depends on other sensory modalities. For example, when you move your head in one direction, your eyes reflexively move in the opposite direction to compensate, allowing you to maintain your gaze on the object that you are looking at. This reflex is called the <strong>vestibulo-ocular reflex<\/strong>. It is achieved by integrating information from both the visual and the vestibular system (which knows about body motion and position). You can experience this compensation quite simply. First, while you keep your head still and your gaze looking straight ahead, wave your finger in front of you from side to side. Notice how the image of the finger appears blurry. Now, keep your finger steady and look at it while you move your head from side to side. Notice how your eyes reflexively move to compensate the movement of your head and how the image of the finger stays sharp and stable. Vision also interacts with your proprioceptive system, to help you find where all your body parts are, and with your auditory system, to help you understand the sounds people make when they speak. You can learn more about this in the multimodal module.<\/p>\n<p>Finally, vision is also often implicated in a blending-of-sensations phenomenon known as\u00a0<strong>synesthesia<\/strong>. Synesthesia occurs when one sensory signal gives rise to two or more sensations. The most common type is <em>grapheme-color<\/em> synesthesia. About 1 in 200 individuals experience a sensation of color associated with specific letters, numbers, or words: the number 1 might always be seen as red, the number 2 as orange, etc. But the more fascinating forms of synesthesia blend sensations from entirely different sensory modalities, like taste and color or music and color: the taste of chicken might elicit a sensation of green, for example, and the timbre of violin a deep purple.<\/p>\n<div class=\"textbox examples\">\n<h3>Link to Learning<\/h3>\n<p>All of this talk about vision may have you wondering what this has to do with psychology. Remember that sensation is input about the physical world obtained by our sensory receptors, and perception is the process by which the brain selects, organizes, and interprets these sensations. In other words, senses are the physiological basis of perception. Perception of the same senses may vary from one person to another because each person&#8217;s brain interprets stimuli differently based on that individual&#8217;s learning, memory, emotions, and expectations. It is for this reason that psychologists study sensation\u2014in order to understand perception, which is clearly a component of behavior and mental processes (the definition of psychology).<\/p>\n<p>To see this all in action, visit the BBC website <a href=\"https:\/\/www.bbc.co.uk\/science\/humanbody\/body\/interactives\/senseschallenge\/senses.swf\" target=\"_blank\" rel=\"noopener noreferrer\">HERE<\/a> to participate in the sensation lab. Complete the twenty exercises and click on the \u201cexplanation\u201d after each question to learn about\u00a0how our senses are easily fooled.<\/p>\n<\/div>\n<div class=\"textbox learning-objectives\">\n<h3>Think It Over<\/h3>\n<section data-depth=\"1\">\n<div data-type=\"exercise\">\n<div data-type=\"problem\">\n<p>Take a look at a few of your photos or personal works of art. Can you find examples of linear perspective as a potential depth cue?<\/p>\n<\/div>\n<\/div>\n<\/section>\n<\/div>\n<\/div>\n<\/div>\n<\/section>\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>afterimage:\u00a0<\/strong>continuation of a visual sensation after removal of the stimulus<\/div>\n<div data-type=\"definition\"><strong>binocular cue:\u00a0<\/strong>cue that relies on the use of both eyes<\/div>\n<div data-type=\"definition\"><strong>binocular disparity:\u00a0<\/strong>slightly different view of the world that each eye receives<\/div>\n<div data-type=\"definition\">\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>\n<div data-type=\"definition\"><strong>depth perception:\u00a0<\/strong>ability to perceive depth<\/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\">\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>\n<div data-type=\"definition\"><strong>linear perspective:\u00a0<\/strong>perceive depth in an image when two parallel lines seem to converge<\/div>\n<div data-type=\"definition\"><strong>monocular cue:\u00a0<\/strong>cue that requires only one eye<\/div>\n<div data-type=\"definition\"><strong>opponent-process theory of color perception:\u00a0<\/strong>color is coded in opponent pairs: black-white, yellow-blue, and red-green<\/div>\n<div data-type=\"definition\">\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\">\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>\n<\/div>\n<div data-type=\"definition\"><strong>synesthesia<\/strong>: the blending of two or more sensory experiences, or the automatic activation of a secondary (indirect) sensory experience due to certain aspects of the primary (direct) sensory stimulation<\/div>\n<div data-type=\"definition\"><strong>trichromatic theory of color perception:\u00a0<\/strong>color vision is mediated by the activity across the three groups of cones<\/div>\n<div data-type=\"definition\"><strong>trough:\u00a0<\/strong>lowest point of a wave<\/div>\n<div data-type=\"definition\"><strong>vestibulo-ocular reflex:<\/strong> coordination of motion information with visual information that allows you to maintain your gaze on an object while you move<\/div>\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\">\n<div data-type=\"definition\">\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<\/div>\n<p>\t<iframe id=\"lumen_assessment_4824\" class=\"resizable\" src=\"https:\/\/assessments.lumenlearning.com\/assessments\/load?assessment_id=4824&#38;embed=1&#38;external_user_id=&#38;external_context_id=&#38;iframe_resize_id=lumen_assessment_4824\" frameborder=\"0\" style=\"border:none;width:100%;height:100%;min-height:400px;\"><br \/>\n\t<\/iframe><\/p>\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-2111\">\n\t\t\t\t\t\t\t <div class=\"licensing\"><div class=\"license-attribution-dropdown-subheading\">CC licensed content, Original<\/div><ul class=\"citation-list\"><li>Vision. <strong>Authored by<\/strong>: OpenStax College. <strong>Located at<\/strong>: <a target=\"_blank\" href=\"http:\/\/cnx.org\/contents\/Sr8Ev5Og@5.52:E-7sLQFP@5\/Vision\">http:\/\/cnx.org\/contents\/Sr8Ev5Og@5.52:E-7sLQFP@5\/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 http:\/\/cnx.org\/contents\/4abf04bf-93a0-45c3-9cbc-2cefd46e68cc@5.48<\/li><li>Modification, adaptation, and original content. <strong>Provided by<\/strong>: Lumen Learning. <strong>License<\/strong>: <em><a target=\"_blank\" rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/\">CC BY: Attribution<\/a><\/em><\/li><\/ul><div class=\"license-attribution-dropdown-subheading\">CC licensed content, Shared previously<\/div><ul class=\"citation-list\"><li>Waves and Wavelenghts. <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><li>Vision, information and visual and ventral and dorsal pathways, Integration with Other Modalities. <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>Project<\/strong>: The Noba Project. <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 class=\"license-attribution-dropdown-subheading\">All rights reserved content<\/div><ul class=\"citation-list\"><li>Amazing Anamorphic Illusions. <strong>Authored by<\/strong>: brusspup. <strong>Located at<\/strong>: <a target=\"_blank\" href=\"https:\/\/www.youtube.com\/watch?v=tBNHPk-Lnkk\">https:\/\/www.youtube.com\/watch?v=tBNHPk-Lnkk<\/a>. <strong>License<\/strong>: <em>Other<\/em>. <strong>License Terms<\/strong>: Standard YouTube License<\/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":29,"menu_order":3,"template":"","meta":{"_candela_citation":"[{\"type\":\"original\",\"description\":\"Vision\",\"author\":\"OpenStax College\",\"organization\":\"\",\"url\":\"http:\/\/cnx.org\/contents\/Sr8Ev5Og@5.52:E-7sLQFP@5\/Vision\",\"project\":\"\",\"license\":\"cc-by\",\"license_terms\":\"Download for free at http:\/\/cnx.org\/contents\/4abf04bf-93a0-45c3-9cbc-2cefd46e68cc@5.48\"},{\"type\":\"cc\",\"description\":\"Waves and Wavelenghts\",\"author\":\"OpenStax College\",\"organization\":\"\",\"url\":\"http:\/\/cnx.org\/contents\/Sr8Ev5Og@5.52:1Cicp6CO@8\/Waves-and-Wavelengths\",\"project\":\"\",\"license\":\"cc-by\",\"license_terms\":\"Download for free at http:\/\/cnx.org\/contents\/4abf04bf-93a0-45c3-9cbc-2cefd46e68cc@5.48\"},{\"type\":\"cc\",\"description\":\"Vision, information and visual and ventral and dorsal pathways, Integration with Other Modalities\",\"author\":\"Simona Buetti and Alejandro Lleras \",\"organization\":\"University of Illinois at Urbana-Champaign\",\"url\":\"http:\/\/nobaproject.com\/modules\/vision\",\"project\":\"The Noba Project\",\"license\":\"cc-by-nc-sa\",\"license_terms\":\"\"},{\"type\":\"cc\",\"description\":\"Waves and Wavelengths\",\"author\":\"OpenStax College\",\"organization\":\"\",\"url\":\"http:\/\/cnx.org\/contents\/Sr8Ev5Og@5.52:1Cicp6CO@8\/Waves-and-Wavelengths\",\"project\":\"\",\"license\":\"cc-by\",\"license_terms\":\"Download for free at http:\/\/cnx.org\/contents\/4abf04bf-93a0-45c3-9cbc-2cefd46e68cc@5.48\"},{\"type\":\"copyrighted_video\",\"description\":\"Amazing Anamorphic Illusions\",\"author\":\"brusspup\",\"organization\":\"\",\"url\":\"https:\/\/www.youtube.com\/watch?v=tBNHPk-Lnkk\",\"project\":\"\",\"license\":\"other\",\"license_terms\":\"Standard YouTube License\"},{\"type\":\"original\",\"description\":\"Modification, adaptation, and original content\",\"author\":\"\",\"organization\":\"Lumen Learning\",\"url\":\"\",\"project\":\"\",\"license\":\"cc-by\",\"license_terms\":\"\"}]","CANDELA_OUTCOMES_GUID":"5bc74b95-37ce-4329-be50-ca192f54b122, 35ccc19f-27d9-40be-bb5a-8aff66972f5b, 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