* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Trichromatic theory of color vision
Neuropsychology wikipedia , lookup
Neurolinguistics wikipedia , lookup
Binding problem wikipedia , lookup
Biology and consumer behaviour wikipedia , lookup
Neuroplasticity wikipedia , lookup
Holonomic brain theory wikipedia , lookup
Proprioception wikipedia , lookup
Optogenetics wikipedia , lookup
Neuroanatomy wikipedia , lookup
Sensory substitution wikipedia , lookup
Microneurography wikipedia , lookup
Perception of infrasound wikipedia , lookup
Metastability in the brain wikipedia , lookup
Sensory cue wikipedia , lookup
Neuroesthetics wikipedia , lookup
Neural correlates of consciousness wikipedia , lookup
Channelrhodopsin wikipedia , lookup
Brain Rules wikipedia , lookup
Embodied cognitive science wikipedia , lookup
Neuropsychopharmacology wikipedia , lookup
Clinical neurochemistry wikipedia , lookup
Feature detection (nervous system) wikipedia , lookup
Psychophysics wikipedia , lookup
Chapter 3 Sensation and Perception McGraw-Hill ©2010 The McGraw-Hill Companies, Inc. All rights reserved. Sensing the World Around Us • Learning Outcomes – Define absolute thresholds – Explain the difference threshold and Weber’s law – Discuss sensory adaptation McGraw-Hill ©2010 The McGraw-Hill Companies, Inc. All rights reserved. 2 Absolute Thresholds: Detecting What’s Out There • Absolute threshold: the smallest intensity of a stimulus that must be present for it to be detected McGraw-Hill ©2010 The McGraw-Hill Companies, Inc. All rights reserved. 3 Sensation and Perception Sensation can be thought of as an organism’s first encounter with a raw sensory stimulus, whereas perception is the process by which that stimulus is interpreted, analyzed, and integrated with other sensory information. For example, if we were considering sensation, we might ask about the loudness of a ringing fire alarm. If we were considering perception, we might ask whether someone recognizes the ringing sound as an alarm and identifies its meaning. Terms Terms essential to sensation and perception: Sensation - The activation of the sense organs by a source of physical energy. Perception - The sorting out, interpretation, analysis, and integration of stimuli by the sense organs and brain. Stimulus - Energy that produces a response in a sense organ. **Tip: Sensation is a physical response, while perception is a psychological response Psychophysics Psychophysics is the study of the relationship between the physical aspects of stimuli and our psychological experience of them. - Stimuli vary in both type and intensity. Different types of stimuli activate different sense organs. - Light activates the sense of sight and allows us to see colors. - Sound activates the sense of hearing and allows us to hear musical sounds. - How intense does light need to be before it can be detected, or how much perfume does a person need to wear before it is noticed are questions related to stimulus intensity. Thresholds: Noticing Distinctions between Stimuli Absolute threshold is the smallest intensity of a stimulus that must be present for it to be detected (Aazh & Moore, 2007). • Our senses are extremely responsive to stimuli. How loud does a noise have to be before you can hear it? How bright does a light have to be before you can see it? At what point can you feel a feather touching your skin? • Absolute thresholds vary due to something psychophysicists refer to as “noise.” Noise is the background stimulation that interferes with the perception of other stimuli, such as crowds of people, traffic jams, television shows, or anything that interferes with the ability to perceive a stimulus. RECAP • Sensation - The activation of the sense organs by a source of physical energy. (Physical response) • Perception - The sorting out, interpretation, analysis, and integration of stimuli by the sense organs and brain. (Psychological response) • Stimulus - Energy that produces a response in a sense organ. • Psychophysics - The study of the relationship between the physical aspects of stimuli and our psychological experience of them. • Absolute Threshold - The smallest intensity of a stimulus that must be present for it to be detected • Noise - The background stimulation that interferes with the perception of other stimuli. Difference Thresholds: Noticing Distinctions between Stimuli Difference threshold (just noticeable difference) - The difference threshold is the smallest level of added or reduced stimulation required to sense that a change in stimulation has occurred. It is the minimum change in stimulation required to detect the difference between two stimuli, so it is also called the “just noticeable difference” (Nittrouer & Lowenstein, 2007). • The stimulus value that constitutes a just noticeable difference depends on the initial intensity of the stimulus. The relationship between changes in the original value of a stimulus and the degree to which a change will be noticed forms one of the basic laws of psychophysics: Weber’s law. McGraw-Hill ©2010 The McGraw-Hill Companies, Inc. All rights reserved. 9 Difference Thresholds: Noticing Distinctions between Stimuli Weber’s law – (pronounced “VAY-ber”) a basic law of psychophysics stating that a just noticeable difference is in constant proportion to the intensity of an initial stimulus. – For example, if you work at the fragrance department of a department store, you will notice the smells of the perfumes immediately. After working there a month, you will not notice the smell any more. This also explains why we often do not recognize the smells in our own home, but we certainly recognize them in other people’s homes. – Weber’s law helps explain why a person in a quiet room is more startled by the ringing of a telephone than is a person in an already noisy room. To produce the same amount of reaction in a noisy room, a telephone ring might have to approximate the loudness of cathedral bells. Similarly, when the moon is visible during the late afternoon, it appears relatively dim—yet against a dark night sky, it seems quite bright. RECAP • The difference threshold is the smallest level of added or reduced stimulation required to sense that a change in stimulation has occurred. • The just noticeable difference is another term for the “difference threshold.” It is the minimum change in stimulation required to detect the difference between two stimuli. • Weber’s law states that a just noticeable difference is in constant proportion to the intensity of an initial stimulus. Rethink Sensations have been described as the physical responses to stimuli, while perceptions are the psychological responses to those same stimuli. Is it possible that people have different perceptions based on the same sensations? On other words, do people interpret sensations differently? Why or why not? Sensory Adaptation: Turning Down Our Responses • Sensory adaptation: an adjustment to sensory capacity when stimuli in the environment are unchanging; “getting used to” a sensory stimulus so that you no longer have the same reaction to it as you initially did – One example of adaptation is the decrease in sensitivity that occurs after repeated exposure to a strong stimulus. If you were to hear a loud tone over and over again, eventually it would begin to sound softer. Similarly, jumping into cold water may be startling, but you eventually get used to the temperature. • Sensory nerve receptors cannot fire off messages to the brain indefinitely. They get used to the constant stimulation, and the result is a decreased sensitivity to constant sensory stimuli. Receptor cells are most responsive to changes in stimulation. McGraw-Hill ©2010 The McGraw-Hill Companies, Inc. All rights reserved. 13 Critical Thinking Exercise (Homework Due Wednesday May 4th) Take a moment to consider the graphics in video games. They are designed to stimulate our senses and imitate real experiences. Many people become so focused on the game they are playing that they cannot hear a person in the same room who calls their name. 1. 2. 3. 4. How do video or virtual reality games appeal to our sense of sight? How do they appeal to our sense of sound? How do they appeal to our sense of touch? Do people experience the bodily sensations of rapid breathing and rapid heart beat when the game gets intense? 5. How do these games arouse emotion in people? Vision: Shedding Light on the Eye • Learning Outcomes – Explain the basic structure of the eye – Compare and contrast color vision with color blindness McGraw-Hill ©2010 The McGraw-Hill Companies, Inc. All rights reserved. 15 Illuminating the Structure of the Eye • Light passes through the cornea, pupil, and the lens before reaching the retina: converts the energy of the light to electrical impulses for transmission to the brain McGraw-Hill ©2010 The McGraw-Hill Companies, Inc. All rights reserved. 16 VISION Vision starts with light, the physical energy that stimulates the eye. Light is a form of electromagnetic radiation waves, which are measured in wavelengths. The sizes of wavelengths correspond to different types of energy. The range of wavelengths that humans are sensitive to is called the visual spectrum. 1. Light waves coming from some object outside the body are sensed by the eye. 2. The eye converts light to a form that can be used by the neurons that serve as messengers to the brain. Illuminating the Structure of the Eye Rods - are thin, cylindrical receptor cells that are highly sensitive to light. They enable you to see in dim light. Rods play a key role in peripheral and night vision. Cones - are cone-shaped, light-sensitive receptor cells that are responsible for sharp focus and color perception, particularly in bright light. Optic nerve - When light energy strikes the rods and cones, it triggers a neural response that moves out of the back of the eyeball and into the brain through a bundle of ganglion axons McGraw-Hill ©2010 The McGraw-Hill Companies, Inc. All rights reserved. 18 Feature Detection Feature detection - Most processing of visual images takes place in the visual cortex of the brain. Neurons in the cortex are extraordinarily specialized and are activated only by visual stimuli of a particular shape or pattern. • Different parts of the brain process nerve impulses in several individual systems simultaneously. For instance, one system relates to shapes, one to colors, and others to movement, location, and depth. • Different parts of the brain are involved in the perception of specific kinds of stimuli, showing distinctions, for example, between the perception of human faces, animals, and inanimate stimuli. RECAP 1. 2. 3. 4. 5. 6. 7. Visual spectrum - the range of wavelengths that humans are able to see. Cornea - the transparent front part of the eye that covers the pupil and iris. The cornea works with the lens to refract light. Pupil - the dark hole in the center of the iris. Rods - thin, cylindrical receptor cells that are highly sensitive to light. They allow you to see in dim light. Cones - cone-shaped, light-sensitive receptor cells that are responsible for sharp focus and color perception, particularly in bright light. Optic nerve – the nerve that transmits visual information from the retina to the brain. Feature detection – the process explaining that neurons in the cortex are extraordinarily specialized and are activated only by visual stimuli of a particular shape or pattern. Color Vision and Color Blindness: The Seven-Million-Color Spectrum Trichromatic theory of color vision: This theory suggests that there are three kinds of cones in the retina, each of which responds to a specific range of wavelengths. • One is most responsive to blue-violet colors, one to green, and the third to yellow-red (Brown & Wald, 1964). According to trichromatic theory perception of color is influenced by the relative strength with which each of the three kinds of cones is activated. • The trichromatic theory does not explain all aspect of color vision. If you stare at a picture for thirty seconds and then look at a piece of blank, white paper, you will see a distorted image of the picture you were just staring at. McGraw-Hill ©2010 The McGraw-Hill Companies, Inc. All rights reserved. 21 Trichromatic theory of color vision Trichromatic theory of color vision • The phenomenon you experienced is called afterimage. It occurs because activity in the retina continues even when you are no longer staring at the original picture. • Now try this while closing one eye. Notice that your eyes cannot transfer an afterimage back and forth. If one eye is shut while you stare at the black light, the shut eye will not see the afterimage. The only eye that will see the afterimage is the eye that was exposed to the image. Color Vision & Color Blind A person with normal color vision is capable of distinguishing no less than seven million different colors, but approximately 50 in 5,000 men and 1 in 5,000 women are color-blind. For most people with color blindness, the world looks quite dull. Red fire engines, green grass, and the three colors of a traffic light all look yellow. In the most common form of color blindness, all red and green objects are seen as yellow. There are other forms of color blindness as well, but they are quite rare. In yellow-blue blindness, people are unable to tell the difference between yellow and blue, and in the most extreme case an individual perceives no color at all. To such a person the world looks something like the picture on a black-and-white television set. http://colorvisiontesting.com/ishihara.htm#plate with 10 Color Vision and Color Blindness: The Seven-Million-Color Spectrum (cont.) Stare at the dot in this flag for about a minute and then look at a piece of plain white paper. What do you see? Most people see an afterimage that converts the colors in the figure into the traditional red, white, and blue U.S. flag. If you have trouble seeing it the first time, blink once and try again. McGraw-Hill ©2010 The McGraw-Hill Companies, Inc. All rights reserved. 25 Color Vision and Color Blindness: The Seven-Million-Color Spectrum Opponent-process theory of color vision: This theory suggests that receptor cells for color are linked in pairs, working in opposition to each other. There are specific pairings: 1. blue-yellow pairing 2. red-green pairing 3. black-white pairing If an object reflects light that contains more blue than yellow, it will stimulate the firing of the cells sensitive to blue, while discouraging or inhibiting the firing of receptor cells sensitive to yellow. The outcome is that the object will appear blue. If a light contains more yellow than blue, the cells that respond to yellow will be stimulated to fire while the blue ones are inhibited, and the object will appear yellow (D. N. Robinson, 2007). - Both opponent processes and trichromatic mechanisms are at work in allowing us to see color. However, they operate in different parts of the visual sensing system: 1. Trichromatic processes work within the retina itself. 2. Opponent mechanisms operate both in the retina and at later stages of neuronal processing. (Gegenfurtner, 2003; Chen, Zhou, & Gong, 2004; Baraas, Foster, & Amano, 2006). McGraw-Hill ©2010 The McGraw-Hill Companies, Inc. All rights reserved. 26 RECAP 1. The trichromatic theory of color vision suggests that there are three kinds of cones in the retina, each of which responds to a specific range of wavelengths. 2. Afterimage – after staring at a picture activity in the retina continues causing you to see an image of distorted colors when looking at a white space. 3. The opponent-process theory of color vision suggests that receptor cells for color are linked in pairs, working in opposition to each other, blueyellow, red-green, and black-white. Hearing and the Other Senses • Learning Outcomes – Describe how we sense sound – Discuss smell and taste – Distinguish the skin senses McGraw-Hill ©2010 The McGraw-Hill Companies, Inc. All rights reserved. 28 Sensing Sound The outer ear acts as a reverse megaphone, designed to collect and bring sounds into the internal portions of the ear, where sounds are processed. The outer ears are located on different sides of the head, which helps to identify the direction from which a sound is coming. Wave patterns in the air enter each ear at a slightly different time, and the brain uses the discrepancy as a clue to the sound’s point of origin. Sound: is the movement of air molecules brought about by a source of vibration. Sounds arrive at the outer ear in the form of these wavelike vibrations. They are funneled into the auditory canal, a tube-like passage that leads to the eardrum. McGraw-Hill ©2010 The McGraw-Hill Companies, Inc. All rights reserved. 29 Sensing Sound When an auditory message leaves the ear, it is transmitted to the auditory cortex of the brain through a complex series of neural interconnections. As the message is transmitted, it is communicated through neurons that respond to specific types of sounds. – Some neurons respond to clicks and whistles – Some neurons respond to specific patterns such as steady tones. – Some neurons respond to intermittent patterns. – Other neurons transfer information about the location of the sound. The auditory cortex provides us with a “map” of sound frequencies, so we are able to identify the sound. Balance Semicircular canals: of the inner ear consist of three tubes containing fluid that sloshes through them when the head moves, signaling rotational or angular movement to the brain. The pull on our bodies caused by the acceleration of forward, backward, or up-and-down motion, as well as the constant pull of gravity, is sensed by the otoliths, tiny, motion-sensitive crystals in the semicircular canals. When we move, these crystals shift like sands on a windy beach. The brain’s inexperience in interpreting messages from the weightless otoliths is the cause of the space sickness experienced by two-thirds of all space travelers (Flam, 1991; Stern & Koch, 1996). Smell • Smell (olfaction) – Molecules enter the nasal passages and pass over olfactory cells (receptor neurons); responses sent to brain, where they are combined for recognition of particular smells – Humans are able to detect more than ten thousand separate smells. We also have a good memory for smells, and long-forgotten events and memories can be brought back with the mere whiff of an odor associated with a memory McGraw-Hill ©2010 The McGraw-Hill Companies, Inc. All rights reserved. 32 SMELL • Results of “sniff tests” have shown that women generally have a better sense of smell than men do. People also have the ability to distinguish males from females on the basis of smell alone. People can distinguish happy from sad emotions by sniffing underarm smells, and women are able to identify their babies solely on the basis of smell just a few hours after birth SMELL • More than a thousand receptor cells, known as olfactory cells, are spread across the nasal cavity. The cells are specialized to react to particular odors. • The sense of smell is sparked when the molecules of a substance enter the nasal passages and meet olfactory cells, the receptor neurons of the nose, which are spread across the nasal cavity. More than a thousand different types of receptors have been identified on those cells so far. Each of these receptors is so specialized that it responds only to a small band of different odors. The responses of the separate olfactory cells are then transmitted to the brain, where they are combined into recognition of a particular smell (Murphy et al., 2004; Zho & Buck, 2006; Marshall, Laing, & Jinks, 2006). SMELL Humans have seven primary odors that help them determine objects. Listed below are the seven odors. Camphoric = Mothballs Musky = Perfume/Aftershave Floral = Roses Pepperminty = Toothpaste Etheral = Dry Cleaning Fluid Pungent = Vinegar Putrid = Rotten Eggs SMELL • Dogs have 1 million smell cells per nostril and their smell cells are 100 times larger than humans! • Humans use insect warning chemicals, called pheromones, to keep away pesky insects! • People who cannot smell have a condition called Anosmia. • If your nose is at its best, you can tell the difference between 4000-10,000 smells! • As you get older, your sense of smell gets worse. • Children are more likely to have better senses of smell than their parents or grandparents. http://www.senseofsmell.org/ TASTE The sense of taste is referred to as gustation. It involves receptor cells that respond to four basic stimulus qualities: sweet, sour, salty, and bitter. The receptor cells for taste are located in roughly ten thousand taste buds, which are distributed across the tongue and other parts of the mouth and throat. The taste buds wear out and are replaced every ten days or so. That’s a good thing, because if our taste buds were not constantly reproducing, we’d lose the ability to taste after accidentally burning our tongues. TASTE TASTE BUD TASTE • Everyone's tastes are different. In fact, your tastes will change as you get older. When you were a baby, you had taste buds, not only on your tongue, but on the sides and roof of your mouth. This means you were very sensitive to different foods. As you grew, the taste buds began to disappear from the sides and roof of your mouth, leaving taste buds mostly on your tongue. As you get older, your taste buds will become even less sensitive, so you will be more likely to eat foods that you thought were too strong as a child. • What if you could not taste anything? Things like medications, smoking, not getting enough of the right vitamins, injury to the head, brain tumors, chemical exposure, and the effects of radiation can cause taste disorders. TASTE The sense of taste differs significantly from one person to another, largely as a result of genetic factors: • Supertasters are highly sensitive to taste; they have twice as many taste receptors as “nontasters.” More females are “supertasters”. Supertasters find sweets sweeter, cream creamier, and spicy dishes spicier. Weaker concentrations of flavor are enough to satisfy any cravings they may have. • Nontasters are relatively insensitive to taste. They may seek out relatively sweeter and fattier foods in order to maximize the taste. As a consequence, they may be prone to obesity. • Average tasters lie somewhere between supertasters and nontasters. TASTE FACTS • We have almost 10,000 taste buds inside our mouths; even on the roofs of our mouths. • Insects have the most highly developed sense of taste. They have taste organs on their feet, antennae, and mouthparts. • Fish can taste with their fins and tail as well as their mouth. • In general, girls have more tastebuds than boys. • Taste is the weakest of the five senses. RECAP 1. Olfaction – the human sense of smell. 2. Olfactory cells - the receptor neurons of the nose, which are spread across the nasal cavity. 3. Gustation – the sense of taste. 4. Supertasters - people who are highly sensitive to taste. 5. Nontasters - people who are relatively insensitive to taste. The Skin Senses: Touch, Pressure, Temperature, and Pain • Skin senses: are identified as touch, pressure, temperature, and pain. They play a critical role in our survival, making us aware of potential danger to our bodies. Most of these senses operate through nerve receptor cells located at various depths throughout the skin, distributed unevenly throughout the body. – For example, some areas, such as the fingertips, have many more receptor cells that are sensitive to touch. These areas are notably more sensitive than other areas of the body. • The lower the average threshold is, the more sensitive a body part is. The fingers and thumb, lips, nose, cheeks, and big toe are the most sensitive. McGraw-Hill ©2010 The McGraw-Hill Companies, Inc. All rights reserved. 44 TOUCH & PAIN • The most extensively researched skin sense is pain. People consult physicians and take medication for pain more than for any other symptom or condition. Losses to U.S. business productivity due to employee pain is more than $60 billion a year, and overall pain costs $100 billion a year in the United States alone. • Pain is a response to a great variety of different kinds of stimuli. A light that is too bright can produce pain, and a sound that is too loud can be painful. One explanation is that pain is an outcome of cell injury. When a cell is damaged, it releases a chemical called substance P that transmits pain messages to the brain. SKIN & TOUCH TOUCH & PAIN • Some people are more susceptible to pain than others. – For example, women experience painful stimuli more intensely than men. These gender differences are associated with the production of hormones related to menstrual cycles. – In addition, certain genes are linked to the experience of pain, so that we may inherit our sensitivity to pain. • However, the experience of pain is not determined by biological factors alone. – For example, women report that the pain experienced in childbirth is moderated to some degree by the joyful nature of the situation. In contrast, even a minor stimulus can produce the perception of strong pain if it is accompanied by anxiety (like a visit to the dentist). Clearly, then, pain is a perceptual response that depends heavily on our emotions and thoughts Gate-Control Theory of Pain According to the gate-control theory of pain, particular nerve receptors in the spinal cord lead to specific areas of the brain related to pain. When these receptors are activated because of an injury or problem with a part of the body, a “gate” to the brain is opened, allowing us to experience the sensation of pain. Another set of neural receptors can, when stimulated, close the “gate” to the brain, thereby reducing the experience of pain. The gate can be shut in two different ways. 1. Other impulses can overwhelm the nerve pathways relating to pain, which are spread throughout the brain. In this case, nonpainful stimuli compete with and sometimes displace the neural message of pain, thereby shutting off the painful stimulus. 2. Psychological factors account for the second way a gate can be shut. Depending on an individual’s current emotions, interpretation of events, and previous experience, the brain can close a gate by sending a message down the spinal cord to an injured area, producing a reduction in or relief from pain. Thus, soldiers who are injured in battle may experience no pain. The lack of pain probably occurs because a soldier experiences such relief at still being alive that the brain sends a signal to the injury site to shut down the pain gate . PAIN MANGEMENT Here are some of the strategies that psychologists and medical specialists have devised to fight pain: 1. Medication – painkilling drugs are used to fight pain and reduce swelling on painful joints. The most recent innovation is to pump pain medication right into the spinal cord . 2. Nerve and brain stimulation – a low-voltage electric current is passed through a specific part of the body that is in pain. Electrodes can also be surgically implanted into the brain. Another process known as transcutaneous electrical nerve stimulation (TENS) uses a handheld battery pack to stimulate nerve cells providing direct relief of pain. 3. Light therapy - one of the newest forms of pain reduction involves exposure to specific wavelengths of red or infrared light. Certain kinds of light increase the production of enzymes that may promote healing. 4. Hypnosis – this technique of deep relaxation can be used to manage pain. PAIN MANAGEMNT 5. Biofeedback and relaxation techniques – processes where people learn to control “involuntary” functions such as heartbeat and respiration. They can also learn to manage pain through progressive relaxation, the relaxation of isolated parts of the body one at a time. 6. Surgery - nerve fibers that carry pain messages to the brain can be cut surgically. Still, because of the danger that other bodily functions will be affected, surgery is a treatment of last resort, used most frequently with dying patients. 7. Cognitive restructuring – the use of positive ways of thinking as a substitute for negative statements like, “This pain will never stop,” or “This pain is ruining my life.” When people increase their sense of control, they can reduce the pain they feel. TOUCH FACTS • You have more pain nerve endings than any other type. • The least sensitive part of your body is the middle of your back. • The most sensitive areas of your body are your hands, lips, face, neck, tongue, fingertips and feet. • Shivering is a way your body has of trying to get warmer. • There are about 100 touch receptors in each of your fingertips. • Rattlesnakes use their skin to feel the body heat of other animals. RECAP 1. The skin senses are identified as touch, pressure, temperature, and pain. 2. People consult physicians and take medication for pain more than for any other symptom or condition. 3. Some people are more susceptible to pain than others. 4. Certain genes are linked to the experience of pain, so that we may inherit our sensitivity to pain. 5. Pain is a perceptual response that depends heavily on our emotions and thoughts. 6. Gate-control theory of pain - The theory that particular nerve receptors lead to specific areas of the brain related to pain. Perceptual Organization: Constructing Our View of the World • Learning Outcomes – Explain the gestalt laws of organization – Identify top-down and bottom-up processing – Define perceptual constancy – Explain depth perception – Relate motion perception to daily life – Determine the importance of perceptual illusions McGraw-Hill ©2010 The McGraw-Hill Companies, Inc. All rights reserved. 53 Perceptual Organization: Constructing Our View of the World (cont.) • The gestalt laws of organization are a series of principles that focus on the ways we organize bits and pieces of information into one whole picture, pattern, or piece of information. These principles were set forth in the early 1900s by a group of German psychologists, led by Max Wertheimer, who studied patterns, or gestalts. Figure-ground organization: we usually perceive objects as a figure standing out against a background McGraw-Hill ©2010 The McGraw-Hill Companies, Inc. All rights reserved. 54 The Gestalt Laws of Organization Principles that describe how we organize pieces of information into meaningful wholes (gestalts = patterns) – Closure - when an object is incomplete, but enough of the shape is indicated for people to fill in the gaps and perceive the whole picture. Even though parts of this panda bear are missing, you are able to perceive the whole picture: McGraw-Hill ©2010 The McGraw-Hill Companies, Inc. All rights reserved. 55 The Gestalt Laws of Organization – Proximity - when elements are placed close together, they tend to be perceived as a group. If the squares below were spread out over this page, the perception would be very different. The Gestalt Laws of Organization - Similarity - when objects look similar, people perceive them as a group or pattern. The Gestalt Laws of Organization (cont.) - Simplicity – when we observe a pattern, we perceive it in the most basic, straightforward manner that we can. McGraw-Hill ©2010 The McGraw-Hill Companies, Inc. All rights reserved. 58 Top-Down and Bottom-Up Processing • Top-down processing: perception is guided by higher-level knowledge, experience, expectations, and motivations Can you figure out the meaning of this sentence? Ca- yo- re-d t-is -en-en-e, w-ic- ha- ev-ry -hi-d l-tt-r m-ss-ng? You were probably able to figure out the meaning of the sentence with the missing letters because of your prior reading experience, and because written English contains redundancies. Not every letter of each word is necessary to decode its meaning. Your expectations played a role in your being able to read the sentence. McGraw-Hill ©2010 The McGraw-Hill Companies, Inc. All rights reserved. 59 Top-Down and Bottom-Up Processing • Bottom-up processing: processing information by progressing from the individual elements of a stimulus and moving up to the perception of the whole • We would make no headway in our recognition of the sentence without being able to perceive the individual shapes that make up the letters. Some perception, then, occurs at the level of the patterns and features of each of the separate letters. • Top-down and bottom-up processing occur simultaneously, and interact with each other, in our perception of the world around us. Bottom-up processing permits us to process the fundamental characteristics of stimuli, whereas top-down processing allows us to bring our experience to bear on perception. Perceptual Constancy • Physical objects are perceived as unvarying and consistent despite changes in appearance or changes in the physical environment – Ex.: the image on your retina of a person far away from you is very small, but you understand (perceive) her to be of “normal” size McGraw-Hill ©2010 The McGraw-Hill Companies, Inc. All rights reserved. 61 Depth Perception: Translating 2-D to 3-D Depth perception: the ability to view the world in three dimensions and to perceive distance The ability to view the world in three dimensions and to perceive distance is due largely to the fact that we have two eyes. Because there is a certain distance between the eyes, a slightly different image reaches each retina. The brain integrates the two images into one composite view, but it also recognizes the difference in images and uses it to estimate the distance of an object from us. The difference in the images seen by the left eye and the right eye is known as binocular disparity. If we view two objects at the same time and one is a lot closer than the other is, the retinal disparity will be large and we will have a greater sense of depth between the two. However, if the two objects are a similar distance from us, the retinal disparity will be minor, and we will perceive them as being a similar distance from us. McGraw-Hill ©2010 The McGraw-Hill Companies, Inc. All rights reserved. 62 Monocular Cues Certain cues permit us to obtain a sense of depth and distance with just one eye. These cues are known as monocular cues: 1. Motion parallax - the change in position of an object on the retina caused by movement of your body relative to the object. For example, if you are a passenger in a moving car, focus your eye on a stable object such as a tree. Objects that are closer than the tree will appear to move backward, and the nearer the object is, the more quickly it will appear to move. In contrast, objects beyond the tree will seem to move at a slower speed, but in the same direction as you are. Your brain is able to use these cues to calculate the relative distances of the tree and other objects. Monocular Cues 2. Binocular disparity - is the difference in the images seen by the left eye and the right eye. 3. Relative size - when two objects are the same size, the one that makes a smaller image on the retina is farter away than is the one that provides a larger image. 4. Texture gradient – the quality and detail of the image helps to judge the distance of that object. 5. Linear perspective – the perspective that distant objects appear to be closer together than nearer objects. For example, follow a pair of railroad tracks to the horizon. They seem to join together as you look farther away. Motion Perception: As the World Turns • How do we perceive motion? – Movement of an object across the retina is perceived relative to an unmoving background – If a stimulus is coming toward you, the image on the retina will expand in size, filling more of the visual field, but we assume the stimulus is approaching rather than it’s growing in size – We factor information about our head and eye movements with information about changes in the retinal image McGraw-Hill ©2010 The McGraw-Hill Companies, Inc. All rights reserved. 65 Perceptual Illusions: The Deceptions of Perceptions • Visual illusions: physical stimuli that consistently produce errors in perception – Muller-Lyer illusion McGraw-Hill ©2010 The McGraw-Hill Companies, Inc. All rights reserved. 66