Ch5 - Sensation CHAPTER PREVIEW Sensation is concerned with...

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Unformatted text preview: Sensation CHAPTER PREVIEW Sensation is concerned with how the outside world gets represented inside our heads, and we are exquisitely sensitive to some of the stimuli around us. Research reveals that we process some information from subliminal stimuli, but only under certain restricted conditions. The task of each sense is to receive stimulus energy, transduce it into neural signals, and send those neural messages to the brain. In vision, light waves are converted into neural impulses by the retina; after being coded, these impulses travel up the optic nerve to the brain’s cortex, where they are interpreted. The Young—Helmholtz and opponent-process theories together help explain color vision. In hearing, sound waves are transmitted to the fluid-filled cochlea, where they are converted to neural messages and sent to the brain. Together, the place and frequency theories explain how we hear both high-pitched and low—pitched sounds. The sense of touch is actually four senses—pressure, warmth, cold, and pain—that combine to produce other sensations such as “hot.” Taste, a chemical sense, is a composite of sweet, sour, salty, bitter, and umami sensations, and of the aromas that interact with information from the taste buds. Smell, also a chemical sense, does not have basic sensations as there are for touch and taste. Our effective functioning also requires a kinesthetic sense and a vestibular sense, which together enable us to detect body position and movement. CHAPTER GUIDE > Introductory Exercise: Fact or Falsehood? > Lectures: Sensation Versus Perception; Top»Down Processing > Videos: Module 8 of Psychology: The Human Experience: Sensation and Perception; Moving Images: Exploring Psychology Through Film, Program 10: Sensation Without Perception: Visual Prosopagnosia; Discovering Psychology, Updated Edition: Sensation and Perception > Transparency: 64 Sensation and Perception: One Continuous Process 1. Contrast sensation and perception, and explain the difference between bottomdtp and top-down processing. Sensation is the process by which we detect physical energy from our environment and encode it as neural signals. Bottom-up processing is analysis that begins with the sense receptors and works up to the brain’s integration of sensory information. Perception is the process of selecting, organ— izing, and interpreting sensory information, enabling us to recognize meaningful objects and events. Top-down processing is information processing guided by our experience and expectations. 35 36 Chapter 5 Sensation Sensing the World: Some Basic Principles Vision > Lectures: Gustav Fechner and Psychophysics; Applying Weber‘s Law; Subliminal Persuasion > Exercises: Backmasking—A Tape for the Classroom; Eye Movements > Projects: The Variability of the Absolute Threshold; Understanding Weber‘s Law; Sensory Adaptation > Video: Module 9 of The Mind Series, 2nd ed.: Studying the Effects of Subliminal Stimulation on the Mind > Transparency: 53 Absolute Threshold Distinguish between absolute and difference thresholds, and discuss whether we can sense stimuli below our absolute threshold and be influenced by them. In studying the relationship between physical energy and psychological experience, researchers in psychophysics identified an absolute threshold as the minimum stimulation needed to detect a particular stimulus 50 percent of the time. Signal detection theory predicts when and how we detect the presence of a faint stimulus, assuming that our individual absolute thresholds vary with our psychological state. The priming effect and other experiments reveal that we can process some information from stim— uli too weak to recognize. But the restricted conditions under which this occurs would not enable advertisers to exploit us with subliminal messages. A dtfierence threshold is the minimum difference between two stimuli that a person can detect 50 percent of the time. In humans, difference thresholds (experienced as a just noticeable difi‘erence [jndD increase in proportion to the size of the stimulus—a principle known as Weber’s law. Describe sensory adaptation, and explain how we benefit from being unaware of unchanging stimuli. Sensory adaptation refers to the diminished sensitivity that is a consequence of constant stimula- tion. The phenomenon of sensory adaptation enables us to focus our attention on informative changes in our environment without being distracted by the uninformative, constant stimulation of garments, odors, and street noise, for example. > Exercises: The Hermann Grid; Illusory Contours; Movement Aftereffect; The Color Vision Screening Inventory and Color Blindness; Subjective Colors > Projects: Locating the Retinal Blood Vessels; Locating the Blind Spot > Lecture: Blindsight > PsychSim 5: Colorful World > Videos: Program ll of Moving Images: Exploring Psychology Through Film: Nonconscious Processing: Blindsight: Moving Images: Exploring Psychology Through Film, Program I l: Nonconscious Processing: Blindsig/it; Modules 8 and 9 of The Brain Series, 2nd ed.: Visual Information Processing: Elementary Concepts and Visual Information Processing: Perception > Transparencies: 65 The Spectrum of Electromagnetic Energy; 66 The Physical Properties of Waves; 67 The Eye; 68 The Retina's Reaction to Light; 69 Pathway from the Eyes to the Visual Cortex: 70 How the Brain Perceives; 71 An Example of the Brain’s Virtual Reality;: Illusory Contours; 72 A Simplified Summary of Visual Information Processing; 73 ColorDeficient Vision Define transduction, and specifiz the form of energy our visual system converts into the neural messages our brain can interpret. Transduction is the process by which our sensory systems encode stimulus energy as neural mes- sages. In vision, we convert light energy into these neural impulses. The energies we experience as visible light are a thin slice from the broad spectrum of electromag— netic radiation. Our sensory experience of light is determined largely by the light energy’s wave— length, which determines the hue of a color, and its intensity, which influences brightness. . ...—~., Chapter 5 Sensation 37 . Describe the major structures of the eye, and explain how they guide an incoming ray of light toward the eye’s receptor cells. After light enters the eye through the pupil, whose size is regulated by the iris, a camera—like lens focuses the rays by changing its curvature, a process called accommodation, on the retina. This light-sensitive surface contains receptors that begin the processing of visual information. Acuity, or sharpness of vision, can be affected by small distortions in the shape of the eye. In nearsightedness, nearby objects are seen more clearly than distant objects because the lens focus- es the image of distant objects in front of the retina. In farsightedness, faraway objects are seen more clearly than near objects because the image of near objects is focused behind the retina. . Contrast the two types of receptor cells in the retina, and describe the retina ’s reaction to light. The retina’s rods and cones (most of which are clustered around the fovea) transduce the light energy into neural signals. These signals activate the neighboring bipolar cells, which in turn acti- vate the neighboring ganglion cells, whose axons converge to form the optic nerve that carries information to the brain. Where the optic nerve leaves the eye, there are no receptor cells—creat- ing a blind spot. The cones enable vision of color and fine detail. The rods detect black, white, and gray; remain sensitive in dim light; and are necessary for peripheral vision. . Discuss the difierent levels of processing that occur as information travels from the retina to the brain’s cortex. We process information at progressively more abstract levels. The information from the retina’s 130 million rods and cones is received and transmitted by the million or so ganglion cells whose axons make up the optic nerve. When individual ganglion cells register information in their region of the Visual field, they send signals to the visual cortex. In the cortex. individual neurons (feature detectors) respond to specific features of a visual stimulus. The visual cortex passes this informa- tion along to other areas of the cortex, which includes higher—level brain cells that respond to spe— cific visual scenes. Other supercell clusters integrate this information and combine it with our assumptions, interests, and expectations. . Define parallel processing, and discuss its role in visual information processing. Subdimensions of vision (color, movement, depth, and form) are processed by neural teams work— ing separately and simultaneously, illustrating our brain’s capacity for parallel processing. Other teams collaborate in integrating the results, comparing them with stored information and enabling perceptions. This contrasts sharply with the step-by—step serial processing of most computers and of conscious problem solving. Some people who have lost part of their visual cortex experience blindsight. . Explain how the Young-Helmholtz and opponent—process theories help us understand color vision. The Young—Helmholtz trichromatic (three-color) theory states that the retina has three types of color receptors, each especially sensitive to red, green, or blue. When we stimulate combinations of these cones, we see other colors. For example, when both red- and green—sensitive cones are stimulated, we see yellow. This additive color mixing differs from the subtractive color mixing of mixing paints. Hering’s opponent-process theory states that there are two additional color processes, one respon— sible for red versus green perception, and one for yellow versus blue plus a third black versus white process. Subsequent research has confirmed that after leaving the receptor cells, visual information is analyzed in terms of the opponent colors red and green, blue and yellow, and also black and white. Thus, in the retina and in the thalamus, some neurons are turned “on” by red, but turned “off” by green. Others are turned on by green but off by red. These opponent processes help explain afterimages. 38 10. Chapter 5 Sensation Explain the importance of color constancy. Color constancy refers to our perceiving familiar objects as having consistent color, even if changing illumination alters the wavelengths reflected by the object. We see color as a result of our brain’s computations of the light reflected by any object relative to its surroundings. Hearing 11. 12. l3. I4. 15. > Exercises: Auditory Demonstrations on CD; Locating Sounds > Lectures: Recognizing Our Own Voice; A Quiet World—Living With Hearing Loss; Hearing Loss > PsychSim 5: The Auditory System > Transparencies: 74 The Intensity of Some Conunon Sounds; 75 Hear There: How We Transform Sound Waves into Nerve Impulses That Our Brain Interprets; 76 How We Locate Sounds; 77 Older People Tend to Hear Low Frequencies Well but Suffer Hearing Loss for High Frequencies Describe the pressure waves we experience as sound. Audition, or hearing, is highly adaptive. The pressure waves we experience as sound vary in amplitude and frequency and correspondingly in perceived loudness and pitch. Decibels are the measuring unit for sound energy. Describe the three regions of the ear, and outline the series of events that triggers the electrical impulses sent to the brain. The visible outer ear channels the sound waves through the auditory canal to the eardrum, a tight membrane that vibrates with the waves. Transmitted via the bones of the middle ear (the hammer, anvil, and stirrup) to the fluid-filled cochlea in the inner ear, these vibrations create movement in tiny hair cells on the basilar membrane, triggering neural messages to be sent (via the thalamus) to the auditory cortex in the brain. Contrast place and frequency theories, and explain how they help us to understand pitch perception. Place theory presumes that we hear different pitches because different sound waves trigger activi— ty at different places along the cochlea’s basilar membrane. Thus, the brain can determine a sound’s pitch by recognizing the place on the membrane from which it receives neural signals. Frequency theory states that the rate of nerve impulses traveling up the auditory nerve matches the frequency of a tone, thus enabling us to sense its pitch. The volley principle explains hearing sounds with frequencies above 1000 waves per second. Place theory best explains how we sense high—pitched sounds, and frequency theory best explains how we sense low-pitched sounds. Some combination of the two theories explains sounds in between. Describe how we pinpoint sounds. Sound waves strike one ear sooner and more intensely than the other ear. We localize sounds by detecting the minute differences in the intensity and timing of the sounds received by each ear. Contrast two types of hearing loss, and describe some of their causes. Problems with the mechanical system that conducts sound waves to the cochlea cause conduction hearing loss. If the eardrum is punctured or if the tiny bones of the middle ear lose their ability to vibrate, the car’s ability to conduct vibrations diminishes. Digital hearing aids may restore hearing by amplifying vibrations for frequencies and by compressing sound. Damage to the cochlea’s hair cell receptors or their associated nerves can cause sensorineural hearing loss. Once destroyed, these tissues remain dead. although a hearing aid may amplify sound to stimulate other hair cells. Disease, biological changes linked with aging, or prolonged exposure to ear-splitting noise or music may cause sensorineural hearing loss. 16. Chapter 5 Sensation 39 Describe how cochlear implants function, and explain why Deaf culture advocates object to these devices. Those who live with hearing loss face social challenges. Cochlear implants are wired into various sites on the auditory nerve, allowing them to transmit electrical impulses to the brain. They enable some hearing by deaf children. But Deaf culture advocates, noting that sign is a complete lan- guage, question the enhancement. Some also argue that sensory compensation, which enhances other senses, gives deaf people advantages that the hearing do not have. Other Important Senses 17. 18. 19. 20. > Lectures: The Amazing Capabilities of Touch; Cultural Differences in Pain; Pain Control; Taste Preferences; Gender— Related Odors; Pheromones; Fragrance Effects; The Remarkable Case of Ian Waterman > Exercises: Two—Point Thresholds; Warm Plus Cold Equals Hot; Touch Localization; The Revised Reducer»Augmenter Scale; Taste: The Basic Taste Sensations; Genetic Effects in Taste; Taste; Identifying Odors; Nystagmus; Vision and Balance > Videos: Modules 20 and 21 of The Mind Series, 2nd ed.: Phantom Limb Pain and Treating Chronic Pain: Programs 4 and 9 of Moving Images: Exploring Psychology Through Film: Brain Reorganization: Phantom Limb Sensations and Firewalking: Mind Over Matter?; Segment 12 of the Scientific American Frontiers Series, 2nd ed.: Tasters and Supertasters; Module ll of The Brain Series, 2nd ed.: Sensory~M0tor Integration > Transparencies: 78 Biopsychosocial approach to pain; 81 The Sense of Smell Describe the sense of touch. Our sense of touch is actually four senses—pressure, warmth, cold, and pain—that combine to produce other sensations, such as “hot.” There is no simple relationship between what we feel and the type of specialized nerve ending found there. Only pressure has identifiable receptors. State the purpose of pain, and describe the biopsychosocial approach to pain. Pain is an alarm system that draws our attention to some physical problem. There is no one type of stimulus that triggers pain, and there are no special receptors for pain. At low intensities, the stim- uli that produce pain cause other sensations, including warmth or coolness, smoothness or rough ness. The gate-control theory of pain is that a “gate” in the spinal cord either opens to permit pain signals traveling up small nerve fibers to reach the brain or closes to prevent their passage. The biopsychosocial approach views pain not only as a product of biological influences but also as a result of psychological influences such as the situation and our past experience and social influ- ences such as cultural expectations and the presence of observers. Pain is controlled through a combination of medical and psychological treatments. Describe the sense of taste, and explain the principle of sensory interaction. Taste, a chemical sense, is a composite of sweet, sour, salty, bitter, and umami sensations and of the aromas that interact with information from the taste buds. Taste buds on the top and sides of the tongue and in the back and roof of the mouth contain taste receptor cells. These cells send information to an area of the temporal lobe near the area where olfactory information is received. Sensory interaction refers to the principle that one sense may influence another, as when the smell of food influences its taste. Describe the sense of smell, and explain why specific odors so easily trigger memories. Smell is also a chemical sense, but without any basic sensations. The five million olfactory recep- tor cells recognize individual odor molecules, with some odors triggering a combination of recep- tors. The receptor cells send messages to the olfactory lobe, then to the temporal lobe and to parts of the limbic system. An odor’s ability to spontaneously evoke memories is due in part to the close connections between brain areas that process smell and those involved in memory storage. 40 Chapter 5 Sensation 21. Distinguish between kinesthesis and the vestibular sense. Kinesthesis is the system for sensing the position and movement of individual body parts. Sensors in the muscles, tendons, and joints are continually providing our brain with information. A com— panion vestibular sense monitors the head’s (and thus the body‘s) position and movement. The biological gyroscopes for this sense of equilibrium are in the inner ear. ...
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Ch5 - Sensation CHAPTER PREVIEW Sensation is concerned with...

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