6 Sensation and Perception

Transcription

1 CHAPTER 6 Sensation and Perception Preview Sensation is the process by which we detect stimls energy from or environment and transmit it to or brain. Perception is the process of organizing and interpreting sensory information, enabling s to recognize meaningfl objects and events. Clear evidence that perception is inflenced by or experience comes from the many demonstrations of perceptal set and context effects. The task of each sense is to receive stimls energy, transform it into neral signals, and send those neral messages to the brain. In vision, light waves are converted into neral implses by the retina; after being coded, these implses travel p the optic nerve to the brain s cortex, where they are interpreted. In organizing sensory data into whole perceptions, or first task is to discriminate figre from grond. We then organize the figre into meaningfl form by following certain rles for groping stimli. We transform two-dimensional retinal images into three-dimensional perceptions by sing binoclar ces, sch as retinal disparity, and monoclar ces, sch as the relative sizes of objects. We also se these ces to perceive motion. The perceptal constancies enable s to perceive objects as endring in color, shape, and size regardless of viewing angle, distance, and illmination. The constancies explain several well-known illsions. Both natre and nrtre shape or perceptions. For example, when cataracts are removed from adlts who have been blind from birth, these persons can distingish figre and grond and can perceive color bt are nable to distingish shapes and forms. At the same time, hman vision is remarkably adaptable. Given glasses that trn the world pside down, people manage to adapt and move abot with ease. In hearing, sond waves are transmitted to the flid-filled cochlea, where they are converted to neral messages and sent to the brain. We locate sonds by differences in the timing and lodness of the sonds received by each ear. Or other senses inclde toch, taste, smell, and body position and movement. The sense of toch is actally for senses pressre, warmth, cold, and pain that combine to prodce other sensations sch as hot. Taste, a chemical sense, is a composite of sweet, sor, salty, bitter, and mami sensations and of the aromas that interact with information from the taste bds. Smell, also a chemical sense, does not have basic sensations as there are for toch and taste. Or effective fnctioning also reqires a kinesthetic sense and a vestiblar sense, which together enable s to detect body position and movement. Althogh we describe the senses separately, they interact. In interpreting the world, or brain blends their inpt. Althogh parapsychologists have tried to docment ESP, most research psychologists remain skeptical, particlarly becase the reslts of experiments have not been reprodcible. 53

2 54 Chapter 6 Sensation and Perception HANDOUT 6 1 Fact or Falsehood? 1. Advertisers can powerflly shape or bying habits throgh sbliminal messages. 2. If we stare at a green sqare for a while and then look at a white sheet of paper, we see red. 3. Infants jst learning to crawl do not perceive depth. 4. Persons who have sight in only one eye are totally nable to gage distances. 5. A person who is born blind bt gains sight as an adlt cannot recognize objects that were familiar by toch. 6. If reqired to look throgh a pair of glasses that trns the world pside down, we soon adapt and coordinate or movements withot difficlty. 7. Toching adjacent cold and pressre spots triggers a sense of wetness. 8. People who are born withot the ability to feel pain may die by early adlthood. 9. Withot their smells, a cold cp of coffee may be hard to distingish from a glass of red wine. 10. Laboratory evidence clearly indicates that some people do have ESP.

3 Chapter 6 Sensation and Perception 55 Gide Learning Objectives Every qestion in the Test Banks is keyed to one of these objectives. Basic Concepts of Sensation and Perception 6-1. Define sensation and perception, and explain the difference between bottom-p and top-down processing Identify the three steps that are basic to all or sensory systems Distingish between absolte thresholds and difference thresholds, and discss what effect, if any stimli below the absolte threshold have on s Discss whether sbliminal stimlation enables sbliminal persasion Explain the fnction of sensory adaptation Explain how or expectations, contexts, motivation, and emotions inflence or perceptions. Vision: Sensory and Perceptal Processing 6-7. Describe the characteristics of the energy that we see as visible light, and identify the strctres in the eye that help focs that energy Describe how the rods and cones process information, as well as the path information travels from the eye to the brain Describe how we perceive color in the world arond s Describe the location and fnction of the featre detectors Explain how the brain ses parallel processing to constrct visal perceptions Describe how Gestalt psychologists nderstood perceptal organization, and explain how figre-grond and groping principles contribte to or perceptions Explain how we se binoclar and monoclar ces to perceive the world in three dimensions and perceive motion Explain how perceptal constancies help s constrct meaningfl perceptions Describe what research on restored vision, sensory restriction, and perceptal adaptation reveals abot the effects of experience on perception. The Nonvisal Senses Describe the characteristics of air pressre waves that we hear as sond Explain how the ear transforms sond energy into neral messages Explain how we detect lodness, discriminate pitch, and locate sonds Describe how we sense toch Describe the biological, psychological, and social-cltral inflences that affect or experience of pain, and discss how placebos, distraction, and hypnosis help control pain Explain how or sense of taste and smell are similar, and how they differ Explain how we sense or body s position and movement Describe how sensory interaction inflences or perceptions, and define embodied cognition List the claims of ESP, and discss the conclsions of most research psychologists after ptting these claims to the test. Introdctory Exercise: Fact or Falsehood? The correct answers to Handot 6 1 are as follows: 1. F 2. T 3. F 4. F 5. T 6. T 7. T 8. T 9. T 10. F

4 56 Chapter 6 Sensation and Perception Podcast/Lectre: Person Perception LanchPad: The Man Who Cannot Recognize Faces Basic Concepts of Sensation and Perception Lectres: Sensation Verss Perception; Top-Down Processing; Thin-Slicing Exercises: A Scale to Assess Sensory-Processing Sensitivity; Hman Senses Demonstration Kits Exercise/Project: The Wndt-Jastrow Illsion 6-1. Define sensation and perception, and explain the difference between bottom-p and top-down processing. Sensation is the process by which or sensory receptors and nervos system receive and represent stimls energies from or environment. Bottom-p processing is analysis that begins with the sensory receptors and works p to the brain s integration of sensory information. Perception is the process of organizing and interpreting sensory information, enabling s to recognize meaningfl objects and events. Top-down processing is information processing gided by or experience and expectations. Transdction and Thresholds 6-2. Identify the three steps that are basic to all or sensory systems. All or senses perform three basic steps: They receive sensory stimlation, transform that stimlation into neral implses, and deliver the neral information to or brain. The process of converting one form of energy into another that or brain can se is called transdction. Psychophysics is the stdy of how what we detect affects or psychological experiences. Lectres: Gstav Fechner and Psychophysics; Sbliminal Smells; Applying Weber s Law Projects: The Variability of the Absolte Threshold; Understanding Weber s Law 6-3. Distingish between absolte thresholds and difference thresholds, and discss what effect, if any, stimli below the absolte threshold have on s. In stdying or awareness of faint stimli, Gstav Fechner identified an absolte threshold as the minimm stimlation needed to detect a particlar stimls 50 percent of the time. Signal detection theory predicts how and when we detect the presence of a faint stimls (signal) amid backgrond stimlation (noise), assming that or individal absolte thresholds vary with or experiences, expectations, motivation, and alertness. The priming effect, as shown in experiments, reveals that we can process some information from stimli too weak to recognize (sbliminal stimli below or absolte threshold), indicating that mch of or information processing occrs atomatically, nconsciosly. In a typical experiment, an image or word is qickly flashed, then replaced by a masking stimls that interrpts the brain s processing before conscios perception. A difference threshold is the minimm difference between two stimli that a person can detect 50 percent of the time. In hmans, difference thresholds (experienced as a jst noticeable difference [jnd]) increase in proportion to the size of the stimls a principle known as Weber s law. Lectre: Sbliminal Persasion 6-4. Discss whether sbliminal sensation enables sbliminal persasion. The effect of sbliminal stimli is too fleeting to enable advertisers to exploit s with sbliminal messages and prodce sbliminal persasion. Sixteen doble-blind experiments evalating sbliminal self-help recordings niformly fond that no recording helped more than a placebo, which works only becase of or belief in it.

5 Chapter 6 Sensation and Perception 57 Sensory Adaptation Exercises: Eye Movements; Sensory Adaptation in the Marketplace Project: Sensory Adaptation 6-5. Explain the fnction of sensory adaptation. Sensory adaptation refers to diminished sensitivity as a conseqence of constant stimlation. Constant, nchanging images on the eye s inner srface fade and then reappear. This continal flitting from one spot to another ensres that stimlation on the eyes receptors continally changes. The phenomenon of sensory adaptation enables s to focs or attention on informative changes in or environment withot being distracted by ninformative backgrond stimlation. Sensory adaptation even inflences how we perceive emotions. Perceptal Set, Context Effects, Motivation, and Emotions Lectre: Do Red Objects Feel Warmer or Colder Than Ble Objects? Exercises: Perceptal Set; Perceptal Set and Gender Stereotypes; Context and Perception 6-6. Explain how or expectations, contexts, motivation, and emotions inflence or perceptions. Clear evidence that perception is inflenced by or experiences or learned assmptions and beliefs as well as by sensory inpt comes from the many demonstrations of perceptal set, a mental predisposition to perceive one thing and not another. Throgh experience, we form concepts, or schemas, that organize and interpret nfamiliar information. Or preexisting schemas for monsters and tree trnks, for example, inflence how we apply top-down processing to interpret ambigos sensations. A given stimls may trigger radically different perceptions, partly becase of or different schemas, bt also becase of the immediate context. For example, we wold perceive the first word in eel is on the wagon as wheel, and the first word in eel is on the orange as peel. Perceptions are inflenced, top-down, not only by or expectations and by the context bt also by or motivations and emotions. For example, we discern whether a speaker said morning or morning or dye or die from the srronding words. Emotions and motives color or social perceptions, too. Vision: Sensory and Perceptal Processing Light Energy and Eye Strctres Lectre: Classroom as Eyeball Exercise/Project: Physiology of the Eye A CD-ROM for Teaching Sensation and Perception Projects: Color the Eyeball; Locating the Retinal Blood Vessels Projects/Exercises: Rods, Cones, and Color Vision; Locating the Blind Spot LanchPad: Vision: How We See 6-7. Describe the characteristics of the energy that we see as visible light, and identify the strctres in the eye that help focs that energy. The energies we experience as visible light are a thin slice from the whole spectrm of electromagnetic energy. Or sensory experience of light is determined largely by the light energy s wavelength, which determines the he of a color, and its intensity (determined by a wave s amplitde, or height), which inflences brightness.

6 58 Chapter 6 Sensation and Perception After light enters the eye throgh the cornea, it passes throgh the ppil, whose size is reglated by the iris; the iris also responds to or cognitive and emotional states. A transparent lens then focses the rays by changing its crvatre, a process called accommodation, on the retina. The retina doesn t see a whole image. Rather, its millions of receptor cells convert particles of light energy into neral implses and forward those to the visal cortex of the brain. There, the implses are reassembled into a perceived, pright-seeming image. And along the way, visal information processing percolates throgh progressively more abstract levels. Information Processing in the Eye and Brain 6-8. Describe how the rods and cones process information, as well as the path information travels from the eye to the brain. The retina s rods and cones (most of which are clstered arond the fovea) transform the light energy into neral signals throgh a chemical reaction. These signals activate the neighboring bipolar cells, which in trn activate the neighboring ganglion cells, whose axons converge to form the optic nerve that carries information via the thalams to the brain. Where the optic nerve leaves the eye, there are no receptor cells creating a blind spot. The cones enable vision of color and fine detail, with each cone transmitting its message to a single bipolar cell. The rods enable blackand-white vision, remain sensitive in dim light, and are necessary for peripheral vision. The information from the retina s nearly 130 million rods and cones is received and transmitted by the million or so ganglion cells whose axons make p the optic nerve. When individal ganglion cells register information in their region of the visal field, they send signals to the occipital lobe s visal cortex. Lectre: Color Vision in Primates PsychSim 6: Colorfl World Exercises: The Color Vision Screening Inventory and Color Blindness; Sbjective Colors 6-9. Describe how we perceive color in the world arond s. Like all aspects of vision, or perception of color resides not in the object itself bt in the theater of or brains. Or difference threshold for colors is so low that we can discriminate more than 1 million different color variations (Neitz et al., 2001). At least most of s can. For abot 1 person in 50, vision is color deficient and that person is sally male, becase the defect is genetically sex linked. Most people who are color deficient lack fnctioning red- or green-sensitive cones, or sometimes both. Their vision is monochromatic or dichromatic instead of trichromatic. The Yong-Helmholtz trichromatic (three-color) theory states that the retina has three types of color receptors, each especially sensitive to red, green, or ble. When we stimlate combinations of these cones, we see other colors. For example, when both red- and green-sensitive cones are stimlated, we see yellow. Hering s opponent-process theory states that there are two additional color processes, one responsible for red verss green perception and one for yellow verss ble pls a third black verss white process. For example, in both the retina and the thalams, some nerons are trned on by red bt trned off by green. Others are trned on by green bt off by red (DeValois & DeValois, 1975). These opponent processes help explain afterimages. Present explanations indicate that color processing occrs in two stages: The retina s red, green, and ble cones respond in varying degrees to different color stimli, as the Yong-Helmholtz trichromatic theory sggested. Their signals are then processed by the nervos system s opponentprocess cells, as Hering s theory proposed.

7 Chapter 6 Sensation and Perception 59 Exercise: Movement Aftereffects Describe the location and fnction of the featre detectors. As discovered by Hbel and Wiesel, individal nerons (featre detectors) in the cortex respond to specific featres of a visal stimls. The visal cortex passes this information along to other areas of the cortex where teams of cells (spercell clsters) respond to more complex patterns. For example, one temporal lobe area by yor right ear enables yo to perceive faces. Lectre: Blindsight LanchPad: Blindsight : Seeing Withot Awareness Explain how the brain ses parallel processing to constrct visal perceptions. Sbdimensions of vision (motion, form, depth, color) are processed by neral teams working separately and simltaneosly, illstrating or brain s capacity for parallel processing. Other teams collaborate in integrating the reslts, comparing them with stored information and enabling perceptions. Some people who have lost part of their visal cortex experience blindsight. Perceptal Organization Lectres: Object Recognition; Visal Agnosia Exercises: Perceptal Illsions and Principles; Perceptal Organization; An Aditory Analoge of the Visal Reversible Figre; The Ganzfeld Projects: Playing Cards and Illsions; Hollow Face Illsion; Instant Object Recognition PsychSim 6: Visal Illsions Describe how Gestalt psychologists nderstood perceptal organization, and explain how figregrond and groping principles contribte to or perceptions. Gestalt psychologists described principles by which we organize or sensations into perceptions. They provided many compelling demonstrations of how, given a clster of sensations, the hman perceiver organizes them into a gestalt, a German word meaning a form or a whole. They frther demonstrated that the whole may exceed the sm of its parts. Clearly, or brain does more than merely register information abot the world. We are always filtering sensory information and constrcting perceptions. Mind matters. Or first task in perception is to perceive any object, called the figre, as distinct from its srrondings, called the grond. We mst also organize the figre into a meaningfl form. Gestalt principles for groping that describe this process inclde proximity (we grop nearby figres together), continity (we perceive smooth, continos patterns rather than discontinos ones), and closre (we fill in gaps to create a whole object). Lectre: Atostereograms Exercises: Binoclar Vision; Identifying Ces to Depth and Distance Exercise/Project: Binoclar Vision Verss Monoclar Vision LanchPad: Depth Ces; The Müller-Lyer Illsion Explain how we se binoclar and monoclar ces to perceive the world in three dimensions and perceive motion. Depth perception is the ability to see objects in three dimensions, althogh the images that strike the eye are two-dimensional. It enables s to jdge distance. Research on the visal cliff (a miniatre cliff with a drop-off covered by strdy glass) reveals that most infants can perceive depth becase they refse to crawl ot onto the glass. Learning seems to help becase as infants become mobile, their experience leads them to fear heights. Binoclar ces reqire information from both eyes. In the retinal disparity ce, the brain comptes the relative distance of an object by comparing the slightly different images an object casts on or two retinas. The greater the difference, the closer the object.

8 60 Chapter 6 Sensation and Perception Monoclar ces enable s to jdge depth sing information from only one eye. The monoclar ces inclde relative size (the smaller image of two objects of the same size appears more distant), interposition (nearby objects partially obstrct or view of more distant objects), relative height (higher objects are farther away), relative motion (as we move, objects at different distances change their relative positions in or visal image, with those closest moving most), linear perspective (the converging of parallel lines indicates greater distance), and light and shadow (dimmer objects seem more distant). Or basic assmption is that shrinking objects are retreating and enlarging objects are approaching. The brain will also interpret a rapid series of slightly varying images as continos movement, a phenomenon called stroboscopic movement. By flashing 24 still pictres a second, a motion pictre creates an illsion of movement. The phi phenomenon, another illsion of movement, is created when two or more adjacent lights blink on and off in sccession. Lighted signs exploit the effect with a sccession of lights that create the impression of, say, a moving arrow. Lectre: Aditory Organization Exercises: Brightness Contrast; Variation in the Size of the Retinal Image; Perceived Distance and Perceived Size; Binoclar Disparity and Size Constancy Exercise/Project: Perceived Lnar Size Project: Visal Captre (for entire section on vision) Explain how perceptal constancies help s constrct meaningfl perceptions. Perceptal constancy is necessary to recognize an object. This top-down process enables s to see an object as nchanging (having consistent shape, size, brightness, and color) even as illmination and retinal images change. Color constancy refers to or perceiving familiar objects as having consistent color, even if changing illmination alters the wavelengths reflected by the object. We see color as a reslt of or brain s comptations of the light reflected by any object relative to the objects srronding it. Brightness constancy (also called lightness constancy) enables s to perceive an object as having a constant brightness even while its illmination changes. This perception of constancy depends on relative lminance, which is the amont of light an object reflects relative to its srrondings. Ths, comparisons govern or perceptions. Shape constancy is or ability to perceive familiar objects (for example, an opening door) as nchanging in shape, and size constancy is or ability to perceive objects as nchanging in size, despite the changing images they cast on or retinas. Given the perceived distance of an object, we instantly and nconsciosly infer the object s size. The perceived relationship between distance and size is generally valid bt, nder special circmstances, can lead s astray. For example, one reason for the Moon illsion is that ces to objects distances at the horizon make the Moon behind them seem farther away. Ths, the Moon on the horizon seems larger. In the distorted (trapezoidal) room designed by Adelbert Ames, we perceive both corners as being the same distance away. Ths, anything in the near corner appears disproportionately large compared with anything in the far corner. Perceptal Interpretation Lectres: Cases of Restored Vision; Living Withot Vision Featre Film: At First Sight Describe what research on restored vision, sensory restriction, and perceptal adaptation reveals abot the effects of experience on perception. In the classic version of the natre nrtre debate, the German philosopher Immanel Kant maintained that knowledge comes from or inborn ways of organizing sensory experiences. On the other side, the British philosopher John Locke arged that we learn to perceive the world throgh

9 or experiences of it. It s now clear that different aspects of perception depend more or less on natre s endowments and on the experiences that inflence what we make of or sensations. When cataracts are removed from adlts who have been blind from birth, these people remain nable to perceive the world normally. Generally, they can distingish figre from grond and perceive colors, bt they are nable to recognize objects that were familiar by toch. In controlled experiments, infant kittens and monkeys have been raised with severely restricted visal inpt. When their visal exposre is retrned to normal, they, too, sffer endring visal handicaps. For many species, infancy is a critical period dring which experience mst activate the brain s innate visal mechanisms. Hearing Exercise: Displacement Glasses LanchPad: Seeing the World Upside Down: Three Brave Sols Hman perception is remarkably adaptable. Given glasses that shift the world slightly to the left or right, or even trn it pside down, people manage to adapt their movements and, with practice, to move abot with ease. The Nonvisal Senses Lectre: Recognizing Or Own Voice Project: Color the Ear PsychSim 6: The Aditory System LanchPad: Hearing: From Vibration to Sond; Animation: Sond and the Cochlea Describe the characteristics of air pressre waves that we hear as sond. Adition, or hearing, is highly adaptive. The pressre waves we experience as sond vary in amplitde and freqency (length) and correspondingly in perceived lodness and pitch. Long waves have low freqency and low pitch. Short waves have high freqency and high pitch. Decibels are the measring nit for sond energy, with zero decibels representing the absolte threshold for hearing Explain how the ear transforms sond energy into neral messages. Chapter 6 Sensation and Perception 61 The visible oter ear channels the sond waves throgh the aditory canal to the eardrm, a tight membrane that vibrates with the waves. Transmitted via a piston made of three tiny bones of the middle ear (the hammer, anvil, and stirrp) to the flid-filled cochlea in the inner ear, these vibrations case the oval window to vibrate, casing ripples in the basilar membrane, which bends the hair cells that line its srface. Hair cell movement triggers implses in the adjacent nerve cells. Axons of those cells converge to form the aditory nerve, which sends neral messages (via the thalams) to the aditory cortex in the brain s temporal lobe.. Damage to the cochlea s hair cell receptors or their associated nerves can case the more common sensorineral hearing loss (or nerve deafness). Biological changes linked with heredity, aging, or prolonged exposre to ear-splitting noise or msic may case sensorineral hearing loss. Problems with the mechanical system that condcts sond waves to the cochlea case condction hearing loss. The only way to restore hearing for people with nerve deafness is a cochlear implant, which is wired into varios sites on the aditory nerve, allowing them to transmit electrical implses to the brain. It helps children to become proficient in oral commnication. Cochlear implants can help restore hearing for most adlts, bt only if their brain learned to process sond dring childhood.

10 62 Chapter 6 Sensation and Perception LanchPad: Animation: Sond and Sond Localization Explain how we detect lodness, discriminate pitch, and locate sonds. We detect lodness according to the nmber of activated hair cells, not the intensity of a hair cell s response. Herman von Helmholtz s place theory presmes that we hear different pitches becase different sond waves trigger activity at different places along the cochlea s basilar membrane. Ths, the brain can determine a sond s pitch by recognizing the place on the membrane from which it receives neral signals. Freqency theory (also called temporal theory) states that the rate of nerve implses traveling p the aditory nerve matches the freqency of a tone, ths enabling s to sense its pitch. The volley principle explains hearing sonds with freqencies above 1000 waves per second. Place theory best explains how we sense high-pitched sonds, and freqency theory best explains how we sense low-pitched sonds. Some combination of the two theories explains sonds in the intermediate range. Exercises: Range of Hman Hearing; Locating Sonds Lectres: Hearing Loss; A Qiet World Living With Hearing Loss Sond waves strike one ear sooner and more intensely than the other ear. We localize sonds by detecting the minte differences in the intensity and timing of the sonds received by each ear. The Other Senses Lectres: The Amazing Capabilities of Toch; The Remarkable Case of Ian Waterman Exercises: Two-Point Thresholds; Toch Localization Exercise/Project: Warm Pls Cold Eqals Hot LanchPad: Losing One s Toch: Living Withot Proprioception Describe how we sense toch. Or sense of toch is actally for senses pressre, warmth, cold, and pain that combine to prodce other sensations, sch as hot. Toch sensations involve more than tactile stimlation, however. A self-prodced tickle prodces less somatosensory cortex activation than does the same tickle from something or someone else. Lectres: Amptating a Phantom Limb; Cltral Differences in Pain; Pain Control; Placebos and Pain Relief; Is Hypnosis an Altered State of Consciosness Exercises: The Revised Redcer Agmenter Scale; Experiencing Phantom Sensations LanchPad: Phantom Limb Sensation; Pickpockets, Placebos, and Pain: The Role of Expectations; Coping With Pain; Hypnosis: Medical and Psychological Applications Describe the biological, psychological, and social-cltral inflences that affect or experience of pain, and discss how placebos, distraction, and hypnosis help control pain. Pain is an alarm system that draws or attention to some physical problem. Withot the ability to experience pain, people may die before early adlthood. Or individal pain sensitivity varies, too, depending on genes, physiology, experience, attention, and srronding cltre. Ths, or experience of pain reflects both bottom-p sensations and top-down cognition. There is no one type of stimls that triggers pain. Instead there are different nociceptors sensory receptors in or skin, mscles, and organs that detect hrtfl temperatres, pressre, or chemicals. Melzack and Wall s gate-control theory of pain is that small fibers in the spinal cord open a gate to permit pain signals to travel p to the brain, or large fibers close the gate to prevent their passage. Pain is not merely a physical phenomenon of injred nerves sending implses to a definable brain area. The brain can also create pain, as it does in people s experiences of phantom limb sensations, after a limb has been amptated.

11 The biopsychosocial approach views pain not only as a prodct of biological inflences, for example, of injred nerves sending implses to the brain, bt also as a reslt of psychological inflences sch as or expectations, and social inflences sch as the presence of others. We have some bilt-in pain controls, the endorphins, that or brain releases. Other pain controls involve distraction, an inert placebo (by dampening the central nervos system s attention and responses to painfl experiences), the tendency to remember only its peak moment or the pain we felt at the end of a procedre, and hypnosis. In trying to explain how hypnosis works, dissociation theory sggests that we have a divided consciosness, as evidenced by the fact that hypnotized people may carry ot posthypnotic sggestions. Social inflence theory believes that hypnosis is a by-prodct of normal social and mental processes. Another form of dal processing selective attention may also play a role in hypnotic pain relief, Lectre: Taste Preferences Exercises: Taste: The Basic Taste Sensations; Genetic Effects in Taste Exercise/Project: Taste Project: Mapping Yor Tonge Explain how or sense of taste and smell are similar, and how they differ. Taste, a chemical sense, is a composite of sweet, sor, salty, bitter, and mami sensations. Taste bds on the top and sides of the tonge contain 200 or more taste bds, each containing a pore that catches food chemicals. In each taste bd pore, 50 to 100 taste receptor cells project antenna-like hairs that sense food molecles. These cells send information to an area of the brain s temporal lobe. Taste receptors reprodce themselves every week or two. As we grow older, the nmber of taste bds and taste sensitivity decrease. Expectations can also inflence taste. Lectres: Anosmia; Specific Anosmias; Odor and Sex Identification; Canine Olfaction Exercise: Identifying Odors Smell (olfaction) is also a chemical sense. We smell something when molecles of a sbstance carried in the air reach a tiny clster of 20 million receptor cells at the top of each nasal cavity. With their approximately 350 different receptor proteins, they recognize individal odor molecles. Some odors trigger a combination of receptors. The receptor cells send messages to the olfactory blb, then to the temporal lobe and to the parts of the limbic system involved in memory and emotion. Gender and age inflence or ability to identify scents. Exercises: Nystagms; Vision and Balance Explain how we sense or body s position and movement. Important sensors in yor joints, tendons, and mscles enable yor kinesthesia, the system for sensing the position and movement of individal body parts. A companion vestiblar sense monitors the head s (and ths the body s) position and movement. The biological gyroscopes for this sense of eqilibrim are in the semicirclar canals and vestiblar sacs in the inner ear. Sensory Interaction Lectre: Synesthesia LanchPad: Synesthesia: The Man Who Tastes Words Chapter 6 Sensation and Perception Describe how sensory interaction inflences or perceptions, and define embodied cognition. Sensory interaction refers to the principle that one sense may inflence another, as when the smell of food inflences its taste. When or senses disagree as when we see a speaker saying one syllable while we hear another we experience the McGrk effect, that is, we may perceive a third syllable that blends both inpts. In interpreting the world, or brain circits blend or bodily sensations with brain circits responsible for cognition. This embodied cognition is niqely illstrated in a few select individals in whom the senses become joined in a phenomenon called synesthesia, in which one kind of sensation sch as hearing sond prodces another sch as seeing color.

12 64 Chapter 6 Sensation and Perception Perception is the prodct of sensation, cognition, and emotion. And that is why we need biological, psychological, and social-cltral levels of analysis. (Critical Thinking) ESP Perception Withot Sensation? Lectre: Belief in ESP Exercises: Belief in ESP Scale; ESP Tricks Project: The Psychic Challenge Project/Exercise: Testing for ESP List the claims of ESP, and discss the conclsions of most research psychologists after ptting these claims to the test. Claims are made by parapsychologists for three varieties of extrasensory perception (ESP): telepathy (mind-to-mind commnication), clairvoyance (perceiving remote events), and precognition (perceiving ftre events). Closely linked with these is psychokinesis, or mind over matter. Research psychologists remain skeptical becase the forecasts of leading psychics reveal meager accracy, becase checks of psychic visions have been no more accrate than gesses made by others, and becase sheer chance garantees that some stnning coincidences are sre to occr. An important reason for their skepticism, however, is the absence of a reprodcible ESP reslt.