Sensation and Perception. Revised by Pauline Davey Zeece, University of Nebraska-Lincoln

Transcription

1 5 Sensation and Perception Revised by Pauline Davey Zeece, University of Nebraska-Lincoln

2 Chapter Overview Basic concepts of sensation and perception Vision: Sensory and perceptual processing The nonvisual senses Sensory interaction ESP Perception without sensation?

3 Basic Concepts of Sensation and Perception From outer energy to inner brain activity Thresholds Thinking critically about: Subliminal sensation and subliminal persuasion Sensory adaptation Perceptual set Context, motivation, and emotion

4 Sensation and Perception Sensation Process by which the sensory receptors and nervous system receive and represent stimulus energies from our environment Perception Process by which the brain organizes and interprets sensory information, transforming it into meaningful objects and events

5 Bottom-Up and Top-Down Processing Bottom-up processing Analysis that begins with the sensory receptors and works up to the brain s integration of sensory information Top-down processing Information processing guided by higher-level mental processes Draws on one s experiences and expectations

6 What s Going on Here? Our sensory and perceptual processes work together to help us sort out complex images, including the hidden couple in Sandro Del-Prete s drawing, The Flowering of Love.

7 Steps That Are Basic to the Sensory Systems Receive sensory stimulation Transform the stimulation into neural impulses Deliver the neural information to the brain

8 Retrieve and Remember 1 What is the rough distinction between sensation and perception?

9 Absolute Threshold Minimum stimulus energy needed to detect a particular stimulus 50 percent of the time Subliminal: Below an individual s absolute threshold for conscious awareness

10 Difference Threshold Minimum difference between two stimuli required for detection 50 percent of the time Individuals experience the difference threshold as a just noticeable difference (or jnd). Weber s law: Principle that two stimuli must differ by a constant minimum percentage to be perceived as different Exact percentage differs based on the stimulus.

11 Thinking Critically Subliminal sensation and subliminal persuasion Individuals can be affected by subliminal sensations. Stimuli that are so weak that people do not consciously notice them Researchers use priming to activate unconscious associations. Individuals can evaluate a stimulus, even when they are not consciously aware of it.

12 Retrieve and Remember 2 Using sound as your example, show how these concepts differ: Absolute threshold Subliminal stimulation Difference threshold

13 Introduction: Sensory Adaptation Reduced sensitivity in response to constant stimulation Helps focus on informative changes in the environment without being distracted by background chatter Influences perceptions of emotions

14 Sensory Adaptation a. A projector mounted on a contact lens makes the projected image move with the eye. b. At first, the person sees the whole image. Then, as the eye grows accustomed to the unchanging stimulus, the image begins to break into fragments that fade and reappear.

15 Emotion Adaptation Gaze at the angry face on the left for 20 to 30 seconds, then look at the center face (looks scared, yes?). Then gaze at the scared face on the right for 20 to 30 seconds, before returning to the center face (now looks angry, yes?).

16 Retrieve and Remember 3 Why is it that after wearing shoes for a while, you cease to notice them (until questions like this draw your attention back to them)?

17 Perceptual Set Mental predisposition to perceive one thing, rather than another Affects what an individual sees, hears, tastes, and feels Believing Is Seeing What do you perceive? Is this Nessie, the Loch Ness monster, or a log?

18 Context, Motivation, and Emotion Affect interpretations of a situation Context creates expectations that influence individual perception. Motives provide energy to work toward a goal. Can cause bias in interpreting neural stimuli Experiences, assumptions, and expectations can shape and color views of reality via topdown processing.

19 Figure Culture and Context Effects

20 Retrieve and Remember 4 Does perceptual set involve bottom-up or top-down processing? Why?

21 Vision: Sensory and Perceptual Processing Light energy and eye structures Information processing in the eye and brain Perceptual organization Perceptual interpretation

22 The Wavelengths We See Wavelengths visible to the human eye extend from the shorter waves of blue-violet light to the longer waves of red light.

23 Light Energy Wavelength: Distance from the peak of one light wave to the peak of the next Hue: Dimension of color that is determined by the wavelength of light Intensity: Amount of energy in a light wave Influences what individuals perceive as brightness or loudness Determined by the wave s amplitude or height

24 Figure The Physical Properties of Waves

25 The Eye The iris controls the amount of light entering the eye. Light hits the lens in the eye after passing through the pupil. The lens focuses the light rays into an image on the retina.

26 Figure The Eye

27 The Retina Light-sensitive inner surface of the eye Contains: Receptor rods and cones Layers of neurons that begin the processing of visual information

28 Figure The Retina s Reaction to Light

29 Information Processing in the Eye and Brain Retinal receptors Rods: Detect black, white, and gray Necessary for peripheral and twilight vision, when cones do not respond Cones: Detect fine detail and give rise to color sensations in daylight or well-lit conditions Optic nerve: Carries neural impulses from the eye to the brain Blind spot: Point where the optic nerve leaves the eye and has no receptor cells

30 Rods and Cones Cones Rods Number 6 million 120 million Location in retina Center Periphery Sensitivity in dim light Low High Color sensitivity High Low Detail sensitivity High Low

31 Figure Pathway from the Eyes to the Visual Cortex

32 Retrieve and Remember 5 Some night-loving animals, such as toads, mice, rats, and bats, have impressive night vision thanks to having many more (rods/cones) than (rods/cones) in their retinas. These creatures probably have very poor (color/black-and-white) vision. Cats are able to open their much wider than we can, which allows more light into their eyes, so they can see better at night.

33 Color Processing Young-Helmholtz trichromatic theory The retina contains three different types of color receptors red, green, and blue. When stimulated in combination, these receptors can produce the perception of any color. Opponent-process theory Opposing retinal processes enable color vision. Opposing retinal processes include red-green, yellow-blue, and white-black.

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36 Color Processing - Current Theory Color processing combines the trichromatic theory and the opponent-processing theory and occurs in two stages. The retina s red, green, and blue cones respond in varying degrees to different color stimuli. The cones responses are processed by opponent-process cells.

37 Retrieve and Remember 6 What are two key theories of color vision? Do they contradict each other, or do they make sense together? Explain

38 Feature Detectors, Part 1 Nerve cells in the brain that respond to specific features of a stimulus Include shape, angles, or movement Pass scene specific information to other cortical areas, where more complex patterns are interpreted

39 Feature Detectors, Part 2 One temporal lobe area by the right ear enables a person to perceive faces. A specialized neural network helps recognize faces from many viewpoints. Interaction between feature detectors and supercells provides instant analyses of objects in the world around people.

40 Well-Developed Supercells In the 2011 World Cup match, USA s Abby Wambach instantly processed visual information about the positions and movements of Brazil s defenders and goalkeeper and somehow managed to get the ball around them all and into the net.

41 Introduction: Parallel Processing Processing many aspects of a problem or scene at the same time Brain s natural mode of information processing for many functions, including vision Damage to neural workstations due to a stroke may render a person unable to perceive movement.

42 Parallel Processing Studies of patients with brain damage suggest that the brain delegates the work of processing motion, form, depth, and color to different areas. After taking a scene apart, the brain integrates these parts into a whole perceived image.

43 A Simplified Summary of Visual Information Processing Scene Retinal processing - Receptor rods and cones bipolar cells ganglion cells Feature detection The brain s detector cells respond to specific features edges, lines, and angles. Parallel processing - Brain cell teams process combined information about color, movement, form, and depth. Recognition The brain interprets the constructed image based on information from stored images.

44 Gestalt Necker cube Refers to an organized whole Gestalt psychologists emphasized the human tendency to integrate pieces of information into meaningful wholes.

45 Perceptual Organization The human brain registers information about the world, filters incoming information, and constructs perceptions. Principles in perceptual organization: Form perception Depth perception Perceptual constancy

46 Form Perception Figure-ground: Organization of the visual field into objects that stand out from their surroundings Grouping: The perceptual tendency to organize stimuli into meaningful groups Proximity Continuity Closure

47 Reversible Figure and Ground A classic example Is this a vase or is it two faces?

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49 Rules for Grouping Illustrate how the perceived whole differs from the sum of its parts. Also applicable for human touch perception

50 Retrieve and Remember 7 In terms of perception, a band s lead singer would be considered (figure/ground), and the other musicians would be considered (figure/ground). What do we mean when we say that, in perception, the whole may exceed the sum of its parts?

51 Depth Perception Ability to see objects in three dimensions, although images that strike the retina are two-dimensional Allows people to judge distance Partly innate in other animals

52 Depth Perception: Visual Cliff Devised by Eleanor Gibson and Richard Walk Laboratory device for testing depth perception in infants and young animals Most infants refuse to crawl across the visual cliff. Crawling, no matter when it begins, seems to increase an infant's fear of heights.

53 Visual Cliff Miniature cliff with a glass-covered drop-off Helps determine whether crawling infants and newborn animals can perceive depth Even when coaxed, infants refuse to climb onto the glass over the cliff.

54 Depth Cues Binocular cue: Depends on the use of two eyes Retinal disparity: The calculation of distance by the brain by comparing images from both eyes Used by 3-D film makers Monocular cue: Cue available to each eye separately Includes relative height, relative size, interposition, relative motion, linear perspective, and light and shadow

55 Figure The Floating Finger Sausage

56 Figure Monocular Depth Cues

57 Retrieve and Remember 8 How do we normally perceive depth?

58 Motion Perception The human brain computes motion based partly on its assumption that: Shrinking objects are moving away Enlarging objects are approaching Humans are imperfect at motion perception. When large and small objects move at the same speed, the large objects appear to move more slowly.

59 Perceptual Constancy Perceiving objects as unchanging, even as illumination and retinal images change Objects have consistent color, brightness, shape, and size. Color constancy Perceiving familiar objects as having consistent color, even if changing illumination alters the wavelengths reflected by the object

60 Color Depends on Context (a) Believe it or not, these three blue disks are identical in color. (b) Remove the surrounding context and see what results.

61 Lightness Constancy The color and brightness of square A and B are the same. 61

62 Lightness Constancy The color and brightness of square A and B are the same. 62

63 Shape and Size Constancies Shape constancy: Perception that the form of a familiar object is constant, even when retinas receive changing images of them Size constancy: Perception that objects have a constant size, even when one s distance from them varies

64 The Moon Illusion The Moon looks up to 50 percent larger when near the horizon than when high in the sky. Monocular cues to an object s distance make the horizon Moon appear farther away. If it s farther away, the brain assumes that it must be larger than the Moon high in the night sky. When the distance cues are taken away, the object will immediately shrink.

65 Perceptual Interpretation According to Immanuel Kant, human beings have the innate ability to process sensory information. John Locke argued that individuals also learn to perceive the world through their experiences. Learn to link an object s distance with its size

66 Experience and Visual Perception Research findings The effect of sensory restriction on infant cats, monkeys, and humans suggests that there is a critical period for normal sensory and perceptual development. In humans and other animals, sensory restrictions do not cause permanent harm later in life.

67 Perceptual Adaptation Ability to adjust to changed sensory input Includes adjustments to an artificially displaced or even inverted visual field Humans constantly adjust to changed sensory input. Early nurture sculpts what nature has provided. Experience guides, sustains, and maintains the pathways in the brain that enable perceptions.

68 Perceptual Adaptation: Hubert Dolezal Oops, missed, thought researcher Hubert Dolezal as he attempted a handshake while viewing the world through inverting goggles.

69 The Nonvisual Senses Hearing Touch Taste Smell Body position and movement

70 Hearing Audition: Sense or act of hearing Helps individuals adapt and survive Provides information and enables relationships Enables individuals to communicate invisibly Hearing loss is an invisible disability. Humans are acutely sensitive to faint sounds and sound differences.

71 Sound Waves Vary in shape Moving molecules of air create waves of compressed and expanded air. Ears detect these brief air pressure changes. The Sounds of Music: A violin's short, fast waves create a high pitch. The longer, slower waves of a cello or bass create a lower pitch.

72 Characteristics of Sound Waves Amplitude or height Determines the perceived loudness of sound waves Frequency or length Number of complete wavelengths that pass a point in a given time Pitch: A tone s experienced highness or lowness that depends on frequency Sound is measured in decibels.

73 Retrieve and Remember 9 The amplitude of a sound wave determines our perception of (loudness/ pitch). The longer the sound waves are, the (lower/higher) their frequency is and the (higher/lower) their pitch.

74 Decoding Sound Waves Sound waves strike the eardrum, causing it to vibrate. Tiny bones in the middle ear pick up the vibrations and transmit them to the cochlea, in the inner ear. Ripples in the cochlea fluid bend the hair cells lining the surface, which trigger impulses in nerve cells. Axons from these nerve cells transmit a signal to the auditory cortex.

75 Figure Transforming Sound Waves into Neural Messages

76 Hearing Loss Sensorineural hearing loss Caused by damage to the cochlea's receptor cells or to the auditory nerves Called nerve deafness Conduction hearing loss Caused by damage to the mechanical system that conducts sound waves to the cochlea Less common form of hearing loss

77 Locating Sounds Two ears are better than one. Sound waves strike one ear sooner and more intensely than the other. From this information, the brain can compute the sound s location.

78 Touch Sense of touch - Mix of four distinct skin senses Pressure Warmth Cold Pain Other skin sensations are variations of the basic skin senses. The human brain influences sensory responses.

79 Pain Body s way of telling the individual that something has gone wrong Greater number of infections and injuries when there are no warnings of pain Reflects both bottom-up sensations and topdown cognition Biopsychosocial event

80 Pain is a Gift Ashlyn Blocker has a rare genetic mutation that prevents her from feeling pain. Everyone in my class asks me about it, and I say, I can feel pressure, but I can t feel pain. Pain! I cannot feel it!

81 Biological Influences of Pain Pain is not triggered by any one type of stimulus. Pain signals are not processed by specialized receptors. Sensory receptors called nociceptors detect hurtful temperatures, pressure, or chemicals. Experience of pain depends on the inherited genes and physical characteristics. The brain sometimes misinterprets its signals and can create pain.

82 Psychological Influences of Pain Attention focused on pain is a powerful influence on human perception of pain. Individuals seem to edit their memories of pain. Pain experienced may not be the pain that is remembered.

83 Distracted from the Pain Halfway through his lap of the 2012 Olympics 1600-meter relay, Manteo Mitchell broke one of his leg bones and kept running.

84 Social-Cultural Influences of Pain Pain is a product of an individual's attention, expectations, and culture. Perception of pain varies with social situation and cultural traditions. Humans feel more pain when others seem to be experiencing pain.

85 Pain Control Therapies Drugs Surgery Acupuncture Electrical stimulation Massage Exercise Hypnosis Relaxation training Thought distraction

86 Acupuncture: A Jab Well Done Acupuncturists attempt to help people gain relief from pain by using needles on points of the patient s body.

87 Built-In Pain Controls: Endorphins and Placebos Endorphins Natural painkiller released by the brain Have a soothing effect that enables pain reduction Placebos Help dampen the central nervous system s attention and responses to painful experiences

88 Built-In Pain Controls Combination of endorphins and distraction Activate brain pathways that decrease pain and increase tolerance Maximum pain relief can be obtained by: Combining a placebo and a distraction Amplifying the resulting effects from the combination via hypnosis

89 Hypnosis Social interaction where one person suggests to another that certain perceptions, feelings, thoughts, or behaviors will spontaneously occur Inhibits pain-related brain activity Explained by the social influence theory and the dissociation theory Does not block the sensory input itself, but it may block individual's attention to those stimuli

90 Dissociation or Social Influence? This hypnotized woman being tested by famous researcher Ernest Hilgard showed no pain when her arm was placed in an ice bath. But when asked to press a key if some part of her felt the pain, she did so. To Hilgard, this was evidence of dissociation, or divided consciousness. The social influence perspective, however, maintains that people responding this way are caught up in playing the role of good subject.

91 Retrieve and Remember 10 Which of the following options has NOT been proven to reduce pain? a. Distraction b. Hypnosis c. Phantom limb sensations d. Endorphins

92 Table The Survival Functions of Basic Tastes Taste Indicates Sweet Energy source Salty Sodium essential to physiological processes Sour Potentially toxic acid Bitter Potential poisons Umami Proteins to grow and repair tissue

93 Taste Involves several basic sensations Sweet, sour, salty, bitter, and umami Gives pleasure and helps people survive Can be influenced by learning and expectations Number of taste buds and taste sensitivity decrease with age Smoking and alcohol can speed up the loss of taste buds.

94 Taste: A Chemical Sense Each bump on the top and sides of the tongue contains 200 or more taste buds. Each bud contains a pore with taste receptor cells. Each receptor reacts to different types of food molecules and sends messages to the brain.

95 Smell: A Chemical Sense Smell is enabled by millions of olfactory receptors that respond selectively to odors. Bypass the thalamus and directly alert the brain Odor molecules exist in many shapes and sizes. Smell s appeal, or the lack of it, depends partly on learned associations. Odors can evoke strong feelings, memories, and behaviors.

96 The Nose Knows Humans have some 20 million olfactory receptors. Bloodhounds have 220 million.

97 Taste, Smell, and Memory Information from the taste buds travels to an area between the frontal and temporal lobes of the brain. It registers in an area not far from where the brain receives information from our sense of smell, which interacts with taste.

98 Retrieve and Remember 11 How does our system for sensing smell differ from our sensory systems for vision, touch, and taste?

99 Body Position and Movement Kinesthesia System for sensing the position and movement of individual body parts Vestibular sense Sense of body movement and position, including the sense of balance These high school competitive cheer team members can thank their inner ears for the information that enables their brains to monitor their bodies position so expertly.

100 Retrieve and Remember 12 Where are kinesthetic sense and vestibular sense receptors located?

101 Sensory Interaction

102 Introduction: Sensory Interaction Principle that one sense may influence another Smell can enhance taste, and touch can influence it. Hearing and vision can interact. Sensation and perception are two points on a continuum. Brain circuits that process bodily sensations may interact with brain circuits that are responsible for cognition.

103 Face-to-Face Seeing the speaker forming the words, which Apple s FaceTime video-chat feature allows, makes those words easier to understand for hardof-hearing listeners.

104 Sensory Interaction Embodied cognition: Influence of bodily sensations, gestures, and other states on cognitive preferences and judgments The brain blends inputs from multiple channels. Synesthesia Condition where one sort of sensation produces another Occurs when brain circuits for two or more senses become joined

105 Table Summarizing the Senses Sensory System Source Receptors Key Brain Areas Vision Light waves striking the eye Rods and cones in the retina Occipital lobes Hearing Sound waves striking the outer ear Cochlear hair cells in the inner ear Temporal lobes Touch Pressure, warmth, cold, harmful chemicals Receptors (nociceptors), mostly in the skin, which detect pressure, warmth, cold, and pain Somatosensory cortex Taste Chemical molecules in the mouth Basic tongue receptors for sweet, sour, salty, bitter, and umami Frontal temporal lobe border Smell Chemical molecules breathed in through the nose Millions of receptors at top of nasal cavities Olfactory bulb Body position kinesthesia Any change in position of a body part, interacting with vision Kinesthetic sensors in joints, tendons, and muscles Cerebellum Body movement vestibular sense Movement of fluids in the inner ear caused by head/ body movement Hair-like receptors in the ears semicircular canals and vestibular sacs Cerebellum

106 ESP Perception Without Sensation?

107 Extrasensory Perception (ESP) Controversial claim that perception can occur apart from sensory input Includes three claims: Telepathy - Mind-to-mind communication Clairvoyance - Perceiving remote events Precognition - Perceiving future events Closely linked to psychokinesis or mind over matter

108 ESP Research and Experiments Most research psychologists and scientists have been skeptical of ESP claims. It is difficult to test ESP claims in a controlled, reproducible environment. Daryl Bem conducted nine experiments that suggested participants could anticipate future events. Critics viewed the methods as badly flawed.

109 Testing Psychic Powers in the British Population Psychologists created a mind machine to see if people could influence or predict a coin toss. Using a touch-sensitive screen, visitors to British festivals were given four attempts to call heads or tails, playing against a computer that kept score.

110 Retrieve and Remember 13 If an ESP event occurred under controlled conditions, what would be the next best step to confirm that ESP really exists?