chapter three sensation and perception. copyright © houghton mifflin company. all rights reserved....
TRANSCRIPT
Copyright © Houghton Mifflin Company. All rights reserved. 3-2
Did You Know That…
• Our sense of smell may not be as keen as that of dogs, but humans can detect the presence of even one drop of perfume dispersed through a small house?
• Roy G. Biv is one of the most famous names learned by psychology students, but he is not a real person?
• Listening to music with headphones or similar device can permanently damage your hearing?
Copyright © Houghton Mifflin Company. All rights reserved. 3-3
Did You Know That… (Cont’d)
• Salmon use the sense of smell to sniff out the streams of their birth when they return to spawn?
• Some people are born with a distaste for broccoli?
• We have a sense that enables us to locate the parts of our body in the dark?
Copyright © Houghton Mifflin Company. All rights reserved. 3-4
Did You Know That… (Cont’d)
• Newborn babies prefer the sounds of their mothers’ voices to the voices of other women?
• The mechanism that makes motion pictures possible lies in the viewer, not the projector?
Copyright © Houghton Mifflin Company. All rights reserved. 3-6
Module 3.1 Preview Questions
• What is sensation?
• What is the difference between absolute thresholds and difference thresholds?
• What factors contribute to signal detection?
• What is sensory adaptation?
Copyright © Houghton Mifflin Company. All rights reserved. 3-7
What Is Sensation?
• The process by which we receive, transform, and process stimuli into neural impulses
• The brain uses these impulses to create experiences of vision, touch, hearing, taste, smell, etc.
Copyright © Houghton Mifflin Company. All rights reserved. 3-8
Sensory Receptors
• Specialized cells that detect sensory stimuli and convert them into neural impulses
• Locations of sensory receptors:• Eyes• Ears• Nose• Mouth• Joints, muscles• Skin
Copyright © Houghton Mifflin Company. All rights reserved. 3-9
Psychophysics
• The study of how physical sources of stimulation relate to the experience of these stimuli in the form of sensations
• Began with the work of 19th century German scientist Gustav Theodor Fechner
Copyright © Houghton Mifflin Company. All rights reserved. 3-10
Absolute and Difference Thresholds
• Absolute Threshold: Smallest amount of a stimulus that a person can reliably detect• Absolute thresholds for different senses
• Difference threshold: The minimal difference between two stimuli that people can reliably detect• Also called “just-noticeable difference” • Weber’s law
Copyright © Houghton Mifflin Company. All rights reserved. 3-11
Table 3.1: Absolute Thresholds for Various Senses
Return
Copyright © Houghton Mifflin Company. All rights reserved. 3-12
Table 3.2: Examples of Weber’s Constants
Copyright © Houghton Mifflin Company. All rights reserved. 3-13
Signal Detection Theory
• The theory that the threshold for detecting a signal depends on:• The intensity of the stimulus• The level of background stimulation• The biological and psychological
characteristics of the perceiver
Copyright © Houghton Mifflin Company. All rights reserved. 3-14
Sensory Adaptation
• The process by which sensory receptors become less sensitive to constant or unchanging stimuli
• May not occur when repeatedly exposed to certain strong stimuli
Copyright © Houghton Mifflin Company. All rights reserved. 3-16
Module 3.2 Preview Questions
• How do the eyes process light?
• What are feature detectors, and what role do they play in visual processing?
• What are the two major theories of color vision?
• What are the two major forms of color blindness?
Copyright © Houghton Mifflin Company. All rights reserved. 3-17
Figure 3.1: The Electromagnetic Spectrum
Copyright © Houghton Mifflin Company. All rights reserved. 3-20
Photoreceptors
• The retina contains specialized receptor cells that are sensitive to light.
• Two types of photoreceptors:• Rods: Allows detection of objects in low light;
also responsible for peripheral vision• Cones: Allows detection of color as well as
fine details of objects in bright light
Copyright © Houghton Mifflin Company. All rights reserved. 3-21
Figure 3.5: Conversion of Light to Neural Impulses
Copyright © Houghton Mifflin Company. All rights reserved. 3-22
Visual Acuity
• The ability to discern visual details.
• Nearsighted if need to be unusually close to discern an object’s details• Eyeball is too long or the cornea is too
curved.
• Farsighted if need to be unusually far away from objects to see them clearly• Eyeball is too short.
Copyright © Houghton Mifflin Company. All rights reserved. 3-23
Feature Detectors
• Neurons that respond to specific features of the visual stimulus
• Visual cortex compiles information from various cells to form meaningful patterns
Copyright © Houghton Mifflin Company. All rights reserved. 3-24
Trichromatic Theory of Color Vision
• Thomas Young (1773-1829)
• Hermann von Helmholtz (1821-1894)
• Eyes have 3 types of color receptors or “cones.”• Red, green, blue-violet
Figure 3.7: Primary Colors
Copyright © Houghton Mifflin Company. All rights reserved. 3-27
Opponent-Process Theory
• Ewald Hering (1834-1918)
• Three pairs of opposing color receptors• Red-Green• Blue-Yellow• Black-White
• When one color is activated, other is inhibited.
Copyright © Houghton Mifflin Company. All rights reserved. 3-28
Which Theory of Color Vision Is Correct?
• Both theories, to a certain extent
• Trichromatic theory is correct at the receptor level.
• Opponent-process is correct with respect to behavior of cells that lie between the cones and the occipital lobe.
Copyright © Houghton Mifflin Company. All rights reserved. 3-29
Figure 3.9: Color Blindness
• Trichromats: Normal color vision
• Monochromats: No color vision
• Dichromats: Can see some colors but not others
Copyright © Houghton Mifflin Company. All rights reserved. 3-31
Module 3.3 Preview Questions
• How does the ear enable us to hear sound?
• What determines our perception of pitch?
• What are the main types and causes of deafness?
Copyright © Houghton Mifflin Company. All rights reserved. 3-33
Characteristics of Sound
• Amplitude determines perceived loudness.• Measured in decibels (dB)
• Frequency determines perceived pitch.• How high or low a sound seems
Copyright © Houghton Mifflin Company. All rights reserved. 3-34
Figure 3.11: Conversion of Sound Waves into Neural Impulses
Copyright © Houghton Mifflin Company. All rights reserved. 3-35
Perception of Pitch
• Place Theory: Location of vibration along basilar membrane determines pitch.• Explains pitch of high-frequency sounds
• Frequency Theory: Basilar membrane vibrates at same frequency as sound wave.• Explains pitch of low-frequency sounds
• Volley Principle: Groups of neurons along basilar membrane fire in rotation.• Suggests how perceive mid-range sounds
Copyright © Houghton Mifflin Company. All rights reserved. 3-37
Hearing Loss
• Conduction Deafness: Damage to middle ear• May benefit from hearing aids
• Nerve Deafness: Damage to hair cells of the inner ear or auditory nerve• Use of cochlear implants sometimes
successful
• Hearing loss is not inevitable.
Copyright © Houghton Mifflin Company. All rights reserved. 3-39
Module 3.4 Preview Questions
• How do we sense odors and tastes?
• What are the skin senses?
• What are the kinesthetic and vestibular senses?
Copyright © Houghton Mifflin Company. All rights reserved. 3-40
Olfaction
• Our sense of smell
• Stimulation depends on the shape of the molecules of chemical substances.
• Capable of sensing about 10,000 different substances
• Only sense that does not pass through the thalamus.
Copyright © Houghton Mifflin Company. All rights reserved. 3-42
Pheromones
• Chemical substances emitted by many species • Found in bodily secretions• Detected by other members of the species
through the sense of smell or taste
• Plays important roles in many behaviors, including sexual attraction
• Do pheromones influence human behaviors?
Copyright © Houghton Mifflin Company. All rights reserved. 3-43
Taste
• Four basic tastes: sweet, sour, salty, bitter
• Flavor derives from: taste, aroma, texture, temperature
Copyright © Houghton Mifflin Company. All rights reserved. 3-44
Factors Influencing Food Preference
• Cultural background
• Genetic factors
• Taste sensitivity• One in 4 are “supertasters”
• Gender and ethnic or racial differences in taste sensitivity
Copyright © Houghton Mifflin Company. All rights reserved. 3-45
The Skin Senses
• Largest sensory organ
• Codes for sensations of touch, pressure, warmth, cold, and pain
• Pain is adaptive.
Figure 3.14
Copyright © Houghton Mifflin Company. All rights reserved. 3-46
Gate-Control Theory Of Pain
• A gating mechanism in the spinal cord controls pain messages.• Bottleneck at the “gate” may block pain.
• Role of endorphins in controlling pain• Release of endorphins may explain benefits
of acupuncture.
Copyright © Houghton Mifflin Company. All rights reserved. 3-47
Kinesthesis
• Body sense that provides information about:• Movement of body parts• Relative position of body parts
• Receptors located in joints, ligaments, and muscles
Copyright © Houghton Mifflin Company. All rights reserved. 3-48
Vestibular Sense
• Functions:• Monitors position of body in space• Helps maintain balance
• Monitors position of head
• Conflict with vision = motion sicknessContinue
Copyright © Houghton Mifflin Company. All rights reserved. 3-49
Figure 3.15: Vestibular Sense
Return
Copyright © Houghton Mifflin Company. All rights reserved. 3-51
Module 3.5 Preview Questions
• What is perception?
• How is perception influenced by attention and perceptual set?
• What are the two general modes of processing visual stimuli?
• What are the Gestalt principles of perceptual organization?
Copyright © Houghton Mifflin Company. All rights reserved. 3-52
Module 3.5 Preview Questions (Cont’d)
• What is perceptual constancy, and what cues do we use to perceive depth and movement?
• What are visual illusions?
• Does subliminal perception exist?
• Does evidence support the existence of ESP?
Copyright © Houghton Mifflin Company. All rights reserved. 3-53
Perception
• The process by which the brain interprets sensations• Turns them into meaningful representations of
the world
• Perception is an active process.
• Perceptions may not accurately reflect external reality.
Copyright © Houghton Mifflin Company. All rights reserved. 3-54
Figure 3.16: Perception vs. Reality?
Copyright © Houghton Mifflin Company. All rights reserved. 3-55
Attention
• First step in perception:• Role of selective attention
• Influenced by:• Motivational states• Repeated exposure
• Constant exposure can lead to habituation.
Copyright © Houghton Mifflin Company. All rights reserved. 3-56
Figure 3.17: What Do You See Here?
• Perceptions are influenced by our expectations or preconceptions.
Is this the Letter B or the Number 13?
Copyright © Houghton Mifflin Company. All rights reserved. 3-57
Visual Processing
• Bottom-Up Processing: Focus on specific shapes, individual features• Brain assembles specific features of shapes
to form patterns.• Patterns are compared with stored images.
• Top-Down Processing: Experience and knowledge shape perception• Recognize patterns as meaningful wholes
Copyright © Houghton Mifflin Company. All rights reserved. 3-58
Figure 3.18: A Duck or a Rabbit?
From Sensation and Perception: An Integrated Approach, From H.R. Schiffman. Copyright © 2000 by John Wiley & Sons Inc., This material is used with permission of John Wiley & Sons Inc.
Copyright © Houghton Mifflin Company. All rights reserved. 3-59
Laws of Perceptual Organization
• Figure and Ground• Reversible figure• Ambiguous figure
• Gestalt Laws of Grouping
Copyright © Houghton Mifflin Company. All rights reserved. 3-60
Figure 3.20: Reversible Figure
ReturnIs this a vase or a profile of two faces?
Copyright © Houghton Mifflin Company. All rights reserved. 3-61
Figure 3.21: Ambiguous Figure
Do you see an old woman or a young one?
Copyright © Houghton Mifflin Company. All rights reserved. 3-63
Figure 3.23: Gestalt Laws of Grouping
Copyright © Houghton Mifflin Company. All rights reserved. 3-64
Perceptual Constancies
• Tendency to perceive an object as remaining the same even when retinal image changes
• Examples:• Shape constancy• Size constancy• Color constancy• Brightness constancy
Continue
Copyright © Houghton Mifflin Company. All rights reserved. 3-66
Binocular Cues for Depth Perception
• Cues that involve both eyes
• Retinal Disparity: Cue for distance based on the slight differences in the visual impressions formed in both eyes
• Convergence: Cue for distance based on the degree of tension required to focus two eyes on the same object
Copyright © Houghton Mifflin Company. All rights reserved. 3-67
Monocular Cues for Depth Perception
• Cues that depend on one eye only
• Examples of cues:• Relative size• Interposition• Relative clarity• Texture gradient• Linear perspective• Shadowing
Copyright © Houghton Mifflin Company. All rights reserved. 3-68
Cues for Motion Perception
• Path of image as it crosses the retina
• The changing size of the object
Copyright © Houghton Mifflin Company. All rights reserved. 3-69
Visual Illusions: Do Your Eyes Deceive You?
• Müller-Lyer illusion and the Ponzo illusion
• Impossible figures
• Moon illusion• Relative-size hypothesis as a possible
explanation.
• Stroboscopic movement
Copyright © Houghton Mifflin Company. All rights reserved. 3-70
Figure 3.27: Müller-Lyer Illusion and Ponzo Illusion
Return
Copyright © Houghton Mifflin Company. All rights reserved. 3-71
Figure 3.28: Impossible Figure
Return
Copyright © Houghton Mifflin Company. All rights reserved. 3-72
Cultural Differences
• Perception influenced by both sensory systems as well as cultural experiences
• Müller-Lyer illusion and the carpentered-world hypothesis
• Ponzo illusion less prominent among people of Guam
Copyright © Houghton Mifflin Company. All rights reserved. 3-73
Subliminal Perception
• Stimuli presented below level of conscious awareness
• Does subliminal perception exist?• A qualified yes• Effects appear to be subtle and depend on
very precise experimental conditions.
• Can it influence attitudes or behavior?• No convincing evidence exists that it can.
Copyright © Houghton Mifflin Company. All rights reserved. 3-74
Extrasensory Perception
• Perception that occurs without benefit of the known senses
• Common forms of paranormal phenomena identified with ESP:• Telepathy• Clairvoyance• Precognition • Psychokinesis
• Has not been demonstrated scientifically
Copyright © Houghton Mifflin Company. All rights reserved. 3-76
Module 3.6 Preview Question
• What have psychologists learned about controlling pain?