Chapter Three Sensation and Perception. Copyright © Houghton Mifflin Company. All rights reserved. 3-2 Did You Know That… Our sense of smell may not be.

Chapter Three

Sensation and Perception

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?


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?


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?

Module 3.1

Sensing Our World: Basic Concepts of Sensation


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?


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.


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


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


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


Table 3.1: Absolute Thresholds for Various Senses

Return


Table 3.2: Examples of Weber’s Constants


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


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

Module 3.2

Vision: Seeing the Light



• 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?


Figure 3.1: The Electromagnetic Spectrum


Figure 3.2: The Color Spectrum


Figure 3.3: Parts of the Eye


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


Figure 3.5: Conversion of Light to Neural Impulses


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.


Feature Detectors

• Neurons that respond to specific features of the visual stimulus

• Visual cortex compiles information from various cells to form meaningful patterns


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


Figure 3.8: Primary Colors


Unnumbered Figure 3.1


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.


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.


Figure 3.9: Color Blindness

• Trichromats: Normal color vision

• Monochromats: No color vision

• Dichromats: Can see some colors but not others

Module 3.3

Hearing: The Music of Sound



• How does the ear enable us to hear sound?

• What determines our perception of pitch?

• What are the main types and causes of deafness?


Figure 3.10: Sound Waves


Characteristics of Sound

• Amplitude determines perceived loudness.• Measured in decibels (dB)

• Frequency determines perceived pitch.• How high or low a sound seems


Figure 3.11: Conversion of Sound Waves into Neural Impulses


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


Figure 3.12: Sounds and Decibels


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.

Module 3.4

Our Other Senses:

Chemical, Skin, and Body Senses



• How do we sense odors and tastes?

• What are the skin senses?

• What are the kinesthetic and vestibular senses?


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.


Figure 3.13: Olfaction


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?


Taste

• Four basic tastes: sweet, sour, salty, bitter

• Flavor derives from: taste, aroma, texture, temperature


Factors Influencing Food Preference

• Cultural background

• Genetic factors

• Taste sensitivity• One in 4 are “supertasters”

• Gender and ethnic or racial differences in taste sensitivity


The Skin Senses

• Largest sensory organ

• Codes for sensations of touch, pressure, warmth, cold, and pain

• Pain is adaptive.

Figure 3.14


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.


Kinesthesis

• Body sense that provides information about:• Movement of body parts• Relative position of body parts

• Receptors located in joints, ligaments, and muscles


Vestibular Sense

• Functions:• Monitors position of body in space• Helps maintain balance

• Monitors position of head

• Conflict with vision = motion sicknessContinue


Figure 3.15: Vestibular Sense

Return

Module 3.5

Perceiving Our World:

Principles of Perception



• 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?


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?


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.


Figure 3.16: Perception vs. Reality?


Attention

• First step in perception:• Role of selective attention

• Influenced by:• Motivational states• Repeated exposure

• Constant exposure can lead to habituation.


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?


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


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.


Laws of Perceptual Organization

• Figure and Ground• Reversible figure• Ambiguous figure

• Gestalt Laws of Grouping


Figure 3.20: Reversible Figure

ReturnIs this a vase or a profile of two faces?


Figure 3.21: Ambiguous Figure

Do you see an old woman or a young one?


Figure 3.23: Old/Young Woman

Return


Figure 3.23: Gestalt Laws of Grouping


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


Figure 3.24: Shape Constancy

Return


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


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


Cues for Motion Perception

• Path of image as it crosses the retina

• The changing size of the object


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


Figure 3.27: Müller-Lyer Illusion and Ponzo Illusion

Return


Figure 3.28: Impossible Figure

Return


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


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.


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

Application Module 3.6

Psychology and Pain Management


Module 3.6 Preview Question

• What have psychologists learned about controlling pain?


Pain Management

• Distraction

• Creating a bottleneck at the “gate”

• Changing thoughts and attitudes

• Obtaining accurate information

• Meditation

• Biofeedback

Chapter Three Sensation and Perception. Copyright © Houghton Mifflin Company. All rights reserved. 3-2 Did You Know That… Our sense of smell may not be.

Documents

perceiver slide

perception slide

muscles skin slide

absolute thresholds

sensory stimuli

minimal difference

sensory adaptation

process stimuli