psy i ch.3

Copyright © Allyn & Bacon 2006

Sensation and Perception

Chapter Three

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•Preparation of any derivative work, including the extraction, in whole or in part, of any images;

•Any rental, lease, or lending of the programSlide author:

Cynthia K. Shinabarger Reed

Book authors:

Samuel Wood

Ellen G. Wood

Denise Boyd


Chapter Three Overview

The Process of Sensation

o The Absolute and Difference Thresholds

o Transduction and Adaptation



Vision

o The Eye

o Vision and the Brain

o Color Vision

o Theories of Color Vision

o Color Blindness



Hearing

o Sound

o The Ear

o Theories of Hearing

o Hearing Loss



Smell and Tasteo Smello Taste

The Skin Senseso Toucho Pain

The Spatial Orientation Senses



Perception

o Principles of Perceptual Organization

o Depth Perception

o Perception of Motion

o Puzzling Perceptions



Influences on Perception

o Prior Knowledge

o Attention

o Social Perception


Sensation and Perception

• Sensation– The process through which the senses

pick up visual, auditory, and other sensory stimuli and transmit them to the brain

• Perception– The process by which sensory

information is actively organized and interpreted by the brain


The Process of SensationThe Absolute and Difference Thresholds• Absolute threshold: The minimum amount

of sensory stimulation that can be detected 50% of the time

• Difference threshold: The smallest increase or decrease in a physical stimulus required to produce the just noticeable difference (JND)

• Just noticeable difference (JND): The smallest change in sensation that a person is able to detect 50% of the time


Absolute Thresholds


The Process of Sensation• Weber’s Law

– The law stating that the JND for all the senses depends on a proportion or percentage of change in a stimulus rather than a fixed amount of change.

– According to Weber’s law, the greater the original stimulus, the more it must be increased or decreased for the difference to be noticeable.

– Weber’s law best fits people with average sensitivities and to sensory stimuli that are neither very strong nor very weak.



• Transduction and Adaptation– Sensory receptors are highly

specialized cells in the sense organs that detect and respond to one type of sensory stimuli – light, sound waves, odors – and transduce (convert) the stimuli into neural impulses.

– Transduction is the process through which the sensory receptors convert the sensory stimulation into neural impulses.



• Transduction and Adaptation (continued)– The sense receptors provide the

essential link between the physical sensory world and the brain.

– Sensory adaptation is the process in which sensory receptors grow accustomed to constant, unchanging levels of stimuli over time.


Vision• Our eyes can respond only to visible light

waves, which form a small subgroup of electromagnetic waves, a band called the visible spectrum.

• The visible spectrum is the narrow band of electromagnetic waves that are visible to the human eye.

• These waves are measured in wavelengths, the distance from the peak of one wave to the peak of the next.


The Electromagnetic Spectrum


Vision

• The Eye– Cornea: the tough, transparent, protective

layer covering the front surface of the eyeball that bends light rays inward through the pupil.

– The cornea performs the first step of vision by bending the light rays inward.

– It directs the light rays through the pupil, the small, dark opening in the center of the iris, or colored part of the eye.


Vision

• The Eye continued– Lens: the transparent structure behind the iris

and the pupil that performs the task of focusing on viewed objects.

– Accommodation: the flattening and bulging action of the lens as it focuses images of objects on the retina.

– With age, the lens loses the ability to change its shape to accommodate for near vision, a condition called presbyopia.


Vision

• The Eye (continued)

– Retina: the layer of tissue located on the inner surface of the eyeball that contains the sensory receptors for vision.

– Nearsightedness (myopia): when the lens focuses images of distant objects in front of, rather than on, the retina.

– Farsightedness (hyperopia): when the lens focuses images of close objects behind, rather than on, the retina.


Vision

The Rods and Cones• At the back of the retina is a layer of light-

sensitive receptor cells – the rods and the cones.

• Names for their shapes, the rods look like slender cylinders, and the cones appear shorter and more rounded.

• There are about 120 million rods and 6 million cones in each retina.


Vision

• Cones: The receptor cells in the retina that enable humans to see color and fine detail in adequate light, but that do not function in very dim light.

• Rods: The extremely light-sensitive cells in the retina that allow the eye to respond to as few as five photons of light.


Vision

• Rhodopsin

– Enables us to adapt to variations in light

– Two components: opsin and retinal

• Opsin and retinal break apart in light adaptation

• Opsin and retinal bond to one another in dark adaptation


Vision

• Fovea

– A small area at the center of the retina that provides the clearest and sharpest area of vision.

– It contains no rods, but has about 30,000 cones tightly packed together.


Vision

Vision and the Brain

• The rods and cones transduce, or change, light waves into neural impulses that are fed to the bipolar cells, which, in turn, pass the impulses along to the ganglion cells.

• The approximately 1 million axon-like extensions of the ganglion cells are bundled together in a pencil-sized cable that extends through the wall of the retina, leaving the eye and leading to the brain.


Vision

Vision and the Brain (continued)• Blind spot: the point in each retina where there

are no rods or cones because the cable of ganglion cells is extending through the retinal wall.

• Optic nerve: the nerve that carries visual information from the retina to the brain.

• Optic chiasm: the point where the two optic nerves come together and some of the nerve fibers cross to the opposite side of the brain.


VisionVision and the Brain (continued)• The nerve fibers from the right half of each retina go to

the right hemisphere, and those from the left half of each retina go to the left hemisphere.

• This crossing over is important because it allows visual information from a single eye to be represented in the primary visual cortex of both hemispheres of the brain.

• It also plays an important role in depth perception.• From the optic chiasm, the optic nerve fibers extend to

the thalamus, where they form synapses with neurons that transmit the impulses to the primary visual cortex.


Vision

Vision and the Brain (continued)

• Primary visual cortex: the part of the brain in which visual information is processed.

• Feature detectors: neurons in the brain that respond to specific visual patterns.


Vision

Color Vision

• Some light waves striking an object are absorbed by it; others are reflected from it.

• The presence of all visible wavelengths gives the sensation of a near-white color.

• If an object does indeed reflect 100% of visible wavelengths, it appears to be pure white.


VisionColor Vision (continued)• Three dimensions of light that combine to

provide the color we experience:– Hue: the specific color perceived.– Saturation: the purity of a color; a color

becomes less saturated, or less pure, as other wavelengths of light are mixed with it.

– Brightness: the intensity of the light energy that is perceived as a color.


Vision

Theories of Color Vision• Trichromatic theory

– First proposed by Thomas Young in 1802 and was modified by Hermann von Helmholtz about 50 years later

– The theory of color vision suggesting that there are three kinds of cones in the retina and that each kind makes a maximal chemical response to one of three colors – blue, green or red.


Vision

Theories of Color Vision (continued)

• Opponent-process theory

– First proposed by physiologist Ewald Hering in 1878 and revised in 1957 by researchers Leo Hurvich and Dorothea Jameson

– The theory that three kinds of cells respond by increasing or decreasing their rate of firing when different colors are present.


Vision

Theories of Color Vision (continued)• Opponent-process theory continued

– Afterimage: the visual sensation that remains after a stimulus is withdrawn.

– After you have stared at one color in an opponent-process pair (red/green, yellow/blue, black/white), the cell responding to that color tires and the opponent cell begins to fire, producing the afterimage.


Vision

Color blindness• The inability to distinguish certain colors

from one another• About 7% of males experience some kind of

difficulty in distinguishing colors while fewer than 1% of females suffer from color blindness.

• Research has shown that color blindness can have degrees; it isn’t simply a matter of either you have it or you don’t.


Hearing

Sound• Sound requires a medium, such as air,

water, or a solid object through which to move.

• This fact was first demonstrated by Robert Boyle in 1660.


Hearing

Sound (continued)• Frequency

– Measured in the unit called the hertz, the number of sound waves or cycles per second, determining the pitch of the sound.

– The pitch – how high or low the sound is – is chiefly determined by the frequency – the higher the frequency, the higher the sound.

– The human ear can hear sound frequencies from low bass tones of around 20 Hz and high-pitched sounds of about 20,000 Hz.


HearingSound (continued)• Amplitude

– Measured in decibels, the magnitude or intensity of sound wave, determining the loudness of the sound

– The measuring unit used, bel, is named after Alexander Graham Bell.

– Because the bel is a rather large unit, sound levels are expressed in tenths of a bel, or decibels (dB).

– The threshold of human hearing is set at 0 dB, the softest sound that can be heard in a very quiet setting.


Hearing

Sound (continued)• Timbre

– The distinctive quality of a sound that distinguishes it from other sounds of the same pitch and loudness.

– Human voices vary in timbre, providing us with a way of recognizing individuals when we can’t see their faces.

– Timbres also vary from one instrument to another.


HearingThe Ear• Audition: the sensation and process of hearing.• Outer ear

– The visible part of the ear, consisting of the pinna and the auditory canal

– The pinna is the oddly shaped, curved flap of cartilage that is the visible part of the outer ear.

– The auditory canal is about 1 inch long, and its entrance is lined with hairs.

– The eardrum (or tympanic membrane) is at the end of the auditory canal and is a thin and flexible membrane about 1/3 inch in diameter; it moves in response to sound waves.


Hearing

The Ear (continued)

• Middle ear: the portion of the ear containing the ossicles.

• Ossicles

• Named the hammer, the anvil, and the stirrup

• Link the eardrum to the oval window

• Amplify sound waves some 22 times


Hearing

The Ear (continued)

• Inner ear

– The innermost portion of the ear, containing the cochlea, the vestibular sacs, and the semicircular canals

– Cochlea

• The snail-shaped, fluid-filled chamber in the inner ear that contains the hair cells

– Hair cells

• Sensory receptors for hearing


The Anatomy of the Human Ear


HearingThe Ear (continued)• The tiny hair bundles are pushed and pulled by the

motion of the fluid inside the cochlea.• If the tip of a hair bundle is moved only as much as

the width of an atom, an electrical impulse is generated, which is transmitted to the brain by way of the auditory nerve.

• We can hear some sounds through bone conduction, the vibrations of the bones in the face and skull.

• Having two ears, one on each side of the head, enables you to determine the direction from which sounds are coming.


Hearing

Theories of Hearing

• Place theory: this theory of hearing holds that each individual pitch a person hears is determined by the particular spot or place along the basilar membrane that vibrates the most.

• Frequency theory: the theory that hair cell receptors vibrate the same number of times per second as the sounds that reach them.


HearingHearing Loss• Conduction deafness: usually caused by

disease or injury to the eardrum or the bones of the middle ear, which prevents sound waves from being conducted to the cochlea.

• Sensorineural hearing loss: damage to either the cochlea or the auditory nerve.

• About 75% of the cases of hearing loss in older adults appear to be caused by life-long exposure to excessive noise rather than by aging.


Smell and Taste

Smell• Olfaction: the sensation of smell.• Olfactory system: the technical

name for the organs and brain structures involved in the sense of smell.

• Your olfactory system aids your survival.


Smell and Taste

The Mechanics of Smell• You cannot smell a substance unless some of its

molecules vaporize.• When odor molecules vaporize, they become

airborne and make their way up each nostril to the olfactory epithelium.

• Olfactory epithelium: Two 1-square-inch patches of tissue, one at the top of each nasal cavity; together these patches contain about 10 million olfactory neurons, which are the receptor cells for smell.


Smell and Taste

The Mechanics of Smell (continued)• The intensity of a smell stimulus is apparently

determined by the number of olfactory neurons firing at the same time.

• Olfactory bulbs: two matchstick-sized structures above the nasal cavities, where smell sensations first register in the brain.

• The process of sensing odors is the same in every individual, but there are large differences in sensitivity to smells.


The Olfactory System


Smell and TasteSmell and Memory

• Brain-imaging studies of human olfactory functioning have established key connections among smell, emotion, and memory.

• The association of memories with odors is thought to occur because the olfactory system first sends information to the limbic system, an area in the brain that plays an important role in emotions and memories.

• The ability to associate odors with memories appears to peak between 6 and 10 years of age.


Smell and Taste

• Pheromones: chemicals excreted by humans and other animals that can have a powerful effect on the behavior of other members of the same species

• Used by animals to mark off territories and to signal sexual receptivity

• Karl Grammer suggested that humans, although not consciously aware of it, respond to pheromones when it comes to mating.


Smell and Taste

Taste• Gustation: the sensation of taste• The Five Basic Tastes

– Sweet– Sour– Salty– Bitter– Umami

• Triggered by the substance glutamate


Smell and Taste

The Taste Receptors• Papillae: the small bumps on your tongue

– Four different types– Three of them contain taste buds

• Taste buds: structures composed of 60 to 100 receptor cells for taste

• The lifespan of the taste receptors is very short – only about 10 days – and they are continually being replaced.


The Tongue’s Papillae and Taste Buds


Smell and TasteTaste Sensitivities• Individuals vary widely in their capacity for

experiencing taste sensations– Nontasters: are unable to taste certain sweet and

bitter compounds, but do taste most other substances

– Supertasters: taste certain sweet and bitter compounds with far stronger intensity than other people

• Researchers know that taste sensitivity is linked to food preferences, but not how these preferences may be connected to nutritional status.


The Skin Senses

Touch• Skin: the largest organ of your body

– Performs many important biological functions while also providing much of what is known as sensual pleasure

• Tactile information is conveyed to the brain when an object touches and depresses the skin, stimulating one or more of the several distinct types of receptors found in the nerve endings.


The Skin Senses

Touch (continued)

• If you could examine the skin from the outermost to the deepest layer, you would find a variety of nerve endings that differ markedly in appearance.

• The more densely packed with these sensory receptors a part of the body’s surface is, the more sensitive it is to tactile stimulation.


The Skin SensesPain

• Pain motivates us to tend to injuries, to restrict activity, and to seek medical help.

• Pain teaches us to avoid pain-producing circumstances in the future.

• Chronic pain is pain that persists for three months or more.

• Three common types

• Low-back

• Headache

• Arthritis


The Skin Senses

Pain (continued)• Gate-control theory (Melzack and Wall)

• The theory that there is an area in the spinal cord that can act like a “gate” and either block pain messages or transmit them to the brain.

• You feel pain when pain messages carried by the small, slow-conducting nerve fibers reach the gate and cause it to open.

• Melzack and Wall contend that messages from the brain to the spinal cord can inhibit the transmission of pain messages at the spinal gate and thereby affect the perception of pain.


The Skin Senses

Psychological and Cultural Influences on the Experience of Pain

• Sullivan and others found that people suffered most from pain when they harbored negative thoughts about it, feared its potential threat to their well-being, and expressed feelings of helplessness.

• Culture influences the way pain is experienced and expressed.

• Culture even influences the experience and expression of pain during childbirth.


The Skin Senses

Endorphins• The body’s own natural painkillers, which

block pain and produce a feeling of well-being

• Some people release endorphins even when they only think they are receiving pain medication but are given, instead, a placebo in the form of a sugar pill or an injection of saline solution.



• Kinesthetic sense: provides information about the position of body parts in relation to each other and the movement of the entire body or its parts.

• Vestibular sense: detects movement and provides information about the body’s orientation in space.

• The vestibular sense organs are located in the semicircular canals and the vestibular sacs in the inner ear.

• The semicircular canals consist of three fluid-filled tubular canals that sense the rotation of your head.


Sensing Balance and Movement


Perception

Gestalt principles of perceptual organization• Figure-ground: as you view your world,

some object (the figure) seems to stand out from the background (the ground)

• Similarity: objects that have similar characteristics are perceived as a unit

• Proximity: objects that are close together in space or time are usually perceived as belonging together


Perception

Gestalt principles of perceptual organization (continued)

• Continuity: we tend to perceive figures or objects as belonging together if they appear to form a continuous pattern

• Closure: we perceive figures with gaps in them to be complete


Perception

• You can see a white vase as figure against a black background, or two black faces in profile on a white background


Perception

Perceptual constancy

• Perceptual constancy: the tendency to perceive objects as maintaining stable properties, such as size, shape, and brightness, despite differences in distance, viewing angle, and lighting.

• Size constancy: Perceiving objects as being about the same size when they move farther away.


Perception

Perceptual constancy (continued)

• Shape constancy: Perceiving objects as having a stable or unchanging shape regardless of changes in the retinal image resulting from differences in viewing angle.

• Brightness constancy: perceiving objects as maintaining a constant level of brightness, regardless of differences in lighting conditions.


PerceptionDepth perception• Depth perception is the ability to see in three

dimensions and to judge distances accurately.

Binocular depth cues• Binocular depth cues are depth cues that depend on

two eyes working together.• Convergence occurs when the eyes turn inward to

focus on nearby objects – the closer the object, the more the two objects appear to come together.

• Binocular disparity (or retinal disparity) refers to difference between the two retinal images formed by the eyes’ slightly different views of the objects focused on.


Perception

Monocular depth cues• Monocular depth cues are depth cues that

can be perceived by only one eye.• Interposition: when one object partly blocks

your view of another, you perceive the partially blocked object as farther away.

• Linear perspective: parallel lines that are known to be the same distance apart appear to grow closer together, or converge, as they recede into the distance.


Perception

Monocular depth cues (continued)

• Relative size: larger objects are perceived as being closer to the viewer, and smaller objects as being farther away.

• Texture gradient: objects close to you appear to have sharply defined textures, while similar objects that are farther away appear progressively less well-defined or fuzzier in texture.

• Atmospheric perspective (sometimes called aerial perspective): objects in the distance have a bluish tint and appear more blurred than objects close at hand.


Perception

Monocular depth cues (continued) • Shadow or shading: when light falls on objects,

they cast shadows, which add to the perception of depth.

• Motion parallax: When you ride in a moving vehicle and look out the side window, the objects you see outside appear to be moving in the opposite direction and at different speeds – those closest to you appear to be moving faster than those in the distance. Objects very far away, such as the moon and the sun, appear to move in the same direction as the viewer.


Perception

Perception of motion

• Real motion: perceptions of motion tied to movements of real objects through space.

• Apparent motion: perceptions of motion that are psychologically constructed in response to various kinds of stimuli.


Perception

Real motion• James Gibson pointed out that our perceptions

of motion appear to be based on fundamental, but frequently changing, assumptions about stability.

• Our brains search for some stimulus in the environment to serve as the assumed reference point for stability.

• Once the stable reference point is chosen, all objects that move relative to that reference point are judged to be in motion.


PerceptionApparent motion• Phi phenomenon: an apparent motion illusion

occurring when two or more stationary lights are flashed on and off in sequence, giving the impression that one light is actually moving from one spot to the next.

• When you watch a motion picture, you are also perceiving this kind of apparent motion, often called stroboscopic motion.

• Autokinetic illusion: perceptions of motion caused by movement of the eyes rather than objects.


PerceptionPuzzling Perceptions• Ambiguous figures

– Can be seen in different ways to make different images– Best known ambiguous figure is “Old Woman/Young Woman,”

by E.G. Boring


PerceptionPuzzling Perceptions (continued)• Impossible figures

– Do not seem unusual at first– Figures that cannot be built


Perception

Illusions

• An illusion is a false perception or a misperception of an actual stimulus in the environment.

• We can misperceive size, shape, or the relationship of one element to another.


Perception

Müller-Lyer Illusion– The two lines above are the same length, but the diagonals

extending outward from both ends of the lower line make it look longer than the upper line


Perception

Cultural Differences in the Perception of Visual Illusions

• R.L. Gregory believed that susceptibility to the Müller-Lyer and other such illusions is not innate; rather the culture in which people live is responsible to some extent for the illusions they perceive.

• Segall and others tested 1,848 adults and children from 15 different cultures to see if susceptibility to illusions is due to experience. The study revealed that experience was a factor.


Perception

Cultural Differences in the Perception of Visual Illusions

• Stewart did a study to see if race offered an explanation for the cultural differences in observing illusions.

• No significant differences were found in susceptibility to the illusions based on race.


PerceptionCultural Differences in the Perception of

Visual Illusions• Pedersen and Wheeler studied Native

American responses to the Müller-Lyer illusion among two groups of Navajos.

• The group who lived in rectangular houses and had experienced corners, angles, and edges tended to see the illusion.

• The other group tended not to see it because their cultural experience consisted of round houses.



Prior Knowledge• Bottom-up processing: Information

processing in which individual components or bits of data are combined in the brain until a complete perception is formed.

• Top-down processing: information processing in which previous experience and conceptual knowledge are applied to recognize the whole of a perception and thus easily identify the simpler elements of that whole.


Influences on PerceptionPrior Knowledge (continued)• Perceptual set: an expectation of what will be

perceived, which can affect what actually is perceived

• Classic Study of Perceptual Set– David Rosenhan and some of his colleagues

were admitted as patients to various mental hospitals with “diagnoses” of schizophrenia.

– Once inside, they acted normal, but the staff members only saw what they expected to see and not what was actually occurring.

– The real patients were the first to realize that the psychologists were not really mentally ill.



Attention

• Inattentional blindness: the phenomenon in which we miss an object in our field of vision because we are attending to another.



Attention (continued)• Simons and his colleagues

– Showed participants a videotape of a basketball game in which one team is uniformed in white and the other in black.

– Instructed them to count how many times the ball was passed from one player to another either on the white or black team.

– About a third of participants typically fail to later recall the presence on the screen of even extremely incongruent stimuli (e.g., a man dressed in a gorilla costume) under such conditions.



Attention (continued)

• David Strayer and his colleagues

– Studies showed that drivers often failed to perceive vehicles braking directly in front of them while engaged in hands-free cell phone conversations.


Influences on PerceptionSocial Perception• Perception of human faces appears to be

particularly complex and distinctive from perceptions of other kinds of visual stimuli.

• James Haxby suggests that there is a “core system” of face perception that uses the universal features of the human face to make judgments about people’s identities.

• Cross-modal perception refers to the way we combine information from two sensory modalities.



Social perception (continued)• When judging motion based on conflicting

visual and auditory cues, we tend to rely on the auditory input.

• In the case of social perception, the opposite is true.

• Facial expressions, the visual cues for emotional perception, often take priority over the auditory cues associated with a person’s speech intonation and volume, as well as the actual words spoken.


Review of Learning Objectives


1. What is the difference between the absolute threshold and the difference threshold?

2. How does transduction enable the brain to receive sensory information?


Review of Learning ObjectivesVision1. How does each part of the eye function in

vision?2. What path does visual information take from

the retina to the primary visual cortex?3. How do we detect the difference between one

color and another?4. What two major theories attempt to explain

color vision?5. Do individuals with color blindness see the

world in black and white?



Hearing

1. What determines the pitch and loudness of a sound, and how is each quality measured?

2. How do the outer ear, middle ear, and inner ear function in hearing?

3. What two major theories attempt to explain hearing?

4. What are some of the major causes of hearing loss?



Smell and Taste1. What path does a smell message take from the

nose to the brain?2. What are the primary taste sensations, and

how are they detected?The Skin Senses1. How does the skin provide sensory

information?2. What is the function of pain, and how is pain

influenced by psychological factors, culture, and endorphins?




1. What kinds of information do the kinesthetic and vestibular senses provide?



Perception• What are the principles that govern perceptual

organization?• What are some of the binocular and monocular

depth cues?• How does the brain perceive real and apparent

motion?• What are three types of puzzling perceptions?




1. How does prior knowledge influence perception?

2. What is inattentional blindness?

3. Do we perceive physical objects and social stimuli in the same way?

psy i ch.3

Health & Medicine

eye vision

overview vision

vision cones

perception sensation

perception chapter

near vision

step of vision

vision rhodopsin