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Bella edwards
myersep11e_lectureslides_ch06.pptxSensation and Perception
Chapter 6
EXPLORING PSYCHOLOGY
DAVID G. MYERS | C. NATHAN DEWALL
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Chapter Overview
Basic Concepts of Sensation and Perception
Vision: Sensory and Perceptual Processing
The Nonvisual Senses
Processing Sensations and Perceptions (part 1)
Sensation and perception are actually parts of one continuous process.
Sensation: The process by which our sensory receptors and nervous system receive and represent stimulus energies from our environment
Perception: The process of organizing and interpreting sensory information, enabling us to recognize meaningful objects and events
Processing Sensations and Perceptions (part 2)
Bottom-up processing: Sensory analysis that begins at the entry level, with information flowing from the sensory receptors to the brain
Top-down processing: Information processing guided by high-level mental processes, as when we construct perceptions by filtering information through our experience and expectations
Processing Sensations and Perceptions (part 3)
All our senses:
Receive sensory stimulation, often using specialized receptor cells
Transform that stimulation into neural impulses
Deliver the neural information to our brain
Transduction
Conversion of one form of energy into another
In sensation, the transforming of stimulus energies, such as sights, sounds, and smells, into neural impulses our brain can interpret
Processing Sensations and Perceptions (part 4)
Absolute threshold
The minimum stimulus energy needed to detect a particular stimulus 50 percent of the time
Tested by defining the point where half the time a stimulus is detected and half the time it is not
Gustav Fechner (1801–1887), a German scientist and philosopher, studied our awareness of these faint stimuli.
Processing Sensations and Perceptions (part 5)
Signal detection theory
Predicts how and when we will detect a faint stimulus (signal) amid background stimulation (noise)
Individual thresholds vary depending on the strength of the signal and on our experience, expectations, motivation, and alertness.
Absolute Threshold (part 1)
Absolute threshold: Minimum stimulation needed to detect a particular stimulus 50% of the time
Can see a far away light in the dark, feel the slightest touch
Subliminal: Input below the absolute threshold for conscious awareness
Priming: Activating, often unconsciously, associations in our mind, thereby setting us up to perceive, remember, or respond to objects or events in certain ways
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Absolute Threshold (part 2)
Can I detect this sound? An absolute threshold is the intensity at which a person can detect a stimulus half the time. Hearing tests locate these thresholds for various frequencies.
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Processing Sensations and Perceptions (part 6)
Difference threshold: Minimum difference that a person can detect between any two stimuli half the time
Increases with stimulus size
A 5-decibel increase in volume will be noticed at a starting point of 40 decibels, but not at 110 decibels
Experienced as a just noticeable difference (JND)
Weber’s law: For an average person to perceive a difference, two stimuli must differ by a constant minimum percentage (not a constant amount).
The exact proportion varies, depending on the stimulus.
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Subliminal Persuasion
Subliminal stimuli are those that are too weak to detect 50 percent of the time; they are below the absolute threshold.
Subliminal sensation exists, but such sensations are too fleeting to enable exploitation with subliminal messages.
Subliminal persuasion may produce a fleeting and subtle but not powerful or enduring effect on behavior (Greenwald, 1992).
Experiments disprove claims of the effectiveness of subliminal advertising and self-improvement.
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Sensory Adaptation
Sensory adaptation
Is diminished sensitivity as a consequence of constant stimulation
Aids focus by reducing background chatter
Influences how the world is perceived in a personally useful way
Our sensory receptors are sensitive to novelty; sensory adaptation even influences how we perceive emotions.
We perceive the world not exactly as it is, but as it is useful for us to perceive it.
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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?). (From Butler et al., 2008.)
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Perceptual Set
Perceptual set: Mental tendencies and assumptions that affect (top-down) what we hear, taste, feel, and see.
What determines our perceptual set?
Schemas organize and interpret unfamiliar information through experience.
Preexisting schemas influence top-down processing of ambiguous sensation interpretation, including gender stereotypes.
Perceptions are influenced, top-down, not only by our expectations and by the context, but also by our emotions and motivation.
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Context Effects
A given stimulus may trigger different perceptions because of the immediate context.
CULTURE AND CONTEXT EFFECTS
What is above the woman’s head? In one classic study, nearly all the East Africans who were questioned said the woman was balancing a metal box or can on her head and that the family was sitting under a tree. What do you think Westerners said?
A given stimulus may trigger different perceptions, partly because of a differing perceptual set, but also because of the immediate context. Westerners, for whom corners and boxlike architecture were more common, were more likely to perceive the family as being indoors, with the woman sitting under a window. (Gregory & Gombrich, 1973.)
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Motivation and Emotion
Perceptions are also influenced by our motivation and emotions.
Walking destinations look farther away when we are fatigued.
Slopes look steeper when we are wearing a heavy backpack (or after listening to sad, heavy classical music).
Water bottles look closer when we are thirsty.
Emotions and motives also influence our social perceptions.
Light Energy and Eye Structures
Wavelength: Distance from the peak of one light wave or sound wave to the peak of the next. Electromagnetic wavelengths vary from the short blips of cosmic rays to the long pulses of radio transmission.
Intensity: Amount of energy in a light wave or sound wave, which influences what we perceive as brightness or loudness. Intensity is determined by the wave’s amplitude (height).
Hue: Dimension of color that is determined by the wavelength of light; what we know as the color names blue, green, and so forth.
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The Stimulus: Light Energy
What is seen as light is only a thin slice of the broad spectrum of electromagnetic energy.
The portion visible to humans extends from the shorter waves of blue-violet light to the longer waves of red light.
Other organisms are sensitive to differing portions of the spectrum; bees, for instance, cannot see what we perceive as red but can see ultraviolet light.
The perceived hue in a light depends on its wavelength, and its brightness depends on its intensity.
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The Wavelengths We See
What we see as light is only a tiny slice of a wide spectrum of electromagnetic energy, which ranges from gamma rays as short as the diameter of an atom to radio waves over a mile long. The wavelengths visible to the human eye extend from the shorter waves of blue-violet light to the longer waves of red light.
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The Physical Properties of Light Waves
Waves vary in wavelength, the distance between successive peaks. Frequency, the number of complete wavelengths that can pass a point in a given time, depends on the length of the wave. Wavelength determines the perceived color of light.
Waves also vary in amplitude, the height from peak to trough (top to bottom). This wave amplitude influences the brightness of colors (light waves), as well as the loudness of sounds (sound waves).
The shorter the wavelength, the higher the frequency. Wavelength determines the perceived color of light and the pitch of sound.
Physical energy seen as light:
Wavelength: Distance from one wave peak to the next.
Hue: Color experienced.
Amplitude: Height.
Intensity: Amount of contained energy; influences brightness.
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Light Energy and Eye Structures (part 1)
The eye
Cornea: Portion of the eye through which light passes (to the pupil and lens) and is bent to help provide focus
Pupil: A small adjustable opening through which the light then passes
Iris: A colored muscle surrounding the pupil that controls its size
Lens: Focuses incoming light rays onto an image on the retina on the eyeball’s sensitive inner surface
After entering the eye and being focused by a lens, light energy particles strike the eye’s inner surface, the retina.
Light Energy and Eye Structures (part 2)
The retina
Contains two types of receptors: rods and cones
Has layers of neurons that begin the processing of visual information
Accommodation
The process by which the eye’s lens changes shape to focus near or far objects on the retina
The Eye
Light rays reflected from a candle pass through the cornea, pupil, and lens.
The curve and thickness of the lens change to bring nearby or distant objects into focus on the retina.
Rays from the top of the candle strike the bottom of the retina. Those from the left side of the candle strike the right side of the retina.
The candle's image appears on the retina upside down and reversed.
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The Eye-to-Brain Pathway
Light-energy particles trigger chemical reactions in receptor cells, rods and cones, that form an outer layer of cells of the retina at the back of the eye.
Rods: Retinal receptors that detect black, white, and gray; sensitive to movement; necessary for peripheral and twilight vision (when cones don’t respond)
Cones: Receptors concentrated near the center of the retina; function in daylight or well-lit conditions; detect fine detail and color
The Retina’s Reaction to Light
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Rods and Cones
Cones are sensitive to detail and color.
Rods are sensitive to faint light.
| 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 |
Rods detect black, white, and gray, and are necessary for peripheral and twilight vision.
Cones are clustered near the center of the retina; they detect fine detail and allow color vision.
Light energy triggers chemical changes in the rods and cones, which activate the bipolar cells.
These cells then activate the ganglion cells of the optic nerve, which transmits the neural impulses from the eye to the brain.
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Information Processing in the Eye and Brain
Retinal processing
Optic nerve: Carries neural impulses from the eye to the brain
Blind spot: The point at which the optic nerve leaves the eye, where no receptor cells are located
Fovea: The central focal point in the retina, around which the eye’s cones cluster
Pathway From the Eyes to the Visual Cortex
Ganglion axons forming the optic nerve run to the thalamus, where they synapse with neurons that run to the visual cortex.
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Color Processing
Color processing is a two-stage process:
Young-Helmholtz trichromatic theory: The retina’s red, green, and blue cones respond in varying degrees to different color stimuli.
Hering’s opponent-process theory: Cones’ responses are then processed by opponent-process cells.
Feature Detection
Feature detectors: Specialized nerve cells in the brain that respond to specific features of the stimulus, such as shape, angle, or movement
These cells receive information from the ganglion cells in the retina.
They pass the information to other cortical areas, where teams of cells (supercell clusters) respond to more complex patterns.
Face Recognition Processing
In social animals such as humans, a large right temporal lobe area (shown here in a right-facing brain) is dedicated to the crucial task of face recognition.
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Parallel Processing (part 1)
Parallel processing: The brain’s ability to do many things at once
A visual scene is first divided into subdimensions.
Perceptions are constructed by integrating separate but parallel subdimensions.
Parallel Processing (part 2)
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 subdimensions into the perceived image.
The brain divides the work of processing into subdimensions—motion, form, depth, color—and works on each aspect simultaneously (Livingstone & Hubel, 1988).
How does the brain do this? The answer to this question is the Holy Grail of vision research.
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Perceptual Organization
Gestalt: An organized whole
Gestalt psychologists propose principles used to organize sensations into meaningful wholes.
In perception, the whole may exceed the sum of its parts.
We filter incoming information and construct perceptions.
Form Perception (part 1)
How do we organize and interpret the shapes and colors into meaningful perceptions?
People tend to organize pieces of information into an organized whole, or gestalt.
A Necker cube
What do you see: circles with white lines, or a cube?
If you stare at the cube, you may notice that it reverses location, moving the tiny X in the center from the front edge to the back.
At times the cube may seem to float forward, with circles behind it.
At other times, the circles may become holes through which the cube appears, as though it were floating behind them.
There is far more to perception than meets the eye. (From Bradley et al., 1976.)
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Form Perception (part 2)
Figure-ground: The organization of the visual field into objects (the figures) that stand out from their surroundings (the ground)
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Form Perception (part 3)
Grouping: The perceptual tendency to organize stimuli into coherent groups
Proximity: Grouping nearby figures together
Continuity: Perceiving smooth, continuous patterns, rather than discontinuous ones
Closure: Filling in gaps to create a complete, whole object
Grouping
Human minds use these grouping strategies to see patterns and objects.
Proximity: We group nearby figures together. We see not six separate lines, but three sets of two lines.
Continuity: We perceive smooth, continuous patterns rather than discontinuous ones. This pattern could be a series of alternating semicircles, but we perceive it as two continuous lines—one wavy, one straight.
Closure: We fill in gaps to create a complete, whole object. Thus, we assume that the circles on the left are complete but partially blocked by the (illusory) triangle. Adding nothing more than little line segments to close off the circles prompts your brain to construct a triangle.
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Depth Perception
Depth perception: The ability to see objects in three dimensions, although the images that strike the retina are two-dimensional
Allows us to judge distance
Is present, at least in part, at birth in humans and other animals
The Visual Cliff
Test of early 3-D perception
Most infants refuse to crawl across the visual cliff
Crawling, no matter when it begins, seems to increase an infant's fear of heights
Depth cue: Pattern on floor
Visual cliff: Eleanor Gibson and Richard Walk devised this miniature cliff with a glass-covered drop-off to determine whether crawling infants and newborn animals can perceive depth. Even when coaxed, infants are reluctant to venture onto the glass over the cliff.
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Depth Perception (part 1)
Binocular cues
Two eyes help with perception of depth
Retinal disparity
Binocular cue for perceiving depth
By comparing images from the retinas in the two eyes, the brain calculates distance
Used by 3-D film makers
Retinal disparity: Binocular cue for perceiving depth.
By comparing images from the two eyes, the brain computes distance.
The greater the disparity (difference) between the two images, the closer the object.
Retinal disparity can differentiate between 1 and 10 feet away, but not between 10 and 100 feet.
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Depth Perception (part 2)
Monocular cues
Depth cue, such as interposition or linear perspective, available to either eye alone
Relative height
Relative size
Interposition
Linear perspective
Light and shadow
Relative motion
Motion perception
Stroboscopic movement
Phi phenomenon
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Perceptual Constancy (part 1)
Perceptual constancy: Objects are perceived as unchanging (having consistent color, brightness, shape, and size), even as illumination and retinal images change.
Perceptual Constancy (part 2)
Color and brightness constancies
Color constancy: Perceiving familiar objects as having consistent color, even if changing illumination alters the wavelengths reflected by the objects
Brightness constancy: Similarly depends on context
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Shape and Size Constancies
Shape constancy: Perceiving the form of familiar objects as constant even when our retinas receive changing images of them
Size constancy: Perceiving objects as having constant size even when distance from them varies
An opening door looks more and more like a trapezoid, yet we still perceive it as a rectangle.
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Experience and Visual Perception
Restored vision and sensory restriction
The effects of sensory restriction on infant cats, monkeys, and humans suggest there is a critical period for normal sensory and perceptual development.
Without stimulation, normal connections do not develop.
Perceptual adaptation
Ability to adjust to an artificially displaced or even inverted visual field
Early nurture sculpts what nature has endowed.
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The Nonvisual Senses: Hearing
Sound waves: From the environment into the brain
Sound waves compress and expand air molecules
Ears detect these brief pressure changes
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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.
Differences in the waves’ height, or amplitude, also create differing degrees of loudness.
The Stimulus Input: Sound Waves (part 1)
Audition: The sense or act of hearing
Amplitude (height) determines intensity (loudness) in sound waves
Length (frequency) determines the pitch
Frequency: The number of complete wavelengths that pass a point in a given time (for example, per second)
Pitch: A tone’s experienced highness or lowness; depends on frequency
Sound is measured in decibels (dB)
Low frequency = long wavelength = low pitch
Decibels
0 dB: The absolute threshold (not the absence of sound, just less than humans can hear)
60 dB: Normal conversation
85+ dB: Prolonged exposure can cause hearing loss
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The Physical Properties of Sound Waves
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The Stimulus Input: Sound Waves (part 2)
Sound waves are bands of compressed and expanded air.
Human ears detect these changes in air pressure and transform them into neural impulses, which the brain decodes as sound.
Sound waves vary in amplitude, which is perceived as differing loudness, and in frequency, which is experienced as differing pitch.
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The Ear
Vibrating air (sound waves) enter the outer ear and pass through the auditory canal to the eardrum.
Middle ear: Chamber between the eardrum and cochlea; contains three tiny bones that amplify the vibrations of the eardrum
Cochlea: A coiled, bony, fluid-filled tube in the inner ear; contains nerve receptors
Inner ear: Innermost part of the ear; contains the cochlea, semicircular canals, and vestibular sacs
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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, a coiled, fluid-filled tube in the inner ear.
Ripples in the fluid of the cochlea 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.
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Transforming Sound Energy Into Neural Messages
Hear here: How we transform sound waves into nerve impulses that our brain interprets. (a) The outer ear funnels sound waves to the eardrum. The bones of the middle ear (hammer, anvil, and stirrup) amplify and relay the eardrum’s vibrations through the oval window into the fluid-filled cochlea. (b) As shown in this detail of the middle and inner ear, the resulting pressure changes in the cochlear fluid cause the basilar membrane to ripple, bending the hair cells on its surface. Hair cell movements trigger impulses at the base of the nerve cells, whose fibers converge to form the auditory nerve. That nerve sends neural messages to the thalamus and on to the auditory cortex.
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The Ear
Sensorineural hearing loss (nerve deafness)
Damage to cell receptors or associated nerves
Conduction hearing loss
Damage to the mechanical system that conducts sound waves to the cochlea
Cochlear implant: A device for converting sounds into electrical signals and stimulating the auditory nerve through electrodes threaded into the cochlea.
A neural response is triggered when the tiny bundles of cilia on top of even one of the 16,000 hair cells on the cochlea are moved even the width of an atom!
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Perceiving Loudness, Pitch, and Location (part 1)
Responding to loud and soft sounds
The brain interprets loudness base on the number of activated receptors.
Soft tones activate fewer hair cells.
People who lose all hearing in one ear often have difficulty locating sounds.
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Perceiving Loudness, Pitch, and Location (part 2)
Hearing different pitches
Place theory in hearing: Theory that links the pitch heard with the place where the cochlea’s membrane is stimulated; best explains high pitches
Frequency theory (temporal theory) in hearing: Theory that the rate of nerve impulses traveling up the auditory nerve matches the frequency of a tone, thus enabling its pitch to be sensed; explains low pitches
Some combination of the place and frequency theories seems to explain the pitches in the intermediate range.
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How We Locate Sounds
Sound waves strike one ear sooner and more intensely than the other.
From this information, our brain can compute the sound’s location.
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The Other Senses: Touch
Sense of touch is actually a mix of four distinct skin senses:
Pressure
Warmth
Cold
Pain
Other skin sensations are variations of these basic four.
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Pain
Women are more sensitive to pain than men.
Pain sensitivity depends on genes, physiology, experience, attention, and surrounding culture.
Gate-control theory: The spinal cord contains a neurological “gate” that either blocks pain signals or allows them to pass on to the brain.
The “gate” is opened by the activity of pain signals traveling up nerve fibers; it is closed by activity in larger fibers or by information coming from the brain.
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Biopsychosocial Approach to Pain
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The Pain Circuit
Sensory receptors (nociceptors) respond to potentially damaging stimuli by sending an impulse to the spinal cord, which passes the message to the brain, which interprets the signal as pain.
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Controlling Pain
Placebo: Reduces CNS attention and responses to pain
Distraction: Draws attention away from painful stimulation
fMRI scans reveal virtual reality play reduces the brain’s pain-related activity.
Hypnosis
Social influence theory
Dissociation: Dual processing; sensory information does not reach areas where pain-related information is processed
Selective attention
Posthypnotic suggestion
The Other Senses: Taste
Like touch, taste:
Involves several basic sensations
Can be influenced by learning, expectations, and perceptual bias
Has a survival function
| 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 |
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Sensory interaction: One sense may influence another
Smell + texture + taste = flavor
Taste
Inside each little bump on the top and sides of the tongue are more than 200 taste buds.
Each bud contains a pore with 50–100 taste receptors.
Each kind of receptor reacts to different types of food molecules and sends messages to the brain.
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The Other Senses: Smell
Olfaction: Experience of smell
Like taste, smell is a chemical sense.
Olfactory receptor cells are located in the olfactory bulb in the nose.
A combination of several odor molecules stimulate different receptors to detect them.
These patterns are interpreted by the olfactory cortex.
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The Sense of Smell
If you are to smell a flower, airborne molecules of its fragrance must reach receptors at the top of your nose. Sniffing swirls air up to the receptors, enhancing the aroma. The receptor cells send messages to the brain’s olfactory bulb, and then onward to the temporal lobe’s primary smell cortex and to the parts of the limbic system involved in memory and emotion.
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.
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Smell (part 1)
The nose knows
Humans have some 20 million olfactory receptors.
A bloodhound has 220 million (Herz, 2007).
Different combinations of receptors identify different smells.
Our brain's circuitry helps explain an odor's power to evoke feelings, memories, and behaviors.
A hotline runs between the brain area that receives information from the nose and brain centers associated with emotions and memories.
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Smell (part 2)
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.
The brain's circuitry for smell also connects with areas involved in memory storage, which helps explain why a smell can trigger a memory.
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The Other Senses: Body Position and Movement
Kinesthesia: System for sensing the position and movement of individual body parts
Interacts with vision
Vestibular sense: Sense of body movement and position, including the sense of balance
Sensory Interaction (part 1)
Senses are not totally separate information channels.
Sensory interaction: The principle that one sense may influence another, as when the smell of food influences taste.
Smell + texture + taste = flavor
Vision + hearing interact
Taste, Smell, and Memory
Information from the taste buds (yellow arrow) 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. The brain’s circuitry for smell (red area) also connects with areas involved in memory storage, which helps explain why a smell can trigger a memory.
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Sensory Interaction (part 2)
Embodied cognition: Influence of bodily sensations, gestures, and other states on cognitive preferences and judgments
Physical warmth may promote social warmth.
Social exclusion can literally feel cold.
Political expressions may mimic body positions.
ESP: Perception Without Sensation?
Most relevant ESP claims
Telepathy, clairvoyance, precognition
ESP is studied by parapsychologists
What do YOU think?
Bem
Nine experiments seemed to suggest participants could anticipate future events
Critics
Methods or analysis viewed as flawed
Most research psychologists and scientists are skeptical
Extrasensory perception (ESP): The controversial claim that perception can occur apart from sensory input, such as through telepathy, clairvoyance, and precognition.
Telepathy: Mind-to-mind communication.
Clairvoyance: Perceiving remote events, such as a house on fire in another state.
Precognition: Perceiving future events, such as an unexpected death in the next month.
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