PSYC

Sensation and Perception

PSYCHOLOGY David G. Myers C. Nathan DeWall Twelfth Edition

Chapter 6

Chapter Overview

 Basic Concepts of Sensation and Perception

 Vision: Sensory and Perceptual Processing  The Nonvisual Senses

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Basic Concepts of Sensation and Perception one continuous process

Sensation  Bottom-up process  Physical sensory system

receives and represents stimuli at the very basic level of sensory receptors

Perception  Top-down mental process of

organizing and interpreting sensory input from experience and expectations

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Bottom –up and Top-down Processing

Bottom – Up Processing

Sensory Driven

Physical Characteristics

No Meaning

Basic

Top – Down Processing

Experience Driven

Meaning Expectation Knowledge

Inside - Out

Complex

Basic Concepts of Sensation and Perception

 Our senses  Receive sensory stimulation, often using specialized

receptor cells  Transform that stimulation into neural impulses  Deliver the neural information to our brain

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? Bottom

–up or Top-dow n

Processing?

Basic Concepts of Sensation and Perception

 Transduction  Conversion of one form of energy into another  In sensation, the transformation of stimulus energies,

such as sights, sounds, and smells, into neural impulses the brain can interpret

 Psychophysics studies the relationships between the physical energy we can detect and its effects on our psychological experiences.

Basic Concepts of Sensation and Perception

 Signal detection theory  Predicts how and when we

will detect a faint stimulus amid background noise.

 Individual absolute thresholds  Vary depending on the

strength of the signal and on our experience, expectations, motivation, and alertness

How much of a stimulus does it take to have a sensation?  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, setting us up to perceive, remember, or respond to objects or events in certain ways

How much of a stimulus does it take to have a sensation?

 Difference threshold (just noticeable difference)  Minimum difference a person can detect between any

two stimuli half the time; increases with stimulus size

 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.

Subliminal Persuasion

 Subliminal stimuli: Stimuli that are too weak to detect 50 percent of the time.

 Subliminal sensation: Sensation that is too fleeting to enable exploitation with subliminal messages.

 Subliminal persuasion: May produce a fleeting, subtle, but not powerful, enduring effect on behavior (Greenwald, 1992).  Experiments discount attempts at subliminal

advertising and self-improvement.

Basic Concepts of Sensation and Perception

 Sensory adaptation  Diminished sensitivity as a consequence of constant

stimulation  Increases focus by reducing background chatter  Influences how the world is perceived in a personally

useful way  Influences emotions

Emotion Adaptation

 Gaze at the angry face on the left for 20 to 30 seconds, then look at the center face (looks scared, yes?).

 Now 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.)

Perceptual Set

• Perceptual set • A mental predisposition to perceive one thing and not

another

• 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.

Perceptual Set: Context Effects

• 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 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?

Perceptual Set: Motivation and Emotion

 Motives give us energy as we work toward a goal. Like context, they can bias our interpretations of neutral stimuli.

 Emotions can move our perceptions in one direction or another.

Can you give examples of motives and emotions in action?

Terms to Learn  Wavelength  Distance from the peak of one light 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 transmissions.

 Hue  Dimension of color that is determined by the wavelength of

light; what we know as the color names blue, green, and so forth.

 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).

Terms to Learn (part 2)

 Retina  The light-sensitive inner surface of the eye, which

contains the receptor rods and cones plus 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

Sensory and Perceptual Processing in Vision  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 blue-violet to the red light wavelengths.

 After entering the eye and being focused by the lens, light energy particles strike the eye’s inner surface, the retina.

 The perceived hue in a light depends on its wavelength; its brightness depends on its intensity.

Light Energy: From the Environment Into the Brain

 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.

 Waves vary in amplitude, the height from peak to trough (top to bottom). Wave amplitude determines the brightness of colors (and the loudness of sounds).

Light Energy: From the Environment Into the Brain

The Anatomy of the Human Eye

The Retina’s Reaction to Light

RODS AND CONES

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Vision: Visual Information Processing

 How does the brain turn light stimuli into useful information about the world?  Collection and

analysis of sensory information

 Linkage of the optic nerve with neurons in the thalamus

Pathway from the eyes to the visual cortex The ganglion axons forming the optic nerve run to the thalamus, where they synapse with neurons that run to the visual cortex.

Information Processing in the Eye and Brain

 Color processing occurs in two stages.  The retina’s red, green, and blue cones respond in

varying degrees to different color stimuli, as suggested by the Young-Helmholtz trichromatic theory.

 Cones’ responses are then processed by opponent- process cells, as Hering’s theory proposed.

Feature Detection

 Feature detection  Nerve cells in the brain respond to specific features of

the stimulus, such as its shape, angle, or movement.

Information Processing in the Eye and Brain

 Hubel and Wiesel Showed brain’s computing system deconstructs and then reassembles visual images

Found specialized occipital lobe neuron cells receive information from ganglion cells and pass to supercell clusters

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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.

Perceptual Organization: Gestalt Principles

 Gestalt psychologists propose principles used to organize sensations into perception.  Form perception  Depth perception  Perceptual constancy

Vision: Visual Organization  How do we organize

and interpret shapes and colors to create meaningful perceptions?

 People tend to organize pieces of information into an organized whole, called a gestalt.

Necker cube

Gestalt Principles: Form Perception

 How do we know where one object begins and another ends?  Figure-ground

 Organization of the visual field into objects that stand out from their surroundings

 Grouping  Perceptual tendency to organize stimuli into meaningful

groups

Grouping: Seeing Gestalts/Wholes

 Human minds use these grouping strategies to see patterns and objects.

Gestalt Principles: 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

Seeing Depth: Binocular Cues

 Binocular cues  Two eyes improve perception of depth

 Retinal disparity  Binocular cue for perceiving depth  The brain calculates distance by comparing images

from the two eyes  Used by 3-D filmmakers

Seeing Depth: Monocular Cues

 Monocular cue  A depth cue, such as interposition or linear

perspective, available to either eye alone  Light and shadow

 Relative motion

 Relative size

 Linear perspective

 Interposition

 Relative height

Motion Perception

 Humans are imperfect at motion perception.  When large and small objects move at the same

speed, the large objects appear to move more slowly.

 Phi phenomenon  An illusion of movement created when two or more

adjacent lights blink on and off in quick succession

Perceptual Constancy

 Objects are perceived as unchanging—having consistent color, brightness, shape, and size— even as illumination and retinal images change.

Color Constancy

 Perceiving familiar objects as having a consistent color, even if changing illumination alters the wavelengths reflected by the object

Relative Luminance

Shape and Size Constancy

 Size constancy  Perception of objects as

having constant size even when our distance from them varies

 Perception of the form of familiar objects as constant even when the retina receives changing images

Experience and Visual Perception: Perceptual Interpretation

 Restored vision and sensory restriction  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 changed sensory input, including

an artificially displaced or even inverted visual field

The Nonvisual Senses: Hearing

 Sound waves: From the environment into the brain  Sound waves

compress and expand air molecules.

 The ears detect these brief 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. Differences in the waves’ height (amplitude) also create differing degrees of loudness.

Hearing: Sound Characteristics

 Amplitude (height) determines the intensity (loudness) of sound waves.

 Length (frequency) determines the pitch.  Sound is measured in decibels (dB).

Hearing: Sound Characteristics

 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.

Hearing: Decoding Sound Waves

 Sound waves strike the eardrum, causing it to vibrate.

 Tiny bones in the middle ear transmit the vibrations 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.

Decoding: Transforming Sound Energy Into Neural Messages

Intensity of Some Common Sounds

Perceiving Loudness, Pitch, and Location

 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 at which nerve impulses travel up the

auditory nerve matches the frequency of a tone, thus enabling its pitch to be sensed; explains low pitches

 Combinations of place and frequency theories  Handle the pitches in the intermediate range

How Do We Locate Sounds?

 Two ears are better than one.  Sound waves strike one ear

sooner and more intensely than they strike the other ear.

 From this information, the brain can compute the sound's location.

The Nonvisual Senses: Touch

 Sense of touch is actually a mix of four distinct skin senses:  Pressure  Warmth  Cold  Pain

 Other skin sensations are variations of the basic four.

Biopsychosocial Approach to Pain

The Pain Circuit

 Sensory receptors (nociceptors) respond to potentially damaging stimuli by sending an impulse to the spinal cord.

 The spinal cord passes the message to the brain, which interprets the signal as pain.

The Nonvisual Senses: Taste

 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

Taste: A Chemical Sense

 Inside each little bump on the top and sides of the tongue are 200-plus taste buds.

 Each bud contains a pore with 50–100 taste receptors.

 Each receptor reacts to different types of food molecules and sends messages to the brain.

The Sense of Smell (Olfaction)

The Nonvisual Senses: Smell

 Smell  A chemical sense  Involves hundreds of

different receptors  Involves odors that can

evoke strong memories

The Nose Knows Humans have 20 million olfactory receptors; a bloodhound has 220 million (Herz, 2007).

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 the sense of smell, which interacts with taste.

The Nonvisual 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

The Nonvisual Senses: Sensory Interaction

 Senses are not totally separate information channels.

 Examples of sensory interaction  Smell + texture + taste = flavor  Vision + hearing

The Nonvisual Senses: Sensory Interaction

 Embodied cognition  Influence of bodily sensations, gestures, and other

states on cognitive preferences and judgments

 Examples  Physical warmth may promote social warmth.  Social exclusion can literally feel cold.  Political expressions may mimic body positions.

Sensory Interaction

 Seeing the speaker forming the words, which Apple’s FaceTime video-chat feature allows, makes those words easier to understand for hard- of-hearing listeners (Knight, 2004).

Thinking Critically: Perception Without Sensation?

 Most relevant ESP claims  Telepathy

 Clairvoyance

 Precognition

 Psychokinesis

What do YOU think?

 Bem  Nine experiments that

suggested participants could anticipate future events

 Critics  Methods or analysis

viewed as flawed

 Most research psychologists and scientists are skeptical