Chapter 3

Copyright © 2008 Allyn & BaconCopyright © 2008 Allyn & Bacon

Chapter 3Chapter 3Sensation and Sensation and PerceptionPerception

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Chapter 3 OverviewChapter 3 Overview

The process of sensationThe process of sensation VisionVision HearingHearing Smell and tasteSmell and taste The skin sensesThe skin senses Balance and movementBalance and movement Influences on perceptionInfluences on perception Principles of perceptionPrinciples of perception Unusual perceptual experiencesUnusual perceptual experiences


The Process of The Process of SensationSensation SensationSensation is the process through is the process through

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

PerceptionPerception is the process by which is the process by which the brain actively organizes and the brain actively organizes and interprets sensory informationinterprets sensory information


What is the difference What is the difference between the absolute between the absolute threshold and the threshold and the difference threshold?difference threshold? What isWhat is the softest sound you can hear the softest sound you can hear

and the dimmest light you can see?and the dimmest light you can see? How much must the volume be turned How much must the volume be turned

up or down for you to notice a up or down for you to notice a difference in the loudness of music?difference in the loudness of music?

Researchers in sensory psychology Researchers in sensory psychology have performed many experiments to have performed many experiments to answer these kinds of questionsanswer these kinds of questions


Absolute thresholdAbsolute threshold

The minimum The minimum amount of sensory amount of sensory stimulation that stimulation that can be detected can be detected 50% of the time50% of the time


Difference thresholdDifference threshold

The smallest increase or decrease in a The smallest increase or decrease in a physical stimulus physical stimulus required to produce a difference in sensation that is noticeable 50% of the time

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


Weber’s Law

The JND for all senses depends on a proportion or percentage of stimulus change rather than on a fixed amount of change– A 2% change is needed for a JND in a weight

you are holding a 1 lb difference is needed for a JND in a 50 lb weight a 2 lb difference is needed for a JND in a 100 lb

weight

– Only a 0.33% change is needed for a JND in the pitch of a sound

– Weber’s law best applies to people with average sensitivities and to stimuli that are not too strong or weak


How does transduction enable How does transduction enable the brain to receive sensory the brain to receive sensory information?information? Sensory receptors Sensory receptors are highly specialized cells are highly specialized cells

in the sense organs that detect and respond to in the sense organs that detect and respond to one type of sensory stimuli and transduce one type of sensory stimuli and transduce (convert) the stimuli into neural impulses(convert) the stimuli into neural impulses

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

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


VisionVision

Our eyes respond to light Our eyes respond to light in the in the visible spectrumvisible spectrum– The band of The band of

electromagnetic waves electromagnetic waves visible to the human eyevisible to the human eye

Electromagnetic waves Electromagnetic waves are measured in are measured in wavelengthswavelengths– The distance from the peak The distance from the peak

of a light wave to the peak of a light wave to the peak of the next waveof the next wave


How does each part of the How does each part of the eye function in vision?eye function in vision?

CorneaCornea– Tough, transparent Tough, transparent

protective layer that protective layer that covers front of eyecovers front of eye

– Bends light rays Bends light rays inward through the inward through the pupilpupil

LensLens– Transparent disk-Transparent disk-

shaped structure shaped structure behind the iris and behind the iris and pupilpupil

– Changes shape as it Changes shape as it focuses on objects at focuses on objects at varying distancesvarying distances

This process is calledThis process is called AccommodationAccommodation


How does each part of the How does each part of the eye function in vision?eye function in vision?

RetinaRetina– Contains sensory Contains sensory

receptors for visionreceptors for vision RodsRods

– Receptor cells that allow Receptor cells that allow eye to respond to low eye to respond to low levels of lightlevels of light

ConesCones– Receptor cells that Receptor cells that

enable us to see color enable us to see color and fine detailand fine detail

FoveaFovea– Area at center of retina Area at center of retina

that provides the that provides the clearest and sharpest clearest and sharpest visionvision

Blind spotBlind spot– Point in each retina Point in each retina

where there are no rods where there are no rods or conesor cones


What path does visual What path does visual information take from the information take from the retina to the primary visual retina to the primary visual cortex?cortex? Optic nerveOptic nerve

– Caries visual Caries visual information from each information from each retina to both sides of retina to both sides of the brainthe brain

Primary visual Primary visual cortexcortex– Part of the brain in Part of the brain in

which visual which visual information is information is processedprocessed

– Feature detectorsFeature detectors respond to specific respond to specific visual patterns, such visual patterns, such as lines or anglesas lines or angles


How do we detect the How do we detect the difference between one color difference between one color and another?and another?

An apple’s skin looks red An apple’s skin looks red because it absorbs short because it absorbs short wavelengths and reflects wavelengths and reflects long wavelengthslong wavelengths

HueHue– The specific color The specific color

perceivedperceived SaturationSaturation

– The purity of a colorThe purity of a color BrightnessBrightness

– The intensity of the light The intensity of the light energy that is perceived as energy that is perceived as a colora color


What two major theories What two major theories attempt to explain color attempt to explain color vision?vision? Trichromatic TheoryTrichromatic Theory

– Three types of cones in the retina each Three types of cones in the retina each make a maximal response to one of three make a maximal response to one of three colors- blue, green, or redcolors- blue, green, or red

Opponent-Process TheoryOpponent-Process Theory– Three kinds of cells respond by increasing Three kinds of cells respond by increasing

or decreasing their rate of firing when or decreasing their rate of firing when different colors are presentdifferent colors are present

Red/green cellsRed/green cells Yellow/blue cellsYellow/blue cells White/black cellsWhite/black cells


A negative afterimageA negative afterimage


HearingHearing

Sound requires a medium, such Sound requires a medium, such as air or water, through which to as air or water, through which to movemove

First demonstrated by Robert First demonstrated by Robert Boyle in 1660Boyle in 1660– Watch in a jar experimentWatch in a jar experiment


What determines the pitch and What determines the pitch and loudness of sound, and how is loudness of sound, and how is each quality measured?each quality measured? FrequencyFrequency

– The number of cycles completed by a sound wave The number of cycles completed by a sound wave in one secondin one second

– Determines the pitch of a soundDetermines the pitch of a sound– Frequency is measured in Frequency is measured in hertzhertz (Hz) (Hz)

AmplitudeAmplitude– The loudness of soundThe loudness of sound– Amplitude is measured in Amplitude is measured in decibelsdecibels (dB) (dB)

TimbreTimbre– The distinctive quality of a sound that distinguishes The distinctive quality of a sound that distinguishes

it from other sounds of the same pitch and it from other sounds of the same pitch and loudnessloudness

– Example: A piano and guitar sound different when Example: A piano and guitar sound different when playing the same noteplaying the same note


Decibel levels of various Decibel levels of various soundssounds

Figure 3.5The loudness of a sound (its amplitude) is measured in decibels. Each increase of 10 decibels makes a sound 10 times louder. A normal conversation at 3 feet measuresabout 60 decibels, which is 10,000 times louder than a soft whisper of 20 decibels. Any exposure to sounds of 130 decibels or higher puts a person at immediate risk for hearing damage, but levels as low as 90 decibels can cause hearing loss if one is exposed to them over long periods of time.


How do the outer ear, middle How do the outer ear, middle ear, and inner ear function in ear, and inner ear function in hearing?hearing? Outer earOuter ear

– Visible part of the ear, Visible part of the ear, consisting of the pinna and consisting of the pinna and auditory canalauditory canal

Middle earMiddle ear– Contains the ossicles, Contains the ossicles,

which connect the ear which connect the ear drum to the oval window drum to the oval window and amplify sound wavesand amplify sound waves

Inner ear Inner ear – Cochlea:Cochlea: Fluid filled Fluid filled

chamber that contains the chamber that contains the basilar membrane and hair basilar membrane and hair cellscells

– Hair cells: Hair cells: Sensory Sensory receptors for hearingreceptors for hearing


What two major theories What two major theories attempt to explain hearing?attempt to explain hearing?

Place theoryPlace theory– Each individual pitch is determined by the Each individual pitch is determined by the

particular location along the basilar particular location along the basilar membrane of the cochlea that vibrates the membrane of the cochlea that vibrates the mostmost

– Provides a good explanation of how we hear Provides a good explanation of how we hear sounds with frequencies higher than 1000 Hzsounds with frequencies higher than 1000 Hz

Frequency theoryFrequency theory– Hair cell receptors vibrate the same number Hair cell receptors vibrate the same number

of times per second as the wave sounds that of times per second as the wave sounds that reach themreach them

– Provides a good explanation of how we hear Provides a good explanation of how we hear low-frequency soundslow-frequency sounds


Smell and TasteSmell and Taste

OlfactionOlfaction– The sense of smellThe sense of smell

GustationGustation– The sense of tasteThe sense of taste


What path does a smell What path does a smell message take from the nose to message take from the nose to the brain?the brain?

Olfactory epitheliumOlfactory epithelium– Two 1-inch square Two 1-inch square

patches of tissue, one patches of tissue, one at the top of each nasal at the top of each nasal cavity, which contain cavity, which contain olfactory neuronsolfactory neurons

Olfactory bulbsOlfactory bulbs– Two structures above Two structures above

the nasal cavity where the nasal cavity where smell sensations first smell sensations first register in the brainregister in the brain

Orbitofrontal cortexOrbitofrontal cortex– Receives messages Receives messages

from olfactory bulbs via from olfactory bulbs via the the thalamusthalamus


What are the primary taste What are the primary taste sensations, and how are they sensations, and how are they detected?detected? Traditionally, four primary taste Traditionally, four primary taste

sensations have been recognizedsensations have been recognized– SweetSweet– SourSour– SaltySalty– BitterBitter

Recent research suggests that there is Recent research suggests that there is a fifth taste sensationa fifth taste sensation– UmamiUmami– This sensation is triggered by glutamateThis sensation is triggered by glutamate


What are the primary taste What are the primary taste sensations, and how are they sensations, and how are they detected?detected?

Taste sensations are detected by receptor cells in the Taste sensations are detected by receptor cells in the taste taste budsbuds

Specialized receptors are activated by each flavor (sweet, Specialized receptors are activated by each flavor (sweet, sour, etc.)sour, etc.)– These receptors send separate messages to the brainThese receptors send separate messages to the brain


The Skin SensesThe Skin Senses

Include the senses of touch and Include the senses of touch and painpain

These senses are critical for These senses are critical for survivalsurvival


How does the skin provide How does the skin provide sensory information?sensory information?

When an object touches and depresses When an object touches and depresses the skin it stimulates receptors in the skinthe skin it stimulates receptors in the skin

These receptors send messages through These receptors send messages through nerve connections to the spinal cord, nerve connections to the spinal cord, through the brainstem and midbrain, and through the brainstem and midbrain, and to the to the somatosensory cortexsomatosensory cortex

Areas on the skin vary in sensitivity to Areas on the skin vary in sensitivity to touch, as measured by the touch, as measured by the two-point two-point thresholdthreshold– Areas with greater sensitivity are more Areas with greater sensitivity are more

densely packed with touch receptorsdensely packed with touch receptors


What is the function of pain, and What is the function of pain, and how is pain influenced by how is pain influenced by psychological factors, culture, and psychological factors, culture, and endorphins?endorphins? Pain serves as an early warning system for Pain serves as an early warning system for

many potentially deadly situationsmany potentially deadly situations Pain can be influenced by several Pain can be influenced by several

psychological factorspsychological factors– Focusing attention elsewhere reduces painFocusing attention elsewhere reduces pain– Placebo effectPlacebo effect reduces pain reduces pain– Negative thoughts increase painNegative thoughts increase pain– Some cultures encourage individuals to suppress, Some cultures encourage individuals to suppress,

or exaggerate, emotional reaction to painor exaggerate, emotional reaction to pain EndorphinsEndorphins are the body’s natural are the body’s natural

painkillerspainkillers– They block pain and produce a sense of well-beingThey block pain and produce a sense of well-being


Balance and MovementBalance and Movement

The The kinesthetickinesthetic and and vestibularvestibular senses provide information about senses provide information about where the parts of the body are where the parts of the body are and where the body is located and where the body is located relative to the physical relative to the physical environmentenvironment


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

TheThe kinesthetic sense kinesthetic sense provides provides information about the position of body information about the position of body parts in relation to each other and the parts in relation to each other and the movement of the entire body or its movement of the entire body or its partsparts

This information is detected by This information is detected by receptors in the joints, ligaments, and receptors in the joints, ligaments, and musclesmuscles


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

The The vestibular sensevestibular sense detects movement and the body’s orientation detects movement and the body’s orientation in spacein space

The vestibular sense organs are located in the The vestibular sense organs are located in the semicircular canalssemicircular canals and and vestibular sacsvestibular sacs in the inner ear in the inner ear– These organs sense rotation of the headThese organs sense rotation of the head


Influences on Influences on PerceptionPerception Perception Perception isis the process the process

through which the brain assigns through which the brain assigns meaning to sensationsmeaning to sensations

Perception is influenced by a Perception is influenced by a number of factors, includingnumber of factors, including– AttentionAttention– Prior knowledgePrior knowledge– Cross-modal perceptionCross-modal perception


What is gained and what is What is gained and what is lost in the process of lost in the process of attention?attention? AttentionAttention is the process of sorting through is the process of sorting through

sensations and selecting some of them for sensations and selecting some of them for further processingfurther processing

When attention is focused on some When attention is focused on some sensations, others are missed altogether or sensations, others are missed altogether or misperceivedmisperceived– Inattentional blindnessInattentional blindness occurs when attention is occurs when attention is

shifted from one object to another and we fail to shifted from one object to another and we fail to notice changes in objects not receiving direct notice changes in objects not receiving direct attentionattention

– The The cocktail party phenomenoncocktail party phenomenon shows that we shows that we focus attention on information that is personally focus attention on information that is personally meaningful meaningful


How does prior knowledge How does prior knowledge influence perception?influence perception?

Bottom-up processingBottom-up processing– Information processing in which individual Information processing in which individual

bits of data are combined until a complete bits of data are combined until a complete perception is formedperception is formed

Top-down processingTop-down processing– Information processing in which previous Information processing in which previous

experience and knowledge are applied to experience and knowledge are applied to recognize the whole of a perceptionrecognize the whole of a perception

– Perceptual set Perceptual set is an expectation of what is an expectation of what will be perceived that can affect what is will be perceived that can affect what is perceivedperceived


How does information from How does information from multiple sources aid multiple sources aid perception?perception?

Cross modal perceptionCross modal perception– The process by which the brain integrates The process by which the brain integrates

information from more than one senseinformation from more than one sense– Cross modal perception is used to process Cross modal perception is used to process

complex stimuli such as speechcomplex stimuli such as speech


Principles of Principles of PerceptionPerception A few principles govern A few principles govern

perceptions in all humansperceptions in all humans


What are the principles that What are the principles that govern perceptual govern perceptual organization?organization?

GestaltGestalt principles of perceptual organization principles of perceptual organization– Similarity: Objects that have similar characteristics are perceived as a Similarity: Objects that have similar characteristics are perceived as a

unitunit– Proximity: Objects that are close together are perceived as belonging Proximity: Objects that are close together are perceived as belonging

togethertogether– Continuity: Figures or objects are perceived as belonging together if Continuity: Figures or objects are perceived as belonging together if

they appear to form a continuous patternthey appear to form a continuous pattern– Closure: FClosure: Figures with gaps in them are perceived as complete


What are some of the What are some of the binocular and monocular binocular and monocular depth cues?depth cues? Depth perceptionDepth perception

– The ability to perceive the visual world in The ability to perceive the visual world in three dimensions and to judge distances three dimensions and to judge distances accuratelyaccurately

Binocular depth cuesBinocular depth cues depend on depend on both eyes working togetherboth eyes working together– ConvergenceConvergence– Binocular disparityBinocular disparity

Monocular depth cuesMonocular depth cues can be can be perceived by one eye aloneperceived by one eye alone


Binocular disparityBinocular disparity

Enables most of us to see 3-D images in stereogramsEnables most of us to see 3-D images in stereograms


Monocular depth cuesMonocular depth cues


How does the brain How does the brain perceive motion?perceive motion?

The brain perceives real motion by The brain perceives real motion by comparing the movement of images comparing the movement of images across the retina to reference points across the retina to reference points that it assumes to be stablethat it assumes to be stable

Autokinetic illusionAutokinetic illusion– An unmoving light in a dark room An unmoving light in a dark room

appears to moveappears to move Your eyes are moving, not the lightYour eyes are moving, not the light In the dark, the brain has no stable In the dark, the brain has no stable

reference point to determine what is reference point to determine what is movingmoving


What are three types of What are three types of puzzling perceptions?puzzling perceptions?

Ambiguous figuresAmbiguous figures– The perceptual system tries to resolve the uncertainty The perceptual system tries to resolve the uncertainty

by seeing the figure first one way and then anotherby seeing the figure first one way and then another Impossible figuresImpossible figures

– May not seem unusual until you examine them closely May not seem unusual until you examine them closely and see the impossibilityand see the impossibility


What are three types of What are three types of puzzling perceptions?puzzling perceptions?

IllusionsIllusions– False perceptions or misperceptions of an actual stimulus in the False perceptions or misperceptions of an actual stimulus in the

environmentenvironment Figure c shows the Figure c shows the MMüüller-Lyer illusionller-Lyer illusion Figure d shows the Figure d shows the Ponzo illusionPonzo illusion


Unusual Perceptual Unusual Perceptual ExperiencesExperiences Subliminal perceptionSubliminal perception

– The capacity to perceive and respond The capacity to perceive and respond to stimuli that are presented below to stimuli that are presented below the threshold of awarenessthe threshold of awareness

Extrasensory perception (ESP)Extrasensory perception (ESP)– Gaining information about objects, Gaining information about objects,

events, or another person’s thoughts events, or another person’s thoughts through means other than known through means other than known sensory channelssensory channels


In what ways does In what ways does subliminal perception subliminal perception influence behavior?influence behavior? Research suggests that subliminal Research suggests that subliminal

information can influence information can influence behavior to some degreebehavior to some degree– But it appears to be ineffective at But it appears to be ineffective at

persuading people to buy products persuading people to buy products or vote in certain waysor vote in certain ways


What have studies of ESP What have studies of ESP shown?shown?

Some studies have suggested Some studies have suggested that ESP existsthat ESP exists

But, in almost all cases, attempts But, in almost all cases, attempts to replicate these studies have to replicate these studies have failedfailed– So most psychologists remain So most psychologists remain

skeptical about existence of ESPskeptical about existence of ESP

Chapter 3

Education

Transcript of Chapter 3