Chapter 3Chapter 3Sensation and Sensation and PerceptionPerception

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 auditory, and other sensory stimuli and transmit them to the stimuli and transmit them to the brainbrain

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

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 the softest sound you can hear and the dimmest light you can hear and the dimmest light you can see?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 difference in the loudness of music?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 amount of sensory 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 The smallest increase or decrease in a physical stimulus decrease in a 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 the smallest change in is the smallest change in sensation that a person is able sensation that a person is able to detect 50% of the timeto detect 50% of the time

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 are highly specialized cells in the sense organs that detect and cells in the sense organs that detect and respond to one type of sensory stimuli and respond to one type of sensory stimuli and transduce (convert) the stimuli into neural transduce (convert) the stimuli into neural impulsesimpulses

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 Our eyes respond to light in the light in the visible visible spectrumspectrum– 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 The distance from the peak of a light wave to peak of a light wave to the peak of the next the peak of the next wavewave

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 protective layer that covers front of that covers front of eyeeye

– 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 focuses on objects at varying distancesat varying distances

This process is This process is calledcalled 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 Receptor cells that allow eye to respond allow eye to respond to low levels of lightto low levels 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 Area at center of

retina that provides retina that provides the clearest and the clearest and sharpest visionsharpest vision

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

where there are no where there are no rods or conesrods or 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 information from each retina to both each retina to both sides of the brainsides of the 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, visual patterns, such as lines or such as lines or anglesangles

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

HueHue– The specific color The specific color perceivedperceived

SaturationSaturation– The purity of a colorThe purity of a color

BrightnessBrightness– The intensity of the The intensity of the light energy that is light energy that is perceived as a colorperceived as a 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 Three types of cones in the retina each make a maximal response to one each make a maximal response to one of three colors- blue, green, or redof three colors- blue, green, or red

Opponent-Process TheoryOpponent-Process Theory– Three kinds of cells respond by Three kinds of cells respond by increasing or decreasing their rate increasing or decreasing their rate of firing when different colors are of firing when different colors are presentpresent

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

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 The number of cycles completed by a sound wave in one secondwave in 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 The distinctive quality of a sound that distinguishes it from other sounds of the distinguishes it from other sounds of the same pitch and loudnesssame pitch and loudness

– Example: A piano and guitar sound Example: A piano and guitar sound different when playing the same notedifferent when playing 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 Visible part of the ear, consisting of the ear, consisting of the pinna and auditory pinna and auditory canalcanal

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 chamber that contains the basilar membrane the basilar membrane and hair cellsand hair cells

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

What two major theories What two major theories attempt to explain attempt to explain hearing?hearing? Place theoryPlace theory

– Each individual pitch is determined by Each individual pitch is determined by the particular location along the the particular location along the basilar membrane of the cochlea that basilar membrane of the cochlea that vibrates the mostvibrates the most

– Provides a good explanation of how we Provides a good explanation of how we hear sounds with frequencies higher than hear sounds with frequencies higher than 1000 Hz1000 Hz

Frequency theoryFrequency theory– Hair cell receptors vibrate the same Hair cell receptors vibrate the same number of times per second as the wave number of times per second as the wave sounds that reach themsounds that reach them

– Provides a good explanation of how we Provides a good explanation of how we hear low-frequency soundshear low-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 message What path does a smell message take from the nose to the take from the nose to the brain?brain?

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

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

Olfactory bulbsOlfactory bulbs– Two structures above Two structures above

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

Orbitofrontal cortexOrbitofrontal cortex– Receives messages Receives messages

from olfactory bulbs from olfactory bulbs via the via 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 Recent research suggests that there is a fifth taste sensationthere is a fifth taste sensation– UmamiUmami– This sensation is triggered by This sensation is triggered by glutamateglutamate

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 Taste sensations are detected by receptor cells in the in the taste budstaste buds

Specialized receptors are activated by each Specialized receptors are activated by each flavor (sweet, sour, etc.)flavor (sweet, 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 Include the senses of touch and painand pain

These senses are critical These senses are critical for survivalfor survival

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 skin it stimulates receptors in the skinthe skin

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

Areas on the skin vary in Areas on the skin vary in sensitivity to touch, as measured by sensitivity to touch, as measured by the the two-point thresholdtwo-point threshold– 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, psychological factors, culture, and endorphins?and 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-They block pain and produce a sense of well-beingbeing

Balance and MovementBalance and Movement

The The kinesthetickinesthetic and and vestibularvestibular senses provide senses provide information about where the information about where the parts of the body are and parts of the body are and where the body is located 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 information about the position of body parts in relation to of body parts in relation to each other and the movement of each other and the movement of the entire body or its partsthe entire body or its parts

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

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 detects movement and the body’s orientation in spacebody’s orientation in 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 in the inner earinner 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 through which the brain assigns meaning to sensationsassigns meaning 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 is the process of sorting through sensations and selecting some through sensations and selecting some of them for further processingof them for further processing

When attention is focused on some When attention is focused on some sensations, others are missed sensations, others are missed altogether or misperceivedaltogether or misperceived– Inattentional blindnessInattentional blindness occurs when occurs when attention is shifted from one object to attention is shifted from one object to another and we fail to notice changes in another and we fail to notice changes in objects not receiving direct attentionobjects not receiving direct attention

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

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

Bottom-up processingBottom-up processing– Information processing in which Information processing in which individual bits of data are combined individual bits of data are combined until a complete perception is formeduntil a complete perception is formed

Top-down processingTop-down processing– Information processing in which Information processing in which previous experience and knowledge are previous experience and knowledge are applied to recognize the whole of a applied to recognize the whole of a perceptionperception

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

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 The process by which the brain integrates information from more integrates information from more than one sensethan one sense

– Cross modal perception is used to Cross modal perception is used to process complex stimuli such as process complex stimuli such as speechspeech

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 Similarity: Objects that have similar characteristics are

perceived as a unitperceived as a unit– Proximity: Objects that are close together are perceived as Proximity: Objects that are close together are perceived as

belonging togetherbelonging together– Continuity: Figures or objects are perceived as belonging together Continuity: Figures or objects are perceived as belonging together

if they appear to form a continuous patternif they 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 The ability to perceive the visual world in three dimensions and to world in three dimensions and to judge distances accuratelyjudge distances accurately

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 Enables most of us to see 3-D images in stereogramsstereograms

Monocular depth cuesMonocular depth cues

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

The brain perceives real motion The brain perceives real motion by comparing the movement of by comparing the movement of images across the retina to images across the retina to reference points that it assumes reference points that it assumes to be stableto 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 The perceptual system tries to resolve the

uncertainty by seeing the figure first one way and uncertainty by seeing the figure first one way and then anotherthen 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 False perceptions or misperceptions of an actual stimulus in the environmentactual stimulus in the environment

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 The capacity to perceive and respond to stimuli that are respond to stimuli that are presented below the threshold of presented below the threshold of awarenessawareness

Extrasensory perception (ESP)Extrasensory perception (ESP)– Gaining information about Gaining information about objects, events, or another objects, events, or another person’s thoughts through means person’s thoughts through means other than known sensory channelsother than known sensory channels

In what ways does In what ways does subliminal perception subliminal perception influence behavior?influence behavior? Research suggests that Research suggests that subliminal information can subliminal information can influence behavior to some influence behavior to some degreedegree– But it appears to be But it appears to be ineffective at persuading ineffective at persuading people to buy products or vote people to buy products or vote in certain waysin 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, But, in almost all cases, attempts to replicate these attempts to replicate these studies have failedstudies have failed– So most psychologists remain So most psychologists remain skeptical about existence of skeptical about existence of ESPESP