Sensation and PerceptionSensation and Perception

Chapter 3Chapter 3

What is sensation ?What is sensation ?

• Your senses are the gateway through Your senses are the gateway through which your brain receives all which your brain receives all information about it’s environmentinformation about it’s environment

• A natural and automatic processA natural and automatic process• Often taken for granted until it is Often taken for granted until it is

interrupted by injury or illnessinterrupted by injury or illness• People with one nonfunctional sense People with one nonfunctional sense

are amazingly adaptiveare amazingly adaptive

Overlapping Processes: Overlapping Processes: Sensation and PerceptionSensation and Perception

• SensationSensation: the detection and sensing of : the detection and sensing of environmental stimuli (sounds, objects, environmental stimuli (sounds, objects, odors)odors)

• PerceptionPerception: occurs when we integrate, : occurs when we integrate, organize, and interpret sensory organize, and interpret sensory information in a meaningful wayinformation in a meaningful way

• No clear boundary line between the two No clear boundary line between the two processes- psychology often regards the processes- psychology often regards the two processes as a single processtwo processes as a single process

SensationSensation

• All sensation is the result of stimulation of All sensation is the result of stimulation of specialized cells, called specialized cells, called sensory receptors, sensory receptors, by some form of by some form of energyenergy..

• The forms of energy most commonly in The forms of energy most commonly in contact with: light, sound, heat, pressure, contact with: light, sound, heat, pressure, chemical energychemical energy

• Sensory receptors convert forms of energy Sensory receptors convert forms of energy into electric impulses that are transmitted into electric impulses that are transmitted via neurons to the brain.via neurons to the brain.

The SensesThe Senses

• Humans have five basic senses, each Humans have five basic senses, each receptive to a different form of energy:receptive to a different form of energy:– SIGHT: receives light energySIGHT: receives light energy– HEARING: receives sound energy or sound HEARING: receives sound energy or sound

waveswaves– TOUCH: receives mechanical energyTOUCH: receives mechanical energy– SMELL: receives airborne chemical energySMELL: receives airborne chemical energy– TASTE: receives chemical energyTASTE: receives chemical energy

SpecializationSpecialization

• We are constantly bombarded by many We are constantly bombarded by many different forms of energy.different forms of energy.

• Sensory receptors are highly specialized Sensory receptors are highly specialized and sensitive to specific types of energyand sensitive to specific types of energy

• For any type of stimulation to be For any type of stimulation to be sensed, the stimulus energy must first sensed, the stimulus energy must first be in the form to be detected by our be in the form to be detected by our receptor cellsreceptor cells

Sensory ThresholdsSensory Thresholds

• Our senses are specialized in other ways- Our senses are specialized in other ways- we do not have an infinite capacity to we do not have an infinite capacity to detect all levels of energydetect all levels of energy

• To be sensed a stimulus must first be To be sensed a stimulus must first be strong enough to be detected- loud strong enough to be detected- loud enough to be heard, concentrated enough enough to be heard, concentrated enough to be smelled, bright enough to be seento be smelled, bright enough to be seen

• The point where the stimulus is strong The point where the stimulus is strong enough to be detected by activating a enough to be detected by activating a sensory receptor cell is called sensory receptor cell is called thresholdthreshold..

Absolute ThresholdAbsolute Threshold

• The minimum amount of energy in The minimum amount of energy in the environment that a sensory the environment that a sensory system can detect (half the time in system can detect (half the time in trials and research)trials and research)

Galanter’s (1962) Galanter’s (1962) Absolute ThresholdsAbsolute Thresholds

• SenseSense Absolute ThresholdAbsolute Threshold– Vision Vision : A candle flame seen from 30 miles : A candle flame seen from 30 miles

away on a clear, dark nightaway on a clear, dark night– Hearing:Hearing: The tick of a watch at 20 feetThe tick of a watch at 20 feet– Taste:Taste: 1 teaspoon of sugar in 2 gallons 1 teaspoon of sugar in 2 gallons

of waterof water– SmellSmell ;;1 drop of perfume through-out a 1 drop of perfume through-out a

3-room apartment3-room apartment– Touch ; Touch ; A bee’s wing falling on your cheek A bee’s wing falling on your cheek

from a height of about ½ inchfrom a height of about ½ inch

Difference ThresholdDifference Threshold

• The smallest possible difference The smallest possible difference between two stimuli that can be between two stimuli that can be detected half the timedetected half the time

• Also called Also called just noticeable difference just noticeable difference (jnd)(jnd)

• The difference threshold will vary; it The difference threshold will vary; it is not a constant , even for a specific is not a constant , even for a specific sensory system sensory system

Weber’s LawWeber’s Law

• A principle of sensationA principle of sensation• For each sense, the size of the just For each sense, the size of the just

noticeable difference (difference noticeable difference (difference threshold) is a constant proportion of threshold) is a constant proportion of the size of the initial stimulusthe size of the initial stimulus

• Whether we can detect a change in Whether we can detect a change in the strength of the stimulus depends the strength of the stimulus depends on the intensity of the on the intensity of the originaloriginal stimulusstimulus

Sensory AdaptationSensory Adaptation

• A gradual decline in sensitivity to a A gradual decline in sensitivity to a constant stimulusconstant stimulus

Subliminal PerceptionSubliminal Perception

• Refers to the perception of stimuli that are Refers to the perception of stimuli that are below the threshold of conscious perception below the threshold of conscious perception or awarenessor awareness

• Can subliminal messages in advertising and Can subliminal messages in advertising and self-help tapes change people’s behavior?self-help tapes change people’s behavior?

• Psychologists have found that the effects of Psychologists have found that the effects of subliminal stimuli tend to be weak or short-subliminal stimuli tend to be weak or short-lived, usually lasting only seconds or minutes.lived, usually lasting only seconds or minutes.

VisionVision

• The sense organ for vision is the eye, The sense organ for vision is the eye, which contains receptor cells that are which contains receptor cells that are sensitive to the physical energy of sensitive to the physical energy of light.light.

• The most important sense to humansThe most important sense to humans• Light is one of many different kinds of Light is one of many different kinds of

magnetic energy that travels in the form magnetic energy that travels in the form of wavesof waves

• Other forms of electromagnetic energy Other forms of electromagnetic energy include X-rays, the microwave oven, and include X-rays, the microwave oven, and ultraviolet light (sunburn)ultraviolet light (sunburn)

Eye Structure: Anatomy and Eye Structure: Anatomy and FunctionsFunctions

• See an object- light waves reflected See an object- light waves reflected from the object enter your eye and from the object enter your eye and pass through the pass through the cornea, pupilcornea, pupil, and , and lenselense..

CorneaCornea

• A clear membrane that covers the A clear membrane that covers the front of the eye, helps gather and front of the eye, helps gather and direct incoming lightdirect incoming light

PupilPupil

• Black opening in the middle of the Black opening in the middle of the eyeeye

IrisIris

• Surrounds the pupil, the colored Surrounds the pupil, the colored structure that we refer to when we structure that we refer to when we say someone has brown or blue eyessay someone has brown or blue eyes

• Consists of a ring of muscles that Consists of a ring of muscles that contracts or expands to precisely contracts or expands to precisely control the size of the pupil and the control the size of the pupil and the amount of light entering the eyeamount of light entering the eye

LensLens

• Behind the pupil is the Behind the pupil is the lenslens, a transparent , a transparent structure held in place by structure held in place by ciliary musclesciliary muscles

• The lens thickens and thins to bend or focus The lens thickens and thins to bend or focus incoming light (incoming light (accommodationaccommodation))

• Abnormally shaped eyeballs cause improper Abnormally shaped eyeballs cause improper focus of incoming light on the retinafocus of incoming light on the retina

• This results in a visual disorder- This results in a visual disorder- nearsightedness, farsightedness, or nearsightedness, farsightedness, or astigmatismastigmatism

Nearsightedness- MyopiaNearsightedness- Myopia

• Light from a distant object is focused Light from a distant object is focused on the front of the retinaon the front of the retina

Farsightedness- HyperopiaFarsightedness- Hyperopia

• Light from an object or image close Light from an object or image close by is focused behind the retinaby is focused behind the retina

• PresbyopiaPresbyopia: during middle age, : during middle age, another form of farsightedness another form of farsightedness caused when the lens becomes caused when the lens becomes brittle and inflexiblebrittle and inflexible

AstigmatismAstigmatism

• An abnormally curved eyeball results An abnormally curved eyeball results in blurry vision for lines in a in blurry vision for lines in a particular directionparticular direction

• Corrected with glasses that intercept Corrected with glasses that intercept and bend the light so that the image and bend the light so that the image falls properly on the retinafalls properly on the retina

The RetinaThe Retina

• A thin, light-sensitive membrane that A thin, light-sensitive membrane that lies at the back of the eye, covering lies at the back of the eye, covering most of its inner surfacemost of its inner surface

• Contains two types of receptors for Contains two types of receptors for light: light: rodsrods and and conescones

• When exposed to light, rods and When exposed to light, rods and cones undergo a chemical reaction cones undergo a chemical reaction that results in a neural signalthat results in a neural signal

RodsRods

• Long and thin with blunt endsLong and thin with blunt ends

• The eye contains about 125 million The eye contains about 125 million rods located in the outer edge of the rods located in the outer edge of the retinaretina

• Specialized function: they are very Specialized function: they are very sensitive to light sensitive to light

• We rely on them for our vision in dim We rely on them for our vision in dim light and at nightlight and at night

ConesCones

• About 6 million per eye located in a small About 6 million per eye located in a small central region of the retina (central region of the retina (foveafovea))

• Cones respond differently to different Cones respond differently to different wave lengths, or colors, of lightwave lengths, or colors, of light

• Responsible for color vision Responsible for color vision • Each cone responds to either red, green, Each cone responds to either red, green,

or blue wavelengthsor blue wavelengths• Cones are very sensitive to small features Cones are very sensitive to small features

in the environment; visual acuityin the environment; visual acuity

Processing Visual Information-Processing Visual Information-from the retina to the brainfrom the retina to the brain

• Rods and cones connect to specialized Rods and cones connect to specialized neurons called neurons called bipolar cellsbipolar cells

• The bipolar cells then funnel the The bipolar cells then funnel the collected raw data on to the collected raw data on to the ganglion ganglion cellscells

• Ganglion cells are specialized neuronsGanglion cells are specialized neurons

• There are one million ganglion cellsThere are one million ganglion cells

How is the information How is the information transmitted from the ganglion transmitted from the ganglion cells of the retina to the brain?cells of the retina to the brain?• The one million axons of the ganglion The one million axons of the ganglion

cells are bundled together to form the cells are bundled together to form the optic nerve, optic nerve, which carries messages which carries messages from each eye to the brainfrom each eye to the brain

• The place where the axons of the The place where the axons of the ganglion cells join to form the optic ganglion cells join to form the optic nerve is called the nerve is called the blind spotblind spot – – an area an area that contains no photo receptors and is that contains no photo receptors and is insensitive to lightinsensitive to light

Optic ChiasmOptic Chiasm

• After the nerve fibers that make up the After the nerve fibers that make up the optic nerve leave the eyes, they optic nerve leave the eyes, they separate, and some of them cross to the separate, and some of them cross to the other side of the head at the other side of the head at the optic optic chiasm.chiasm.

• The nerve fibers from the right side of The nerve fibers from the right side of each eye travel to the right hemisphere each eye travel to the right hemisphere of the brain; those from the left side of of the brain; those from the left side of the eye travel to the left hemispherethe eye travel to the left hemisphere

Neural pathways in the Neural pathways in the brainbrain

• thalamus- thalamus- processes information processes information about form, color, brightness, and about form, color, brightness, and depthdepth

• midbrainmidbrain- processes information - processes information about the location of an objectabout the location of an object

• visual cortex: visual cortex: processes information processes information about form- such as angels, lines, about form- such as angels, lines, movement and distance of objectsmovement and distance of objects

Color Vision: 3 Properties of Color Vision: 3 Properties of Color Color

• Humans can see a range of colorsHumans can see a range of colors

• 1.Hues1.Hues: different colors we see; varies with : different colors we see; varies with the wavelength of lightthe wavelength of light

• 2.Saturation2.Saturation: vividness or richness of the : vividness or richness of the hue (purity)hue (purity)

• 3.Brightness:3.Brightness: perceived intensity perceived intensity

• The color of an object is determined by the The color of an object is determined by the wavelength of light that the object reflects.wavelength of light that the object reflects.

Color and other speciesColor and other species

• Many animals have some color vision:Many animals have some color vision:– Trichromats: can see all hues-(humans, Trichromats: can see all hues-(humans,

monkeys, apes)monkeys, apes)– Dichromats: can only see reds or greens, Dichromats: can only see reds or greens,

blues or yellows (most mammals)blues or yellows (most mammals)– Monochromats: completely color blind Monochromats: completely color blind

(reptiles, fish, insects, shellfish)(reptiles, fish, insects, shellfish)

HearingHearing

• SoundSound is air in motion is air in motion

• When an object vibrates, it causes When an object vibrates, it causes the air around it to move in wavesthe air around it to move in waves

• Waves travel 700 MPHWaves travel 700 MPH

• Humans detect vibrations of a Humans detect vibrations of a frequency between 30 and 20,000 frequency between 30 and 20,000 hertzhertz (cycles per second) (cycles per second)

3 Dimensions of Sound3 Dimensions of Sound

• PitchPitch- determined by the frequency - determined by the frequency of soundof sound

• LoudnessLoudness- the result of the sound’s - the result of the sound’s intensity, or energyintensity, or energy

• TimbreTimbre- the nature of the sound, or - the nature of the sound, or the “shape”the “shape”

The Ear: Structure and The Ear: Structure and TransductionTransduction

• The ear is divided into three areas: The ear is divided into three areas: outer, middle, innerouter, middle, inner

• OUTER EAROUTER EAR: : – Sounds enters through flap- Sounds enters through flap- pinnapinna– Sounds travels through the air-filled Sounds travels through the air-filled

auditory canalauditory canal

Middle EarMiddle Ear

• Sound enters middle ear – hits Sound enters middle ear – hits tympanictympanic membranemembrane (eardrum) which vibrates with (eardrum) which vibrates with soundsound

• Behind the eardrum- 3 small bones- Behind the eardrum- 3 small bones- hammer, anvil, stirruphammer, anvil, stirrup

• Stirrup vibrates onto the Stirrup vibrates onto the oval windowoval window, a , a membrane which covers an opening in the membrane which covers an opening in the middle earmiddle ear

Inner Ear Inner Ear

• CochleaCochlea- transmits auditory - transmits auditory information, contains 3 separate fluid-information, contains 3 separate fluid-filled canalsfilled canals

• Canals spiral inside the cochlea, which Canals spiral inside the cochlea, which wraps around like a snail’s shellwraps around like a snail’s shell

• Cochlea comprises the Cochlea comprises the CortiCorti- organ - organ which contains auditory receptor cellswhich contains auditory receptor cells

Conductive DeafnessConductive Deafness

• Conductive deafness:Conductive deafness: ear is not ear is not carrying sounds from the outer ear to carrying sounds from the outer ear to the inner portionthe inner portion

• Bones of inner ear may be damaged, orBones of inner ear may be damaged, or

• may be an accumulation of dirt in the may be an accumulation of dirt in the earear

• Person will be equally deaf to high and Person will be equally deaf to high and low toneslow tones

Nerve DeafnessNerve Deafness

• Person has hard time hearing high -Person has hard time hearing high -pitched tonespitched tones

• Damage to the auditory nervous Damage to the auditory nervous systemsystem

• Hair cells in the cochlea may be Hair cells in the cochlea may be damaged- can no longer transduce damaged- can no longer transduce vibrations of the cochlea fluid into vibrations of the cochlea fluid into neural impulsesneural impulses

TouchTouch

• Skin has 4 main senses of touch: Skin has 4 main senses of touch: Cutaneous Cutaneous senses-senses- cold, warmth, pressure, pain cold, warmth, pressure, pain

• Free nerve fibers-Free nerve fibers- responsible for temperature responsible for temperature sensation- an increase in body temperature elicits sensation- an increase in body temperature elicits a responsea response

• Pressure-sensitive cellsPressure-sensitive cells: cells create receptor : cells create receptor potentials when skin is bent or deformedpotentials when skin is bent or deformed

• Basket nerve endingBasket nerve ending: structure that sense : structure that sense pressure at the roots of hairspressure at the roots of hairs

• Pacinian corpusclesPacinian corpuscles: respond when one feels : respond when one feels deep pressure, such as in a massagedeep pressure, such as in a massage

Taste (Gustation)Taste (Gustation)

• Taste receptors: sensitive to sweet, sour, Taste receptors: sensitive to sweet, sour, bitter, salty tastesbitter, salty tastes

• SalivaSaliva- food enters mouth, mixes with liquid- food enters mouth, mixes with liquid• Solution flows into tiny “holes” in the tongue: Solution flows into tiny “holes” in the tongue:

taste porestaste pores• Each pore contains slim, hair like structures Each pore contains slim, hair like structures

which are part of the taste budwhich are part of the taste bud• When stimulated, receptor potential formsWhen stimulated, receptor potential forms• Nerves pass from tongue to the brain- tastes Nerves pass from tongue to the brain- tastes

have different patterns of neural activityhave different patterns of neural activity

Smell (Olfaction)Smell (Olfaction)

• The sense of smell is entwined with tasteThe sense of smell is entwined with taste• Sense of smell can evoke distant memories Sense of smell can evoke distant memories

and has connection to the temporal lobeand has connection to the temporal lobe• Stimulus for smell is air-born chemicalsStimulus for smell is air-born chemicals• Olfactory receptors-Olfactory receptors- lie beneath nose in two lie beneath nose in two

patches of mucous membranespatches of mucous membranes• Chemicals in the air dissolve in the mucous Chemicals in the air dissolve in the mucous

and stimulate olfactory hair cells, and stimulate olfactory hair cells, ciliacilia• Olfactory mucosaOlfactory mucosa- contains free nerve - contains free nerve

endings that sense noxious substances like endings that sense noxious substances like ammonia ammonia

Sensory DeprivationSensory Deprivation

• What would you do if you couldn’t What would you do if you couldn’t sense anything at all?sense anything at all?

• Sensory deprivation studies:Sensory deprivation studies:– 1. external stimuli kept to a minimum 1. external stimuli kept to a minimum

(sound proof room with no light)(sound proof room with no light)– 2. changing or distorting the subject’s 2. changing or distorting the subject’s

environment (may hear a constant environment (may hear a constant buzzing)buzzing)

– 3. a monotonous environment, with no 3. a monotonous environment, with no change in stimulichange in stimuli

Sensory Deprivation in Sensory Deprivation in AdultsAdults

• Standard symptoms: (depending on Standard symptoms: (depending on type of deprivation)type of deprivation)

• Problems thinking clearly and Problems thinking clearly and concentrating, and score low on concentrating, and score low on intelligence testsintelligence tests

• Difficulty counting above 20Difficulty counting above 20

• Hallucinate Hallucinate

Sensory Deprivation in Sensory Deprivation in InfantsInfants

• When infants are deprived at critical When infants are deprived at critical stages of development, they may stages of development, they may never develop normal abilitiesnever develop normal abilities

• Orphanage babies vs. Nursing home Orphanage babies vs. Nursing home babiesbabies