Sensation and Perception

Psychology: An IntroductionCharles A. Morris & Albert A. Maisto

© 2005 Prentice Hall

Sensation and Perception

Chapter 3



Sensation vs. PerceptionSensation

The experience of sensory stimulationPerception

The process of creating meaningful patterns from raw sensory information



The Nature of Sensation



The Basic ProcessReceptor cells

Specialized cells that respond to a particular type of energy

Doctrine of specific nerve energiesOne-to-one relationship between stimulation

of a specific nerve and the resulting sensory experience

For example, applying pressure with your finger to your eye results in a visual experience



Sensory Thresholds Absolute threshold

The minimum amount of energy that can be detected 50% of the time



Absolute Thresholds Taste: 1 gram (.0356 ounce) of table salt in 500

liters (529 quarts) of water Smell: 1 drop of perfume diffused throughout a

three-room apartment Touch: the wing of a bee falling on your cheek

from a height of 1cm (.39 inch) Hearing: the tick of a watch from 6 meters (20

feet) in very quiet conditions Vision: a candle flame seen from 50km (30

miles) on a clear, dark night



Sensory ThresholdsSensory adaptation

An adjustment of the senses to the level of stimulation they are receiving

Difference thresholdThe smallest change in stimulation that can

be detected 50% of the timeAlso called the just noticeable difference



Sensory ThresholdsWeber’s Law

States that the difference threshold is a constant proportion of the specific stimulus

Senses vary in their sensitivity to changes in stimulation



Subliminal PerceptionThe notion that we may respond to stimuli

that are below our level of awarenessResearch shows that the effect only

occurs in controlled laboratory studiesResearch outside the laboratory shows no

significant effect of subliminal information



Extrasensory PerceptionRefers to extraordinary perception such as

Clairvoyance – awareness of an unknown object or event

Telepathy – knowledge of someone else’s thoughts or feelings

Precognition – foreknowledge of future eventsResearch has been unable to conclusively

demonstrate the existence of ESP



Vision



The Visual System Cornea

Transparent protective coating over the front of the eye

Pupil Small opening in the

iris through which light enters the eye

Iris Colored part of the eye



The Visual System Lens

Focuses light onto the retina

Retina Lining of the eye

containing receptor cells that are sensitive to light

Fovea Center of the visual

field



Receptor CellsCells in the retina that are sensitive to lightVisual receptors are called rods and cones



Receptor CellsRods

About 120 million rodsRespond to light and darkVery sensitive to lightProvide our night vision

ConesAbout 8 million conesRespond to color as well as light and darkWork best in bright lightFound mainly in the fovea



Receptor Cells Bipolar cells

Receive input from receptor cells

Ganglion cells Receive input from

bipolar cells Blind spot

Area where axons of ganglion cells leave the eye



AdaptationDark adaptation

Increased sensitivity of rods and cones in darkness

Light adaptationDecreased sensitivity of rods and cones in

bright lightAfterimage

Sense experience that occurs after a visual stimulus has been removed



From Eye to Brain Optic nerve

Made up of axons of ganglion cells

carries neural messages from each eye to brain

Optic chiasm Point where part of

each optic nerve crosses to the other side of the brain



Color VisionProperties of color

Hue – refers to colors such as red and greenSaturation – refers to the vividness of a hueBrightness – the nearness of a color to white



Theories of Color VisionAdditive color mixing

Mixing of lights of different huesLights, T.V., computer monitors (RGB)

Subtractive color mixingMixing pigments, e.g., paints



Theories of Color VisionTrichromatic theory

Three different types of conesRedGreenBlue-violet

Experience of color is the result of mixing of the signals from these receptors

Can account for some types of colorblindness



Forms of Colorblindness Approximately 10% of

men and 1% of women have some form of colorblindness

Dichromats People who are blind to

either red-green or blue-yellow

Monochromats People who see no color at

all, only shades of light and dark



Theories of Color VisionTrichromatic theory cannot explain all

aspects of color visionPeople with normal vision cannot see

“reddish-green” or “yellowish-blue”Color afterimages



Theories of Color VisionOpponent-process theory

Three pairs of color receptorsYellow-blueRed-greenBlack-white

Members of each pair work in oppositionCan explain color afterimages

Both theories of color vision are valid



Color Vision in Other SpeciesOther species see colors differently than

humansMost other mammals are dichromatsRodents tend to be monochromats, as are

owls who have only rodsBees can see ultraviolet light



Hearing



Sound Sound waves

Changes in pressure caused by molecules of air moving

Frequency Number of cycles per

second in a wave, measured in Hertz (Hz)

Frequency determines pitch



Sound Amplitude

Magnitude (height) of sound wave

Determines loudness, measured in decibels (dB)

Overtones Multiples of the basic tone

Timbre Quality of texture of sound



The Ear Eardrum Middle ear

Contains three small bones; the hammer, anvil, and stirrup

These bones relay and amplify the incoming sound waves



The Ear Oval window

Membrane between middle ear and inner ear

Cochlea Part of inner ear

containing fluid that vibrates

This causes the basilar membrane to vibrate



The Ear Basilar membrane

Membrane in the cochlea which contains receptor cells, called hair cells

Auditory nerve Connection from ear to

brain Provides information

to both sides of brain



Theories of HearingPlace theory

Pitch is determined by location of vibration along the basilar membrane

Frequency theoryPitch is determined by frequency hair cells

produce action potentialsVolley Principle

Pattern of sequential firing determines pitch



Hearing DisordersAbout 28 million people have some form of

hearing damage in the U.S.Can be caused by

InjuryInfectionsExplosionsLong-term exposure to loud noises



The Other Senses



Smell Detecting common odors

Odorant binding protein is released and attached to incoming molecules

These molecules then activate receptors in the olfactory epithelium

Axons from those receptors project directly to the olfactory bulb



SmellWomen have a better sense of smell than

menAnosmia

Complete loss of the ability to smell



Smell Pheromones

Used by animals as a form of communication Provides information about identity Also provides information about sexual receptivity

Pheromones stimulate the vomeronasal organ (VNO)

Information from the VNO is sent to a special part of the olfactory bulb used for pheromonal communication



TasteFour basic tastes

SweetSaltySourBitter

Recent discovery of fifth tasteUmami



Taste Receptor cells are

located in taste buds Taste buds are

located in papillae on the tongue

Chemicals dissolve in saliva and activate receptors



The Other Senses



Kinesthetic SensesKinesthetic senses provide information

about speed and direction of movementStretch receptors sense muscle stretch and

contractionGolgi tendon organs sense movement of

tendons



Vestibular SensesVestibular senses provide information

about equilibrium and body positionFluid moves in two vestibular sacsVestibular organs are also responsible for

motion sicknessMotion sickness may be caused by

discrepancies between visual information and vestibular sensation



The Skin SensesSkin is the largest sense organThere are receptors for pressure,

temperature, and painTouch appears to be important not just as

a source of information, but as a way to bond with others



PainServes as a warning about injury or other

problemLarge individual differences in pain

perceptionGate control theory

Neurological “gate” in spinal cord which controls transmission of pain to brain



Pain Biopsychosocial theory

Holds that pain involves not just physical stimulus, but psychological and social factors as well

Placebo effect Shows that when a person believes a medication

reduces pain, their pain is often reduced even though no medication was given

Pain relief is likely the result of endorphin release



PainAlternative approaches

HypnosisSelf-hypnosisAccupuncture



Perception



Perceptual Organization Figure-ground

We perceive a foreground object (figure) against a background (ground)

Animals may look like the background they inhabit as a way of destroying figure-ground distinction



Perceptual Organization Other principles of

organization Proximity Similarity Closure Continuity



Perceptual Organization Perceptual Constancy

Our tendency to perceive objects as stable and unchanging despite changing sensory information

Size constancy Shape constancy Brightness constancy Color constancy



Perception of Distance and Depth

Monocular cues – those that require only one eye Aerial perspective Texture gradient Linear perspective Motion parallax Superposition



Perception of Distance and Depth

Binocular cues – those that require both eyesRetinal disparityConvergence



Localizing Sounds We use both monaural

and binaural cues Loudness

Louder sounds are perceived as being closer

Time of arrival Sounds will arrive at one

ear sooner than the other This helps determine

direction of the sound



Perception of MovementApparent movement

Illusion that still objects are movingAutokinetic illusion

Perceived motion of a single objectStroboscopic motion

Created by a rapid series of still picturesPhi phenomenon

Apparent motion created by lights flashing in sequence



Visual Illusions Occur because of

misleading cues in the stimulus

Gives rise to false perceptions



Individual Differences and Culture in Perception

MotivationOur desires or needs shape our current

perceptionsValuesExpectationsCognitive StyleExperience and CulturePersonality

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Sensation and Perception