Sensation and Perception

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

© 2005 Prentice Hall

Sensation and Perception

Chapter 3



Sensation vs. Perception

SensationThe experience of sensory stimulation

PerceptionThe process of creating meaningful patterns

from raw sensory information



The Nature of Sensation



The Basic Process

Receptor cellsSpecialized cells that respond to a particular

type of energyDoctrine of specific nerve energies

One-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 thresholdThe 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 Thresholds

Sensory adaptationAn adjustment of the senses to the level of

stimulation they are receiving Difference threshold

The smallest change in stimulation that can be detected 50% of the time

Also called the just noticeable difference



Sensory Thresholds

Weber’s LawStates that the difference threshold is a

constant proportion of the specific stimulusSenses vary in their sensitivity to changes in

stimulation



Subliminal Perception

The notion that we may respond to stimuli that are below our level of awareness

Research shows that the effect only occurs in controlled laboratory studies

Research outside the laboratory shows no significant effect of subliminal information



Extrasensory Perception

Refers to extraordinary perception such asClairvoyance – awareness of an unknown

object or eventTelepathy – knowledge of someone else’s

thoughts or feelingsPrecognition – foreknowledge of future events

Research 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 Cells

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



Receptor Cells

Rods About 120 million rods Respond to light and

dark Very sensitive to light Provide our night

vision

Cones About 8 million cones Respond to color as

well as light and dark Work best in bright

light Found 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



Adaptation

Dark adaptationIncreased sensitivity of rods and cones in

darknessLight adaptation

Decreased sensitivity of rods and cones in bright light

AfterimageSense 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 Vision

Properties of colorHue – 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 Vision

Additive color mixingMixing of lights of different huesLights, T.V., computer monitors (RGB)

Subtractive color mixingMixing pigments, e.g., paints




Trichromatic theoryThree different types of cones

RedGreenBlue-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




Trichromatic theory cannot explain all aspects of color visionPeople with normal vision cannot see

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




Opponent-process theoryThree pairs of color receptors

Yellow-blueRed-greenBlack-white

Members of each pair work in oppositionCan explain color afterimages

Both theories of color vision are valid



Color Vision in Other Species

Other species see colors differently than humans

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

owls who have only rodsBees can see ultraviolet light



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 Hearing

Place theoryPitch is determined by location of vibration

along the basilar membraneFrequency theory

Pitch is determined by frequency hair cells produce action potentials

Volley PrinciplePattern of sequential firing determines pitch



Hearing Disorders

About 28 million people have some form of hearing damage in the U.S.

Can be caused byInjuryInfectionsExplosionsLong-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



Smell

Women have a better sense of smell than men

AnosmiaComplete 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



Taste

Four basic tastesSweetSaltySourBitter

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 Senses

Kinesthetic senses provide information about speed and direction of movementStretch receptors sense muscle stretch and

contractionGolgi tendon organs sense movement of

tendons



Vestibular Senses

Vestibular senses provide information about equilibrium and body position

Fluid 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 Senses

Skin 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



Pain

Serves as a warning about injury or other problem

Large individual differences in pain perception

Gate control theoryNeurological “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



Pain

Alternative approachesHypnosisSelf-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




Other principles of organization Proximity Similarity Closure Continuity




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 Movement

Apparent movementIllusion that still objects are moving

Autokinetic illusionPerceived motion of a single object

Stroboscopic motionCreated by a rapid series of still pictures

Phi phenomenonApparent 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

Sensation and Perception

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