© 2007 the mcgraw-hill companies, inc. all rights reserved slide 1 sensation and perception 4

© 2007 The McGraw-Hill Companies, Inc. All Rights Reserved

Slide 1

Sensation and Perception

4


Slide 2

Sensation: Receiving Messages About the World

• Sense organs– See, hear, taste, smell, touch, balance, and

experience the world

– Sensory receptor cells transmit sensation

– Perception – interpreting information and forming images

– Stimulus



Slide 3

Translating Messages for the Brain

• Transduction – translates one form of energy (incoming stimuli) into another (sensory information)

– Receptor cells to neural impulses



Slide 4

Sensory Limits: How Strong Must Messages Be?

• Threshold – lower limits

• Absolute threshold – smallest to be detected

• Difference threshold – smallest difference between 2 stimuli to be detected 50% of time

• Sensory adaptation – one’s sensitivity to a stimulus varies from time to time– Fatigue, inattention, repeated exposure



Slide 5Sensory Thresholds

VisionA candle flame seen at 30 mi. on a clear, dark night

Hearing The tick of a watch under quiet conditions at 20 ft.

TasteOne teaspoon of sugar in 2 gallons of water

Smell1 drop of perfume diffused into the entire volume of a 3 room apartment

TouchThe wing of a bee falling on your cheek from a height of 1 cm


Slide 6

Sensory Limits: How Strong Must Messages Be?

• Psychophysics – studies sensory-related matters

• Weber’s law – amount of change needed for detection 50% of time is always in direct proportion to intensity of original stimulus



Slide 7

Vision: Sensing Light• Light

– Electromagnetic radiation

• Waves - frequency

• Wavelength – determines hues seen

• Intensity – brightness

– The more wavelengths in light, the less saturated or pure its hue is



Slide 8

The Eye: How Does It Work?

• Light passes through cornea

• Iris regulates light through pupil into lens

• Lens held in place by ciliary muscle

• Retina has rods and cones for receptors

Fovea – center of retina

• Visual acuity – clarity and sharpness



Slide 9

The Eye

Cornea

Iris

Pupil

Lens

Ciliary muscle

Retina

Fovea

Optic nerve


Slide 10

Photoreceptors

Cones

Rods


Slide 11

The Eye

• Rods– Not located in fovea

– Responsible for peripheral vision

– Hundreds of times more sensitive to light than cones

– Produce images perceived with less visual acuity than cones

– Do not detect color



Slide 12

The Eye

• Cones– Give brain more precise information

– Code information about color

– Respond only in bright light

• Optic nerve – has no cones or rods

• Blind spot – no visual reception in optic nerve

• Optic chiasm



Slide 13

Vision

Optic chiasm

Optic nerve

Blind spot


Slide 14

Dark and Light Adaptation

• Dark adaptation – Receptors receive new supply of chemicals– After 30 minutes in the dark - level of

sensitivity about 100,000 times greater than in bright light

• Light adaptation– Rods and cones highly responsive – overload– Bleaching out of receptor chemicals occurs



Slide 15

Vision

• Night blindness – vitamin A deficiency

• Color vision– Wavelengths determine colors seen– Any color can be created from combinations of

red, blue, and green

• Trichromatic theory – 3 kinds of cones in eye responding mostly to light in either red, blue, or green range of wavelengths



Slide 16

Trichromtic theory (Young-Helmholtz)


Slide 17

Color Vision

• Color afterimages

– Complementary colors – yellow and blue, red and green

– Prolonged staring causes ghostly afterimage in complementary colors

– Occurs in all for complementary colors



Slide 18

Color Vision

• Opponent-process theory

– Two kinds of color-processing mechanisms receiving messages from three kinds of cones

– Each mechanism responds in opposite ways corresponding to two pairs of complementary colors



Slide 19

Fast FastSlowSlow

Opponent-Process Theory (Hering)


Slide 20

Color Blindness

• Affects about 8% of males, 1% of females

• Partial color blindness – difficulty distinguishing between two colors

– Red-green blindness due to genetic defect

– Yellow-blue blindness due to absence of blue pigment in cones



Slide 21

Color Blindness


Slide 22

Hearing: Sensing Sound Waves

• Audition - detection of sound waves• Frequency of cycles

– Compression – increased density of waves

– Rarefaction – reduced density of waves

– Determines pitch of sound

– Intensity measured in decibel (db) units• Prolonged exposure to over 85 db causes

hearing loss

– Timbre – quality of sound



Slide 23

Maximum level of industrial noise considered safe

Characteristics of Sound Waves

20 40 60 80 100 1600 120 180140

Loud thunder or rock concert

Pain Pain ThresholdThreshold

City bus

Normal conversation

Subway

db

Noisy automobile

Absolute threshold of human hearing

Quiet office

Whisper Rocket launch


Slide 24

The Ear: How Does It Work?• Outer ear

– Pinna – external part of ear that collects sound

– External auditory canal – connects outer and middle ear

• Middle ear– Cardum – tympanic membrane; 1st structure

– Eardrum - outermost structure of middle ear• Passes vibration to interconnected bones

(hammer, anvil, and stirrup)



Slide 25

The Ear

Pinna

External auditory canal

Eardrum

Hammer Anvil

Stirrup

Oval window

Cochlea

Round window

Semicircularcanals

Nerve tobrain

Eustachiantube

Outer ear Middle ear Inner ear


Slide 26

The Ear

Cochlea

Oval window

Round window

Basilar membrane

Hair cells


Slide 27

The Ear: How Does It Work?

• Inner ear– Oval window – eardrumlike structure at end of

cochlea– Round window – eardrumlike structure at other

end of cochlea– Basilar membrane – forms floor for ear’s

sensory receptors– Organ of Corti – contains hairlike receptor cells



Slide 28

Body Sensations: Messages About Myself

• Orientation and movement– Vestibular organ – 2 sets of sensory structures

• Semicircular canals• Saccule and utricle

– Kinesthetic receptors – throughout body

• Skin senses– Pressure sensitivity– Temperature sensitivity



Slide 29

The Skin Senses Pressure

Free nerve endings

Tactile discs

hair

Specialized end bulbs

basket cell around hair

Temperature


Slide 30

BA C D E G

Braille Alphabet H I

U W

F

S T X Y ZV

L NJ K O P Q RM


Slide 31

Pain

• Nerve endings in body act as nocioceptors– Neural messages transmitted along two distinct

pathways• Rapid – detects first pain sensation• Slow – detects second long-lasting pain

– Endorphins and endogenous morphine



Slide 32

Pain

• Nerve endings in body act as nocioceptors– Pain gates regulate pain signals in 3 areas

• Brain stem – gate-control theory of pain• Spinal cord • Peripheral regulation of pain

– Phantom limbs• Up tp 70% of amputees experience this



Slide 33

Direction of pain message

neuro-transmitter molecules in axon of slow-pain neuron

Endorphin receptor

Axon of inhibitory pain gate neuron

endorphin

Neuron in slow-pain fiber

Inhibitory pain gate neuron

Stimulation of endorphin receptors inhibits firing of axon of slow-pain neuron

Close-up view of inhibitory pain gates

Somatosensory area of cortex

Limbric system

Area of pain gates

Pathway of fast-pain fibers

Pathway of slow-pain fibers

Gate-control theory of pain


Slide 34

Human Diversity: Culture and Pain

• Bariba society – cultural emphasis on pain– Tolerate pain easily– Calm response to pain is part of Bariba pride– Pregnant women don’t show labor pain reaction,

experience labor pain and birth alone

• Medical professionals can overestimate or underestimate effects of pain if impact of culture is not considered



Slide 35

Chemical Senses: The Flavors and Aromas of Life

• Senses of gustation (taste) and olfaction (smell) differ from all other senses– Taste cells and papillae on tongue– Taste buds detect


Sweetness - mostly sugars Sourness - mostly acidsSaltiness - mostly saltsBitterness - toxins, chemicalsFattiness - fats


Slide 36

Surface of tongue

Receptor cells

Pore

Bitter

Sour

Salty

Sweet and fatty

Sensory nerve fiber

Taste


Slide 37

Chemical Senses: The Flavors and Aromas of Life

• Olfaction– Olfactory epithelium – top of nasal cavity – Pheromone detection of sweat and urine

• Vomeronasal organ• Influence human female reproductive cycles• Inhalation of male sex hormone and mood

changes• Males may respond to sex hormones



Slide 38

Olfactory nerve to brain

Olfactory epithelium

Nasal cavity


Slide 39

Perception: Interpreting Sensory Messages

• Perception– Some unique aspects in different cultures– There is some common reality in shared world

• Visual perception– Perceptual organization

• Figure-ground • Continuity• Proximity


• Similarity • Closure


Slide 40

Laws of Perceptual Organization

Figure-Ground


Slide 41


Law of Continuity

Law of Proximity


Slide 42


Law of Closure

Law of Similarity


Slide 43

Perception: Interpreting Sensory Messages


• Perceptual Constancy

– Brightness constancy

– Color constancy

– Size constancy

– Shape constancy


Slide 44

Depth Perception

• Retina has two-dimensional surface

• Monocular cues – perception of one eye

– Texture gradient

– Linear perspective

– Superposition

– Shadowing


– Speed of movement

– Aerial perspective

– Accommodation

– Vertical position


Slide 45

Depth PerceptionSensation and Perception

• Binocular cues – perception with two eyes– Convergence– Retinal disparity

• Visual Illusions– Ponzo illusion– Vertical-horizontal

illusion

• Color perception

– Zollner illusion– Moon illusion– Poggendorf illusion


Slide 46

Visual Illusions

The Ponzo Illusion

The Müller - Lyer Illusion


Slide 47

Visual Illusions

Kanizsa square

EDR


Slide 48

Multisensory Integration

• Integrate and interpret information from multiple senses simultaneously– Limited ability and accident occurrence

• Motivation, Emotion, and Perception– Motivation and emotions influence perception

• Past experiences influence all perceptions



Slide 49

The End

4Sensation and Perception

© 2007 the mcgraw-hill companies, inc. all rights reserved slide 1 sensation and perception 4

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