kgavura unit 4

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PSYCHOLOGY(9th Edition)

David Myers

PowerPoint SlidesAneeq Ahmad

Henderson State University

Worth Publishers, © 2010

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Sensation and Perception

Chapter 6

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Sensation

Sensing the World:Some Basic Principles Thresholds Sensory Adaptation

Vision The Stimulus Input: Light Energy The Eye Visual Information Processing Color Vision

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Hearing The Stimulus Input: Sound Waves

The Ear

Hearing Loss and Deaf Culture

Other Important Senses Touch

Pain

Taste

Smell

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Perceptual Organization Form Perception

Depth Perception

Motion Perception

Perceptual Constancy

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Perceptual Interpretation Sensory Deprivation and

Restored Vision

Perceptual Adaptation

Perceptual Set

Perception and the Human Factor

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Is There Extrasensory Perception? Claims of ESP

Premonitions or Pretensions?

Putting ESP to Experimental Test

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Sensation & Perception

How do we construct our representations of the external world?

To represent the world, we must detect physical energy (a stimulus) from the

environment and convert it into neural signals. This is a process called sensation.

When we select, organize, and interpret our sensations, the process is called perception.

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Bottom-up Processing

Analysis of the stimulus begins with the sense receptors and works up to the level of

the brain and mind.

Letter “A” is really a black blotch broken down into features by the brain that we perceive as an

“A.”

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Top-Down Processing

Information processing guided by higher-level mental processes as we construct perceptions, drawing on our experience

and expectations.

THE CHT

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Our sensory and perceptual processes work together to help us sort out complex images.

Making Sense of Complexity

“The Forest Has Eyes,” Bev Doolittle

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Sensing the World

Senses are nature’s gift that suit an organism’s needs.

A frog feeds on flying insects; a male silkworm moth is sensitive to female sex-attractant odor; and we as human beings are sensitive to sound frequencies that represent the range of human voice.

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Exploring the Senses

What stimuli cross our threshold for conscious awareness?

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Psychophysics

A study of the relationship between physical characteristics of stimuli and

our psychological experience with them.

Physical WorldPsychological

World

Light Brightness

Sound Volume

Pressure Weight

Sugar Sweet

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Thresholds

Absolute Threshold: Minimum stimulation needed to detect a particular stimulus 50% of the time.

Pro

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of

“Yes”

Resp

on

ses

0.0

0

0

.50

1.0

0

0 5 10 15 20 25 Stimulus Intensity (lumens)

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Subliminal Threshold

Subliminal Threshold: When stimuli are below one’s absolute threshold for conscious awareness.

Kurt Scholz/ Superstock

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Weber’s Law

Two stimuli must differ by a constant minimum percentage (rather than a constant amount), to be perceived as

different. Weber fraction: k = I/I.

StimulusConstant

(k)

Light 8%

Weight 2%

Tone 3%

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Sensory Adaptation

Diminished sensitivity as a consequence of constant stimulation.

Put a band aid on your arm and after awhileyou don’t sense it.

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Now you see, now you don’t

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Vision

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Transduction

In sensation, the transformation of stimulus energy (sights, sounds, smells) into neural

impulses.

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VisibleSpectrum

The Stimulus Input: Light Energy

Bot

h P

hoto

s: T

hom

as E

isne

r

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Physical Characteristics of Light

1. Wavelength (hue/color)

2. Intensity (brightness)

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Wavelength (Hue)

Hue (color) is the dimension

of color determined by the wavelength

of the light.

Wavelength is the distance

from the peak of one wave to the peak of the

next.

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Wavelength (Hue)

Different wavelengths of light resultin different colors.

400 nm 700 nmLong wavelengthsShort wavelengths

Violet Indigo Blue Green Yellow Orange Red

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Intensity (Brightness)

Intensity: Amount of energy in a

wave determined

by the amplitude. It is related to perceived

brightness.

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Intensity (Brightness)

Blue color with varying levels of intensity.As intensity increases or decreases, blue color

looks more “washed out” or “darkened.”

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The Eye

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Parts of the eye

1. Cornea: Transparent tissue where light enters the eye.

2. Iris: Muscle that expands and contracts to change the size of the opening (pupil) for light.

3. Lens: Focuses the light rays on the retina.

4. Retina: Contains sensory receptors that process visual information and sends it to the brain.

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The LensLens: Transparent

structure behind the pupil that changes

shape to focus images on the retina.

Accommodation: The process by which the eye’s lens changes shape to help focus

near or far objects on the retina.

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Retina

Retina: The light-sensitive inner

surface of the eye, containing

receptor rods and cones in addition to layers of other neurons (bipolar,

ganglion cells) that process

visual information.

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Optic Nerve, Blind Spot & Fovea

http://www.bergen.org

Optic nerve: Carries neural impulses from the eye to the brain. Blind Spot: Point where the optic nerve leaves the eye because there are no receptor cells located there. Fovea: Central point in the retina around which the eye’s cones cluster.

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Test your Blind Spot

Use your textbook. Close your left eye, and fixate your right eye on the black dot. Move the page towards your eye and away from

your eye. At some point the car on the right will disappear due to a blind spot.

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Photoreceptors

E.R. Lewis, Y.Y. Zeevi, F.S Werblin, 1969

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Bipolar & Ganglion Cells

Bipolar cells receive messages from photoreceptors and transmit them to ganglion cells, which converge to form the optic nerve.

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Visual Information Processing

Optic nerves connect to the thalamus in the middle of the brain, and the thalamus

connects to the visual cortex.

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Feature Detection

Nerve cells in the visual cortex respond to specific features, such as edges, angles,

and movement.

Ros

s K

inna

ird/

Alls

port

/ Get

ty I

mag

es

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Shape Detection

Specific combinations of temporal lobe activity occur as people look at shoes,

faces, chairs and houses.

Isha

i, U

nger

leid

er, M

artin

and

Hax

by/ N

IMH

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Visual Information Processing

Processing of several aspects of the stimulus simultaneously is called parallel processing. The

brain divides a visual scene into subdivisions such as color, depth, form, movement, etc.

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From Sensation to Recognition

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Color VisionTrichromatic theory: Young and von

Helmholtz suggested that the eye must contain three receptors that are sensitive to

red, blue and green colors.

Blue Green Red

Medium LowMax

Standard stimulus

Comparison stimulus

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Color Blindness

Ishihara Test

Genetic disorder in which people are blind to green or red colors. This supports the

Trichromatic theory.

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Opponent Colors

Gaze at the middle of the flag for about 30Seconds. When it disappears, stare at the dot and report

whether or not you see Britain's flag.

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Hearing

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Hearing

The Stimulus Input: Sound Waves

Sound waves are compressing and expanding air molecules.

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Sound Characteristics

1. Frequency (pitch)2. Intensity

(loudness)

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The Ear

Dr. Fred H

ossler/ Visuals U

nlimited

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The Ear

Outer Ear: Collects and sends sounds to the eardrum.

Middle Ear: Chamber between eardrum and cochlea containing three tiny bones (hammer, anvil, stirrup) that concentrate the vibrations of the eardrum on the cochlea’s oval window.

Inner Ear: Innermost part of the ear, containing the cochlea, semicircular canals, and vestibular sacs.

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Cochlea

Cochlea: Coiled, bony, fluid-filled tube in the inner ear that transforms sound

vibrations to auditory signals.

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Intensity (Loudness)

Intensity (Loudness):

Amount of energy in a wave,

determined by the amplitude, relates to the perceived

loudness.

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Loudness of Sound

70dB

120dB

Richard K

aylin/ Stone/ Getty Im

ages

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Frequency (Pitch)

Frequency (pitch): The dimension of

frequency determined by the wavelength

of sound.

Wavelength: The distance from

the peak of one wave to the peak

of the next.

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Localization of Sounds

Because we have two ears, sounds that reach one ear faster than the other ear

cause us to localize the sound.

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Localization of Sound

1. Intensity differences2. Time differences

Time differences as small as 1/100,000 of a second can cause us to localize sound. The head acts as a “shadow” or partial sound

barrier.

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Touch

The sense of touch is a mix of four distinct skin senses—pressure, warmth, cold, and pain.

Bru

ce A

yers

/ Sto

ne/ G

etty

Im

ages

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Skin Senses

Only pressure has identifiable receptors. All other skin sensations are variations of

pressure, warmth, cold and pain.

Burning hot

Pressure Vibration Vibration

Cold, warmth and pain

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Pain

Pain tells the body that something has gone wrong. Usually pain results from damage to the skin and other tissues. A rare disease exists in

which the afflicted person feels no pain.

Ashley Blocker (right) feels neither painnor extreme hot or cold.

AP Photo/ Stephen M

orton

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Biopsychosocial Influences

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Gate-Control Theory

Melzack and Wall (1965, 1983) proposed that our spinal cord contains neurological “gates” that either block pain or allow it to be sensed.

Gary C

omer/ PhototakeU

SA.com

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Pain Control

Pain can be controlled by a number of therapies including, drugs, surgery, acupuncture, exercise,

hypnosis, and even thought distraction.

Todd R

ichards and Aric V

ills, U.W

. ©

Hunter H

offman, w

ww

.vrpain.com

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Taste

Traditionally, taste sensations consisted of sweet, salty, sour, and bitter tastes. Recently, receptors

for a fifth taste have been discovered called “Umami”.

Sweet Sour Salty Bitter Umami(Fresh

Chicken)

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Sensory Interaction

When one sense affects another sense, sensory interaction takes place. So, the taste of strawberry interacts with its smell and its

texture on the tongue to produce flavor.

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SmellLike taste, smell is a chemical sense.

Odorants enter the nasal cavity to stimulate 5 million receptors to sense smell. Unlike taste,

there are many different forms of smell.

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Smell and Memories

The brain region for smell (in red) is

closely connected with the brain

regions involved with memory (limbic

system). That is why strong memories are

made through the sense of smell.

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Body Position and Movement

The sense of our body parts’ position and movement is called kinesthesis. The

vestibular sense monitors the head (and body’s) position.

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Whirling Dervishes Wire Walk

Bob D

aemm

rich/ The Im

age Works

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Perceptual Organization

How do we form meaningful perceptions from sensory information?

We organize it. Gestalt psychologists showed that a figure formed a “whole”

different than its surroundings.

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Organization of the visual field into objects (figures) that stand out from their

surroundings (ground).

Form Perception

Tim

e Savings S

uggestion, © 2003 R

oger Sheperd.

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Grouping

After distinguishing the figure from the ground, our perception needs to organize the figure into

a meaningful form using grouping rules.

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Grouping & Reality

Although grouping principles usually help us construct reality, they may occasionally lead us

astray.

Both photos by W

alter Wick. R

eprinted from G

AM

ES

Magazine. .©

1983 PCS G

ames L

imited Partnership

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Depth Perception

Visual Cliff

Depth perception enables us to judge distances. Gibson and Walk (1960) suggested that human infants (crawling age) have depth perception. Even newborn animals show depth perception.

Inne

rvis

ions

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Binocular CuesRetinal disparity: Images from the two eyes differ. Try looking at your two index fingers when pointing them

towards each other half an inch apart and about 5 inches directly in front of your eyes. You will see a

“finger sausage” as shown in the inset.

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Monocular Cues

Relative Size: If two objects are similar in size, we perceive the one that casts a

smaller retinal image to be farther away.

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Monocular Cues

Interposition: Objects that occlude (block) other objects tend to be perceived as

closer.R

ene Magritte, The B

lank Signature, oil on canvas, N

ational Gallery of A

rt, Washington. C

ollection of M

r. and Mrs. Paul M

ellon. Photo by Richard C

arafelli.

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Monocular Cues

Relative Height: We perceive objects that are higher in our field of vision to be farther away than those that are

lower.

Image courtesy of S

haun P. V

ecera, Ph. D

., adapted from

stimuli that appered in V

ecrera et al., 2002

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Monocular Cues

Relative motion: Objects closer to a fixation point move faster and in opposing direction to those objects that are farther away from a fixation

point, moving slower and in the same direction.

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Monocular Cues

Linear Perspective: Parallel lines, such as railroad tracks, appear to converge in the distance. The more the lines converge, the

greater their perceived distance.

© T

he New

Yorker C

ollection, 2002, Jack Ziegler

from cartoonbank.com

. All rights reserved.

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Monocular Cues

Light and Shadow: Nearby objects reflect more light into our eyes than more distant objects. Given two identical objects, the dimmer one appears to

be farther away.

From

“Perceiving S

hape From

Shading” by V

ilayaur S

. Ram

achandran. © 1988 by S

cientific Am

erican, Inc. A

ll rights reserved.

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Perceptual Constancy

Perceiving objects as unchanging even as illumination and retinal

images change.

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Perceiving familiar objects as having consistent color even when changing illumination filters

the light reflected by the object.

Color Constancy

Color Constancy

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Size-Distance Relationship

The distant monster (below, left) and the top red bar (below, right) appear bigger

because of distance cues.

From Shepard, 1990

Alan C

hoisnet/ The Im

age Bank

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Size-Distance RelationshipBoth girls in the room are of similar height.

However, we perceive them to be of different heights as they stand in the two corners of the

room.

Both photos from S. Schwartzenberg/ The Exploratorium

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Ames Room

The Ames room is designed to demonstrate the size-distance illusion.

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Lightness Constancy

The color and brightness of square A and B are the same.

Courte

sy E

dwar

d A

delso

n

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Perceptual Interpretation

Immanuel Kant (1724-1804) maintained that knowledge comes from our inborn ways of

organizing sensory experiences.

John Locke (1632-1704) argued that we learn to perceive the world through our

experiences.

How important is experience in shaping ourperceptual interpretation?

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Sensory Deprivation & Restored Vision

After cataract surgery, blind adults were able to regain sight. These

individuals could differentiate figure and ground relationships, yet they had difficulty distinguishing a circle

and a triangle (Von Senden, 1932).

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Facial Recognition

After blind adults regained sight, they

were able to recognize distinct features, but

were unable to recognize faces.

Normal observers also show difficulty in facial recognition when the

lower half of the pictures are changed.

Courtesy of R

ichard LeG

rand

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Kittens raised without exposure to horizontal lines later had difficulty

perceiving horizontal bars.

Blakemore & Cooper (1970)

Sensory Deprivation

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Perceptual Adaptation

Visual ability to adjust to an

artificially displaced visual field, e.g., prism glasses.

Courtesy of H

ubert Dolezal

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Perceptual Set

A mental predisposition to perceive one thing and not another. What you see in the center picture is influenced by flanking pictures.

From

Shepard, 1990.

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(a) Loch ness monster or a tree trunk; (b) Flying

saucers or clouds?

Perceptual Set

Other examples of perceptual set.

Frank Searle, photo Adam

s/ Corbis-Sygm

a

Dick R

uhl

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Is the “magician cabinet” on the floor or hanging from the ceiling?

Context Effects

Context can radically alter perception.

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To an East African, the woman sitting is balancing a metal box on her head, while the family is sitting

under a tree.

Cultural Context

Context instilled by culture also alters perception.

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Perception Revisited

Is perception innate or acquired?

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Is There Extrasensory Perception?

Perception without sensory input is called extrasensory perception (ESP). A large

percentage of scientists do not believe in ESP.

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Claims of ESP

1. Telepathy: Mind-to-mind communication. One person sending thoughts and the other receiving them.

2. Clairvoyance: Perception of remote events, such as sensing a friend’s house on fire.

3. Precognition: Perceiving future events, such as a political leader’s death.