Sensation and Perception

Module 12

Objectives

– Contrast sensation and perception, and explain

the difference between bottom-up processing

and top down processing.

– Distinguish between absolute and difference

threshold.

– To discuss perceptional differences using

theories such as Weber’s Law, JND, signal

detection, etc

How would you define

sensation?

formal definition - immediate

response in the brain caused by

excitation of a sensory organ

What are the sense organs?

Eyes, ears, tongue, skin, and

nose

Based on what we know about

the brain, do all the sense organs

relay information to the same

place?

NO!

How would you define

perception?

formal definition – process by which

we select, organize and interpret

sensations

Read the following passage

• Aoccdrning to rscheearch at Cmabrigde

uinervtisy, it desn’t maettr in what oredr the

ltteers in a word are, the olny iprmoetnt

tihng is that the frist and lsat ltteer be at the

rgiht plcae. The rset can be a toatl mses and

you can still raed it wouthit a porbelm. This

is bcuseae the hmuan mnid deos not raed

ervey lteter by islef, but the word as a

wlohe.

8

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 sensed as a black blotch decomposed into features by the brain and perceived as an “A” by our

mind .

9

Top-Down Processing Information processing guided by higher-level mental processes as we construct perceptions drawing on our experience and expectations.

THE CHT

Subliminal Persuasion

• What is it?

• Why do we believe this exists?

• Popular Movies

– Post Korean War = Manchurian Candidate

– Modern = Long Kiss Goodnight, Bourne Series

Back Masking

• Is

• Here is an example Stairway to Heaven

Localization of function

The principal that the type of

sensation experienced is related to

the area of the brain activated.

How do data reduction systems

work?

One: Our sensory receptors are all biological

transducers…

…meaning they naturally convert energy from

one system into another.

Two: Each sense organ is most sensitive to a

select type and range of energy.

As your sensory receptors transduce

information, they also analyze the

environment before they send the message to

the brain.

This separation of sensory

information into important features

is called sensory analysis.

• Our sensory receptors are pre-tuned to

specific stimulus patterns, called feature

detectors.

• The basic elements of a stimulus, such as

lines, shapes, edges, colors, are called

perceptual features.

• Example: In a series of straight lines, a

diagonal line would stand out to the eye.

Studies have shown that faces

that are more symmetrical are

found to be more attractive.

Based on what we’ve just

discussed, why would that be

true?

Back to the data reduction system…

• Once our sensory receptors have selected

and analyzed information, they must code

it.

• This is when they convert important

features of the world into neural messages

that can be understood by the brain.

• This is called sensory coding.

• These messages are then sent to certain areas of the

brain, which respond according to their function.

• So if someone punches you in the eye, your sensory

receptors in the eye will respond somewhat to

pressure, but they code the information visually, so

you see bright spots and/or flashes of color.

Remember!!

• All of your sensory experiences actually take

place in the brain.

Psychophysics

• The study of the relationship between physical stimuli and the sensations they evoke in a human observer.

• One of the basic questions psychophysics asks is…

• “What is the absolute minimum amount of energy necessary for a sensation to occur?”

20

Psychophysics

A study of the relationship between physical characteristics of stimuli and our psychological

experience of them.

Physical World

Psychological World

Light Brightness

Sound Volume

Pressure Weight

Sugar Sweet

Absolute threshold

• The minimum amount of of physical energy needed to produce a sensation.

• Vision – 3 photons of light

• Equivalent to seeing a candle flame 30 miles away on a clear, dark night (remember this??)

22

No

Detection

Intensity

Absolute Threshold

Detected

Yes Yes No No

Observer’s Response

Tell when you (observer) detect the light.

Difference threshold

• A change in stimulus intensity that is

detectable to an observer.

Just noticeable difference

(JND)

• Any noticeable difference in a stimulus.

24

Difference Threshold Difference Threshold: Minimum difference

between two stimuli required for detection 50% of the time, also called just noticeable difference

(JND). Difference Threshold

Tell when you (observer) detect a difference in the light.

No Observer’s Response

No Yes

25

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.

Stimulus Constant (k)

Light 8%

Weight 2%

Tone 3%

Weber’s Law

• The JND is a constant proportion of the

original stimulus intensity.

• Time for a demonstration!

Do absolute thresholds differ for

different people?

Of course!

Type of stimulus, state of a person’s nervous

system,costs of false “detections” and

emotional states all effect the absolute

threshold, even within the same individual

• Unpleasant stimuli may raise the threshold

for recognition.

• Resistance to perceiving threatening or

disturbing stimuli is called perceptual

defense.

• We process stimuli on more than one level.

• Subliminal perception – perception of a

stimulus below the threshold for conscious

recognition

What do you see at first an old lady or a

young woman?

Optical Illustions

Here is an example

31

Inattentional Blindness Inattentional blindness refers to inability to see a an object or a person amidst an engrossing scene.

Here is an example.

Dan

iel

Sim

ons,

Univ

ersi

ty o

f Il

linois

Change Blindness

• Definition: phenomenon that occurs when a

person viewing a visual scene apparently

fails to detect large changes in the scene

Here is an example

33

Signal Detection Theory (SDT) Predicts how and when we detect the presence of a faint stimulus (signal) amid background

noise (other stimulation). Assumes that there is no single absolute threshold and detection

depends on:

Person’s experience Expectations Motivation Level of fatigue

Caro

l Lee/ T

ony S

tone Im

ages

Signal Detection Theory (SDT)

• Examples:

– Is my phone ringing or is it the phone on the

TV?

– Is this crazy story true?

– (In the car) Is someone squealing tires or is it

the ad on the radio?

– Let’s try an experiment.

35

SDT Matrix

Decision

Yes No

Signal

Present Hit Miss

Absent False

Alarm Correct

Rejection

The observer decides, whether she hears the tone or not, based on the signal being present or not.

This translates into four outcomes.

36

Shape Detection Is

hai

, U

nger

leid

er,

Mar

tin a

nd

Hax

by/

NIM

H

Review of Sensation

Racial and ethnic stereotypes can

sometimes bias our perceptions of others'

behaviors. This best illustrates the impact

of:

A. retinal disparity.

B. interposition.

C. top-down processing.

D. perceptual adaptation.

The fact that perceptions involve

more than the sum of our sensations

best illustrates the importance of:

A. top-down processing.

B. interposition.

C. retinal disparity.

D. visual capture.

Which of the following is TRUE?

A. Humans cannot sense stimuli below the absolute threshold.

B. Humans cannot be affected by stimuli below the absolute threshold at all.

C. Stimuli presented below the absolute threshold can have a subtle, brief effect on behavior.

D. Stimuli presented below the absolute threshold exert a strong, powerful effect on behavior.

If you move your watchband up your

wrist an inch or so, you will feel it for

only a few moments. This best

illustrates:

A. parallel processing.

B. accommodation.

C. sensory adaptation.

D. Weber's law.

Which of the following activities requires

you to use the absolute threshold for

sensation?

A. telling the difference between sweet and

salty

B. detecting a tiny, faint light on a radar screen

C. deciding if two glasses contain the same

amount of water

D. telling if your guitar is in tune

Your roommate, who has trouble

understanding Weber’s Law, asks you,

“How different do two stimuli need to be,

in order for a person to notice the

difference?” You explain that:

A. the stimuli must differ by at least ten percent.

B. the difference threshold decreases with the magnitude of the stimulus.

C. the minimum difference needed for detection depends on the type of stimulus.

D. Weber’s Law does not address this issue.

Vision:Module 13

Objectives

– To introduce the concept of transduction and

the physical characteristics of sight and hearing

that make it possible

– To identify problems that can occur (such as

colorblind and conductive deafness)

– To understand depth cues and retinal disparity.

44

Transduction In sensation, transformation of stimulus energy

into neural impulses.

Phototransduction: Conversion of light energy into neural impulses that brain can understand.

45

Light Characteristics

1. Wavelength (hue/color)

2. Intensity (brightness)

3. Saturation (purity)

46

Wavelength (Hue)

Hue (color): dimension of

color determined by wavelength of

light.

Wavelength the distance from the peak of one wave to the peak of the

next.

47

Wavelength (Hue)

Different wavelengths of light result in different colors.

400 nm 700 nm Long wavelengths Short wavelengths

Violet Indigo Blue Green Yellow Orange Red

48

Intensity (Brightness)

Intensity Amount of energy in a

wave determined by

amplitude; related to perceived

brightness.

49

The Eye

50

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 opening (pupil) for light.

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

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

51

The Lens Lens: Transparent

structure behind 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.

52

The Lens Nearsightedness: A condition in which

nearby objects are seen more clearly than

distant objects.

Farsightedness: A condition in which faraway objects are

seen more clearly than near objects.

53

Retina Retina: The light-

sensitive inner surface of the eye,

containing receptor rods and cones plus

layers of other neurons (bipolar,

ganglion cells) that process visual information.

54

Optic Nerve, Blind Spot & Fovea

http://www.bergen.org

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

55

Photoreceptors

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

56

Bipolar & Ganglion Cells Bipolar cells receive messages from

photoreceptors and transmit them to ganglion cells, which form the optic nerve.

57

Visual Information Processing Optic nerves connect to the thalamus in the

middle of the brain, and the thalamus to the visual cortex.

58

Ganglion & Thalamic Cells Retinal ganglion cells and thalamic neurons

break down visual stimuli into small components and have receptive fields with

center-surround organization.

Action Potentials

ON-center OFF-Surround

Review of the anatomy of the eye

Young-Helmholtz

Trichromatic Theory

As we look at a flower, the intensity

of the color we see is related to the

light wave’s:

A. amplitude.

B. hue.

C. length.

D. placement on the spectrum.

The eye’s “blind spot” is related to:

A. light rays focusing too far in front of the

retina.

B. light rays focusing too far behind the retina.

C. a cluster of cells around the fovea which

contains cones, but no rods.

D. an area without receptor cells where the

optic nerve leaves the eye.

Rather than saying a person is

“colorblind,” it would be more

accurate to say that the person:

A. has a blind spot.

B. lacks red- or green-sensitive cones.

C. is experiencing an overstimulation of the

red- and green-sensitive cones.

D. has an excess of blue-sensitive cones.

Researcher James Hixby (2001) stated,

“We can tell if a person is looking at a

shoe, a chair, or a face, based on the

pattern of their brain activity.” This

statement is relevant to:

A. sensory adaptation.

B. feature detection.

C. opponent-process theory.

D. place theory.

Hearing: Module 14

Objectives

– Describe the three regions of the ear and outline

the series of events that triggers the electrical

impulses sent to the brain

– Contrast place and frequency theories, and

explain how they help us to understand pitch

and perception.

– Describe how cochlear implants function, and

explain shy Deaf culture advocates object to

these devices.

65

The Stimulus Input: Sound Waves

Sound waves are composed of compression and rarefaction of air molecules.

Acoustical transduction: Conversion of sound waves into neural impulses in the hairs cells of the

inner ear.

66

Sound Characteristics

1. Frequency (pitch)

2. Intensity (loudness)

3. Quality (timbre)

67

Frequency (Pitch)

Frequency (pitch): Dimension of

frequency determined by wavelength of

sound.

Wavelength: The distance from the peak of one wave to the peak of the

next.

68

Intensity (Loudness)

Intensity (Loudness):

Amount of energy in a wave

determined by amplitude relates to perceived loudness.

69

Loudness of Sound

70dB

120dB

Rich

ard K

aylin

/ Sto

ne/ G

etty Im

ages

70

Quality (Timbre)

Quality (Timbre): Characteristics of sound from a zither and a guitar allows the ear to distinguish

between the two.

http

://ww

w.1ch

ristian.n

et

ww

w.jam

esjon

esinstru

men

ts.com

Zither

Guitar

71

Overtones

Overtones: Make the distinction among musical instruments possible.

72

The Ear

Dr. F

red H

ossler/ V

isuals U

nlim

ited

74

The Ear Outer Ear: Pinna. Collects sounds.

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.

75

Cochlea

Cochlea: Coiled, bony, fluid-filled tube in the inner ear that transduces sound vibrations to

auditory signals.

76

Theories of Audition

Place Theory suggests that sound frequencies stimulate basilar membrane at specific places

resulting in perceived pitch.

http

://ww

w.p

c.rhu

l.ac.uk

77

Theories of Audition

Frequency Theory states that the rate of nerve impulses traveling up the auditory nerve matches the frequency of a tone, thus enabling us to sense

its pitch.

Sound Frequency

Auditory Nerve Action Potentials

100 Hz 200 Hz

78

Hearing Loss

Conduction Hearing Loss: Hearing loss caused by damage to the mechanical system that conducts sound waves to the cochlea.

Sensorineural Hearing Loss: Hearing loss caused by damage to the cochlea’s receptor cells or to the auditory nerve, also called nerve deafness.

Other Sense: Module 15

Objective

• To identify the functions of taste, touch/pain,

smell and vestibular senses as well as the major

components needed for them to work correctly

(topics include gate theory, pressure stimulation,

taste buds, olfactory nerve, semicircular canals

and vertigo)

80

Gate-Control Theory Melzak and Wall (1965, 1983) proposed that our spinal cord contains neurological “gates” that

either block pain or allow it to be sensed. G

ary C

om

er/ Pho

totak

eUS

A.co

m

Gate Control

Theory

82

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

hypnosis and even thought distraction.

To

dd

Rich

ards an

d A

ric Vills, U

.W.

©H

unter H

offm

an, w

ww

.vrp

ain.co

m

Endorphins and Pain

• Endorphins are the brain’s naturally

occurring opiates

• related to decreased pain perception and an

increased sense of well-being

• euphoria and the famed "runner's high."

Adrenaline and Pain

85

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) Science of Taste

86

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.

Lets try for ourselves!

87

Smell Like taste smell is a chemical sense. Odorants enter the nasal cavity to stimulate 5 millions receptors to sense smell. Unlike taste there are many different

forms of smells.

88

Smell and Memories

Brain region (red) for smell is closely

connected with brain regions (limbic system) involved with memory,

that is why strong memories are made through the sense of

smell.

89

Body Position and Movement The sense of our body parts’ position and

movement is called kinesthesis. And the vestibular sense monitors the head (and body’s) position.

http

://ww

w.h

eyo

kam

agazin

e.com

Whirling Dervishes Wire Walk

Bob D

aemm

rich/ T

he Im

age W

ork

s

Vertigo

• the feeling that you or your environment is

moving or spinning

• describes an illusion of movement

• Benign paroxysmal positional vertigo

(BPPV) is the most common form of

vertigo and is characterized by the sensation

of motion initiated by sudden head

movements or moving the head in a certain

direction

Vertigo

• may also be caused

by inflammation

within the inner ear

(labyrinthitis),

which is

characterized by the

sudden onset of

vertigo and may be

associated with

hearing loss.

What is umami?

A. a taste sensation for which researchers

recently discovered receptors on the tongue

B. receptors on the tongue that respond only to

bitter tastes

C. receptors on the tongue that allow us to taste

nutrients in food, such as proteins and

vitamins

D. a condition in which there is a loss of the

sensation of taste

You are going to design an experiment to

determine whether there are special areas on

the tongue to detect the taste of sweet, or

whether the taste can be detected in all areas

of the tongue. Which of these must be done

before you can start the experiment?

A. operationally define sweet.

B. pick out subjects who like sweet tastes.

C. pick out the items that you will use for sweet tastes.

D. none of these are necessary.

Perceptual Organization

Objectives

– To identify the major Gestalt rules and apply

those rules to everyday examples

– To analyze the use of monocular cues in art to

give the illusion of depth

95

Perceptual Organization When vision competes with other senses vision

usually wins – a phenomenon called visual capture.

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.

96

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 new born animals show depth perception.

Inner

vis

ions

97

Binocular Cues

Retinal disparity: Images from the two eyes differ. Try looking at your two fingers half an inch apart

about 5 inches away. You will see a “finger sausage” as shown in the inset.

98

Binocular Cues

Convergence: Neuromuscular cues. When two eyes move inward (towards the nose) to see near objects, and outward (away from the nose) to see

far away objects.

99

Monocular Cues

Relative Size: If two objects are similar in size, we perceive one that casts a smaller retinal image as

farther away.

100

Monocular Cues

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

Ren

e Mag

ritte, Th

e Bla

nk S

ign

atu

re, oil o

n can

vas,

Natio

nal G

allery o

f Art, W

ashin

gto

n. C

ollectio

n o

f

Mr. an

d M

rs. Pau

l Mello

n. P

ho

to b

y R

ichard

Carafelli.

101

Monocular Cues Relative Clarity: Because light form distant objects passes through more air, we perceive hazy objects

as farther away than sharp clear objects.

102

Monocular Cues

Texture Gradient: Indistinct (fine) texture signals increasing distance.

© E

ric Lessin

g/ A

rt Reso

urce, N

Y

103

Monocular Cues

Relative Height: We perceive objects higher in our field of vision as farther away.

Imag

e cou

rtesy o

f Sh

aun

P. V

ecera, Ph

. D.,

adap

ted fro

m stim

uli th

at app

ered in

Vecrera et al., 2

00

2

104

Monocular Cues

Relative motion: Objects closer to a fixation point move faster and in opposing direction to objects farther away from a fixation point, which move

slower and in the same direction.

Gestalt Principles • Figure and Ground

– Similar elements (figure) are contrasted with dissimilar elements (ground)

to give the impression of a whole

• Closure

– is the tendency of ambiguous perceptual experiences to pop back and forth

unstably between two or more alternative interpretations

– Object is incomplete or the space is not completely closed

• Similarity

– Objects look similar to one another and are often perceived as a group or

pattern.

• Proximity or Contiguity

– Occurs when object are placed close together and tend to be seen as a

group

• Continuity

– Occurs when the eye is compelled to move through one object and

continue to another object

Gestalt Principles

Figure and Ground

Real World

Applications?

Gestalt Principles

Figure and Ground

• Application? Camouflage

Gestalt Principles

Closure

Gestalt Principle

Similarity

Gestalt Principles

Proximity

Gestalt Principles

Continuity

Makers of 3-D movies rely most heavily

on:

A. the visual cliff.

B. the Müller-Lyer illusion.

C. retinal disparity.

D. shape constancy.

As we perceive the environment, we use Gestalt

principles of good form to help organize things

into meaningful groups and forms. In observing a

football game on TV we are immediately able to

recognize the players as members of their

respective teams, regardless of their positions on

the field. Which Gestalt principle is most

responsible for this ability? A. closure

B. proximity

C. similarity

D. continuity

In the same football game, we watch as a team

attempts a field goal. Since the goal posts are

distant and the time to make a decision is short, the

referee must use many perceptual cues to decide

whether the kick is good or not. One important

ability is depth perception. Which of the following

cues might be most helpful in deciding whether the

field goal is successful?

A. linear perspective

B. motion parallax

C. convergence

D. interposition

You are an artist and you are interested in

completing a painting that gives a three-

dimensional appearance. You want to show a

beach in the foreground of the painting, people

swimming in the ocean, and sailboats in the

distance. Which perceptual principles will be most

helpful as you complete your painting?

A. binocular depth cues

B. monocular depth cues

C. Gestalt principles of proximity and continuity

D. perceptual principles only operate in “real life” situations

You are most likely to observe the

phi phenomenon while:

A. looking at a string of Christmas tree lights

that blink quickly in succession.

B. staring at a Necker cube.

C. comparing the size of the moon while its in

the sky to its size near the horizon.

D. attempting to catch fly ball that is quickly

coming toward you.