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Sensation & Perception

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.

2

Bottom-up ProcessingAnalysis of the stimulus begins with the sense

receptors and works up to the level of the brain and mind. ASSOCIATE WITH SENSATION.

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

“A.”

3

Top-Down Processing

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

ASSOCIATE WITH PERCEPTION (schemas also)

THE CHT

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ThresholdsAbsolute Threshold: Minimum stimulation needed

to detect a particular stimulus 50% of the time.P

rop

ort

ion

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 ThresholdSubliminal Threshold: When

stimuli are below one’s absolute threshold for conscious awareness.

Kurt Scholz/ Superstock

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SUBLIMINAL STIMULATION

The priming effect = the activation, often unconsciously, of certain associations, thus predisposing one’s perception, memory, or response.

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WEBER’S LAW

•Weber’s Law JND = KI. To be perceived as different, two stimuli must differ by a constant minimum percentage.

K = constant (see chart from Bernstein)I = intensity

•Major principle: Our thresholds for detecting differences are a roughly constant proportion of the size of the original stimulus)

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Signal Detection Theory (SDT)

Predicts how and when we detect the presence of a faint stimulus (signal) amid

background noise (other stimulation). SDT assumes that there is no single

absolute threshold and detection depends on:

Person’s experienceExpectationsMotivationLevel of fatigue

Carol L

ee/ Tony Stone Im

ages

9

SDT Matrix

Decision

Yes No

Signal

Present Hit Miss

Absent FalseAlarm

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.

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Sensory Adaptation

Diminished sensitivity as a consequence of constant stimulation (unchanging stimulus).

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

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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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Intensity (Brightness)

Intensity Amount of energy in a

wave determined by the amplitude. It is related to

perceived brightness.

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The Eye

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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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The LensNearsightedness: 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.

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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 (rods

and cones) that process visual information and send it to the brain. Rods and cones contain photopigment – chemicals that respond to light.

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RETINAL PROCESSING

The axons of the ganglion cells form the optic nerve (where it leaves the eye, a blind spot is created.

Ganglion cells have a center surround receptive field. How the light hits the center vs the outside helps us to see edges and contrasts between light and dark.

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Visual Information Processing

Optic nerves connect to the thalamus (specific region = LGN the lateral geniculate nucleus)

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

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Feature DetectionNerve cells in the visual cortex respond to specific features hierarchically, such as

edges, angles, and movement. Discovered by Hubel and Wiesal – won

Nobel Prize

Ros

s K

inna

ird/

Alls

port

/ Get

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Visual Information ProcessingProcessing of several aspects of the stimulus

simultaneously is called parallel processing (the opposite of serial processing). The brain divides a visual scene into subdivisions such as color,

depth, form and movement etc.

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SUMMARYColor processing has two stages.

The retina’s red, green, and blue cones respond to different color stimuli in different ratios (Trichromatic Theory).

Then, the nervous system’s ganglion cells with their center surround feature process information on its way to the visual cortex (Opponent-Process Theory) . Afterimage demonstrates

22

VISUAL CAPTURE

• How important is vision?

• Is vision more important than the other senses?

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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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Intensity (Loudness)

Intensity (Loudness):

Amount of energy in a wave,

determined by the amplitude, relates to the perceived

loudness.

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The Ear

Dr. Fred H

ossler/ Visuals U

nlimited

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

vibrations to auditory signals.

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AUDITION

• The cilia or hair cells, respond to ripples in the basilar membrane.

• Auditory nerve sends message to thalamus and then temporal lobe’s auditory cortex

• Loudness determined by the number of activated hair cells.

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Theories of AuditionVon Helmholtz’s Place Theory suggests

that sound frequencies stimulate the basilar membrane at specific places resulting in perceived pitch. Best

explains sensing high pitches.

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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. Best explains low pitches.

SoundFrequency

Auditory NerveAction Potentials

100 Hz200 Hz

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Theories of Audition

• Volley principle: subset of Frequency theory – Alternating firing of neural cells allows to sense very high frequencies.

• Combination of place and frequency theories best explains intermediate range

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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

Timing and Intensity help in localizing sound

• The brain uses parallel processing - processing timing differences and intensity differences as well as other features of sound such as contrast SIMULTANEOUSLY

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Hearing Loss

Conduction Hearing Loss: Hearing loss caused by damage to the mechanical system (3 bones) 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.

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NERVE DEAFNESS

• Often linked to heredity, aging and prolonged exposure to loud sounds

• These tissues cannot be regenerated once dead

• Digital hearing aids little help for nerve deafness

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• DEFINITION: slight enhancement of other senses

• Example: people with aphasia (inability to express language) are more accurate with nonverbal cues

SENSORY COMPENSATION

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Other Important SensesThe sense of touch (essential to development) 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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TOUCH AND TEMPERATURE = SOMATIC

SENSES1. The stimulus and receptors for touch

– a.when hairs on skin are bent, they deform the skin beneath them

– b.receptors that transduce this deformation into neural activity are in or near the skin

2. Some areas are more sensitive because they have more receptors

Adaptation – change is the most important information

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PAIN• 1. Pain is necessary!

– a. Different thresholds for pain; hyperalgesia: extreme sensitivity

– b. Damage = release of bradykinin, a chemical that fits into specialized receptors in pain neurons

– C .Mylinated to carry message faster (A. Delta); C fibers carry dull pain

– d. Emotional aspects of pain – expectation

– e. Natural analgesics = endorphins and serotonin

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Gate-Control TheoryMelzak 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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GUSTATION

• Receptors for taste are located in the taste buds grouped together in papillae

• 10,000 in mouth, mostly on the tongue, also in back of tongue

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GUSTATION

• Gustation is a chemical sense– Taste receptor cells project hairs into pores– Can reproduce themselves, but decrease

with age

Flavor: Smell + taste, also affected by temperature

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OLFACTION

• Odors are sensed in the upper part of the nose, where receptors detect molecules that pass into the moisture of the lining of the nose.

• They are the only neurons which are exposed and replace themselves

• Diminish with age, smoking, Alzheimer’s, Parkinson’s, and alcoholism

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OLFACTION

• Olfaction is a dual sense because we detect odors that are either

• Internal entering through the mouth, or• External entering through the nose• We have particular receptors for particular smells• Axel and Beck received the Nobel prize for discovering

receptor proteins embedded in surface of nasal cavity• Odors trigger a combination of receptors, then interpreted

by olfactory cortex

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PROPRIOCEPTION

• Sensory systems giving information about the position of the body and what each part is doing

• Sensorimotor co-ordination

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Body Position and MovementThe 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

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VESTIBULAR SYSTEM

• Vestibular System = information about the position and movement of the head

• Located in Inner Ear

• Semicircular Canals

• Vestibular sacs - connect canals with cochlea

• Fluid and otoliths (crystals) on hair

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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).

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VESTIBULAR SENSE

• Movement influences fluid in sacs and canals

• Neural connections with

• Cerebellum = balance

• ANS = affects digestive system

• Muscles of eyes (vestibular-ocular reflex)

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iClicker Questions for

Chapter 5: Sensation

Psychology, 8th Edition

by David G. Myers Karla Gingerich, Colorado State University

51

1.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.

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2.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.

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3.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.

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4.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.

55

5.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.

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6.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.

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7.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.

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8.The malleus, incus, and stapes are found in the:

A. middle ear.

B. inner ear.

C. cochlea.

D. outer ear.

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9.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

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10.As a professional chef, which of the following sensations would you

rely on most?

A. hearing

B. seeing

C. balance

D. smell

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Critical Thinking Questions

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11.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

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12.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.

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13.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.

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14.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.

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15.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.

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Perception

Chapter 6

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Perception

The process of selecting, organizing, and interpreting sensory information,

which enables us to recognize meaningful objects and events

(Top down processing).

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Selective AttentionPerceptions about objects change

from moment to moment. Example: the Stroop Task - what is it?

Necker Cube

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Inattentional Blindness

Inattentional blindness refers to the inability to see an object or a person

in our midst.

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Change Blindness

Change blindness is a form of inattentional blindness in which two-thirds of individuals giving directions failed to notice a change

in the individual asking for directions.

© 1998 Psychonomic Society Inc. Image provided courtesy of Daniel J. Simmons.

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POP-OUT

• A STRIKINGLY DISTINCT STIMULUS DRAWS OUR EYE

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SELECTIVE ATTENTION

• Attentional resources are limited• Overt vs covert orienting• When can we divide attention?

– How automatic?– Different kinds of attentional resources– Stress narrows attention

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Perceptual IllusionsIllusions provide good examples in understanding how perception is

organized. Studying faulty perception is as important as studying other

perceptual phenomena. Muller-Lyer Illusion:

Line AB is longer than line BC.

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Perceptual OrganizationWhen vision competes with our other

senses, vision usually wins – a phenomena 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.

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PERCEPTUAL ORGANIZATION

• Sensation (bottom up processing) and Perception (top down processing) blend into one continuous process

• Fundamental point: We constantly filter sensory information and infer perceptions in ways that make sense to us. Mind matters.

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

surroundings (ground). Another example: cocktail party phenomena

Form Perception

Tim

e Savings S

uggestion, © 2003 R

oger Sheperd.

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REVERSIBLE FIGURE GROUND

• Reversible figure-ground illusions demonstrate that the same stimulus can trigger more than one perception.

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GroupingAfter distinguishing the figure from the

ground, our perception needs to organize the figure into a meaningful form using grouping rules (Gestalt psychologists).

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OTHER GROUPING PRINCIPLES

• LIKLIHOOD PRINCIPLE: we tend to perceive objects in the way that experience tells us is the most likely physical arrangement

• Auditory scene analysis– Sound localization– Visual capture

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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. Depth perception

appears to be innate, amplified by experience

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rvis

ions

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DEPTH PERCEPTION

• Two dimensional images fall on our retina, how do we see three dimensionally?

• Depth perception (seeing objects in three dimensions) allows us to judge distance

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Binocular Cues

Retinal disparity: Images from the two eyes differ. Brain compares these images, their differences

provide cues to relative distance of different objects

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

objects.

Accomodation – muscles surrounding the lens tightening

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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 CuesInterposition: Objects that occlude

(block) other objects tend to be perceived as closer.

Rene M

agritte, The Blank Signature, oil on canvas,

National G

allery of Art, W

ashington. Collection of

Mr. and M

rs. Paul Mellon. Photo by R

ichard Carafelli.

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Monocular CuesRelative Clarity: Because light from distant

objects passes through more light than closer objects, we perceive hazy objects to

be farther away than those objects that appear sharp and clear.

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Monocular Cues

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

© E

ric Lessing/ A

rt Resource, N

Y

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Monocular CuesRelative 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 CuesRelative 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 CuesLinear 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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Motion PerceptionMotion Perception: Objects traveling towards us grow in size (looming) and those moving away shrink in size. The same is true when the observer moves to or from an object.

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Apparent MotionPhi Phenomenon: When lights flash at a

certain speed they tend to present illusions of motion. Neon signs use this principle to

create motion perception.

Two lights flashing one after the other.One light jumping from one point to another: Illusion of motion.

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Perceptual ConstancyPerceiving objects as unchanging even as

illumination and retinal images change. Brain needs to recognize the object without being deceived by

changes. Perceptual constancies include constancies of shape and size.

Shape Constancy

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Size ConstancyStable size perception amid changing size

of the stimuli.

Size 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. Cultural experience also influences.

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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Lightness Constancy

The color and brightness of square A and B are the same. Depends on relative luminance - the amount of light an object reflects relative to its

surroundings.

Courte

sy E

dwar

d A

delso

n

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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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Perceptual InterpretationImmanuel 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?

102

Kittens raised without exposure to horizontal

lines later had difficulty perceiving

horizontal bars. Influence of critical

periods shown.

Blakemore & Cooper (1970)

Sensory Deprivation

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

Whisper Down the Lane example.

From

Shepard, 1990.

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Allport and Postman

• LEVELING - perceiver drops certain details because they don’t “fit”

• SHARPENING - details consistent with values and interests are emphasized

• ASSIMILATION - padding and organization used to make central theme fit subject’s expectations

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PERCEPTUAL SET

What determines perceptual set?

• Through experience we form concepts, or schemas, that organize and interpret unfamiliar information.

– Example: a child’s simplified drawing of people

• Our innate schemas for faces primes us, especially attune to the eyes and mouth

106

Children's schemas represent reality as well as their abilities to represent what they see.

SchemasSchemas are concepts that organize and

interpret unfamiliar information.

Courtesy of A

nna Elizabeth V

oskuil

107

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

under a tree.

Cultural ContextContext instilled by culture also alters

perception.

108

Perception RevisitedIs perception innate or acquired?

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Perception & Human Factors

Human Factor Psychologists design machines that assist our natural perceptions.

The knobs for the stove burners on the right are easier to understand than those on the left.

Photodisc/ P

unchstock

Courtesy of G

eneral Electric

110

Human Factors & Misperceptions

Understanding human factors enables us to design equipment to prevent disasters.

Two-thirds of airline crashes caused by human error are largely due to errors of perception.

111

iClicker Questions for

Chapter 6: Perception

Psychology, 8th Edition

by David G. Myers Karla Gingerich, Colorado State University

112

1.As you talk with a friend at a party, her voice is distinct from all the other voices you hear. This

illustrates the perceptual principle of:

A. grouping.B. proximity.C. closure.D. figure-ground.

113

2.The way in which you quickly group the individual letters in this test item into separate words best

illustrates the principle of:

A. closure.

B. proximity.

C. continuity.

D. convergence.

114

3.Makers of 3-D movies rely most heavily on:

A. the visual cliff.

B. the Müller-Lyer illusion.

C. retinal disparity.

D. shape constancy.

115

4.After hearing that Bryce had served a prison sentence, Janet began to perceive his friendly behavior as

insincere and manipulative. This best illustrates the impact of:

A. perceptual sets.B. visual capture.C. bottom-up processing.D. sensory adaptation.

116

5.Which is easier to recognize?

A. an actual picture of a face

B. the caricature of the face

C. the anticaricature of the face

D. an upside-down picture of the face

117

6.If a person were able to sense that his friend’s dog was lost and needed

help, this person would be said to have:

A. psychokinesis.

B. telepathy.

C. precognition.

D. clairvoyance.

118

Critical Thinking Questions

119

6.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. closureB. proximityC. similarityD. continuity

120

7.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 parallaxC. convergenceD. interposition

121

8.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 cuesB. monocular depth cuesC. Gestalt principles of proximity and continuityD. perceptual principles only operate in “real life” situations

122

9.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.