what influences our perception? sensation sensation and 1 ... · visual perception b. depth...

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Sensation and Perception

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What influences our perception?

1. Experience

2. Expectations

3. Context

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I. The Perceptual Experience

Definitions

Sensation

Receptor cells stimulated,

relay info to brain

Biological

Perception

Organism interprets sensory input

to give it meaning

Psychological

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Two levels of analysis

“Bottom-up analysis”

Begins at receptors

Works up to more complex tasks

E.g., how are colors and

shapes combined to form

the perception of a flower?


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“Top-down analysis”

Begins at perceptual level

Past experience helps identify

patterns


E.g., Memory of flowers helps

recognize them more quickly

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Psychophysics

Study of relationship between physical

stimuli and people’s conscious

experience of them

Sensory thresholds

– Absolute Thresholds

Minimum stimulation to excite

perceptual system


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Absolute Thresholds

Vision

Candle from 30 miles at night

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Absolute Thresholds

Hearing Tick of watch from 20 feet

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Absolute Thresholds

Taste Tsp sugar in 2 gallons water

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Absolute Thresholds

Smell Drop of perfume in 3 room apartment

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Absolute Thresholds

Touch Wing of bee falling on cheek from 1cm

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Subliminal Perception

Subliminal

stimuli that are below absolute threshold (detectable < 50% of time)

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Subliminal Advertising

Pepsi’s “neon” cans (1990)

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1. Types of Thresholds

b. Difference Thresholds

• Change necessary to:

be noticed

accurately report 50% of time that stimulus has changed

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Studying Thresholds

Signal Detection Theory

Perception depends on

intensity of stimulus

observer’s motivation

criteria set by observer

background noise

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How trustworthy are my senses?

Inattentional Blindness

inability to perceive something

that is within one's direct

perceptual field because one is

paying attention to something

else

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II. Vision

Sight is arguably the most important

sense

Eyes have 70% of sense receptors

Stimulus =

electromagnetic radiation

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The Electromagnetic Spectrum

• Visible light = small fraction of

electromagnetic energy

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A. Structure of the Eye

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A. Structure of the Eye Iris

Colored part

Changes size to regulate light

Lens Focuses light

Pupil Lets light in

Cornea Protective covering

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Retina

Has rods and cones (photoreceptors)

RODS

CONES

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Rods and Cones

Duplicity theory of vision

Two different types of receptors in

the retina

rods and cones

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Rods and Cones

120 million

periphery

sensitivity

night vision

light and dark

8 million

central & fovea

sharpness

best in bright light

color vision

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Fovea

Point of focus

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HOW DO WE SEE

THESE WORDS?

Words you are now reading are hitting the fovea while the rest of what you see (background) is striking other areas of the retina.

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A. Structure of the Eye Optic nerve

Sends message to visual cortex

Blind spot

No photoreceptors

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Normal vision

Image focused on retina

Myopia (near-sightedness)

Image focused in front of retina

Hyperopia (far-sightedness)

Image focused behind retina

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Rods and Cones

Explain light and dark adaptation

– Less sensitivity after being in bright

place

– Dark Adaptation

• Increased sensitivity after being in

dark

• Caused by photoreceptor chemicals

regenerating in the dark

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Electrochemical

Basis of Perception

Perception is electrochemical

Receptors stimulated

Transduction

Electrochemical signals sent to brain

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Eye Movements

Provide important information about

what is being processed

Saccades

Rapid voluntary eye movements

Delay of 200-250 msecs. between

saccades = fixation

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Color Vision

1. Psychological dimensions of color

a. Hue (color)

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Color Vision


b. Brightness

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Color Vision


a. Saturation

- “purity”

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Color Vision

2. Theories of Color Vision

A. Trichromatic Theory

B. Opponent-Process Theory

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Hermann

von Helmholtz ophthalmoscope

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Theories of Color Vision Trichromatic Theory

Young-Helmholtz Theory

Colors made by mixing three different colors:

Red

Green

Blue

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Theories of Color Vision Trichromatic Theory (cont’d)

Special photoreceptors sensitive to each color

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Theories of Color Vision

Opponent-Process Theory

Assumes six colors and three types

of receptors

RED–GREEN

BLUE–YELLOW

BLACK–WHITE

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Theories of Color Vision

Opponent-Process Theory

Every receptor fires in response to

all wavelengths

In each pair, one receptor fires

more strongly than the other

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Afterimages

Opponent-process theory may explain afterimages:

continual viewing of red weakens ability to inhibit green

remove red and you see green

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Color Blindness

Most people = trichromats

<1% = monochromats

Most color blindness = dichromats

8% of men and 1% of women

Transmitted on the X chromosome

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Color Blindness

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Visual Perception

A. Perceptual Constancy

Perceiving objects as unchanging

despite changes in retinal image

1. Color

2. Shape

3. Size

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Perceptual Constancy

& Illusions Forced

perspective

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Visual Perception

B. Depth Perception

Allows person to:

Estimate distance from object

Estimate distance between objects

Perceive height, width, depth

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Depth Perception

The Visual Cliff

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Depth Perception

Two types of cues

1. Monocular Cues

Uses one eye

Used for paintings and far distances

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Monocular Cues

Cues from the

stimulus

Linear perspective

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Monocular Cues

Cues from the

stimulus

Interposition

Hey Ralph, stay behind me.

We’re demonstrating

interposition for Doyle.

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Monocular Cues

Cues from the stimulus

Texture gradient

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Monocular Cues

Cues from the stimulus

Atmospheric

perspective

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Linear perspective

Interposition

Texture gradient

Atmospheric perspective

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Binocular Cues Use both eyes

Close distances

Two types

a. Retinal disparity

images from two eyes differ

closer the object, larger the disparity

b. Convergence

two eyes move inward for near objects

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Gestalt Laws of

Perceptual Organization

integrate pieces

of information

into meaningful

wholes

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Gestalt Laws of

Perceptual Organization Figure and Ground

Organization of visual

field into objects

(figures) that stand out

from surroundings

(ground)

Figure

Ground

M.C. Escher

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Gestalt Laws of


Grouping

organizing stimuli into meaningful groups

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Gestalt Laws of


Proximity Similarity

Continuity Closure Connectedness

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C. Illusions

Why are our brains and eyes fooled

by such illusions?

– backgrounds against which they are

seen

– illusions are usually due to short-cuts

that the brain makes

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C. Illusions

– Müller-Lyer Illusion

• Which line is longer?

Hearing

What is sound?

Vibrating objects produce sound waves

in the air

Waves cause changes in air pressure that

affects various ear structures

Anatomy of the Ear

Pinna Part you can see

OUTER EAR INNER EAR

MIDDLE EAR

Eardrum

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Anatomy of the Ear

OUTER EAR INNER EAR

MIDDLE EAR

Ossicles 3 tiny bones

Anatomy of the Ear

Ossicles 3 tiny bones

Hammer Anvil Stirrup

Anatomy of the Ear

OUTER EAR INNER EAR

MDL. EAR

Cochlea

Contains tiny hair cells that sense motion, converting it to electrical impulses

Auditory nerve

Carries info to auditory cortex

Basilar membrane

Inside cochlea, analyzes frequencies

Anatomy of the Ear

Auditory cortex

Sound Waves

Sound waves vary in:

1. Frequency

speed of wave; perceived as pitch (high/low)

2. Amplitude

height of wave; perceived as loudness

3. Timbre

complexity of wave; distinctive sound or

quality different things

Sound Localization

Ability to identify where a sound is

coming from

Sounds arrive at each ear at slightly

different times/volumes

Objects equidistant from each ear can

be hard to locate!

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Measuring Sounds

Unit of measure is decibel (dB)

Logarithmic scale

10 dB increases perceived volume

by 10 times

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Decibel Levels of Everyday Sounds Sound Average

dB

Typical Response After Repeated Exposure

Firecrackers 140-150 Pain & ear injury; permanent hearing loss

Shouting in ear 110 Permanent hearing loss possible in < 2 min

Max smartphone; very loud

radio; rock concert

105-110 Hearing loss possible in < 5 min

Motorcycle 95 Damage to hearing possible after about 50 min

Lawnmower 90 Damage to hearing possible after 2 hours

City traffic (inside car) 80-85 Annoyed

Washing machine 70

Normal conversation 60

No hearing damage at these dB levels Refrigerator hum 40

Normal breathing 10

Threshold 0

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Hearing Loss

16% of adults

Can happen from

one time exposure to very loud sound

daily exposures to moderately loud

sounds

also from disease, aging, etc.

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sensorineural conduction

Hearing Loss

Two kinds

1. conduction hearing loss (outer/middle)

2. sensorineural hearing loss (inner)

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Conduction Hearing Loss

Physical problems sending sound waves

through outer or middle ear

E.g., punctured eardrum or damage to

ossicles (bones)

Hearing aids are common treatment

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Sensorineural Hearing Loss

More common than conductive hearing loss

Inner ear nerve problems

Damage to hair cells or auditory nerve

Damaged cells can be temporary or permanent

Cochlear implant is only treatment

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Super Important Question

WHY DOES MY VOICE SOUND SO WEIRD

WHEN I HEAR A RECORDING OF IT?

Super Important Question

When you speak, the sound of your voice that

you hear is the result of…

the sound waves you’re putting into the air

External cues

the vibrations of your vocal cords, which

are conducted through your bones

This emphasizes the lower frequencies and

makes your voice sound deeper and richer

Internal cues

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A chemical sense

Food dissolved in saliva releases

chemicals that stimulate the taste buds

Located in tiny trenches between the

papillae (bumps) on the tongue

Each consists of 5 to 150 taste cells

Taste The Physiology of Taste

fungiform papillae

taste buds found

around the papillae

The Physiology of Taste

Average person has approx. 10,000

taste buds

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Gustatory

cortex


NOT TRUE

Taste

Some areas of the tongue are more

sensitive to taste stimuli than others

Taste sensitivity

seems to be genetically determined

differs between individuals

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Taste

What are the basic tastes?

sweet

sour

salty

bitter

and…

umami

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What is umami?

Japanese word for “deliciousness”

Identified in early 20th century by Japanese

scientist

Hard to describe; often defined as

meaty, savory, satisfying

High level of glutamate

Monosodium glutamate (MSG) adds umami

flavor to foods

What is umami?

Foods with lots of umami:

parmesan

cheese seaweed soy sauce ketchup

mushrooms pepperoni pizza

chicken soup yeast extract

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Individual Differences

Supertasters vs. non-tasters

Based on number of papillae

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Individual Differences

Supertasters (lots of papillae) often find

common foods too bitter, sweet, or spicy

Non-tasters (few papillae) can handle

much more “intense” foods

Sensory Adaptation

Food that rests on tongue a long time

loses its ability to stimulate the taste

buds

Taste, like other perceptual

experiences, depends not only on the

sensory stimulus, but on past

experience

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Olfaction

Chemical sense

Stimuli = chemicals in air

Absorbed into mucus that covers olfactory

receptor cell

Humans can detect about 10,000 different odors

No classification scheme for smells

Combines with taste info to create flavor

About 80% from smell!

Smell

Why is the memory for

smells so strong?

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The Physiology of Smell

Neurons in nose lead to olfactory bulb

Top of nasal cavity, ties in with limbic system

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Animals secrete pheromones

Chemicals detected as scents by other

animals

Means of communication

Probably not as strong in humans

Smell and Animals

Dogs’ sense of smell > 10,000 X better

than humans

Smell and Animals

Proportionally,

40 times more brain

devoted to smell

Analogy…

If smell were like vision:

• The level of detail that you and I can see looking out

the classroom window at the police station, about 300

yards away, a dog could see from more than 1,800

miles away — and still see as well.

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V. Touch and Pain

A. Touch

Touch receptors are located in the skin

• Three layers of skin

1. Epidermis

2. Dermis

3. Hypodermis

• Specialized receptors for touch,

pain, and temperature

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A. Touch

Being tickled

– Response is physical AND psychological

• Response to humor and tickling may be related

• Why can’t you tickle yourself?

• Being tickled requires

Intimacy with the tickler

Element of surprise

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B. Pain

– Pain receptors are free nerve endings

• Microscopic ends of afferent neurons

– Body parts have different sensitivities

– Activates autonomic N.S.

– Perception of pain is both physical &

psychological

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Pain Management

– Treating chronic pain is challenging

• Drug treatment may be ineffective or

dangerous

– Pain may be maintained by non-physical

causes

• May elicit attention

• May distract the sufferer from other

problems

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4. Pain Management

Hypnosis

– Estimated to be effective in 15–20%

of cases

• Anxiety and worry can worsen pain

• Negative attitude can worsen pain

– Cognitive coping strategies can help

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VII. How Do We Keep Our

Balance?

A. Kinesthesis

Awareness of movements of muscles,

tendons, and joints

Based on proprioceptive cues

Produced by ears, muscles, etc.

B. Vestibular Sense

Sense of bodily orientation and postural

adjustment

Helps maintain balance

Provides information about orientations of head

and body

Essential structures are in ear

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VIII. Extrasensory Perception

ESP includes four phenomena

Telepathy

Clairvoyance

Precognition

Psychokinesis

Experimental evidence for ESP is generally

weak

what influences our perception? sensation sensation and 1 ... · visual perception b. depth...

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