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?
I. The Perceptual Experience
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“Top-down analysis”
Begins at perceptual level
Past experience helps identify
patterns
I. The Perceptual Experience
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
I. The Perceptual Experience
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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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A. Structure of the Eye
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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A. Structure of the Eye
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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A. Structure of the Eye
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
1. Psychological dimensions of color
b. Brightness
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Color Vision
1. Psychological dimensions of color
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
Perceptual Organization
Grouping
organizing stimuli into meaningful groups
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Gestalt Laws of
Perceptual Organization
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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The Physiology of Taste
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Gustatory
cortex
The Physiology of Taste
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