Transcript Sensation and Perception

SENSATION AND
PERCEPTION
Unit IV
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Sensation: the process
of absorbing
information, in the
form of energy, from
our environment
Uses sensory organs
and nervous system
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Perception: the process
of organizing and
interpreting
information to
determine what is
meaningful
Happens in brain
What’s in this picture?
http://www.pc.rhul.ac.uk/staff/J.Zanker/PS1061/L10/PS1061_10.htm
Spiral or circles?
http://www.shutterstock.com/pic-84801493/stock-vector-optical-illusion-forces-tosee-a-spiral-when-actually-figures-are-located-on-a-circle.html
Bottom-Up Processing
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Analysis that starts with sensory receptors and
works up to the brain’s integration of information
Happens when we have no prior knowledge of
something
usslave.blogspot.com
Top-Down Processing
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Analysis that uses prior knowledge and experience to
construct meaning
Focusing on details requires effort
EX: Aoccdring to rscheearch at CmabrigdeUinervtisy,
it deosn’tmttaer in wahtoredr the ltteers in a wrod
are, the olnyiprmoetnttihng is taht the frist and
lsatltteer be at the rghitpclae. The rset can be a
total mses and you can still raed it wouthit a
porbelm. Tihs is bcuseae the huamnmniddeos not
raederveylteter by istlef but the wrod as a wolhe.
Theories on top-down processing
Likelihood principal: we perceive the most
likely object based on context and experience
 Hypothesis testing: perception uses sensory
data to make and revise hypotheses about the
world
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Selective Attention
We consciously focus on a very small amount of
the sensory information we take in and ignore
the rest
 Ex: you can have a conversation with one
person in a crowded room
 ADHD may be a lack of selective attention
 Demonstration!
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Inattentional blindness
We often don’t notice things, especially if
we are focused on one thing in particular
 Video break: a famous experiment on
inattentional blindness
 Research suggests the unconscious may
pick up on unnoticed information
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Change Blindness
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We often fail to notice changes in our
environment
 Happens when we are distracted from the
changed object
 More quickly noticed when the object is central
to the scene
 You must pay attention to the object at some
point to notice a change
 Paying attention to an object is not always
enough to notice a change
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Video break: Mind Games “Pay Attention”
Mindsight?
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Some people may be able to “sense” change
before they find exactly what the change is
 Using secondary visual system?
 Or verifying conscious detection of change?
Thresholds
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Absolute threshold: minimum stimulation necessary
for detection 50% of the time
 May
change slightly because of lapses of attention,
slight fatigue, or other factors
 Ex: hearing tests
Signal Detection Theory
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Says signal detection depends on experience,
expectations, motivations, and alertness
Predicts how often weak signals will be picked out
of “background noise”
Would mean that absolute thresholds vary
significantly
Ex: TSA agents looking for guns in suitcases
Subliminal Stimuli
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We do sometimes unconsciously sense stimuli below
the absolute threshold
Priming with images or smells can shape people’s
responses to other people
This effect is short-lived and mild (doesn’t work for
advertising)
Difference Thresholds
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AKA just noticeable difference
Three ways to test (discovered by Gustav Fechner):
 Method
of limits: start with a standard stimulus and
increase the difference between it and another stimulus
until someone notices
 Method of right and wrong cases: present a pair of
stimuli and ask if they are different
 Method of adjustment: Adjust a stimulus until it is
identical to the standard and measure the error
Weber’s Law
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Two stimuli must differ by a constant percentage
(not amount) to be perceived as different
Weight: 2%
Pitch: 0.3%
Light intensity: 8%
Also applicable to economics
Demonstration!
Sensory Adaptation
Our sensitivity decreases with constant/repetitive
stimulation
Helps us to focus on changes to the environment more informative/important than things that are
always present
Ex: disappearing disc
Vision
Vision
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Light Energy
 Wavelength
- distance from one peak to another
(determines color)
 Intensity - amount of energy, depends on height of
wave, influences brightness
Figure 4.10The eye Light rays reflected from the candle pass through the cornea, pupil, and lens.
The curvature and thickness of the lens change to bring either nearby or distant objects into focus on
the retina. Rays from the top of the candle strike the bottom of the retina and those from the left side
of the candle strike the right side of the retina. The candle’s retinal image is thus upside-down and
reversed.
© 2010 by Worth Publishers
Figure 4.11 The retina’s reaction to light
© 2010 by Worth Publishers
The Eye cont.
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Light goes through the lens, which focuses light for
different distances (accommodation)
Image hits retina upside-down
Light goes to rods and cones at the back of the
retina, causes chemical reaction
bipolar cells (middle layer of retina) activate and
pass signal to ganglion cells (upper layer of retina)
Ganglion cells converge into optic nerve
The Eye Cont.
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Blind spot exists where optic nerve leaves the eye
 Usually
eyes work together to get complete picture and
brain will fill in a gap
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Cones: mostly in/around fovea, spot of central focus
on retina; detect color and detail
Rods: mostly on peripheral of retina, detect blackand-white, work in dim light
Visual Processing
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Retinal cells send initial information through
thalamus to visual cortex
Feature detectors respond to specific characteristics
- lines, movements, angles
Supercell clusters of neurons interpret more complex
patterns - faces, complete objects
 Some
supercells are specialized
 Some integrate information from others
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Parallel processing: The brain processes color,
movement, form, and depth simultaneously
Damage to specific areas will disrupt these specific
functions
 Blindsight:
research on patients with damage suggests a
secondary, intuitive visual system
Visual Processing
Color Vision
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Color is a construct of our minds
Young-Helmholtz trichromatic theory: the eye has 3
types of cones for seeing red, blue, and green
All other colors are combinations of those - green
and red light make yellow, etc.
Color-deficient vision is caused by a lack of one or
two types of cones (usually red and/or green)
Color-deficiency test
Opponent Colors
Opponent Process Theory
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Opponent colors: red-green, blue-yellow, blackwhite
Some neurons are turned off by red and on by
green and vice versa
Modern color theory uses both Young-Helmholtz and
opponent-process: color is seen by combinations of
cones and then goes through opponent-process cells
to visual cortex
Hermann Grid
Problems with Vision
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Color deficiency
Nearsightedness – lens focuses objects in front of
the retina instead of on the retina (see things better
up close)
Farsightedness – lens focuses objects behind the
retina (see things better far away)
Blindness due to damage or from birth
Hearing
Hearing
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Audition is very sensitive, esp. to human-created
sounds
Sound waves are air molecules moving in
pressurized waves - vibrations
Frequency of sound waves determines pitch
Amplitude of sound waves determines volume
 Measured
in decibels - 0 = absolute threshold, 10
decibels is a 10x increase in intensity
 Ex: Conversation at 60 db is 10,000x more intense
than 20 db whisper
Structure of the Ear
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Outer Ear: moves sound through auditory canal to eardrum
Middle Ear: transfers vibrations from eardrum through 3 tiny
bones - hammer, anvil, and stirrup - to cochlea
Inner Ear: Hair cells inside the cochlea sway when the
cochlea vibrates, triggering neurons to fire
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Most hearing loss is because of damage to hair cells
Loudness is perceived based on the number of hair cells that fire
Sensorineural hearing loss
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Damage to hair cells
caused by
 Sustained
noise above
85 decibels
 Aging
 Heredity
 Disease
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http://health.howstuffworks.com/humanbody/systems/ear/loud-noise-ear.htm
Hearing can be
restored with cochlear
implants – mechanical
device wired into ear
Theories on Perceiving Pitch
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Place theory - different pitches trigger activity on
different parts of the cochlea
 Explains
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Frequency theory - pitch determines how often neural
cells all over the cochlea will fire (higher frequency =
faster firing)
 Explains
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high pitches but not low ones
low sounds but not high ones
Volley principle - cells alternate firing to get a faster
combined frequency
Modern sound theory uses a combination of place and
frequency theory
Locating Sounds
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Having two ears means we can determine the
location of sound
Our brains can detect minute differences in the
timing and intensity of sound waves between the
ears
We struggle to identify sounds that are equidistant
to both ears (overhead, directly behind, etc)
because there is no time lag
 Cope
by cocking your head
Other Senses
Touch
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4 types of skin sensations: pressure, warmth, cold,
and pain (only pressure receptors have been
identified
Hairy skin detects movement and pressure
Galbrous skin (no hair) is more sensitive
Touch is influenced by top-down processing and
expectations (rubber hand experiments)
Kinesthesis and Vestibular Senses
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Kinesthesis is the sense of body position and
movement
 Measured
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by sensors in joints, tendons, bones, and ears
Interacts with vision
Related to vestibular sense, which monitors head
position and movement
 Determined
by fluid in the semicircular canals of the
inner ear – moving fluid activates hair cells
 Essential for balance
Pain
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Pain alerts us to problems so we can take care of
them
Many causes of pain trigger the same receptors
Some pain signals come from the brain, as with
phantom limbs
Level of pain depends on social-cultural context
 We
perceive more pain when others are also feeling
pain
Gate-Control Theory
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Pain signals travel through spinal cord in small nerve
fibers
Other sensory signals travel in large nerve fibers
Small fiber signals open a “gate” in the spinal cord
and you feel pain
Large fiber signals or messages from the brain close
the gate
 Stimulating
area by rubbing can block pain signals
 Endorphins limit experience of pain
Psychological effects on pain
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Distraction limits perception of pain
We remember peak moment of pain and level of
pain at the end of a painful experience
 Medical
procedures can seem less painful if they are
longer but the level of pain tapers off
Taste
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5 taste sensations: sweet, sour, salty, bitter, and
umami (savory, meaty)
Humans have >200 taste buds, each with 50-100
receptor cells
Receptors are mostly specific to one taste sensation,
reproduce every 2 weeks
Taste sensitivity decreases with age, smoking, and
alcohol use
Taste Perceptions
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Brain responds more negatively to a taste when you
are warned it will be bad
Price of food influences our perception of how good
it will taste
People prefer familiar foods to unfamiliar ones
Tastes (and taste aversions) may be acquired or
learned over time
Smell (Olfaction)
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Smell and taste are both chemical senses
Molecules of substances are caught in receptor cells in
the top of the nasal cavity
Different odors activate different combinations of
receptors
Smell does not go through the thalamus, but it does go
past the prefrontal cortex, which helps process
emotional memories
 This
may explain why smells are associated so strongly
with memories
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Infants and mothers identify each other by smell
The ability to identify scents peaks in early
adulthood
Attractiveness of smells depends on learned
associations
Women have slightly better senses of smell than
men
Sensory Interaction
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Our senses influence each other, especially smell
and taste
 (ex:
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no flavor when you have a cold)
Vision and hearing work together to help
understand language
Synesthesia: stimulating one sense causes the
perception of another sense
 Ex:
tasting shapes, seeing letters in specific colors