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Sensations vs. Perception
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Sensation & Perception
How do we construct our representations of the external world?
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.
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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 really a black blotch broken down into features by the brain that we perceive as an
“A.”
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Top-Down Processing
Information processing guided by higher-level mental processes as we construct perceptions, drawing on our experience
and expectations.
THE CHT
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Top-Down Processing
Aoccdrnig to rscheearch at Cmabrigde Uinervtisy, it deosn't mttaer in waht oredr the ltteers in a wrod are, the olny iprmoetnt tihng is taht the frist and lsat ltteer be at the rghit pclae. The rset can be a total mses and you can sitll raed it wouthit a porbelm. Tihs is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the wrod as a wlohe.
Our experience and expectations enable us to immediately perceive the scrambled letters as meaningful words and sentences.
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Making Sense of Complexity
Our sensory and perceptual processes work together to help us sort out complex
images.
“The Forest Has Eyes,” Bev Doolittle
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Sensing the World
Senses are nature’s gift that suit an organism’s needs.
A frog feeds on flying insects; a male silkworm moth is sensitive to female sex-attractant odor; and we as human beings are sensitive to sound frequencies that represent the range of human voice.
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Exploring the Senses
1. What stimuli cross our threshold for conscious awareness?
2. Could we be influenced by stimuli too weak (subliminal) to be perceived?
3. Why are we unaware of unchanging stimuli, like a band-aid on our skin?
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PsychophysicsA study of the relationship between
physical characteristics of stimuli and our psychological experience with them.
Physical WorldPsychological
World
Light Brightness
Sound Volume
Pressure Weight
Sugar Sweet
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Detection
No
Intensity
AbsoluteThreshold
Detected
YesYesNo No
Observer’s Response
Tell when you (the observer) detect the light.
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Thresholds
Absolute Threshold: Minimum stimulation needed to detect a particular stimulus 50%
of the time.
Pro
port
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 Threshold
Subliminal Threshold: When stimuli are below one’s absolute threshold
for conscious awareness.
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Difference Threshold
Difference Threshold: Minimum difference between two stimuli required for detection 50% of the time, also called just noticeable
difference (JND).DifferenceThreshold
Tell when you (observer) detect a difference in the light.
No
Observer’s Response
No Yes
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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 Images
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Sensory Adaptation
Diminished sensitivity as a consequence of constant stimulation.
Put a band aid on your arm and after awhileyou don’t sense it.
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Smelly Marker Experiment
1. Get a partner and choose a marker that is different than your partner’s marker.
2. Follow my directions.
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WHY DO WE SEE WHAT WE SEE?
Vision
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Transduction
In the definition of sensation, transduction is the transformation of stimulus energy
into neural impulses.
Phototransduction: Conversion of light energy into neural impulses that the brain
can understand.
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The Stimulus Input: Light Energy
VisibleSpectrum
Bot
h P
hoto
s: T
hom
as E
isne
r
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Light Characteristics
1. Wavelength (hue/color)2. Intensity (brightness)3. Saturation (purity)
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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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Wavelength (Hue)
Different wavelengths of light resultin different colors.
400 nm 700 nmLong wavelengthsShort wavelengths
Violet Indigo Blue Green Yellow Orange Red
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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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Intensity (Brightness)
Blue color with varying levels of intensity.As intensity increases or decreases, blue color
looks more “washed out” or “darkened.”
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Purity (Saturation)
Monochromatic light added to green and redmakes them less saturated.
Saturated
Saturated
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The Eye
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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 that
process visual information and sends it to the brain.
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The Lens
Lens: 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 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.
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Retina
Retina: The light-sensitive inner surface of the
eye, containing receptor rods and cones in
addition to layers of other neurons (bipolar, ganglion
cells) that process visual information.
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Optic Nerve, Blind Spot & Fovea
http://www.bergen.org
Optic nerve: Carries neural impulses from the eye to the brain. Blind Spot: Point where the optic nerve leaves the eye because there are no receptor cells located there. This creates a blind spot. Fovea: Central point in the retina around which the eye’s cones cluster.
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Test your Blind Spot
Use your textbook. Close your left eye, and fixate your right eye on the black dot. Move the page
towards your eye and away from your eye. At some point the car on the right will disappear due to a
blind spot.
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Photoreceptors
E.R. Lewis, Y.Y. Zeevi, F.S Werblin, 1969
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Visual Information Processing
Optic nerves connect to the thalamus in the middle of the brain, and the thalamus
connects to the visual cortex.
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Perception in Brain
Our perceptions are a combination of sensory (bottom-up) and cognitive (top-
down) processes.
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Visual Information Processing
Processing of several aspects of the stimulus simultaneously is called parallel
processing. The brain divides a visual scene into subdivisions such as color, depth, form
and movement etc.
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From Sensation to RecognitionT
im B
iebe
r/ T
he I
mag
e B
ank
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Theories of Color Vision
Trichromatic theory: Based on behavioral experiments, Helmholtz suggested that
the retina should contain three receptors that are sensitive to red, blue and green
colors.
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Subtraction of Colors
If three primary colors (pigments)
are mixed, subtraction of all
wavelengths occurs and the
color black is the result.
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Addition of ColorsIf three primary colors (lights) are mixed, the wavelengths are added and the color
white is the result.
Fritz Goro, L
IFE m
agazine, © 1971 T
ime W
arner, Inc.
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PhotoreceptorsRed
ConesGreenCones
Longwave
Mediumwave
Shortwave
MacNichol, Wald and Brown (1967)
measured directly the absorption
spectra of visual pigments of single cones
obtained from the retinas of humans.
BlueCones
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Color BlindnessGenetic disorder in which people are blind to green or red colors. This supports the
Trichromatic theory.
Ishihara Test
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Opponent Colors
Gaze at the middle of the flag for about 30Seconds. When it disappears, stare at the dot and report
whether or not you see Britain's flag.
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Opponent Process TheoryHering proposed that we process four
primary colors combined in pairs of red-green, blue-yellow, and black-white.
Cones
RetinalGanglion
Cells
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Color ConstancyColor of an object remains the same under
different illuminations. However, when context changes the color of an object may
look different.
R. B
eau Lotto at U
niversity College, L
ondon
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HOW AND WHY DO WE TASTE CERTAIN SENSATIONS?
Taste
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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)
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Taste Receptors on the Tongue
The receptors for the human sense of taste are located on the tongue and on the soft palate. There are just five stimuli to which these receptors respond. These are: sweet (as in sugar) sour (as in acidic substances like lemon juice) bitter (strong coffee or quinine in tonic water) salt (table salt) umami (monosodium glutamate, savouries, soya
sauce, crisps)
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Old Research
The traditional view is that tastes are detected on different parts of the tongue.
New researchThe taste buds are
still found in the same areas on the tongue but each one can detect all five tastes.
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Taste Receptors on the Tongue
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Perception of Taste
Smell: chewing helps to transfer more odor from the mouth to the back of the nose. several million receptor cells per square centimeter
respond to thousands of chemicals in the food. Sight: plays an unexpectedly important role
in our perception of flavors. The taste of a colorless, shapeless food is extremely difficult to recognize.
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HOW CAN WE HEAR WHAT WE DO?
Audition
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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
hair cells of the inner ear.
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Sound Characteristics
1. Frequency (pitch)2. Intensity (loudness)3. Quality (timbre)
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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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Our Friends the Elephants
Elephants are very vocal creatures and yet we didn't really know this until Katy Payne discovered in 1984 that much of their talk is below the threshold of human hearing. We can only hear 40% of the
sounds elephants make. An Elephant greeting! http://
www.birds.cornell.edu/brp/elephant/sections/dictionary/greetings.html
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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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Loudness of Sound
70dB120dB
Richard K
aylin/ Stone/ Getty Im
ages
Thunderhttp://youtu.be/0hcvmnnDzJ0
Rock Band http://youtu.be/CSvFpBOe8eY
Subway Noiseshttp://youtu.be/7ws4cnnLYiU
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Quality (Timbre)Quality (Timbre): Characteristics of sound from a zither and a guitar allows the ear to
distinguish between the two.
http
://ww
w.1
christia
n.n
et
ww
w.ja
mesjo
nesin
strum
en
ts.com
Zither http://www.youtube.com/watch?v=bxKdKUZP41Y
Guitar http://www.youtube.com/watch?v=JsD6uEZsIsU
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OvertonesOvertones: Makes the distinction among
musical instruments possible.
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The EarD
r. Fred Hossler/ V
isuals Unlim
ited
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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.
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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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Theories of Audition
Place Theory suggests that sound frequencies stimulate the basilar
membrane at specific places resulting in perceived pitch.
http
://ww
w.p
c.rhu
l.ac.u
k
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74Theories of AuditionFrequency 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.
SoundFrequency
Auditory NerveAction Potentials
100 Hz200 Hz
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Localization of SoundsBecause we have two ears, sounds that reach one ear faster than the other ear
cause us to localize the sound.
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76Localization of Sound1. Intensity differences
2. Time differences
Time differences as small as 1/100,000 of a second can cause us to localize sound. The head acts as a “shadow” or partial sound
barrier.
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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.
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Hearing Deficits
Older people tend to hear low frequencies well but suffer hearing loss when listening for high
frequencies.
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Deaf Culture
Cochlear implants are electronic devices that enable the brain to hear sounds.
Cochlear ImplantDeaf Musician
EG
Images/ J.S. W
ilson ©
Wolfgang G
stottner. (2004) Am
erican Scientist, V
ol. 92, Num
ber 5. (p. 437)
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WHAT SENSATIONS DO WE FEEL AND HOW?
Touch
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Other Important Senses
The sense of touch 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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Pain
Pain tells the body that something has gone wrong. Usually pain results from damage to
the skin and other tissues. A rare disease exists in which the afflicted person feels no
pain.
Ashley Blocker (right) feels neither painnor extreme hot or cold.
AP Photo/ Stephen M
orton
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Biopsychosocial Influences
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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.
Gary C
omer/ PhototakeU
SA.com
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Pain Control
Pain can be controlled by a number of therapies including, drugs, surgery,
acupuncture, exercise, hypnosis, and even thought distraction.
Todd Richards and A
ric Vills, U
.W.
©H
unter Hoffm
an, ww
w.vrpain.com
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WHY DO SMELLS TRIGGER OTHER SENSES?
Smell
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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.
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Smell
Like taste, smell is a chemical sense. Odorants enter the nasal cavity to stimulate
5 million receptors to sense smell. Unlike taste, there are many different forms of
smell.
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Age, Gender, and Smell
Ability to identify smell peaks during early adulthood, but steadily declines after that. Women are better at detecting odors than
men.
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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). That is why strong memories are
made through the sense of smell.
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The process of selecting, organizing, and interpreting sensory information, which
enables us to recognize meaningful objects and events.
Chapter 6 Perception
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Selective Attention
Perceptions about objects change from moment to moment. We can perceive different forms of the Necker cube;
however, we can only pay attention to one aspect of the object at a time.
Necker Cube
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Inattentional Blindness
Inattentional blindness refers to the inability to see an object or a person in our midst.
Simmons & Chabris (1999) showed that half of the observers failed to see the gorilla-suited assistant in a
ball passing game.
Brain Games video clip.
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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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Perceptual Illusions
Illusions provide good examples in understanding how perception is
organized. Studying faulty perception is as important as studying other
perceptual phenomena.
Line AB is longer than line BC.
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Tall Arch
In this picture, the vertical
dimension of the arch looks
longer than the horizontal
dimension. However, both
are equal.
Rick F
riedman/ B
lack Star
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