Sensation and Perception
Chapter 3
Sensation & Perception
• There are five primary senses:
• vision,
• hearing,
• touch,
• taste,
• and smell—
• And several secondary senses including:
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balance and pain.
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Chapter Goals
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Learn how the senses detect sensory information
Learn how this sensory information is actively
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organized
interpreted
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What is the difference between
Sensation and Perception?
Sensation and perception are intimately related in
everyday experience, but they are not the same.
• Sensation is the sensory process that
• detects visual, auditory, and other sensory stimuli
• and transmits them to the brain.
• Perception is the brain process that:
• actively organizes sensory information
• and interpretes sensory information
Sensation furnishes the raw material of sensory experience,
while perception provides the finished product.
Sensation
Basic Definitions
• Absolute Threshold
• Difference Threshold
• Signal Detection Theory
• Transduction
• Sensory Adaptation
Absolute Threshold
• The minimum stimulus intensity that a person can detect.
• Psychologists arbitrarily define the absolute threshold as
“the minimum amount of sensory stimulation that can be
detected 50% of the time.”
Absolute thresholds for the
five primary senses in humans
Let’s see how well y’all do at estimating these thresholds
1. Vision, a candle flame ? mile(s) away on a clear night
2. Hearing, a watch ticking ? feet away;
3. Taste, 1 teaspoon of sugar dissolved in ? of water
4. Smell, a single drop of perfume in a ? .
5. Touch, a bee’s wing falling a distance of ? onto your
cheek.
Absolute thresholds for the
five primary senses in humans
1. vision, a candle flame 30 miles away on a clear night
2. hearing, a watch ticking 20 feet away
3. taste, 1 teaspoon of sugar dissolved in 2 gallons of water
4. smell, a single drop of perfume in a three-room house
5. touch, a bee’s wing falling a distance of 1 centimeter onto
the cheek.
Difference Threshold
• The minimum amount by which stimulus intensity must
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be changed in order to produce a just noticeable change
in sensation.
The JND is the smallest change in sensation that a
person is able to detect 50% of the time.
Weber’s law:
The law states that the just noticeable difference
(JND) for all the senses depends on a proportion or
percentage of change in a stimulus rather than on a
fixed amount of change.
Signal Detection Theory
• A quantitative treatment of detection and
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discrimination performance, in which the observer is
characterized as a maker of statistical decisions.
The system also prescribes techniques that allow the
observer's sensitivity to the stimulus to be estimated
independently of the observer's criterion, or
preference for particular responses.
The view that the detection of a sensory stimulus
involves both discriminating that stimulus from
“noise” and deciding whether the stimulus is actually
present. Deciding that a stimulus is present depends
partly on the probability that the stimulus will occur
and partly on the receiver biases.
Also called signal decision theory.
Noise
• Two Types:
• External
• Internal
• Characteristics
• Always present
• Independent of signal
• Level varies
• Sensory systems always attempting to compensate
for noise.
Transduction
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The process where by receptors change or convert the
sensory stimulation into neural impulses.
The neural impulses are transmitted to precise
locations in the brain
You experience a sensation only when
the appropriate part of the brain is stimulated.
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Sensory receptors
• The body’s sense organs contain specialized cells
called sensory receptors
• They detect and respond to one type of sensory stimuli
• They provide the essential link between the physical
sensory world and the brain.
• discriminating a stimulus from background “noise”
• deciding whether the stimulus is actually present.
• They can be stimulated by noise but are designed to
minimize these effects.
Inappropriate Stimulation
• Can result in
unusual sensations!
Sensory Adaptation - Definition
The process of becoming less sensitive to an
unchanging sensory stimulus over time.
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Sensory Adaptation
• All of our senses are more receptive, more
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finely tuned, to changes in sensory stimuli
than to sameness.
After a time the sensory receptors grow
accustomed to constant,unchanging levels of
stimuli so that we notice them less and less, or
not at all.
After Images in Color
•Stare at the eye of the red parrot while you count slowly to 20, then
look immediately at one spot in the empty bird cage.
•The faint, ghostly image of a blue-green bird will appear in the cage.
•Try the same thing with the green cardinal.
•A faint magenta bird will appear in the cage.
Vision
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Light
Particle or wave?
Electromagnetic spectrum
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Electromagnetic Spectrum
760 – 380 nm
“Radio” Spectrum
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1,000
Kilo Hertz (KHz)
1,000,000
Mega Hertz (MHz)
1,000,000,000 Giga Hertz (GHz)
• AM Radio
• FM Radio
• Cordless Phone,
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1 x 103
1 x 106
1 x 109
550 KHz to 1600 KHz
88 MHz to 108 MHz
Wi-Fi b
Microwave oven
New Cordless Phone
Wi-Fi a
Modern CPUs
2.5 GHz
2.5 GHz
5 GHz
1- 3 GHz
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The Eye
• Cornea, Iris, and
• Pupil
• Lens and Retina
• Rods and Cones
• Retina to Brain
• Visual Cortex
The Pupils
• The pupils respond to emotions as well as to light.
• When a person looks at someone or something highly
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desirable, the pupils dilate
The pupils also dilate when a person is frightened,
telling a lie, or sexually aroused.
Pupil size is also related to mental effort—the more
intense the mental activity, the larger the pupils
become.
That’s My Story
Artist: Collin Raye
she said Where you been; so I thought real hard
and said I fell asleep in that hammoc in the yard
she said You don't know it boy but you just blew it
and I said Well that's my story and I'm stickin' to it
That's my story - Oh that's my story
Well I ain't got a witness and I can't prove it
But that's my story and I'm stickin' to it
(signature)
I got that "deer in the headlight" look
She read my face like a cover of a book
and said Don't expect me to believe all that static
Cause just last week I threw that hammoc in the attic
I must've got sucked in, cause you can see right through it
And I stutterred well that's my story and I'm stiiiiickin' to it
That's my story - (that's my story)
Oh that's my story - (that's my story)
Yeah I ain't got a witness and I can't prove it
But that's my story and I'm stickin' to it
(slide solo)
YOU KNOW THE TIME COMES WHEN A WISE MAN KNOWS
THE BEST THING THAT HE CAN DO
IS JUST LOOK HER IN THE EYE AND
BEG FOR MERCY AND FACE THE BITTER TRUTH
Well honey me and the boys played cards all night
There wadn't any hanky panky; not a woman in sight
I know I should've called and baby IIII'm really sorry
Let's get a cellular phone and you won't have to worry
You know how much I love you and I'm ready to prove it
And that's my story and I'm stickin' to it
That's my story - (that's my story)
Wo that's my story - (that's my story)
Well I ain't got a witness and you know I can't prove it
But that's my story and man I'm stickin' to it
You know I ain't gonna do a thing darlin' unless you approve it
Well that's my story and I'm stickin' to it
The Lens
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Composed of many thin layers
Looks like a transparent disc.
Allows focusing on objects closer than 20 feet.
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It flattens as it focuses on objects viewed at a distance
It becomes more spherical, bulging in the center, as it
focuses on close objects.
This flattening and bulging action of the lens is known as
accommodation.
The Lens and Age
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With age, the lens loses some elasticity.
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it loses the ability to change its shape to
accommodate for near vision,
• called presbyopia (“old eyes”).
Focus Errors
End Part “a”
Color Vision
• Hue
• Saturation
• Brightness
• Theories
• Trichromatic
• Opponent-Process
News Flash! New receptors detected in the human eye.
These receptors apparently send an “illumination level”
Signal directly to the brain.
Hearing
• The Ear
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Outer Ear
Middle Ear
Inner Ear
• Theories of Hearing
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Place Theory
Frequency Theory
http://www.bigchalk.com/cgi-bin/WebObjects/WOPortal.woa/wa/HWCDA/file?fileid=115378&flt=High_
School&pathTitles=/Hearing_Balance_(Ear)/Anatomy_of_the_Ear/Ear_--_
general_description_diagrams&version=2&tg=Science
Hearing Additional Reading
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Additional Links:
Auditory & vestibular pathways -- tutorial
Cochlear fluids
Ear -- general description & diagrams
Ear -- general information With diagrams
Inner ear anatomy -- diagram
Inner ear anatomy -- pictures & descriptions
Signals From a hair cell
Virtual tour of the ear -- very comprehensive site
What Is Earwax?
http://www.bigchalk.com/cgi-bin/WebObjects/WOPortal.woa/Homework/
High_School/Science/Sensory_Systems/Hearing_Balance_(Ear)/Anatomy_
of_the_Ear_54024.html
The Human Ear 2
• Bone Conduction
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Description
Issues for Hearing Aids
Role of bone conduction in
the self-perception of speech
Testing Babies
• Hearing Loss
• Bone Conduction Aids
• NIOSH
• Commercial View
• Rockers!
Rhodes Audiophone
A bone conduction fan made by R. S. Rhodes
is shown in this illustration. Assuming a good
set of teeth, this fan provided a benefit of up
to 30 dB, a gain comparable to listening to
someone speaking from a distance of 2 feet
rather than 64 feet.
Smell and Taste
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Smell (Olfaction)
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Olfactory epithelium
Olfactory bulbs
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Taste
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Taste Buds
Taste Sensitivities
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Non-tasters
Medium-tasters
Super-tasters
Skin Sense
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Pain
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The Gate-Control Theory
Psychological and Cultural Influences
Endorphins
Gestalt Principals of Perceptual
Organization
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Figure-Ground
Grouping
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Similarity
Proximity
Continuity
Closure
Demonstrations
Main Page
Squirming
Interesting Perceptual Links
 http://www.rdc.ab.ca/scottpsych/webite/frames/perception.htm
Figure Ground: The Law
Figure Ground: In Art
Gestalt Principals of Perceptual
Organization, Cont.
• Perceptual Constancy
• Shape Constancy
• Brightness Constancy
• Color Constancy
Depth Perception
• Binocular Depth Cues
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Convergence
Binocular Disparity
• Monocular Depth Cues
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Interposition
Linear perspective
Relative size
Texture gradient
Atmospheric perspective
Shadow or shading
Motion parallax
Extraordinary Perceptions
• Ambiguous Figures
• Impossible Figures
• Illusions
• Muller-Lyer Illusion
• Ponzo Illusion
• Cultural Differences
Additional Influences on Perception
• Bottom-Up and Top-Down Processing
Bottom-up processing approaches emphasize incoming sensory stimuli and
the operations performed on them to build up to a meaningful perceptual
representation.
Top-down processing models emphasize the varying degrees to which
incoming sensory information is shaped, selected, and influenced by
context, expectations, and prior learning.
• Psychological Factors
End of Lecture