1 Sensation and Perception. 2 Sensation & Perception How do we construct our representations of the...
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Transcript of 1 Sensation and Perception. 2 Sensation & Perception How do we construct our representations of the...
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Sensation & PerceptionSensation & Perception
How do we construct our representations of How do we construct our representations of the external world?the external world?
To represent the world, we must detect To represent the world, we must detect physical energy (a stimulus) from the physical energy (a stimulus) from the
environment and convert it into neural environment and convert it into neural signals. This is a process called signals. This is a process called sensationsensation..
When we select, organize, and interpret our When we select, organize, and interpret our sensations, the process is called sensations, the process is called
perceptionperception..
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Bottom-up ProcessingBottom-up Processing
Analysis of the stimulus begins with the Analysis of the stimulus begins with the sense receptors and works up to the level of sense receptors and works up to the level of
the brain and mind.the brain and mind.
Letter “A” is really a black blotch broken down Letter “A” is really a black blotch broken down into features by the brain that we perceive as an into features by the brain that we perceive as an
“A.”“A.”
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Top-Down ProcessingTop-Down Processing
Information processing guided by higher-Information processing guided by higher-level mental processes as we construct level mental processes as we construct perceptions, drawing on our experience perceptions, drawing on our experience
and expectations.and expectations.
TTHHE CE CHHTT
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Our sensory and perceptual processes work Our sensory and perceptual processes work together to help us sort out complex images.together to help us sort out complex images.
Making Sense of Making Sense of ComplexityComplexity
“The Forest Has Eyes,” Bev Doolittle
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TransductionTransduction
In sensation, the transformation of In sensation, the transformation of stimulus energy into neural stimulus energy into neural
impulses.impulses.
Example:Example:
Phototransduction:Phototransduction: Conversion of Conversion of light energy into neural impulses light energy into neural impulses
that the brain can understand.that the brain can understand.
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PsychophysicsPsychophysics
A study of the relationship between A study of the relationship between physical characteristics of stimuli and physical characteristics of stimuli and
our psychological experience with them.our psychological experience with them.
Physical WorldPhysical World Psychological Psychological WorldWorld
LightLight BrightnessBrightness
SoundSound VolumeVolume
PressurePressure WeightWeight
SugarSugar SweetSweet
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No
DetectionDetection
Intensity
AbsoluteThreshold
Detected
YesYesNo No
Observer’s Response
Tell when you (the observer) detect the light.
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ThresholdsThresholds
Absolute Threshold:Absolute Threshold: Minimum stimulation needed Minimum stimulation needed to detect a particular stimulus 50% of the time.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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Difference ThresholdDifference Threshold
Difference Threshold:Difference Threshold: Minimum Minimum difference between two stimuli required difference between two stimuli required for detection 50% of the time, also called for detection 50% of the time, also called
just noticeable difference (JND).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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Weber’s LawWeber’s Law
Two stimuli must differ by a constant Two stimuli must differ by a constant minimum percentage (rather than a minimum percentage (rather than a constant amount), to be perceived as constant amount), to be perceived as
different. Weber fraction: k = different. Weber fraction: k = I/I.I/I.
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Signal Detection Theory Signal Detection Theory (SDT)(SDT)
Predicts how and when we detect the Predicts how and when we detect the presence of a faint stimulus (signal) amid presence of a faint stimulus (signal) amid
background noise (other stimulation). SDT background noise (other stimulation). SDT assumes that there is no single absolute assumes that there is no single absolute
threshold and detection depends on:threshold and detection depends on:
Person’s experienceExpectationsMotivationLevel of fatigue
Carol L
ee/ Tony Stone Im
ages
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SDT MatrixSDT Matrix
DecisionDecision
YesYes NoNo
SignalSignal
PresentPresent HitHit MissMiss
AbsentAbsentFalseFalseAlarmAlarm
Correct Correct RejectionRejection
The observer decides whether she hears the tone or not, based on the signal being present or not. This translates into four
outcomes.
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Sensory AdaptationSensory Adaptation
Diminished sensitivity as a consequence of Diminished sensitivity as a consequence of constant stimulation.constant stimulation.
Put a band aid on your arm and after awhileyou don’t sense it.
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Subliminal PerceptionSubliminal Perception
sensing without awarenesssensing without awareness
is it possible?is it possible?
can it be used for persuasion?can it be used for persuasion?
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Perception in BrainPerception in Brain
Our perceptions are a combination of sensory (bottom-up) and cognitive (top-
down) processes.
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Other Important SensesOther Important Senses
The sense of touch is a mix of four distinct The sense of touch is a mix of four distinct skin senses—pressure, warmth, cold, and skin senses—pressure, warmth, cold, and
pain.pain.
Bru
ce A
yers
/ Sto
ne/ G
etty
Im
ages
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Skin SensesSkin Senses
Only pressure has identifiable receptors. All Only pressure has identifiable receptors. All other skin sensations are variations of other skin sensations are variations of
pressure, warmth, cold and pain.pressure, warmth, cold and pain.
Burning hot
Pressure Vibration Vibration
Cold, warmth and pain
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PainPain
Pain tells the body that something has gone Pain tells the body that something has gone wrong. Usually pain results from damage to the wrong. Usually pain results from damage to the skin and other tissues. A rare disease exists in skin and other tissues. A rare disease exists in
which the afflicted person feels no pain.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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Gate-Control TheoryGate-Control Theory
Melzak and Wall (1965, 1983) proposed that Melzak and Wall (1965, 1983) proposed that our spinal cord contains neurological “gates” our spinal cord contains neurological “gates” that either block pain or allow it to be sensed.that either block pain or allow it to be sensed.
Gary C
omer/ PhototakeU
SA.com
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Pain ControlPain Control
Pain can be controlled by a number of therapies Pain can be controlled by a number of therapies including, drugs, surgery, acupuncture, exercise, including, drugs, surgery, acupuncture, exercise,
hypnosis, and even thought distraction.hypnosis, and even thought distraction.
Todd R
ichards and Aric V
ills, U.W
. ©
Hunter H
offman, w
ww
.vrpain.com