unit 4(b): thresholds and sensory adaptation mr. mccormick a.p. psychology
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Unit 4(B):Unit 4(B):Thresholds and Thresholds and
Sensory AdaptationSensory AdaptationMr. McCormickMr. McCormick
A.P. PsychologyA.P. Psychology
PsychophysicsPsychophysics
Psychophysics:Psychophysics: The study of relationships between the physical The study of relationships between the physical
characteristics of stimuli (such as their intensity) and characteristics of stimuli (such as their intensity) and our psychological experience of themour psychological experience of them
Physical World
Psychological World
Light Brightness
Sound Volume
Pressure Weight
Sugar Sweet
PsychophysicsPsychophysics
What are someWhat are some factors factors that that influence how youinfluence how you perceiveperceive the the physical worldphysical world??
Why is Why is perceptionperception subjectivesubjective??
ThresholdsThresholds
Absolute Threshold:Absolute Threshold: The minimum stimulation needed to detect a The minimum stimulation needed to detect a
particular stimulus 50% of the timeparticular stimulus 50% of the time
Pro
port
ion
of
“Yes”
R
esp
on
ses
0.0
0 0
.50
1.0
0
0 5 10 15 20 25 Stimulus Intensity (lumens)
Signal Detection TheorySignal Detection Theory
Signal Detection Theory:Signal Detection Theory: 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 stimulation (noise)background stimulation (noise)
Assumes there is no single absolute thresholdAssumes there is no single absolute threshold Assumes detection depends partly on a Assumes detection depends partly on a
person’s experience, expectations, person’s experience, expectations, motivation, and alertnessmotivation, and alertness
Signal Detection TheorySignal Detection Theory
ThresholdsThresholds
Subliminal:Subliminal: Below one’s absolute threshold for conscious Below one’s absolute threshold for conscious
awarenessawareness
ThresholdsThresholds
Difference Threshold:Difference Threshold: The minimum difference between two stimuli The minimum difference between two stimuli
required for detection 50% of the timerequired for detection 50% of the time Just Noticeable Difference (JND)Just Noticeable Difference (JND)
ThresholdsThresholds
Why is it Why is it easiereasier to to
detectdetect the the differencedifference
of the weight of a of the weight of a quarter quarter
when one is when one is notnot holding holding anything else?anything else?
ThresholdsThresholds
Weber’s Law:Weber’s Law: The principle that, to be perceived as different, two The principle that, to be perceived as different, two
stimuli must differ by a constant percentage (rather stimuli must differ by a constant percentage (rather than a constant amount)than a constant amount)
Light: Light: Differ in intensity by 8%Differ in intensity by 8% Weight: Weight: Differ by 2%Differ by 2% Sound: Sound: Differ in frequency by 0.3%Differ in frequency by 0.3%
Sensory AdaptationSensory Adaptation
Sensory Adaptation:Sensory Adaptation: Diminished sensitivity as a consequence of Diminished sensitivity as a consequence of
constant stimulationconstant stimulation
ReviewReview
What is What is psychophysicspsychophysics? How does it ? How does it connect connect sensationsensation with with perceptionperception??
What is an What is an absolute thresholdabsolute threshold??
What are some What are some implications implications of of Signal Signal Detection TheoryDetection Theory??
What does What does Weber’s Law Weber’s Law suggestsuggest about about difference thresholdsdifference thresholds??
HomeworkHomework
Unit 4 Key PeopleUnit 4 Key People
Research Study Response #5: Research Study Response #5: “Take a “Take a Long Look” (Pgs. 36-42)Long Look” (Pgs. 36-42)
Unit 4 Quiz:Unit 4 Quiz: “Sensation and Perception”“Sensation and Perception” (T) 11/15/11(T) 11/15/11
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