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