Chapter 6 B Thresholds and Sensory Adaptation Psychophysics

Chapter 6 (B): Thresholds and Sensory Adaptation

Psychophysics § Psychophysics: § The study of relationships between the physical characteristics of stimuli (such as their intensity) and our psychological experience of them Physical World Psychological World Light Brightness Sound Volume Pressure Weight Sugar Sweet

Psychophysics § What are some factors that influence how you perceive the physical world? § Why is perception subjective?

Thresholds § Absolute Threshold: Proportion of “Yes” Responses 0. 00 0. 50 1. 00 § The minimum stimulation needed to detect a particular stimulus 50% of the time 0 5 10 15 20 Stimulus Intensity (lumens) 25

Signal Detection Theory § Signal Detection Theory: § Predicts how and when we detect the presence of a faint stimulus (signal) amid background stimulation (noise) § Assumes there is no single absolute threshold § Assumes detection depends partly on a person’s experience, expectations, motivation, and alertness

Signal Detection Theory

Thresholds § Subliminal: § Below one’s absolute threshold for conscious awareness

Thresholds § Difference Threshold: § The minimum difference between two stimuli required for detection 50% of the time § Just Noticeable Difference (JND)

Thresholds § Why is it easier to detect the difference of the weight of a quarter when one is not holding anything else?

Thresholds § Weber’s Law: § The principle that, to be perceived as different, two stimuli must differ by a constant percentage (rather than a constant amount) § Light: Differ in intensity by 8% § Weight: Differ by 2% § Sound: Differ in frequency by 0. 3%

Sensory Adaptation § Sensory Adaptation: § Diminished sensitivity as a consequence of constant stimulation

Review § What is psychophysics? How does it connect sensation with perception? § What is an absolute threshold? § What are some implications of Signal Detection Theory? § What does Weber’s Law suggest about difference thresholds?

Homework § Research Study Response #5: “Take a Long Look” (Pgs. 36 -42)