1. Unit 4(B): Thresholds and Sensory Adaptation Mr. McCormick A.P. Psychology

2. 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 LightBrightness SoundVolume PressureWeight SugarSweet

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

4. Thresholds  Absolute Threshold:  The minimum stimulation needed to detect a particular stimulus 50% of the time Proportion of “Yes” Responses 0.00 0.50 1.00 0 5 10 15 20 25 Stimulus Intensity (lumens)

5. 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

6. Signal Detection Theory

7. Thresholds  Subliminal:  Below one’s absolute threshold for conscious awareness

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

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

10. 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%

11. Sensory Adaptation  Sensory Adaptation:  Diminished sensitivity as a consequence of constant stimulation

12. 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?

13. Homework  Unit 4 Key People  Research Study Response #5: “Take a Long Look” (Pgs. 36-42)  Unit 4 Quiz: “Sensation and Perception”  (T) 11/15/11