1. Chapter 6 (B): Thresholds and Sensory Adaptation

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
Light
Brightness
Sound
Volume
Pressure
Weight
Sugar
Sweet

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
Stimulus Intensity (lumens)
Absolute Threshold:

5. 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
Type I. Error: False Positive “Miss”
Type II. Error: False Negative “False Alarm”

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. of the weight of a quarter when one is not holding anything else?
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
Research Study Response #5: “Take a Long Look” (Pgs )