Psychology 3215 - 2021

("C-19 Here Again" Edition)

Questions about Psychophysics
to Ponder before Test 1

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1. What was Fechner trying to accomplish when he founded psychophysics? From his viewpoint, what is the absolute threshold and why is it important?

2. How do you determine the absolute threshold? How is it determined using the Method of Limits, the Method of Constant Stimuli, and the Method of Adjustment? How are the methods similar and how are they different?

3. Using the Method of Constant Stimuli, explain how a psychophysical function for the absolute threshold is produced and calculated.

4. What is a difference threshold? How are the data collected? How are the results plotted?

5. Examine the psychophysical function for a difference threshold on the class web site. Be able to determine and explain the reasoning behind such terms as the Point of Subjective Equality, Upper Difference Limen, Lower Difference Limen, the Interval of Uncertainty, and the Just Noticeable Difference.

6. What is Weber's Law? Explain the meaning of the mathematical formula. Be able to interpret JNDs. Be able to compute a JND using Weber’s Law. How can it be used practically?

7. What is Fechner's Law? Explain the meaning of the mathematical formula. What are the units of his scales? What does the shape of the function tell us about the fundamental relationship between perceptual experience and changes in the physical world?

8. What is Stevens' Law?  Explain the meaning of the mathematical formula.  How does his magnitude estimation procedure work and how are the results from that procedure used in his Power Law.

9. Compare and contrast Stevens' and Fechner’s approach to the definition of units on psychological scales.

10. Know the difference in procedures between a Signal Detection experiment and the classical absolute threshold experiment.

11. Know the matrix of possible outcomes for a trial in a Signal Detection experiment.

12. According to Signal Detection Theory, our tendency to say "Yes, I detected it" is controlled by our criterion or decision rule (bias, beta, criterion) and our sensitivity to the difference between the event being there or not (d’). Know how outcome matrices should be examined to separate these two factors. Could a person with a 100% Hit rate be a bad detector?

13. What is a ROC plot? What is on each axis? What is the meaning of the diagonal line?  Practice interpreting curves and points which indicate differences in sensitivity vs. differences in strategy.

14. What is the general detection issue in detecting events like the presence of cancer or bombs?