PSY 429 Experimental Psychology
Class Exercise #4
Psychophysics
PSY 429 Experimental Psychology
Class Exercise #4
Psychophysics
1. Use the method of limits to determine the absolute threshold for a visual stimulus. The data from one subject are provided below.
Light Intensity 1 2 3 4 5 6 10 YES 9 YES YES YES 8 YES YES YES YES 7 YES NO YES YES YES YES 6 NO NO YES NO YES NO 5 NO NO NO NO NO 4 NO NO NO 3 NO NO NO 2 NO NO 1 NO
2. Use the method of limits to measure an observer's ability to detect sweetness. The data from one subject are provided below.
Arbitrary Units of
Sweetness 1 2 3 4 5 6 1 Not Sweet NO NO NO 2 NO NO NO NO NO NO 3 NO YES NO YES YES YES 4 YES YES YES YES YES 5 Very Sweet YES YES YES
3. Suppose you manufacture candy bars and you want to produce a new version of a popular favorite that is noticeably larger, but you don't want it to be too big because of the expense. Use the method of limits to determine what size is perceived to be larger than the original bar. Suppose the original bar of candy is 6 ounces. For the data below, L stands for "larger" and S stands for "smaller" and E stands for "equal." [Assume that the six trials below are representative of the data from 1000 trials.]
Ounces 1 2 3 4 5 6 9.0 L L 8.5 L L L 8.0 L L L 7.5 E E L 7.0 E L E L L 6.5 E E E E E 6.0 S E S L E E 5.5 E E S E 5.0 E E S 4.5 S E S 4.0 S S S 3.5 S S S 3.0 S S S 2.5 S S S 2.0 S S 1.5 S 1.0 S
4. Draw the signal + noise (signal present) distribution and the noise (signal absent) distribution under the circumstances in which the observer has occasional difficulty detecting the presence of the signal.
5. Draw the signal + noise (signal present) distribution and the noise (signal absent) distribution under the circumstances in which the observer has the ability to detect the presence of the signal 100% of the time.
6. Draw the signal + noise (signal present) distribution and place the decision criterion to reflect a HIT rate of
a. 0.95b. 0.75
c. 0.50
d. 0.25
7. Draw the noise (signal absent) distribution and place the decision criterion to reflect a FALSE ALARM rate of
a. 0.25b. 0.50
c. 0.75
d. 0.95
8. Define a "liberal" decision criterion.
9. Define a "conservative" decision criterion.
10. Draw an ROC (receiver operating characteristic) function and label the two axes, identify d' and identify the part of the graph reflecting a liberal decision criterion and the part reflecting a conservative decision criterion.
11. What factors or conditions can affect the decision criterion, whether it will be liberal or conservative?
12.What does d' reflect?
13. What does B (beta) reflect?
14. Typical results are presented in the table below of a subject's response pattern when told that the stimulus (signal) is presented 90% of the time. Calculate d'.
Present 0.95 0.05 Absent 0.63 0.37
15. Typical results are presented in the table below of a subject's response pattern when told that the stimulus (signal) is presented 10% of the time. Calculate d'.
Present 0.35 0.65 Absent 0.04 0.96
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