Study Questions: Psychophysics/Signal Detection Theory





1.  Define "Psychophysics". Name the psychophysical measures for "detection" and "discrimination", respectively.  Name the methods for measuring them.

2.  Briefly describe each of the above methods for measuring "absolute threshold" in terms of (a) how stimuli are presented, (b) what the subject is required to respond, and (c) its advantages and disadvantages, (d) the expected percentage correct (if that makes any sense) for a stimulus that is extremely weak.

3.  Briefly describe each of the above methods for measuring "difference threshold" in terms of (a) how stimuli are presented, and (b) what the subject is required to respond.

4.  How is "absolute threshold" defined? Why is it defined in this way? Name the labels on x- and y-axes for a psychometric function derived from a detection experiment. Sketch a psychometric function generally obtained.

5.  Define "difference threshold" (i.e. the jnd). Name the labels on x- and y-axes for a psychometric function derived from a discrimination experiment. Describe Weber's law.

6.  An experimenter presented an observer with a light of 100 units intensity and then varied its intensity.  The observer did not notice the change until the light reached an intensity of 110 units. (a) What is the jnd for this case? (b) What is the value of the Weber's fraction? (c) How many units of light intensity are required to discriminate from a light of 1000 units?

7.  Name the laws that specify the relationship between the magnitude of sensation and stimulus magnitude (e.g., intensity).

8.  Briefly state Fechner's law. What is its fundamental assumption? How did Fechner use Weber's results to derive the psychophysical relation?

9.  Briefly state Steven's law. What is its fundamental assumption? What are the typical experimental paradigms used to derive Steven's law?

10.  [If this material is covered] Briefly describe the two classes of static invariances. Give an example to each of the classes.

11.  How can theories of psychophysical threshold deal with the fact that subjects on occasion report the presence of a stimulus which was in fact absent?

12.  SDT (signal detection theory or sensory decision theory). (a) What are the two kinds of trials in such an experiment? (b) What are the two kinds of responses in such an experiment? (c) Give a table of the possible outcomes of such an experiment. (d) Name three ways an experimenter can cause a subject in such an experiment to modify his/her criterion for saying "yes".