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".