Psychoacoustics & Signal Detection Theory

Question 1

What brought about the study of psychoacoustics?

Answer 1

• In the 1960s, all psychoacousticians were behavioral psychologists whose findings were based on their own observations (i.e. Skinner)
• No way of quantitatively measuring abstract concepts
• Opposed such explanations based on private non-observable events (i.e. cognition)

Question 2

What is Signal Detection Theory?

Answer 2

-Theory of how decisions are made in uncertain contexts (noisy signals)

Question 3

What does SDT need?

Answer 3

• Clear operational definitions
• Behavior to be measurable/observable
• Behavior consequence of actions
• Behavior studied in strict, scientific manner

Question 4

Describe psychometric functions.

Answer 4

• Y axis: P(correct)
• X axis: Stimulus level (dB)
• Want to find point where listener hears stimulus 50% of the time (threshold)

Question 5

What is threshold?

Answer 5

• Absolute limen; smallest detectable value of a stimulus

- Not a realistic definition because there is variability in an individual’s responses as per SDT

Question 6

What are types of psychoacoustic tasks?

Answer 6

• Detection (yes-no)
• Discrimination
• Scaling
• Matching

Question 7

Describe method of constant stimuli.

Answer 7

• Test all signal levels/conditions with randomized order
• Pros: order effects/learning effects distributed over all conditions
• Cons: slow, can miss threshold

Question 8

Describe adaptive (staircase) procedure.

Answer 8

• Starts easy gets harder
• Need: rule for adaptation, number of turnarounds, average of N turnarounds to get JND
• Just interested in threshold
• Pros: fast
• Cons: learning effects, get stuck in bad place if non-monotonic psychometric function, participant fatigue, highly affected by subject-specific factors, need to do multiple measurements/over multiple sessions, need multiple conditions/randomization

Question 9

What assumptions underlie SDT?

Answer 9

• There exists an internal decision variable that is monotonically related to the magnitude of the stimulus
• The value of the decision variable fluctuates from trial-to-trial
• The variability arises from noise (internal or external), following a Gaussian distribution
• Addition of a signal only changes the mean of the distribution, not the variance
• The subject establishes a cutoff point (decision criteria) to determine if a signal is present

Question 10

Does an unbiased decision criteria always yield the maximum percent correction?

Answer 10

-Yes