Topic Seventeen - Psychophysical Methods

Question 1

What is the difference between absolute (detection) thresholds and difference thresholds?

Answer 1

• The absolute threshold is the smallest detectable stimulus
• The difference threshold is the magnitude of the smallest change in a stimulus property that can be detected

Question 2

What is the relationship between absolute and difference thresholds to sensitivity and resolution?

Answer 2

• For absolute thresholds, a high sensitivity means a low threshold
• For difference thresholds, a high resolution corresponds to a low just noticeable difference

Question 3

How is the method of limits applied?

Answer 3

• Made up of descending and ascending staircases
• Puretone audiometry protocols

Question 4

How is the method of adjustment applied?

Answer 4

• Subject controls the magnitude of the stimulus and alters the parameter until the stimulus is barely detectable or at the same level as another stimulus
• The difference between the variable stimuli and the standard one is recorded. The mean is then taken giving an average error.
• Bekesy audiometry

Question 5

How is the method of constant stimuli applied?

Answer 5

• Several values of the stimulus are presented at a random order
• Allows for full sampling of the psychometric function
• Threshold is detected at a performance level halfway between the worst and best possible scores

Question 6

What is the effect of response bias on our ability to determine sensitivity and how may it be reduced?

Answer 6

• Response bias is the individual differences participants may have when determining to response or not.
• For example, someone who is worried about making mistakes will wait until they are 100% sure
• It can be reduced by using forced choice
• Minimum response level is 1/number of choices, threshold is the midpoint between minimum response and perfect score

Question 7

How can adaptive tracks be used to target specific points on the psychometric function?

Answer 7

• Adaptive tracks change the stimulus level based upon the participant’s responses
• Changing the stimulus level after certain combinations of correct / incorrect responses transforms the effective psychometric function so that the threshold being tracked is somewhere other than 50%
• 1-up, 1-down will converge on the 50% threshold
• 1-up, 2-down will converge on the 70.7% threshold

Question 8

How does Weber’s law relate to just-noticeable differences?

Answer 8

• The law states that the difference limen is a constant proportion of the original stimulus
• This means that for smaller stimulus, a smaller difference is needed for a participant to notice
• For a larger stimulus, a larger change is needed for someone to notice a difference
• Weber’s law is not valid for extreme values

Question 9

How is Steven’s Power law applied across multiple stimulus modalities?

Answer 9

• The law states that magnitude ratings follow a power function
• The perceived sensation is proportional to the stimulus intensity raised to a power
• Relates to loudness perception, light perception.