Psychophysical Models

Question 1

What are psychophysical models?

Answer 1

Mapping the relation between physical stimuli and sensation of that stimuli.

Question 2

Why use psychophyical models?

Answer 2

As designers,need to know not just if two stimuli are different, or if a stimulus is there, but if people can detect the difference, or the existence.

(Exampe: Can they even hear the tone? See that the light is on, and flashing?)

Question 3

What are some examples of psychophysical models?

Answer 3

1) How much difference in coloration can exist before customers notice (implications for process control)?
2) How much change in vibration is necessary before the change is detectable?
3) How much does an element have to change before that change is detectable?

Question 4

What is Just Noticeable Difference (JND)?

Answer 4

Smallest noticeable change in sensation.

Question 5

Difference Threshold (DT)?

Answer 5

Amount of change in the stimuli which causes the JND.

Question 6

What is Absolute Threshold?

Answer 6

The smallest amount of stimuli that can be detected.

Question 7

What is Weber’s Law?

Answer 7

DT is proportional to the stimulus intensity () phi

(DT = k )

(for louder sounds, takes more of a change to be noticed)

Question 8

What is the measurement of absolute threshold?

Answer 8

When stimulus value is perceptible 50% of the time.

Question 9

What is the measurement of DT?

Answer 9

Given a standard stimulus, what is the DT that produces a JND?

Question 10

What is Point of Subjective Equality (PSE)?

Answer 10

Value of comparison stimulus that is judged greater than the standard 50% of the time. P(greater) = .5 (chance)

Question 11

What are examples of psychophysical measurement usage?

Answer 11

• Examined sensitivity of inspectors for feeling cracks in metal cylinders
• Felt with metal probe of different diameter end
• Plotted p(said crack) vs. crack size
• Compared absolute threshold across probe sizes – increased as probe tip increased (less sensitive)