Psychophysics

Question 1

What is the psychophysical function?

Answer 1

‘If I put twice as much salt in my soup, is it twice as salty?’
NOT TRUE, psychological intensity varies to actual intensity (grows exponentially).

Question 2

Define the Just-Noticeable Difference

Answer 2

The smallest difference you can detect in a change in stimulus.
Changes depending on the magnitude of the stimulus.

Question 3

Weber’s Law

Answer 3

The JND is a constant proportion of the stimulus intensity, how much you have to change a stimulus for it to be noticeable.
Specific for each sense:
-Pitch = 1/333
-Brightness = 1/60
-Loudness = 1/10
-Taste = 1/5

Question 4

Outline perceptual thresholds

Answer 4

When is a stimulus just perceivable? or when is a difference perceivable?
No absolute threshold for perception, neural machinery is noisy and lacks consistency.

Question 5

What are the three threshold finding methods?

Answer 5

1. Method of constant stimuli
2. Method of adjustment
3. Method of limits
   ALL HAVE RESPONDER BIAS

Question 6

Outline Method of Constant Stimuli

Answer 6

• Non-sequential choices

- Slower, no order effects

Question 7

Outline Method of Adjustment

Answer 7

• PP adjusts stimulus

- Quick

Question 8

Method of Limits

Answer 8

• Uses ascending and descending trials

- Can predict when stimulus is close.

Question 9

Outline Signal Detection Theory

Answer 9

• You make a trade-off between these types of errors depending on your threshold, trading off false alarms and misses.
• If you reduce your false alarms, you might get an increase in misses
• Where you place your threshold depends on the costs and biases of errors

Question 10

Example of Signal Detection Theory

Answer 10

• Phantom phone buzz, because you perceive messages as important so don’t really mind if its a false alarm because you don’t want misses.
• Your perceptual system through experience lowers your criteria/threshold

Question 11

Outline ROC Curves

Answer 11

• Graph the number of false positives on the x-axis and the number of hits on the y-axis, put a point where the individual hits.
• If there’s fewer hits, consequently fewer false alarms (A), with more hits there will be more false alarms (B).
• A and B have the same sensitivity but just have different biases.

Question 12

What is d’ ?

Answer 12

A measure of sensitivity

d’ = Z(fa) - Z(hits)

Question 13

What is a Z-score?

Answer 13

Distance in standard deviations from the extended score.
Converts a number into another number
In –> a proportion between 0 and 1
Out –> a number between -infinity and +infinity

Question 14

How can you measure accuracy in detection and discrimination where bias can’t contribute?

Answer 14

Use forced choice decisions e.g. is the stimulus on the left or right?