Perception

Question 1

What is psychophysics?

Answer 1

The study and measurement of the relationship between physical qualities and the corresponding mental perceptions (mental representations/ percepts_

Question 2

Which isn’t a psychophysical question?

a) how much louder is a stero is for each notch you turn up the volume
b) is it easier to see a candle on a dark night at 200m or hear a pin drop in a quiet room from 2m
c) whether tea taste better with milk added before or after the tea
d) how a persons mood effects their memory

Answer 2

d) how a persons mood affects their memory

Question 3

What is the name for the amount of change in some physical quantity that is sufficient to trigger a noticeable change in the percept?

Answer 3

The just-noticeable difference

Question 4

The Weber fraction for perceived intensity of white light is 1/60
If a football pitch has lights of 60,000 lumens (measure of physical light emitted) , but change to 70,000 strength can an average person tell?

Answer 4

Yes

As an increase in 10,000 = change in 1/6th= well above Weber fraction which is defines the JND

Question 5

Afifa is great at reading other peoples emotions, but worries excessively that she has offended people
How would you describe her?

Answer 5

Afifa has a strong bias towards making FALSE ALARMS, high also high sensitivity

Question 6

In signal detection terms, if you adjust your criterion so that you minimise misses what is also likely to happen?

Answer 6

The number of hits will increase, and the number of false alarms will increase

Question 7

d’(d prime) is a measure of sensitivity. Rashid has a higher d’ than Pierre. Which of these is defs true?

a) Rashid has fewer false alarms than Pierre
b) Pierre makes more mistakes than Rashid
c) Rashid makes fewer false alarms than he does misses
d) Pierre makes more correct rejections than he does hits

Answer 7

b) Pierre makes more mistakes than Rashid

We know Rashid is more sensitive so his rate of errors will be lower

Question 8

d'= z(hits) -z(false alarms)
Misha has a hit rate of 0.8, and a false alarm rate of 0.1
z(0.8)= 1.34
z(0.1)= -0.79
What is Mishas d'score?

Answer 8

2.12
= d’= z(hits)-z(false alarms)
= z(0.8)-z(0.1)
= 1.34-(-0.79)= 2.12

Question 9

What is the psychophysical function?

Answer 9

e.g. if we double the sound does this double the physical intensity?
No, the psychophysical function is a curve on a graph
- y axis= magnitude estimate (psychological intensity)
- x axis = stimulus magnitude (physical intensity)
- the mind has compressed the range of possible physical stimuli- so you can perceive and understand a huge range in physical variation and compress into a psychological range
= shrinking large amount of physical variation into a comprehendible amount of psychological range

Question 10

What is a consequence of the psychophysical function?

Answer 10

The amount of psychological changed compared to physical change depends on where you are on the graph

Question 11

What is a core problem of psychology?

Answer 11

• Psychometrics = techniques of measurement
• are peoples responses reliable
• are they consisten
• are they true reports

Question 12

What is the Just Noticeable Difference (JND) ?

Answer 12

The smallest difference you can detect in change in stimulus
= the amount of change in some physical quantity that is sufficient to trigger a noticeable change in the percept

Question 13

What is Webers Fraction?

Answer 13

Tells you how sensitive each sense is for changes in that particular stimulus

• threshold= when a stimulus is just perceivable
• threshold isn’t clear cut= people not perfectly consistent

Question 14

What is Webers Law?

Answer 14

The JND is a constant proportion of the stimulus intensity
= look at picture
= change in intensity/ intensity = constant
= how much you have to change a stimulus for it to be noticeable

Question 15

How do you find a threshold for Webers Fraction?

Answer 15

1) Method of constant stimuli
2) method of limits
3) method of adjustment

Question 16

What is the method of constant stimuli?

Answer 16

• e.g. take screenshots of the blured candycrush

show 2/10, then 7/10, then 8/10 etc and ask each time if see the stimulus = takes out the sequence

Question 17

What is the method of limits

Answer 17

• start at one end= from nothing and go up= gradually reduce noise and say when you see the desired stimuli
  = candy crush example= mix up and gradually get clearer

Question 18

What is the method of adjustment?

Answer 18

• pts adjusts stimulus themselves to find their threshold

= quick

Question 19

What is the issue with methods of adjustment, method of constant stimuli and method of limits?

Answer 19

Respondent bias
= influence the response of pts away from accurate/truthful response]
- all measures in psych have this issue

Question 20

What is Signal Detection Theory?

Answer 20

= way of categorising the errors and trade off inherent in that respondent bias
= using hits or misses
- depending on your threshold you will trade off false alarms and misses e.g. increase false alarms= decrease in misses

Question 21

How does Signal Detection Theory link to biases and sensitivity?

Answer 21

Signal Detection Theory gives a method for distinguishing the sensitivity from the bias of the respondent
- all perceivers have a bias (not a bad thing) and it will be influenced by the costs and benefits of the response outcomes

Question 22

What is a ROCE curve?

Answer 22

Receiver Operator Characteristics curve
= graph of no. of false positivies on the x axis and the no. of hits on the y axis
- aim to be as far from the diagonal line as possible
- shows how hits and false alarms vary as bias varies
- all the points in the curve have the same sensitivity but different biases
- different curves have different sensitivities

Question 23

What is d’?

Answer 23

d' = d prime
= measure of sensitivity 
d'= z(hits)- z(false alarms)
- z-score= distance in SDs from the expected score 
- z is a function

Question 24

What is the difference between the psychophysical function and the psychometric function?

Answer 24

PSYCHOPHYSICAL FUNCTION=
specific curve (graph) showing stimulus intensity against perceived magnitude.
PSYCHOMETRIC FUNCTION=
a curve relating a stimulus property to detection or discrimination ability