Perception Flashcards
What is psychophysics?
The study and measurement of the relationship between physical qualities and the corresponding mental perceptions (mental representations/ percepts_
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
d) how a persons mood affects their memory
What is the name for the amount of change in some physical quantity that is sufficient to trigger a noticeable change in the percept?
The just-noticeable difference
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?
Yes
As an increase in 10,000 = change in 1/6th= well above Weber fraction which is defines the JND
Afifa is great at reading other peoples emotions, but worries excessively that she has offended people
How would you describe her?
Afifa has a strong bias towards making FALSE ALARMS, high also high sensitivity
In signal detection terms, if you adjust your criterion so that you minimise misses what is also likely to happen?
The number of hits will increase, and the number of false alarms will increase
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
b) Pierre makes more mistakes than Rashid
We know Rashid is more sensitive so his rate of errors will be lower
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?
2.12
= d’= z(hits)-z(false alarms)
= z(0.8)-z(0.1)
= 1.34-(-0.79)= 2.12
What is the psychophysical function?
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
What is a consequence of the psychophysical function?
The amount of psychological changed compared to physical change depends on where you are on the graph
What is a core problem of psychology?
- Psychometrics = techniques of measurement
- are peoples responses reliable
- are they consisten
- are they true reports
What is the Just Noticeable Difference (JND) ?
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
What is Webers Fraction?
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
What is Webers Law?
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
How do you find a threshold for Webers Fraction?
1) Method of constant stimuli
2) method of limits
3) method of adjustment
What is the method of constant stimuli?
- 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
What is the method of limits
- 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
What is the method of adjustment?
- pts adjusts stimulus themselves to find their threshold
= quick
What is the issue with methods of adjustment, method of constant stimuli and method of limits?
Respondent bias
= influence the response of pts away from accurate/truthful response]
- all measures in psych have this issue
What is Signal Detection Theory?
= 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
How does Signal Detection Theory link to biases and sensitivity?
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
What is a ROCE curve?
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
What is d’?
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
What is the difference between the psychophysical function and the psychometric function?
PSYCHOPHYSICAL FUNCTION=
specific curve (graph) showing stimulus intensity against perceived magnitude.
PSYCHOMETRIC FUNCTION=
a curve relating a stimulus property to detection or discrimination ability
