Psycho-physics Flashcards
What is the psychophysical function?
The relation between INTENSITY OF STIMULI and the MAGNITUDE OF SENSATION FELT
Who was the ‘Just noticeable difference’ first described by?
Weber
The intensity level of stimulus may play a role in the just noticeable difference.
If a light is very dim…
You will be more likely to notice a change in intensity
If a BRIGHT LIGHT was turned up
And a dim light was turned up, by the same amount
Which change are you likely to notice?
Dim light
Weber fraction
As stimulus intensity increases, threshold for noticing it (difference threshold) will also increase (constant proportion)
What kind of relationship is the Weber fraction?
A linear relationship
Weber Fraction -
As the ratio between the magnitudes of two stimuli increases…
The more easily the difference between the two stimuli will be perceived
The just noticeable difference is subject to…
Individual differences
What is signal detection theory?
The ability to differentiate between informative stimulus and background/random patterns
What is the signal detection theory relevant to?
Any domain where a detector wishes to make a judgement about a stimulus
What are the four possible outcomes of signal detection theory?
HIT
CORRECT REJECTION
MISS
FALSE ALARM
Signal Detection Theory
What are we aiming for?
HITS and CORRECT REJECTIONS
A radiologist is examining a CT scan for tumours.
What theory is the radiologist adopting?
Signal detection theory
What might increase the chances of getting a Hit or a Correct Rejection?
Information acquisition
Increasing criterion
How can the criterion be adjusted (STD)?
When experimenter is in control of how much info they receive
When the experimenter is in control of how much information they receive, the choices are not difficult and they can pick a criterion to…
Get a nearly perfect hit rate
Almost no false alarms
The most widely used measure of sensitivity is…
D prime
What is D prime
A measure of sensitivity
D prime allows for comparison…
between different people
If a signal is ABOVE our criterion, we will…
Detect it
What is the criterion?
The internal threshold against which one judges a stimuli
Do people have a different criterion?
Yes
Subjective
Why can’t we always make perfect decisions?
Tradeoff
There will always be ‘system noise’
ROC curves capture various alternatives available to an individual as they….
Move their criterion up and down the scale
If the criterion is very HIGH, the…
Low false alarm rate
Low hit rate
If the criterion is very LOW, the…
High false alarm rate
High hit rate
If the criterion is intermediate…
Hit/false alarm rate will take on intermediate values
What is an example of SDT and hits/false alarms in terms of statistics?
Type 1 and Type 2 errors
Define ‘absolute threshold’
Smallest amount of stimulus energy necessary to detect it
What are psychometrics?
Measurement of psychological qualities
What is the JND?
Min amount stimulus intensity must be changed in order to notice
3 basic methods for determining absolute threshold
methods of limits
adjustment
constant stimuli
What is sensitivity?
Being able to detect a stimulus/differentiate between stimulus and absence
What kind of task is SDT used in?
Judgement task
We want to maximise…..
And minimise…
Hits
Correct rejections
False alarms
Misses
Which type of eyewitness identification originally was thought to reduce false alarms?
Sequental presentation
^ This is wrong
What is the statistic that gives you a measure of sensitivity?
d’
what is the d prime calculation?
Z(hits) - Z(false alarms)
A small d prime would indicate….
More mistakes
What is an ROC curve used to calculate?
D prime
The psychophysical approach to perception focuses on…
Relationship between STIMULI and PERCEPTUAL RESPONSES
Absolute threshold
Smallest amount of stimulus energy needed to detect it
Smallest amount of stimulus energy needed to detect it
What is this?^
Absolute threshold
The smallest difference between two stimuli that a person can detect
The difference threshold
The difference threshold is..
The smallest difference between two stimuli that a person can detect
When the difference between a standard and a comparison weight is small, it will be difficult to…
Detect the difference in the weights
If the DL (difference threshold) for an 100g weight is 2g, what would the difference threshold be for a 200g weight and why?
4g
Constant proportion
The ratio of the difference threshold and the standard stimulus is constant. This is called the…
Weber fraction
Magnitude estimation is…
Measure of relationship between magnitude PERCEPTION and actual stimulus intensity
Doubling the intensity of a light does not necessarily double…
The perceived brightness
Doubling the intensity of a light does not necessarily double the perceived brightness. This is called…
Response compression
Some perceptual research use methods that require the observer to respond as quickly as possible to a scene. This is called
Visual search
An everyday example of a visual search would be
Searching for a friends face in a crowd
When it comes to detecting stimulus, every person has a different…
Response criterion
Is response criterion the same as sensitivity?
No
If the response criteria of two different people is different, can their sensitivity be the same?
Yes
If you have a low criterion, you are more likely to make…
False alarms
Less correct rejections
If you have a high criterion, you are more likely to make…
Less hits but also less false alarms
If you have a VERY high criterion, there will be more…
Correct rejections
A correct rejection is saying
No when there is no tone/stimulus
A persons sensitivity is indicated by the _____ of the ROC curve
Shape
The shape of the ROC curve indicates a persons
Sensitivity
Why can noise often be mistaken for the signal? SDT)
The signal is usually very faint and hard to detect
In an SDT experiment, will the intensity of the tone shift?
No - it will remain constant
Criterion may be one of three forms: L, N and C
Liberal
Neutral
Conservative
What shape will an ROC curve be if a person is more sensitive (their d prime is high)
Bowed
A high d prime would indicate that an individual is more
Sensitive
