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Problem 3 perception & decision making (Receiver Operatic…
Problem 3 perception & decision making
Psychometric function graph
Absolute threshold
the sudden step up
the smallest amount u need to perceive the info
Methods
method of constant stimuli
presenting different intensities of stimuli
method of limits
presenting the intensities around the threshold
can either be ascending or descending
adaptive testing
the intensity of the stimulus depends on the subject's hearing ability
signal detection theory
assumption
any stimulus must be detected against the background of endogenous noise in our sensory systems
no absolute threshold
only series of observation
each observation must be categorized as a signal present of signal absent
catch trials
people may feel reluctant to answer yes or no a lot
people may not pay attention
only noise without a signal is presented to the subject
shows how a person is able to detect a signal, independent of any motivational or expection bias
motivation & expectation will determine where the criterion(b) is placed
if the sensation level is...
above the criterion ---> the participant says 'yes'
below the criterion ---> the participant says 'no'
the upper bell curve
right side = false alarms
left side = the proportion of correct rejections
the lower bell curve
the right part = the proportion of hits
the left part = the proportion of misses
the location of the criterion value
DOES NOT change sensitivity(d);how well one can detect a signal)
DOES change the response pattern
How to calculate sensitivity (d)
2) slide the criterion sheet across the sheet below until the criterion cuts the signal absent distribution curve
3) add the signal present distribution sheet to the stack
1) put the criterion on top of the diagram of the signal absent distribution
4) adjust the criterion until it meets the signal present distribution cure at the point of proportions of hits
5) the d value can be read off the layered distributions
experiment
hit
saying 'yes' when the answer is 'yes'
false alarm
when the subject says 'yes' but the answer is 'no'
signal present trial
when the noise is combined with the signal
correct negative
when the subject says 'no' when the answer is 'no'
signal absent trial
a catch trial where the subject is presented with only noise
miss
when the subject says 'no' when the answer is 'yes'
outcome matrix
shows either how many hits, false alarms, correct negatives and misses a subject has
Discrimination
determining whether two stimuli are the same or different
the study
to determine how big the difference between two stimuli has to be
to know that there is a difference between the two of them
difference threshold
interval of uncertainty /2
compare stimuli only on one dimension
stimuli
standard stimulus (what you compare to)
comparison stimulus
Weber's law
the difference threshold increases linearly with the magnitude of the standard
Delta I = kI
Delta = difference threshold
I = intensity (magnitude) of the standard stimulus
k = constant
Weber fraction
Delta I / I
the difference threshold is larger for larger standards
describes the relation between the size of the difference threshold & the magnitude of the standard
manipulating motivation
can change criterion level by offering payoffs
make someone more liberal by offering money for hits
Receiver Operatic Characteristic Curve
shape of the line indicates the level of sensitivity
shows how good the observation is
a linear line
a worthless observation
the more exponential the line is, the better the observation
far left
conservative criterion
not much of false alarms
the middle part
neutral criterion
some false alarms
far right
liberal criterion
the importance of detecting something is very high
the effect of a false alarm outweighs missing a hit
