Psychophysics Flashcards
psychophysics
sensory psychology that quantifies the relationship between “stimulus magnitude” and “responses”
psychometrics
develops a scale or function which describes a person’s performance
nominal data
NAMED variable, no quantitative relation
ordinal data
Increasing number corresponds to a monotonic change in parameters - ORDERED Categories (ranking, order, or scaling)
Efron scale
degree of conjunctival redness
interval
difference between any two adjacent numbers is equal
ratio
proportion of numerical measurement
threshold measurement
minimum intensity of stimulus required for an individual to just detect
absolute threshold
the presence of a stimulus
relative threshold
the difference between two stimuli
chance of seeing a stimulus at threshold
75 percent
chance of seeing a stimulus at infrathreshold
50 percent
intensity discrimination
subjects match multiple brightness or until just different from stimuli
standard of deviation of intensity discrimination
just noticeable difference
method of limits
vary stimulus magnitudes in fixed small steps until response changes
descending limits
start above threshold - First no or last yes
ex: Snellen chart
ascending limits
start below threshold - first yes or last no
advantage(s) of method of limits
quick procedure
disadvantage(s) of method of limits
criterion; error of expectation; error of habituation
criterion
when subject decides a stimulus is present or absent (bias on on practicioner/patient)
constant stimuli
randomly presents stimulus at various magnitudes
advantage(s) of constant stimuli
no error of habituation or expectation
disadvantage(s) of constant stimuli
criterion; long and boring
method of adjustment
subject tracks or brackets between seeing and not seeing
advantage(s) of adjustment method
quick and offers some randomization
disadvantage(s) of adjustment method
criterion; apparatus artifacts (physical errors due to apparatus)
adaptive staircase
change stimulus magnitude by a given ratio (“steps”) depending on previous responses
advantage(s) of adjustment method
criterion-free
classic techniques
based on threshold concept - all have problem of criterion
modern techniques
criterion free (not biased free)
forced choice
formulated questions so the subjects response is NOT DIRECTLY related to stimulus magnitude AND subject must always respond with one of the permissible answers
Landolt C
Forced choice where the C is open
Threshold percent correct
(100% + guess rate)/2
Guess Rate
1/#of choices in %
4 alternative-spatial forced choice
measure thresholds (brightness) to spots of light using 4 alternative-spatial forced choice “which quadrant”
threshold determined by forced choice vs classical methods
forced choice is lower threshold than classical methods
