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stopping rule
refers to the point at which a certain number of reversals has been met and you stop the staircase procedure (typically 6 or 7 reversals)
1-down-1-up
staircase procedure: decreasing the stimulus intensity after 1 "yes" response and increasing the stimulus intensity after 1 "no" response
1-down-1-up
What is the specific kind of staircase procedure shown in this graph?
1-up-2-down
What is the specific kind of staircase procedure shown in this graph?
subject responds each trial if the stimulus is stronger than standard or not, next intensity shown is based on their response, goes until a certain number of reversals
How is the staircase procedure used to find difference threshold? (procedure)
forced choice method
With MOL, MOA, MCS, and the staircase method, this may lead to strong response bias and even guessing, which can have a big effect on the threshold measurements. How can we control or reduce the influence of response bias and guessing?
2-4 stimuli are showed to subject, subject has to pick one based on their perception
How is the forced choice method a more objective technique to measure perception? (procedure)
false
(must be paired with another psychophysical method)
True or false: The forced choice procedure can be used alone.
MOL, MCS, staircase
Which 3 psychophysical methods can the forced choice method be paired with?
plot percentage correct vs. stimulus intensity, absolute threshold is 75% value
In classical MCS, we plot percentage "yes" vs. stimulus intensity and determine absolute threshold as the 50% value. What about with (2 alternative) forced choice with MCS?
standard and comparison stimuli presented in a pair, 5-9 fixed levels of comparison are shown in a randomized order, subject responds which stimulus is stronger
How is the (2 alternative) forced choice method with MCS used to find difference threshold? (procedure)
true
True or false: The forced choice method more accurately measures threshold for subjects with both strict and lax criteria.
catch trials
refers to trials in which the subject is presented with stimuli that should never be detected or should always be detected in order to determine their guessing rate
(observed yes responses - guessing rate)/(1 - guessing rate)
How are catch trials used to calculate the true rate of "yes" responses? (formula)
25%
For the 4 alternative forced choice method, what is always the guessing rate? (where the psychometric function should theoretically begin)
33%
For the 3 alternative forced choice method, what is always the guessing rate? (where the psychometric function should theoretically begin)
true
True or false: We can train animals to participate in forced choice tasks.
preferential looking
research technique that involves giving the subject a choice of what object to look at; assumes that the longer a subject spends looking at a stimulus, the more they prefer that "interesting" stimulus over others (preferred object gets more fixations per unit period of time than the non-preferred object)
**can be used to test infants, children, nonverbal adults, and animals
adult's choice where stimulus is
(then we evaluate accuracy of that response)
What do we measure in forced choice with preferential looking (FCPL)?
staircase procedure, forced choice, preferential looking
What are three ways that method of limits can be improved?
staircase procedure
(also called up-down method)
stimulus level can be varied in relation to the subjects responses; adaptive procedure in MOL in which the sequence of stimulus presentations is varied according to the subject's responses
ex. stimulus intensity may be continually increased as long as the subject is making incorrect responses
reversals (transition points)
In order to determine absolute threshold, the staircase procedure keeps going until it reaches a certain number of what?
**point at which the direction of the stimulus intensity adjustment changes
subject responds each trial whether or not they detect a stimulus, next intensity shown is based on their response, goes until a certain number of reversals
How is the staircase procedure used to find absolute threshold? (procedure)
average of all reversals
How do we use the results in the staircase procedure to find absolute threshold?
1-up-2-down
staircase procedure: decreasing the stimulus intensity after 2 "yes" responses and increasing the stimulus intensity after 1 "no" response
place the stimuli next to each other
How are the options presented in a spatial forced choice task?
place the stimuli on separate screens not shown simultaneously
(target stimulus could be located in either interval, and its placement is randomly chosen for every trial)
How are the options presented in a temporal forced choice task?
window with one target stimulus (5-9 possibilities) and window with background only are presented in a pair, subject responds where the target is, order of stimuli is randomized
How is the (2 alternative) forced choice method with MCS used to find absolute threshold? (procedure)
window with one target stimulus and window with background only are presented in a pair, subject responds where the target is, next stimulus shown is based on previous response
How is the (2 alternative) forced choice method with staircase used to find absolute threshold? (procedure)
same (average of all reversals)
In regular staircase procedure, we calculate absolute threshold as the average of all the reversals. What about forced choice with staircase?
subject has to rely on their true perception to make a decision instead of just guessing if stimulus can be detected
How does the forced choice method help control response bias?
50%
For the 2 alternative forced choice method, what is always the guessing rate?
50%
In (2 alternative) forced choice with MCS, when the observed percentage of correct responses is 75%, what is the true response rate?
true
True or false: We can train babies to participate in forced choice tasks.
present 2 different stimuli next to each other (e.g., Teller acuity cards, Lea paddles), record which stimulus the baby looks at first and how long it looks at each
How can we use preferential looking with babies in an optometric clinical setting?
which stimulus baby looks at first, how long baby looks at each stimulus, how many times baby fixates on each stimulus
What do we measure in a regular preferential looking method?
adult observer presents 2 different stimuli next to each other without knowing which is on which side and makes forced choice response on where target stimulus is based on infant's preference
How can forced choice be used in the preferential looking method with babies (FCPL)?
false
(almost always pairs with MOL, MCS, or staircase; procedures when pairing FCPL with one of these 3 techniques are similar when pairing regular forced choice with these techniques)
True or false: Unlike the regular forced choice procedure, FCPL can be used alone.
