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Delay & Probability Discounting Procedure (Richards et al., 1999)
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Script Author: Meticulously handcrafted from the finest code by David Nitz (nitz.david@gmail.com) for Millisecond Software, LLC.
last updated: 02-21-2022 by K. Borchert (katjab@millisecond.com) for Millisecond Software, LLC
Script Copyright © 02-21-2022 Millisecond Software
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BACKGROUND INFO
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This script implements a Delay and Probability Discounting Procedure to establish
a) the hypothetical payoffs at which people start to discount higher monetary rewards
in favor of shorter wait periods (Delay Discounting)
b) the fictional payoffs at which people start to discount high monetary rewards of unsure events
in favor of lower monetary rewards of sure wins (Probability Discounting)
The implemented procedure is based on:
Richards, J. B., Zhang, L., Mitchell, S. H., & De Wit, H. (1999). Delay or probability
discounting in a model of impulsive behavior: Effect of alcohol. Journal of the Experimental
Analysis of Behavior, 71(2), 121-143.
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TASK DESCRIPTION
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Participants choose between a standard amount of money ($10) with different time/probability delays
or a variable amount with no delay until an indifference point for each delay is found or until
the maximum number of trials has been run for each delay (default: 30).
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DURATION
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the default set-up of the script takes appr. 15 minutes to complete
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DATA FILE INFORMATION
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The default data stored in the data files are:
(1) Raw data file: 'dpdt_richards_raw*.iqdat' (a separate file for each participant)
build: The specific Inquisit version used (the 'build') that was run
computer.platform: the platform the script was run on (win/mac/ios/android)
date, time: date and time script was run
subject, group: with the current subject/groupnumber
session: with the current session id
blockcode, blocknum: the name and number of the current block (built-in Inquisit variable)
trialcode, trialnum: the name and number of the currently recorded trial (built-in Inquisit variable)
Note: trialnum is a built-in Inquisit variable; it counts all trials run; even those
that do not store data to the data file such as feedback trials. Thus, trialnum
may not reflect the number of main trials run per block.
trialcount Total number of trials run (including distractor trials).
latency the participant’s response latency (in ms) for the current trial (in ms)
response the selected response of the participant for the current trial (for most trials: A or B)
text.question.currentitem: the actual decision question presented to participant
questiontype: 1 = temporal delay question; 2 = probabilistic delay question
text.subjectquestion.currentitem: the question that was randomly selected to determine participant’s reward
text.subjectanswer.currentitem: The participant’s response to the win question
var: 'Variable' amount of money offered in the current trial. This value is computed according to the proper bottom and top limits (see below) by expressions 't1_var' through 'p5_var'.
std: 'Standard' amount of money to use throughout the task. Default is 10.
The following variable is only relevant for trials with Question Type = 1
t: Value of the current temporal delay used in a given trial.
The following variable is only relevant for trials with Question Type = 2
p: Value of the current probabilistic 'delay' used in a given trial.
The following variables are only relevant for trials trialcode = “t1”
t1_bmax: The respective maximum bottom limits for temporal delay t1. Used to determine the variable amount of money offered in a given t1 trial and to adjust the limits for subsequent t1 trials.
t1_bmin: The respective minimum bottom limits for temporal delay t1. Used to determine the variable amount of money offered in a given t1 trial and to adjust the limits for subsequent t1 trials.
t1_tmin: The respective minimum top limits for the temporal delay t1. Used to determine the variable amount of money offered in a given t1 trial and to adjust the limits for subsequent t1 trials.
t1_tmax: The respective maximum top limits for the temporal delay t1. Used to determine the variable amount of money offered in a given t1 trial and to adjust the limits for subsequent t1 trials.
t1_var: 'variable' amount for temporal delays t1. The valid range is restricted by the respective maximum bottom and maximum top limits. Values returned lie between those limits in 0.5 increments.
t1_count: Number of trials for temporal delay t1.
t1_ip_found: Value reflecting whether an indifference point has been successfully determined ('1') or not ('0') for temporal delay t1.
t1_ip: Obtained indifference point estimate for temporal delay t1
parameters.t1: Predetermined value for temporal delay t1 questions in this script (t1 = 0)
(same for all temporal delays t2-t5)
The following variables are only relevant for trials trialcode = “p1”
p1_bmax: The respective maximum bottom limits for probabilistic ‘delay’ p1. Used to determine the variable amount of money offered in a given p1 trial and to adjust the limits for subsequent p1 trials.
p1_bmin: The respective minimum bottom limits for probabilistic ‘delay’ p1. Used to determine the variable amount of money offered in a given p1 trial and to adjust the limits for subsequent p1 trials.
p1_tmin: The respective minimum top limits for the probabilistic ‘delay’ p1. Used to determine the variable amount of money offered in a given p1 trial and to adjust the limits for subsequent p1 trials.
p1_tmax: The respective maximum top limits for the probabilistic ‘delay’ p1. Used to determine the variable amount of money offered in a given p1 trial and to adjust the limits for subsequent p1 trials.
p1_var: 'variable' amount for probabilistic ‘delay’ p1. The valid range is restricted by the respective maximum bottom and maximum top limits. Values returned lie between those limits in 0.5 increments.
p1_count: Number of trials for probabilistic ‘delay’ p1.
p1_ip_found: Value reflecting whether an indifference point has been successfully determined ('1') or not ('0') for probabilistic ‘delay’ p1.
p1_ip: Obtained indifference point estimate for probabilistic ‘delay’ p1
p1: Predetermined value for probabilistic ‘delay’ for p1-questions in this script (p1 = 100)
(same for all probabilistic delays p2-p5)
Relevant for all trials
nips: The total number of successfully determined indifference points.
The procedure determines a total of 10 different indifference points
(for five temporal delays, 't1' to 't5', and five probabilistic 'delays', 'p1' to 'p5').
The procedure is stopped as soon as 'expressions.nips' returns 10, i.e. when all
indifference points at question have been obtained.
distractorstart: Number of trials to run *before* distractor trials should be added to the mix.
Default is 70, i.e. after 70 experimental trials ('t1' to 'p5') have been run,
every second trial will be a distractor trial ('d0').
d0_count: Total number of distractor trials run
d0_var: Computes a random 'variable' amount to be used in distractor trials ('d0').
The value returned always lies between 0 and the defined 'standard' amount ($10) in 0.5 increments
(2) Summary data file: 'dpdt_richards_summary*.iqdat' (a separate file for each participant)
inquisit.version: Inquisit version run
computer.platform: the platform the script was run on (win/mac/ios/android)
startdate: date script was run
starttime: time script was started
subjectid: assigned subject id number
groupid: assigned group id number
sessionid: assigned session id number
elapsedtime: time it took to run script (in ms); measured from onset to offset of script
completed: 0 = script was not completed (prematurely aborted);
1 = script was completed (all conditions run)
nips The total number of successfully determined indifference points. The procedure determines a total of 10 different indifference points (for five temporal delays, 't1' to 't5', and five probabilistic 'delays', 'p1' to 'p5'). The procedure is stopped as soon as 'expressions.nips' returns 10, i.e. when all indifference points at question have been obtained.
t1_ip_found: Value reflecting whether an indifference point has been successfully determined ('1') or not ('0') for temporal delay t1.
t1_ip: Obtained indifference point estimate for temporal delay t1
t2_ip_found: Value reflecting whether an indifference point has been successfully determined ('1') or not ('0') for temporal delay t2.
t2_ip: Obtained indifference point estimate for temporal delay t2
t3_ip_found: Value reflecting whether an indifference point has been successfully determined ('1') or not ('0') for temporal delay t3.
t3_ip: Obtained indifference point estimate for temporal delay t3
t4_ip_found: Value reflecting whether an indifference point has been successfully determined ('1') or not ('0') for temporal delay t4.
t4_ip: Obtained indifference point estimate for temporal delay t4
t5_ip_found: Value reflecting whether an indifference point has been successfully determined ('1') or not ('0') for temporal delay t5.
t5_ip: Obtained indifference point estimate for temporal delay t5
p1_ip_found: Value reflecting whether an indifference point has been successfully determined ('1') or not ('0') for probabilistic delay p1.
p1_ip: Obtained indifference point estimate for probabilistic ‘delay’ p1
p2_ip_found: Value reflecting whether an indifference point has been successfully determined ('1') or not ('0') for probabilistic delay p2.
p2_ip: Obtained indifference point estimate for probabilistic ‘delay’ p2
p3_ip_found: Value reflecting whether an indifference point has been successfully determined ('1') or not ('0') for probabilistic delay p3.
p3_ip: Obtained indifference point estimate for probabilistic ‘delay’ p3
p4_ip_found: Value reflecting whether an indifference point has been successfully determined ('1') or not ('0') for probabilistic delay p4.
p4_ip: Obtained indifference point estimate for probabilistic ‘delay’ p4
p5_ip_found: Value reflecting whether an indifference point has been successfully determined ('1') or not ('0') for probabilistic delay p5.
p5_ip: Obtained indifference point estimate for probabilistic ‘delay’ p5
text.subjectquestion.currentitem: the question that was randomly selected to determine participant’s reward
text.subjectanswer.currentitem: The participant’s response to the win question
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EXPERIMENTAL SET-UP
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* 5 temporal delays and 5 probability "delays"; tested within in a mixed design
temporal delays are 0, 2, 30, 180 and 365 days
probability delays are: 100, 90, 75, 50 and 25 percent
=> change delays under section EDITABLE PARAMETERS
* 1 standard amount (10), variable amounts between 0 <=variable amount <= 10
* once an indifference point is found for a particular delay, that delay is not run any further
* potentially 30 trials can be run for each delay -> can be edited under block.DPDT
* after a predetermined amount of trials (see EDITABLE PARAMETERS), a distractor trial is run after each test trial
* script stops if an indifference point has been found for all delays or the maximum number of trials
has been run for each delay (default: 30).
Description of the adjustment procedure:
If a subject picks the 'variable' amount on a given trial, the respective top and the bottom
limits are decreased according to the following three rules:
(a) If the 'variable' amount is less than the minimum top limit, the minimum top limit is set to
equal the 'variable' amount. The maximum top limit is set equal to the previous minimum top
limit.
(b) If the 'variable' amount is greater than the minimum top limit, the maximum top limit is
set to equal the 'variable' amount. The minimum top limit is left unchanged.
(c) If the 'variable' amount is less than the minimum bottom limit, the minimum bottom limit
is set to equal the 'variable' amount. The maximum bottom limit is set equal to $0.
If a subject picks the 'standard' amount ($10) on a given trial, the respective top and bottom
limits are increased according to the following three rules:
(a) If the 'variable' amount is greater than the minimum bottom limit, the minimum bottom
limit is set to equal the 'variable' amount. The maximum bottom limit is set equal to the
previous minimum bottom limit.
(b) If the 'variable' amount is less than the minimum bottom limit, the maximum bottom limit
is set to equal the 'variable' amount. The minimum bottom limit is left unchanged.
(c) If the 'variable' amount is greater than the minimum top limit, the minimum top limit is
set to equal to the current 'variable' amount. The maximum top limit is set to equal the
'standard' amount ($10).
As soon as the difference between the respective maximum bottom limit and maximum top
limit reaches $0.50, the corresponding variable amount is recorded as estimate of the
respective indifference point.
After an indifference point has been successfully determined for a particular temporal or
probabilistic delay, no more trials of that type will be run.
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INSTRUCTIONS
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see section EDITABLE INSTRUCTIONS
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EDITABLE CODE
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check below for (relatively) easily editable parameters, stimuli, instructions etc.
Keep in mind that you can use this script as a template and therefore always "mess" with the entire code
to further customize your experiment.
The parameters you can change are:
pretrialdelay: Adjustable pretrialpause in milliseconds. Change as needed.
posttrialdelay: Adjustable posttrialpause in milliseconds. Change as needed.
distractorstart: Number of trials to run *before* distractor trials should be
added to the mix. Default is 70, i.e. after 70 experimental
trials ('t1' to 'p5') have been run, every second trial will be a
distractor trial ('d0').
std: 'Standard' amount of money to use throughout the task.
Default is 10.
t1 to t5: Values for the five temporal delays. The procedure estimates
indifference points for five different temporal delays. Defaults
are 0, 2, 30, 180 and 365 days.
p1 to p5: Values for the five probabilistic 'delays'. The procedure
estimates indifference points for five different probabilities.
Defaults are 100, 90, 75, 50 and 25 percent.
