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Minute Discounting Task
SCRIPT INFO
Script Author: Katja Borchert, Ph.D. (katjab@millisecond.com) for Millisecond Software, LLC
Date: 03-06-2018
last updated: 01-15-2019 by K.Borchert (katjab@millisecond.com) for Millisecond Software LLC
Script Copyright © 01-15-2019 Millisecond Software
BACKGROUND INFO
*Purpose*
This script implements the Minute Discounting Task described by:
Koffarnus, M.N. & and Warren K. Bickel, W.K (2014). A 5-Trial Adjusting Delay Discounting Task: Accurate Discount Rates in
Less Than One Minute. Experimental and Clinical Psychopharmacology, 22, 222–228.
The Minute Discounting Tasks, an adjusting delay task, offers a quick way to estimate discount rates.
*Task*
Participants receive 5 questions that ask whether they prefer a smaller amount (default: $5) now
or a larger amount (default: S10) at variable delays (delays depend on previous choices).
The task takes about a minute. The discount rate k is calculated.
DATA FILE INFORMATION:
The default data stored in the data files are:
(1) Raw data file: 'minutediscounting_raw*.iqdat' (a separate file for each participant)*
build: Inquisit build
computer.platform: the platform the script was run on
date, time, subject, group: date and time script was run with the current subject/groupnumber
blockcode, blocknum: the name and number of the current block
trialcode, trialnum: the name and number of the currently recorded trial
(Note: not all trials that are run might record data; by default data is collected unless /recorddata = false is set for a particular trial/block)
/delayedAmount: the promised delayed amount (default: $10)
/immediateAmount: the promised immediate amount (default: $5)
/trialcount: a running count of the choice trials run
/choiceNo: stores the current choice trial number (1-5) attached to the current index (should always be equal to the number of choice trials run = values.trialcount)
/index: the index of the current choice values (choice trial #1 starts with index = 16)
/indexAdjustment: the current index adjustment value
/delayChoice: the variable delay choice assigned to the current index
response: the participant's response: selected response button
"now" vs. "delayed"
latency: the response latency (in ms); measured from: onset of response buttons
/ED50: stores the estimated ED50 (in days)
Effective Delay 50% (ED50): can be directly translated into k-values
/k: Main DV = stores the absolute k-value (discount rate, inverse of ED50)
The higher the discount rate, the less participant is willing to wait for the delayed higher reward
and the more the lesser, immediate reward is preferred.
(2) Summary data file: 'minutediscounting_summary*.iqdat' (a separate file for each participant)*
script.startdate: date script was run
script.starttime: time script was started
script.subjectid: subject id number
script.groupid: group id number
script.elapsedtime: time it took to run script (in ms)
computer.platform: the platform the script was run on
/completed: 0 = script was not completed (prematurely aborted); 1 = script was completed (all conditions run)
/delayedAmount: the promised delayed amount (default: $10)
/immediateAmount: the promised immediate amount (default: $5)
/ED50: stores the estimated ED50 (in days)
Effective Delay 50% (ED50): can be directly translated into k-values
/k: Main DV = stores the absolute k-value (discount rate, inverse of ED50)
The higher the discount rate, the less participant is willing to wait for the delayed higher reward
and the more the lesser, immediate reward is preferred.
/meanRT: the mean choice reaction time (measured from onset of the response buttons)
* separate data files: to change to one data file for all participants (on Inquisit Lab only), go to section
"DATA" and follow further instructions
EXPERIMENTAL SET-UP
1 Test block with 5 choice trials
* each trial presents a choice between the immediate amount and the delayed amount
=> based on response the new delay gets selected for the next trial based on
adjusting the index of the selected delays (see item.delayChoices under section STIMULUS)
* delay parameters used in this script to calculate the discount rate k are published in: Koffarnus & Bickel (2014, Table 1, p.224)
Adjustment Rule of the indices:
* the first delay always uses index = 16 ("3 weeks")
* the index adjustment value starts at 16/2=8 and is halved for each new trial (8, 4, 2, 1)
* if the immediate amount is selected: the index is adjusted down by the current adjustment value
* if the delayed amount is selected: the index is adjusted up by the current adjustment value
Example:
* the index adjust amount in trial 1 = 8:
if the immediate amount is selected in trial 1 (index always 16), trial 2 presents the delay for index 8 (16-8) ("1 day")
if the delayed amount is selected in trial 1 (index always 16), trial 2 presents the delay for index 24 (16 + 8) ("2 years")
* the index adjust amount in trial 2 = 4:
if the immediate amount is selected in trial 2 (e.g. index 8), trial 3 presents the delay for index 4 (8-4)("4 hours")
if the delayed amount is selected in trial 2 (e.g. index 8), trial 3 presents the delay for index 12 (8 + 4)("4 days")
etc.
INSTRUCTIONS
provided by Millisecond Software - can be edited under section Editable Instructions
EDITABLE CODE:
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:
/delayedAmount: the promised delayed amount (default: $10)
/immediateAmount: the promised immediate amount (default: $5)
/iti: the intertrial interval between each choice trial (default: 1000)
Note: the options are blacked out during the iti