Script Author: Katja Borchert, Ph.D. (katjab@millisecond.com), Millisecond
Created: January 12, 2012
Last Modified: January 04, 2024 by K. Borchert (katjab@millisecond.com), Millisecond
Script Copyright © Millisecond Software, LLC
This script provides the Police Officer Dilemma Task (PODT); a computer-simulated task to measure racial bias in shooting decisions.
Correll, J., Park, B., Judd, C.M., & Wittenbrink, B. (2002). The Police Officer's Dilemma: Using Ethnicity to Disambiguate Potentially Threating Individuals. Journal of Personality and Social Psychology, 83, 1314-1329. (Experiment 1)
Correll, J., Hudson, S.M., Guillermo, S., & Ma, D.S. (2014). The Police Officer’s Dilemma: A Decade of Research on Racial Bias in the Decision to Shoot. Social and Personality Psychology Compass 8/5 (2014): 201–213.
•Adjustments to z-scores (for signal detection parameter calculations) as recommended by: Gregg, A. & Sedikides, C. (2010). Narcissistic Fragility: Rethinking Its Links to Explicit and Implicit Self-esteem, Self and Identity, 9:2, 142-161 (p.148)
All images used in this script are the originals. Millisecond thanks Dr. Correll et al for providing generous assistance!
15 minutes
Participants see a series of men, either White or Black, that either hold harmless objects or guns, and have to decide -within a short timeframe- whether to 'shoot' (if there is a gun) or not to 'shoot' (no gun present). 'Shooting' is done via response button presses. Before each target appears, participants see a varying number of backgrounds. The targets (men with objects) appear in the last background shown.
Design: 2 (ethnicity: black vs. white) x 2 (gun vs. no gun) = 4 experimental conditions,
all tested within participants in a mixed design (see Correll et al, 2002)
1 Practice Block: 20 trials
1 Test Block: 80 Trials, 20 trials in each of the 4 conditions, conditions are randomly sampled without replacement
(see list.condition for details)
- shoot keys are counterbalanced by groupnumber
- Number of background images in background slideshow:
randomly (with replacement) determined, between 1-4 (see list.repetition) (-> Correll et al, 2002)
Trials Sequences:
Fixation (500ms)-> Background (variable number) (500-1000ms)-> target (850ms)-> Feedback (3000ms)
original pictures; editable under section Editable Stimuli
Current Instructions modelled after the latest instructions used by Correll et al (these later instructions are
less detailed than the original 2002 instructions)
Instructions are provided by Millisecond
as htm/html pages and can be edited by changing the provided htm/html files.
To edit htm/html-files: open the respective documents in simple Text Editors such as TextEdit (Mac)
or Notepad (Windows).
File Name: podt_summary*.iqdat
| Name | Description |
|---|---|
| inquisit.version | Inquisit version number |
| computer.platform | Device platform: win | mac |ios | android |
| startDate | Date the session was run |
| startTime | Time the session was run |
| subjectId | Participant ID |
| groupId | Group number |
| sessionId | Session number |
| elapsedTime | Session duration in ms |
| completed | 0 = Test was not completed 1 = Test was completed |
| group | Group number |
| total | Keeps a running tab of the total money earned (or lost) |
| accBlackGun | Proportion correct shoot decision for Black guys holding a gun |
| rtCorrectBlackGun | Mean reaction time (in ms) to correctly shoot for Black guys holding a gun |
| accBlackObject | Proportion correct 'non-shoot' decisions for Black guys holding an object |
| rtCorrectBlackObject | Mean reaction time (in ms) to correctly hit 'not shoot' key for Black guys holding an object |
| accWhiteGun | Proportion correct shoot decision for White guys holding a gun |
| rtCorrectWhiteGun | Mean reaction time (in ms) to correctly shoot for White guys holding a gun |
| accWhiteObject | Proportion correct 'non-shoot' decisions for White guys holding an object |
| rtCorrectWhiteObject | Mean reaction time (in ms) to correctly hit 'not shoot' key for White guys holding an object countGunBlack- |
| countObjectWhite | Counts the trials in each of the 8 conditions sumBlackHits- |
| sumWhiteCRs | Keeps a running total of Hits, Misses, FAs, CRs for each ethnicity meanRTBlackHits- |
| meanRTWhiteCRs | The mean reaction times for Hits, Misses, FAs, CRs for each ethnicity (in ms) percentBlackHits- |
| percentWhiteCRs | The percentages of Hits-Misses and CRs-FAs, separately for each ethnicity Signal Detection Analysis for hits and false alarms |
| dPrime | Computes d' (parametric measure of discriminability btw. signals (here: guns) and noise(here: objects)) with d' = z(hitrate) - z(FalseAlarm rate) => Range (in this script) -5.1516586840152740479 <= dprime <= 5.1516586840152740479 (=perfect performance) => The higher the value, the better signals (guns) were overall distinguished from noise (objects) (d' = 0: chance performance; negative d-primes: participant treated nontargets as targets and targets as nontargets) |
| criterionC | Calculates the criterion to 'shoot' vs. not 'shoot' with criterionC = - (z(hitrate) + z(FalseAlarm rate))/2 * values around 0: no bias towards shooting or not shooting *the more negative the value, the more lax the criterion to shoot (bias towards shooting) *the more positive the value, the more stringent the criterion to shoot (bias towards not shooting) |
| dPrimeBlack | Computes d' for Black targets |
| criterionCBlack | Calculates the criterion to 'shoot' vs. not 'shoot' Black targets |
| dPrimeWhite | Computes d' for White targets |
| criterionCWhite | Calculates the criterion to 'shoot' vs. not 'shoot' White targets Correll et al (2014) report that generally d-prime values tend to be similar between the two groups, showing that participants are able to distinguish between guns and objects similarly well for Black and White targets. The criterions 'to shoot', however, tend to differ in that it is more lax ('biased towards shooting') for Black actors than it is for White actors. |
File Name: podt_raw*.iqdat
| Name | Description |
|---|---|
| build | Inquisit version number |
| computer.platform | Device platform: win | mac |ios | android |
| date | Date the session was run |
| time | Time the session was run |
| subject | Participant ID |
| group | Group number |
| session | Session number |
| blockCode | Name of the current block |
| blockNum | Number of the current block |
| trialCode | Name of the current trial |
| trialNum | Number of the current trial |
| group | Group number |
| condition | Practice: "gun" vs. "object" test 1 = Gun White 2 = Gun Black 3 = Object White 4 = Object Black |
| itemNumber | Itemnumber of the target image |
| selectBackground | Selected background picture is selected |
| repetition | How many background images are presented |
| backgroundDuration | How long each background slide is presented (in ms) |
| countBackground | Counts how many background slides have been presented |
| image | The presented target pictures |
| response | The participant's response (scancode of response button) 30: A (group1 -> shoot; group2 -> nonshoot) 38: L (group2 -> shoot; group1 -> nonshoot) |
| responseCat | "shoot", "not shoot", "no response" |
| correct | The correctness of the response (1 = correct; 0 = incorrect) |
| result | Either "Hit", "Miss", "CR" (correct rejection), "FA" (false alarm) or "no response" |
| latency | The response latency (in ms); measured from onset of target picture |
| total | Keeps a running tab of the total money earned (or lost) |
The procedure can be adjusted by setting the following parameters.
| Name | Description | Default |
|---|---|---|
| key2 | The scancodes of the shoot and noshoot keys (keys are counterbalanced), default: "A" and "L" for the script to run correctly on touchscreen, key1 should be the left key and key2 should be the right key. | |
| optionalSummaryFeedback | True (1) = Participants receive a summary feedback matrix (with %correct and incorrect responses as well as response times for correct choices) (default) false (0) = no final feedback is provided |