PEBL Hub — IRB Fact Sheet — 2026-08-23
Urns Task
Category:Risk & Decision Making
Duration:~12 minutes
Parameters:17 configurable parameters available
Version:1.0
Input:Keyboard
Description
An 'urns' or 'marbles' task examining decision-making under uncertainty and impulsivity. Participants sample colored marbles from a hidden urn and must decide which of two urns (with different color distributions) is being used. More evidence-gathering improves accuracy but costs points.
Key Parameters
| col1 | Color 1 (PEBL color name) (default: red2) |
| col2 | Color 2 (PEBL color name) (default: blue) |
| colnull | Null color (PEBL color name) (default: grey) |
| col1name | Display name for color 1 (default: red) |
| col2name | Display name for color 2 (default: blue) |
| colnullName | Display name for null color (default: grey) |
| urn1bias1 | Urn 1 bias for color 1 (probability) (default: 0.8) |
| urn1bias2 | Urn 1 bias for color 2 (probability) (default: 0.2) |
| urn2bias1 | Urn 2 bias for color 1 (probability) (default: 0.2) |
| urn2bias2 | Urn 2 bias for color 2 (probability) (default: 0.8) |
| ballsize | Size of balls in pixels (default: 20) |
| drawlimit | Maximum number of draws permitted per trial (default: 12) |
| trialsperjar | Number of trials per jar/urn (default: 25) |
| drawcost | Point cost per draw (default: 25) |
| CorrectBonus | Points awarded for correct response (default: 1000) |
| IncorrectCost | Points deducted for incorrect response (default: 5000) |
| binsize | Number of balls to display in urn (default: 50) |
Example Data Output (5 sample rows)
| sub | trial | drawlimit | type | resp | corr | count | time | stimseq | evidencbias | totalpoints |
|---|---|---|---|---|---|---|---|---|---|---|
| 1515 | 1 | 12 | 1 | <lshift> | 1 | 10 | 5253 | 112211211 | 1.33333 | 1775 |
| 1515 | 2 | 12 | 2 | <rshift> | 1 | 8 | 4254 | 2222222 | 2 | 2600 |
| 1515 | 3 | 12 | 2 | <rshift> | 1 | 4 | 1597 | 222 | 2 | 3525 |
| 1515 | 4 | 12 | 1 | <lshift> | 1 | 5 | 1460 | 1111 | 1 | 4425 |
| 1515 | 5 | 12 | 2 | <rshift> | 1 | 5 | 1708 | 2221 | 1.75 | 5325 |