PEBL Hub — IRB Fact Sheet — 2026-08-23
Chimp Test (Iconic/Eidetic and Spatial Memory)
Category:Memory
Duration:~10 minutes
Parameters:12 configurable parameters available
Version:1.0
Description
An iconic/eidetic and spatial memory task based on the famous Ayumu chimp memory test. Participants must memorize spatial positions of numbered boxes displayed briefly on a grid, then click them in numerical order.
Numbers appear on a 5×8 grid. In the masking task, numbers remain visible until the first click, then all hide. In the limited-hold task, numbers are shown briefly (210-650ms) then all masked before clicking begins. Participants click boxes in numerical order (1, 2, 3, etc.). Correct clicks turn green, incorrect clicks turn red and end the trial. The masking task uses adaptive difficulty (4-9 items), while limited-hold tasks use fixed 5-item sequences.
Notes
- Grid spacing is 10% of box width and scales proportionally with visual angle
- Supports 7 languages: English, Portuguese, Italian, Spanish, French, German, Dutch
- Screen calibration ensures consistent visual angle across different displays
- Multiple parameter presets available for different conditions (quick, hold210, hold430, hold650, multiblock)
Scoring & Interpretation
Primary measure: Maximum level achieved (highest number of items recalled correctly in masking task).
Accuracy: Proportion of trials completed correctly (allCorrect=1).
Mean correct items: Average number of items recalled before first error.
Limited-hold performance: Percentage correct on 5-item sequences at different display durations (650ms, 430ms, 210ms).
Note: This task became famous when Ayumu the chimpanzee outperformed university students, but typical human performance varies with practice and age.
Accuracy: Proportion of trials completed correctly (allCorrect=1).
Mean correct items: Average number of items recalled before first error.
Limited-hold performance: Percentage correct on 5-item sequences at different display durations (650ms, 430ms, 210ms).
Note: This task became famous when Ayumu the chimpanzee outperformed university students, but typical human performance varies with practice and age.
| Validation | This is a PEBL implementation of the task used in the Inoue & Matsuzawa (2007) study that made Ayumu the chimpanzee famous for exceptional visual working memory. |
Data Output Columns
| subnum | Participant ID |
| trial | Trial number |
| block | Block number (0=practice) |
| condition | Task condition: 'self-timed' (masking) or 'timed' (limited-hold) |
| showDuration | Display duration in milliseconds (0=masking task) |
| phase | Trial phase: 'practice' or 'test' |
| level | Number of items in sequence |
| stimPositions | Stimulus sequence (semicolon-separated numbers) |
| respSequence | Response sequence (semicolon-separated numbers) |
| numCorrect | Number of correct clicks before first error |
| allCorrect | All clicks correct (1=yes, 0=no) |
| totalTime | Total trial time in milliseconds |
| pixelsPerCm | Display calibration (pixels per cm) |
| eyeDistanceCm | Eye distance from screen in cm |
| screenWidthCm | Screen width in cm |
| screenHeightCm | Screen height in cm |
| boxSizePixels | Actual box size in pixels |
| boxSizeDegrees | Requested visual angle in degrees |
| spacing | Spacing between boxes in pixels |
References
Inoue, S., & Matsuzawa, T. (2007). Working memory of numerals in chimpanzees. Current Biology, 17(23), R1004-R1005.