Digit-Symbol Substitution Test
System Requirements
Minimum: 1024×768
Recommended: 1280×800
Description
A processing speed and associative learning task requiring participants to match symbols with digits or letters with digits using a mapping key displayed on screen.
Measures: Processing speed, visual scanning, sustained attention, working memory, and symbol-digit paired-associate learning ability.
Processing Speed Working Memory Attention
Ages: 7+ · Populations: adults, children, research, clinical, neuropsychological-assessment
About This Test
Participants view a mapping of symbols or letters paired with digits (1-9) at the top of the screen. On each trial, a stimulus appears in the center, and participants must respond with the corresponding digit (or vice versa). The task supports four directional modes: (1) symbol→digit (DSST forward), (2) digit→symbol (DSST reverse), (3) letter→digit (classic PEBL letterdigit), (4) digit→letter. Input can be via keyboard or clickable button interface (required for symbol/letter responses). This implements an enhanced version of the previous PEBL letterdigit task with expanded functionality.
- Replaces and extends the previous PEBL 'letterdigit' task with additional functionality
- Supports both letters and Unicode symbols (─ ⊥ ⊐ ⌐ ∪ ○ △ ⋈ ≡) matching clinical DSST
- Four task modes: symbol→digit, digit→symbol, letter→digit, digit→letter
- Flexible input: keyboard for digit entry, clickable interface for symbol/letter entry
- Can operate in trial-count mode (default 30 trials) or timed mode (e.g., 2 minutes)
- Clinical DSST typically uses 2-minute time limit; default here is trial-count for consistency
- Includes 7 language translations: English, Spanish, French, German, Italian, Dutch, Portuguese
- Migrated to PEBL 2.3 with Layout system, LSL markers, and UploadFile support
Test Details
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Scientific Background
Original Task References:
These references describe the original task that this PEBL implementation is based on.
- Wechsler, D. (1981). WAIS-R manual: Wechsler adult intelligence scale-revised. Psychological Corporation.
- Lezak, M. D., Howieson, D. B., Bigler, E. D., & Tranel, D. (2012). Neuropsychological assessment (5th ed.). Oxford University Press.
Validation status: Not-validated
Related Tests
Data Output
Creates two data files: (1) digitsymbol-<subnum>.csv with trial-by-trial data including stimulus type, direction, response mode, accuracy and reaction time; (2) digitsymbol-summary-<subnum>.txt with overall performance statistics.
Key Variables
| Variable | Description |
|---|---|
| subnum | Participant identifier code |
| stimtype | Type of stimulus: 'letter' or 'symbol' |
| direction | Task direction: 'stimulus_to_digit' (forward DSST/letterdigit) or 'digit_to_stimulus' (reverse DSST) |
| inputmethod | Response input mode: 'keyboard' (digit keys), 'click' (mouse/touch buttons), or 'auto' (automatically selected based on direction) |
| block | Block type: 0=practice trials, 1=test trials |
| trial | Trial number within block |
| probe | The stimulus presented to participant (letter, symbol, or digit) |
| cresp | Correct response for the trial |
| resp | Participant's actual response |
| corr | Response accuracy (1=correct, 0=incorrect) |
| rt | Response time in milliseconds from stimulus onset |
Example Data
digitsymbol-example.csv Primary
Trial-by-trial data with columns: subnum (participant code), stimtype (letter/symbol), direction (stimulus_to_digit or digit_to_stimulus), inputmethod (keyboard/click/auto), block (0=practice, 1=test), trial (trial number), probe (stimulus presented), cresp (correct response), resp (participant response), corr (accuracy: 1/0), rt (response time in ms)
| subnum | stimtype | direction | inputmethod | block | trial | probe | cresp | resp | corr | rt |
|---|---|---|---|---|---|---|---|---|---|---|
| 111 | symbol | stimulus_to_digit | auto | 0 | 1 | △ | 7 | 7 | 1 | 5016 |
| 111 | symbol | stimulus_to_digit | auto | 0 | 2 | ∪ | 5 | 5 | 1 | 2949 |
| 111 | symbol | stimulus_to_digit | auto | 0 | 3 | ≡ | 9 | 9 | 1 | 1359 |
| 111 | symbol | stimulus_to_digit | auto | 1 | 1 | ∪ | 5 | 5 | 1 | 4012 |
| 111 | symbol | stimulus_to_digit | auto | 1 | 2 | ─ | 1 | 1 | 1 | 1137 |
| 111 | symbol | stimulus_to_digit | auto | 1 | 3 | ─ | 1 | 1 | 1 | 635 |
| 111 | symbol | stimulus_to_digit | auto | 1 | 4 | ∪ | 5 | 5 | 1 | 1495 |
| 111 | symbol | stimulus_to_digit | auto | 1 | 5 | ∪ | 5 | 5 | 1 | 2116 |
| 111 | symbol | stimulus_to_digit | auto | 1 | 6 | ⋈ | 8 | 8 | 1 | 1334 |
digitsymbol-summary-example.txt Summary
Text summary report containing: test metadata, participant code, stimulus-digit mapping, total trials, number correct, proportion correct, mean/median/min/max RT, RT range, standard deviation and variance
---------------------------------------------- PEBL Digit-Symbol Substitution Test (DSST) Version 2.0 Released into public domain 2008-2026 by Shane T. Mueller, Ph.D. Sat Jan 31 12:21:49 2026 PEBL Version 2.3 ---------------------------------------------- Participant code: 111 Stimulus type: symbol Direction: stimulus_to_digit Input method: auto ---------------------------------------------- Mapping: ─ → 1 ⊥ → 2 ⊐ → 3 ⌐ → 4 ∪ → 5 ○ → 6 △ → 7 ⋈ → 8 ≡ → 9 ---------------------------------------------- Number of trials: 13 Number correct: 13 Proportion correct: 1 Percent correct: 100% Mean RT: 1848 ms Median RT: 1652 ms Min RT: 635 ms Max RT: 4012 ms RT Std Dev: 813 ms ----------------------------------------------
Sample data showing typical output format. Actual values will vary by participant.
About This Test
A processing speed and associative learning task requiring participants to match symbols with digits or letters with digits using a mapping key displayed on screen.
Category: Processing Speed
Estimated Duration: 5 minutes
Available Translations: 7 languages
Documentation Sources:
Test description file, Test implementation, Parameter schema
Documentation Status: Complete