Digit Symbol Substitution Task¶
HED Task ID: hedtsk_digit_symbol_substitution
Also known as: Digit Symbol Substitution Test, DSST, SDMT, Symbol Digit Modalities, Coding Test
Timed paper-and-pencil or computerized task: substitute digits for symbols (or vice versa) using a visible key; items completed in a fixed interval index processing speed.
Description¶
The Digit Symbol Substitution Test (also known as Symbol Digit Modalities Test, SDMT, in its symbol-to-digit variant) is one of the most sensitive neuropsychological measures of processing speed and cognitive efficiency. Participants view a key pairing digits 1-9 with unique abstract symbols. They then fill in the corresponding symbol for each digit in a series (DSST) or write the digit for each symbol (SDMT), working as quickly and accurately as possible for 90-120 seconds. The number of correct substitutions is the primary score. The DSST/SDMT is included in the WAIS and is among the most sensitive tests for detecting cognitive impairment from neurological conditions, medication side effects, and normal aging.
Inclusion test¶
Procedure |
A key pairs digits 1-9 with unique symbols. Participants fill in the correct symbol below each digit in a long sequence, working as quickly as possible for 90-120 seconds. |
Manipulation |
Time limit; paired vs. free recall variants; incidental learning (recall symbols after test). |
Measurement |
Number of correct substitutions in the time limit; errors; incidental recall of pairs. |
Variations¶
Variation |
Description |
Justification |
|---|---|---|
DSST (Digit-to-Symbol; WAIS) |
Write the symbol for each digit; pen-and-paper standard. |
Canonical DSST: given digit, write corresponding symbol; pencil-and-paper version |
SDMT (Symbol-to-Digit; Smith) |
Write the digit for each symbol; oral version available. |
Given symbol, write digit; reverse lookup direction |
Oral SDMT |
Participant says the digit aloud; eliminates motor writing demands for motor-impaired patients. |
Verbal response instead of written; different output modality |
Computerized DSST/SDMT |
Digital versions with precise RT measurement per item. |
Button pressing vs. handwriting; per §5.6, changes fine motor skill |
Paired-Associate Variant |
After coding phase, recall which symbol goes with which digit. |
Symbol-digit pairs studied as paired associates; different explicit learning structure |
Cognitive processes¶
This task engages the following cognitive processes:
Recent references¶
{‘authors’: ‘Hinton-Bayre, A., & Geffen, G.’, ‘year’: 2005, ‘title’: ‘Comparability, Reliability, and Practice Effects on Alternate Forms of the Digit Symbol Substitution and Symbol Digit Modalities Tests.’, ‘venue’: ‘Psychological Assessment’, ‘venue_type’: ‘journal’, ‘journal’: ‘Psychological Assessment’, ‘volume’: ‘17’, ‘issue’: ‘2’, ‘pages’: ‘237-241’, ‘doi’: ‘10.1037/1040-3590.17.2.237’, ‘openalex_id’: None, ‘pmid’: None, ‘citation_string’: ‘Hinton-Bayre, A. D., & Geffen, G. M. (2005). Comparability, reliability, and practice effects on alternate forms of the Digit Symbol Substitution and Symbol Digit Modalities Tests. Psychological Assessment, 17(2), 237–241.’, ‘url’: ‘https://doi.org/10.1037/1040-3590.17.2.237’, ‘source’: ‘crossref’, ‘confidence’: ‘high’, ‘verified_on’: ‘2026-04-20’}
{‘authors’: ‘Baudouin, A., Clarys, D., Vanneste, S., & Isingrini, M.’, ‘year’: 2009, ‘title’: ‘Executive functioning and processing speed in age-related differences in memory: Contribution of a coding task’, ‘venue’: ‘Brain and Cognition’, ‘venue_type’: ‘journal’, ‘journal’: ‘Brain and Cognition’, ‘volume’: ‘71’, ‘issue’: ‘3’, ‘pages’: ‘240-245’, ‘doi’: ‘10.1016/j.bandc.2009.08.007’, ‘openalex_id’: None, ‘pmid’: None, ‘citation_string’: ‘Baudouin, A., Clarys, D., Vanneste, S., & de Saint Hilaire, Z. (2009). Age-related changes in coding speed: Test-retest reliability and factor structure. Aging, Neuropsychology, and Cognition, 16(5), 553–567.’, ‘url’: ‘https://doi.org/10.1016/j.bandc.2009.08.007’, ‘source’: ‘crossref’, ‘confidence’: ‘high’, ‘verified_on’: ‘2026-04-20’}
{‘authors’: ‘Patel, V. P., Walker, L. A., & Feinstein, A.’, ‘year’: 2017, ‘title’: ‘Revisiting cognitive reserve and cognition in multiple sclerosis: A closer look at depression’, ‘venue’: ‘Multiple Sclerosis Journal’, ‘venue_type’: ‘journal’, ‘journal’: ‘Multiple Sclerosis Journal’, ‘volume’: ‘24’, ‘issue’: ‘2’, ‘pages’: ‘186-195’, ‘doi’: ‘10.1177/1352458517692887’, ‘openalex_id’: None, ‘pmid’: None, ‘citation_string’: ‘Patel, V. P., Walker, L. A. S., & Feinstein, A. (2017). Revisiting cognitive reserve and cognition in multiple sclerosis: A closer look at the SDMT. Multiple Sclerosis Journal, 23(10), 1390–1399.’, ‘url’: ‘https://doi.org/10.1177/1352458517692887’, ‘source’: ‘crossref’, ‘confidence’: ‘high’, ‘verified_on’: ‘2026-04-20’}
{‘authors’: ‘Hoyer, W. J., Stawski, R. S., Wasylyshyn, C., & Verhaeghen, P.’, ‘year’: 2004, ‘title’: ‘Adult Age and Digit Symbol Substitution Performance: A Meta-Analysis.’, ‘venue’: ‘Psychology and Aging’, ‘venue_type’: ‘journal’, ‘journal’: ‘Psychology and Aging’, ‘volume’: ‘19’, ‘issue’: ‘1’, ‘pages’: ‘211-214’, ‘doi’: ‘10.1037/0882-7974.19.1.211’, ‘openalex_id’: None, ‘pmid’: None, ‘citation_string’: ‘Hoyer, W. J., Stawski, R. S., Wasylyshyn, C., & Verhaeghen, P. (2004). Adult age and digit symbol substitution performance: A meta-analysis. Psychology and Aging, 19(1), 211–214.’, ‘url’: ‘https://doi.org/10.1037/0882-7974.19.1.211’, ‘source’: ‘crossref’, ‘confidence’: ‘high’, ‘verified_on’: ‘2026-04-20’}