The HED Task Catalog is under development. IDs are not stable until formal release. Comments are welcome at github.com/hed-standard/hed-task/issues.

Digit Symbol Substitution Task

HED task ID: hedtsk_digit_symbol_substitution

Family: Motor performance and speeded response tasks

Also known as: Digit Symbol Substitution Test, DSST, SDMT, Symbol Digit Modalities, Coding Test, Digit Symbol Substitution

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

An experiment is an instance of this task when its procedure matches, it manipulates at least one of the listed variables, and it records at least one of the listed measures.

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

Named versions that change what the participant experiences or does. The identifier of a variation is hedvar_<task>__<variation>.

Variation

Description

Justification

DSST (Digit-to-Symbol; WAIS)

hedvar_digit_symbol_substitution__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)

hedvar_digit_symbol_substitution__sdmt_symbol_to_digit_smith

Write the digit for each symbol; oral version available.

Given symbol, write digit; reverse lookup direction

Oral SDMT

hedvar_digit_symbol_substitution__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

hedvar_digit_symbol_substitution__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

hedvar_digit_symbol_substitution__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 is designed to engage the following processes:

Further references

  • 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. (DOI, PubMed)

  • 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.

  • 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. (DOI, PubMed)

  • 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. (DOI, PubMed)