Information processing speed

SDMT — Symbol Digit Modalities

The Symbol Digit Modalities Test, introduced by Aaron Smith in 1982, is one of the most robust processing-speed tests, widely used in MS, TBI, and cognitive screening. This module uses original symbols (not the Smith 1982 copyrighted key).

DifficultyExpert = strict academic parameters

Age band (for scoring reference)Not signed in (scores won't count toward profile)

Intermediate: 9 symbols, 75 s.

The key (symbol ↔ digit) is shown at the top. A sequence of symbols appears below. Press the matching digit on your keyboard, or click the numeric buttons. Complete as many as you can in 90 seconds.

History

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References: Smith (1982); Sheridan et al. (2006); Strauss et al. (2006).

Scientific basis

SDMT · scientific basis

Information processing speed

The Symbol Digit Modalities Test was published by Aaron Smith in 1982, pairing 9 abstract symbols with digits 1-9 under a 90-second limit. Strauss, Sherman & Spreen (2006) compendium provides consolidated norms.

Expert-mode parameters

These are the standard parameters from the canonical paradigm (used by the "Expert" difficulty).

Parameter	Standard value	Source
Key	9 symbols ↔ digits 1-9	Smith 1982
Test items	110	Smith 1982
Time limit	90 seconds	Smith 1982 (all versions)
This module	Original symbols (not Smith 1982 copyright)	Project

Healthy-population norms (by age)

Based on Smith 1982 written-version adult norms and Sheridan 2006 community child norms; the oral version scores ~2-6 points higher. 'Excellent' = mean + 1 SD (matches in 90 s, higher is better). Assessment mode matches your actual age to the corresponding band.

Limitations： Smith 1982 adult norms (n>400 stratified) and Sheridan 2006 community child norms (n=3020, ages 6-17) are both peer-reviewed large-sample references — evidence strength is high overall. Main caveats: (a) this module uses an original geometric symbol set to avoid Smith 1982 copyright, but completion rate can drift ±2 items from the standard SDMT; (b) SDMT is strongly education-dependent (Sheridan reports +0.7 items per additional year of schooling), and this table does not stratify education; (c) the written version (handwriting digits) differs in timing from keyboard entry — this site is keyboard-based and may run somewhat faster. Cross-reference with on-site TMT-A as another processing-speed measure.

Age band	Excellent (90 s)	Mean	SD	Evidence
8-9	≥ 36	~29	~7	medium-strong
10-11	≥ 45	~37	~8	medium-strong
12-13	≥ 53	~44	~9	medium-strong
14-15	≥ 58	~49	~9	medium-strong
16-17	≥ 63	~53	~10	medium-strong
18-24	≥ 63	~55.2	~7.5	strong
25-34	≥ 60	~53.6	~6.6	strong
35-44	≥ 59	~51.0	~7.5	strong
45-54	≥ 56	~47.5	~8.5	strong
55-64	≥ 53	~43.0	~10.0	strong
65+	≥ 49	~37.4	~11.4	strong

Standard output metrics

·Total correct — Correct matches in 90 s (primary)
·Errors — Error count (healthy adults usually <2)
·Age-scaled score — Age-adjusted standard score

Citations

Smith, A. (1982). Symbol Digit Modalities Test (SDMT): Manual (revised). Los Angeles: Western Psychological Services. wpspublish.com
Sheridan, L. K., et al. (2006). Normative Symbol Digit Modalities Test performance in a community-based sample. Arch Clin Neuropsychol, 21(1), 23-28. DOI
Strauss, E., Sherman, E. M. S., & Spreen, O. (2006). A Compendium of Neuropsychological Tests (3rd ed.). Oxford University Press. global.oup.com
Arango-Lasprilla, J. C., et al. (2017). Symbol Digit Modalities Test: Normative data for Spanish-speaking pediatric population. NeuroRehabilitation, 41(3), 581-592. DOI

All reference ranges come from published peer-reviewed literature. For personal training reference only — not a medical diagnosis. Full methodology: docs/PARADIGMS.md.

This tool is for educational and entertainment purposes only and does not constitute medical advice or a clinical diagnosis.