Digit memory.
Can you hold in mind the digits that appear one at a time on screen, and type them first in the same order, then in reverse?
Original study
- Jacobs, J. (1887). Experiments on "prehension". Mind, 12(45), 75–79. Source
- Miller, G. A. (1956). The magical number seven, plus or minus two: Some limits on our capacity for processing information. Psychological Review, 63(2), 81–97. Source
- Cowan, N. (2001). The magical number 4 in short-term memory: A reconsideration of mental storage capacity. Behavioral and Brain Sciences, 24(1), 87–114. Source
- Baddeley, A. D., Thomson, N., & Buchanan, M. (1975). Word length and the structure of short-term memory. Journal of Verbal Learning and Verbal Behavior, 14(6), 575–589. Source
- Ellis, N. C., & Hennelly, R. A. (1980). A bilingual word-length effect: Implications for intelligence testing and the relative ease of mental calculation in Welsh and English. British Journal of Psychology, 71(1), 43–51. See also: Stigler, J. W., Lee, S.-Y., & Stevenson, H. W. (1986). Digit memory in Chinese and English: Evidence for a temporally limited store. Cognition, 23(1), 1–20. https://doi.org/10.1016/0010-0277(86)90051-X Source
- Woods, D. L., Kishiyama, M. M., Lund, E. W., Herron, T. J., Edwards, B., Poliva, O., Hink, R. F., & Reed, B. (2011). Improving digit span assessment of short-term verbal memory. Journal of Clinical and Experimental Neuropsychology, 33(1), 101–111. Source
- Ericsson, K. A., Chase, W. G., & Faloon, S. (1980). Acquisition of a memory skill. Science, 208(4448), 1181–1182. Source
Our adaptation
A visually presented adaptation of Jacobs' (1887) digit span task. Digits appear one at a time in the middle of the screen for 800 ms with a 200 ms gap (one digit per second); the keypad is hidden during presentation, after which the digits are typed with the on-screen keypad or a keyboard. Round 1 asks for the same order (forward, starting at 3 digits), round 2 for the reverse order (backward, starting at 2 digits). Each length has two trials; the sequence grows if at least one is correct, and the round ends if both are wrong.
Differences from the original study
- In most norm studies digits are read aloud and repeated orally; here they are shown on screen and typed.
- We cannot check whether digits were written down or rehearsed aloud.
Measured variables
The columns of the open data file. List fields are expanded into numbered columns (for example rt_60, est_3); JSON columns contain only numbers and fixed stimulus names.
| Column | Type | Description |
|---|---|---|
fwd | integer | Forward span: longest sequence with at least one correct trial. |
bwd | integer | Backward span: longest sequence with at least one correct trial. |
total | integer | Sum of forward and backward span. |
trials | JSON | Trials: [{"d": f = forward / b = backward, "len": sequence length, "ok": correct}], in presentation order. |
Columns present in every file (14)
row_id | string | Row code. Regenerated at random in every release; it does not identify a person and cannot be matched across releases or experiments. |
experiment | string | Short name of the experiment (URL slug). |
experiment_version | integer | Version of the answer format. For experiments whose format changed, only the current format is published. |
date | YYYY-MM-DD | YYYY-Www | YYYY-MM | Day the answer was given (Istanbul time). If fewer than 5 answers share the same day, language and device, it is coarsened to the ISO week, and to the month if that is still too few. |
date_precision | day | week | month | Precision of the date column. |
lang | tr | en | (boş) | Interface language. Language recording started in the first week of October 2026; for earlier answers it is known only in experiments whose stimuli depend on the language, and empty otherwise. |
device | desktop | mobile | tablet | (boş) | Device class reported by the browser (class only; browser details are neither stored here nor published). |
source | site | embed | Where the answer came from: the balabs site or the experiment embedded on another site. The embedding site is not published. |
mode | free | daily | challenge | race | session | (boş) | Play mode in scored experiments: free play, daily round, challenge, race room, experiment session. Empty for unscored experiments and for older answers that did not store it. |
color_vision | normal | rg | by | contrast | (boş) | In color-based experiments, the color vision mode the participant chose: normal, red-green, blue-yellow or high contrast. Stimuli are generated along different axes per mode, so compare within a mode. Empty for other experiments. |
first_play | 1 | Every row is a participant’s first play of this experiment (always 1). Replays are stored only as leaderboard scores and are not part of the open data. |
seen_before | yes | no | unsure | (boş) | Participant’s own report of whether they had seen this experiment or its known answer before (in experiments that ask). |
duration_s | number | Time from the start of the experiment to submitting the answer, in seconds (measured in the browser, 0.1 s). |
play_score | number | Leaderboard score of the first play (scored experiments; defined on the method card). Empty for unscored experiments. |
Exclusion criteria
The server checks the forward and backward span against the trial records; inconsistent submissions are rejected. Spans must be between 0 and 12.
- Only each participant's first answer to this experiment; replays are not included.
- Simulated rows, bots, banned and sample accounts are not included.
- Answers before 3 October 2026 are not included (the first day the open data notice was live).
Scoring
Leaderboard score: forward + backward span; higher is better.
Leaderboard measure: digits (higher is better). The play_score column in the open data is this score for the first play.
Version notes
- October 2026
Memory span is now checked against the trial records (longest error-free forward and backward sequence); inconsistent submissions are rejected.
- October 2026
This experiment started storing the play mode (free, daily, challenge, race, session) with the answer; the mode column is empty for earlier answers.
- October 2026
The interface language (lang) started being stored with each answer; for earlier answers it is known only in experiments whose stimuli depend on the language, and empty otherwise.