Digit span as a measure of immediate memory

Digit span asks how many items you can hold in mind and reproduce after a single presentation. A string of digits appears, you type it back, and the longest string you manage is your span. Forward mode repeats them in the order shown, leaning on storage alone. Backward mode asks for them in reverse, adding a manipulation step — holding the items and reordering them at the same time — which is why backward span is normally shorter, typically by about two digits.

How a run is administered

The test begins at length 3 and follows the two-attempt rule of clinical-style administration: digits appear one at a time, each shown for 800 ms followed by a 300 ms blank, so every digit occupies 1.1 seconds of your attention. After the last digit the screen clears and you type the sequence and submit. One correct answer advances you to the next length and restores both attempts; two failures at the same length end the test.

Scoring is an exact whole-string match against the sequence shown, with no partial credit: transpose two digits or drop one and the attempt is wrong even if you clearly remembered most of it. Your span is the longest length answered correctly, and the summary also lists the length you were attempting when the test stopped, the number of sequences you got right, and a level-by-level table. Spaces are stripped as you type, so 5 8 3 is read as 583, but the digits must be exactly right and in the right order.

A worked run, forward mode

You pass length 3, pass 4, pass 5, then fail twice at length 6. The three-, four- and five-digit levels cost 3.3 s, 4.4 s and 5.5 s to present, and the two failed six-digit attempts 6.6 s each — about 26.4 seconds of digits before you type anything. The summary reads: span 5, the longest sequence answered correctly; stopped at length 6, the length being attempted when two failures exhausted your attempts; and 3 sequences correct, since levels 3, 4 and 5 each passed first time. Note the two headline numbers differ by one: a span of 5 does not mean you failed at length 5, it means you never got a six-digit string right. The bands applied are indicative rather than diagnostic — 7 or more marked typical-to-high, 5 or 6 middling, 4 or below low. For orientation, Miller's 1956 paper famously put the immediate memory limit at around seven items, and a backward span near five is unremarkable for an adult.

What can go wrong with a home span test

• All-or-nothing scoring. Assessments often give partial credit for digits recalled in the correct position. Here a single transposition zeroes the attempt, so your number can come out a digit lower than a scored assessment would give.
• Two attempts per length. A momentary lapse at the wrong moment can end the run one level early, so a single run is a coarse estimate.
• Typing and presentation. A typo is indistinguishable from a memory failure, and clinical digit span is usually read aloud rather than shown, which makes this a related but different task.
• Strategy and practice. Chunking helps a lot, and someone who has just done the test knows how to group the digits next time. Improvement on a second attempt reflects technique, not memory.

Common questions

Why do I get two tries at each length?

To reduce the chance that a single slip ends the test, as standard administration also does.

Is my score the last length I passed, or the one I failed?

The last length passed. The failed length is reported separately as the stopping point.

Does backward count the same as forward?

Same scale, harder task — a backward span below your forward span is the normal pattern.

Why does the length step up by one each time?

Correct answers always advance by one, so the test keeps climbing until you miss twice. There is no way to skip a length.