No. 02
Forward vs Backward Digit Span — What's the Difference?
Repeating digits in the order you heard them and saying them in reverse make different demands. A comparison of what each task measures, with common strategies and mistakes.
Digit span tasks come in two directions. In forward span you recall the digits in the order they were presented; in backward span you recall them in reverse, starting with the last. The same string suddenly becomes much harder when you have to say it backward, because the two tasks use the same memory but ask it to do different things.
What forward span requires
In forward span you simply hold the string as you heard it and play it back. The phonological loop, with its silent rehearsal, does most of the work. That's why forward span gives a fairly direct picture of your ability to keep short sequences in mind while paying attention.
What backward span adds
Backward span requires you to hold the string and reverse its order at the same time. While you retrieve digits from the end, you must keep the earlier ones you haven't said yet, so storage and manipulation happen together. For this reason backward span is interpreted as placing more demand on the manipulation (central executive) side of working memory. For most people, backward span comes out shorter than forward span.
| Comparison | Forward | Backward |
|---|---|---|
| --- | --- | --- |
| What you do | Hold in order → output as is | Hold + reverse the order → output |
| Main function used | Phonological loop (silent rehearsal) | Phonological loop + central executive (manipulation) |
| Common strategies | Rehearse with a rhythm, group in 3s or 4s | Picture the digits on a mental screen and read from the end, reverse in small groups |
| Common mistakes | Swapping digits in the middle, dropping a digit | Outputting a group in forward order, forgetting the early digits |
How standard tests use it
The Digit Span subtest of the Wechsler Adult Intelligence Scale, Fourth Edition (WAIS-IV) consists of three tasks: Digit Span Forward, Digit Span Backward and Digit Span Sequencing (repeating the digits in ascending order). Clinicians sometimes look at forward and backward scores separately; when only one is unusually low, it can be a clue for forming a hypothesis about whether the difficulty lies in attention and storage or in manipulation. That kind of interpretation, however, is done by professionals alongside standard procedures, norms and other test results, and is not something this site's scores can do.
What helps with backward span
- Lock it in forward first: people often lose the early digits while concentrating on reversing. While the digits are being presented, focus on rehearsing them in order.
- Reverse in small groups: with 7 digits, split them 3-4, reverse and type the last group first, then reverse and type the first group.
- Use a mental screen: some people find it works to picture the digits in a line and read them from the right-hand end. Try practicing in all-at-once mode.
How to look at the gap between your scores
The gap between forward and backward scores differs from person to person and also depends on presentation (seeing or hearing) and speed. This site stores personal bests and averages for each direction separately, so repeat each with the same settings and compare your own trends.
Sources: Baddeley & Hitch (1974) · Wechsler, D. (2008) WAIS-IV Technical and Interpretive Manual, Pearson · Lezak, M. D. et al. (2012) Neuropsychological Assessment, 5th ed., Oxford University Press