Can you memorize a phone number for long enough to write it down? How about two phone numbers at the same time?

Digit Span tests your ability to remember a sequence of numbers that appear on the screen, one at a time. When you hear a beep, click on the numbers you just saw, in order. If you correctly recall all of the numbers, then the next sequence will be one number longer. If you make a mistake, then the next sequence will be one number shorter. After three mistakes, the test will end.

## Optimizing Performance

In this test:

• Accuracy does matter; after three errors, the test ends. However, wrong answers do not subtract from your score, which is the maximum number of digits you correctly remember.
• Speed does not matter. You have as long as you want to answer—but it might be hard to remember if you wait too long!

So to get maximum points, pay careful attention and reach the longest string of digits you can possibly remember.

Video instructions.

Performance tips:

• Your digit span can be increased with the right strategies. Experiment with your mental approach to the test to find strategies that work for you.
• For most people, "chunking" is an effective strategy—instead of thinking about each digit separately, think of groups of digits that form a smaller number of meaningful units (chunks).
• For example, instead of thinking about 1 4 2 8 5 7 as six digits, thinking of it as three numbers—14, 28, and 57—could make it easier to recall. It's not easy, and requires a lot of practice to master.

## Domain Scores

Your score on this test contributes to:

• Your verbal ability score (a lot).
• Your short-term memory score (a bit).

That's right, perhaps surprisingly, it's more closely related to verbal ability than to memory. The contribution of each test to each performance category is based on a "factor analysis" that looked at how tests tend to clump together when measuring a massive set of data. The results were published in Neuron in 2012 (Hampshire, Highfield, Parkin, & Owen, 2012). The exact contribution of each test to each performance category may change as more data is collected.

## The Science Behind Digit Span

The science behind digit span reveals why it's associated more with verbal ability than short-term memory alone. Scientists refer to short-term memory, or working memory, as the cognitive system that allows the temporary storage and manipulation of information. According to one influential cognitive theory, this system has specialised components, one of which, the "phonological loop," underlies verbal working memory abilities (Baddeley & Hitch, 1974). The phonological loop comprises a verbal storage system and a rehearsal system. As you do this test, you may find yourself mentally rehearsing the string of digits as they appeared on screen; this is the rehearsal system in action. It allows the visual inputs to be recoded so that they can enter your short term verbal store, and it also refreshes decaying representations—without refreshing digits verbally, they would soon be forgotten.

We have been studying how the brain remembers verbal information for nearly ten years. Our research has revealed that, while you are performing the digit span task, areas of your frontal cortex become activated.

In one study (Owen et al, 2000), participants either had to recall digits in the order presented (forward recall), or in reverse order (backward recall), with backward being a much more demanding task. We found that both tasks engaged the mid-ventrolateral frontal cortex, but only when participants were recalling in reverse order did the mid-dorsalateral frontal cortex become activated. Both of these tasks required verbal working memory, yet different activation patterns were observed in the brain. On this basis, we concluded that frontal-lobe activity in this task relates to the type of memory process being performed (i.e., storage, reordering) and is not specific to the type of information that is being remembered (i.e., verbal memory).

An average adult is thought to have a digit span of 7 items (plus or minus 2; Miller, 1956). As mentioned above, one of the best studied methods for improving verbal memory is through the use of "chunking" strategies, in which items are recoded into meaningful units or "chunks." In one study, by training a volunteer to use complex chunking strategies over the course of 20 months, scientists were able to increase digit span from 7 to a massive 79 items (Ericcson et al, 1980)!

Our colleagues have studied the underlying brain activity involved in chunking. When recoding strategies were used to remember digit sequences, increased activation was observed in the lateral prefrontal and posterior parietal cortex. On this basis, we have hypothesised that this prefrontal-parietal network underlies strategic recoding in working memory (Bor et al., 2004, 2006).

## Digit Span in the Real World

Verbal working memory is involved in many everyday tasks, from remembering a telephone number while you enter it into your phone, to understanding long and difficult sentences. Think about it; how could you understand a whole sentence if you couldn't remember the words at the beginning long enough to connect with the words at the end! Verbal working memory is also thought to be one of the elements underlying intelligence, so the digit span task is a common component of many IQ tests, including the widely used WAIS (Wechsler Adult Intelligence Scale). Performance on the digit span task is also closely linked to language learning abilities; improving your verbal memory capacity may therefore help you to master a new language or to expand your vocabulary.

Some people have even made a sport out of increasing their digit span. Every year, the World Memory Championship tests how many digits can be remembered, in various types of games. In the 2015 competition, when given an hour to memorize digits, the current world record holder, Alex Mullen, recalled 3029 digits!

Reaching 3029 digits is probably not feasible for the average person, but some strategies (like chunking, described above), alongside lifestyle optimization, can increase your digit span. Stress and exercise may not have an effect right away ; the results of studies looking at their immediate impact on Digit Span are inconsistent. Getting the right amount of sleep, however, may boost your scores right away. In one study (Sadeh, Gruber, & Raviv, 2003), children asked to increase their sleep by just one hour significantly increased their Digit Span performance. Try varying your own sleep schedule to see how Digit Span changes.

## References

• Baddeley, A. D., & Hitch, G. (1974). Working memory. In G. A. Bower (Ed.), Recent advances in learning and motivation, Vol. 8. New York: Academic Press.
• Bor., D., Cumming, N., Scott, C. E. M., & Owen, A. M. (2004). Prefrontal cortical involvement in verbal encoding strategies. European Journal of Neuroscience, 19(12), 3365-3370. Read Abstract
• Bor, D., & Owen, A. M. (2007). A common prefrontal-parietal network for mnemonic and mathematical recoding strategies within working memory. Cerebral Cortex, 17, 778-786. Download PDF
• Ericcson, K. A., Chase, W. G., & Falloon, S. (1980). Acquisition of a memory skill. Science, 208, 181-1182.
• Miller, G. A. (1956). The magical number seven, plus or minus two: Some limits on our capacity for processing information. Psychological Review, 63, 81-97.
• Owen, A. M., Lee, A. C. H., & Williams, E. J. (2000). Dissociating aspects of verbal working memory within the human frontal lobe: Further evidence for a 'process-specific' model of lateral frontal organization. Psychobiology, 28(2), 146-155. Read Abstract
• Sadeh, A., Gruber, R., & Raviv, A. (2003). Effects of sleep restriction and extension on school-age children : What a difference an hour makes. Child Development, 74(2), 444-455. Download PDF