Working memory
We hold about four things in mind at once, not seven.
Take the experiment
Look at the code, answer one small question, then type the code back. It grows one character longer each round.
Round 1 of 6 · 4 characters
Here is your code. Take as long as you like, then move on.
····
Why should I care?
Ask people to remember a code or a step from another screen and many will lose it: keep what they need in front of them.
- About 4things we can hold in mind at once, not seven.
- 4 in 5children with ADHD struggle to hold things in mind.
- 51 studiesshow that stress leaves us holding less.
What it means for your website
- Let people paste codes, never retype them.
- Keep what they need on the screen.
- Show long numbers in short groups.
More, if you want it
Why this matters
Picture a customer reading a code off their phone and typing it into your website. We can only hold a few things in mind at once, and one interruption is enough to lose them.
Working memory is what you hold on to for a moment while you use it, the way you carry things in your hands from one room to the next. You’ll see a code, answer a small question on the next screen, then type the code back. It grows by one character each round, the way a reference number or a code from a text message does.
Not seven things at once, but four
In 1956 the psychologist George Miller wrote one of the most quoted papers in psychology, “The magical number seven, plus or minus two”.
It is often read as a rule that people can remember seven things. Miller was careful to say something subtler1: that memory is limited by the number of meaningful chunks, not the number of letters or digits, and that the sevens turning up in his data were probably “a pernicious, Pythagorean coincidence”. In 2001 Nelson Cowan reviewed the evidence and put the real limit, when people cannot repeat or group what they are holding, at about four chunks2.
Chunking is why a phone number is written in groups. “4821 7730 2291” is three things to hold; “482177302291” is twelve.
Everyone holds less on a bad day
What you can carry at your best is not what you can carry when it matters.
Acute stress reduces working memory, according to a review of 51 studies3, and so does losing a night’s sleep. It declines steadily with age from our twenties, even as what we know keeps growing. An estimated four in five children with ADHD show a significant working-memory difficulty.
Researchers have also argued that money worries take up mental room: in a much-discussed 2013 study, poorer shoppers did worse on reasoning tests after thinking about a large bill. Later attempts to repeat it have had mixed results, so it is better taken as a question than a settled fact. Either way, the person filling in your form may be anxious, tired or interrupted, often all three.
Every code you ask a customer to copy
Each time a site makes someone carry something from one screen to another, it is spending their working memory.
A verification code sent by text, an order number from an email, a price from the page before, a choice made three steps ago: some people will drop them, and blame themselves. The accessibility guidelines now say so plainly. A sign-in that makes people retype a code by hand, with no way to paste it, does not comply8, and a process must not ask for the same information twice9.
Menus are the opposite case. People do not memorize a menu they can see; they recognize what they want in it. That is why Miller’s number says nothing about how long a menu may be.
All the advice, in full
Never make people retype a code
Let one-time codes be pasted and filled in automatically (
autocomplete="one-time-code"), and let password managers work (WCAG 3.3.8).Don’t ask twice
If someone has already given you something in the same process, fill it in or offer it to choose (WCAG 3.3.7 Redundant Entry).
Show it where it’s needed
Keep the order number, the account details or the question being answered on screen at the moment people need them.
Group long strings
Show long codes and numbers in short groups, and give people a one-click way to copy them.
Design for the tired user
Plan for someone stressed, short of sleep, older or interrupted, not a rested volunteer in a lab.
Save progress
Let people leave and come back without losing what they entered, and warn them well before anything times out.
An experiment on you
This one runs here, on this page: it measures you, not a design. Use what it shows you when you review a prototype or a live page with the other tools.
What people get wrong
- Menus should have seven items, plus or minus two
- Miller wrote about remembering and judging, not menus. People recognize items in a menu they can see; they do not memorize it.
- Working memory holds seven things
- Closer to four chunks when people cannot rehearse or group, and it varies with the person and the moment.
- Poverty lowers IQ by thirteen points
- That comparison comes from one much-debated study. Several attempts to repeat it found no effect.
- Multitasking permanently damages memory
- The evidence is weak. Heavy multitaskers may filter distractions less well, but repeat studies largely failed.
Where these numbers come from
Every figure on this page comes from one of these 10 sources. The small numbers in the text point here.
Peer-reviewed study
The magical number seven, plus or minus two: some limits on our capacity for processing information·
Psychological Review
Review
The magical number 4 in short-term memory: a reconsideration of mental storage capacity·
Behavioral and Brain Sciences
Review
The effects of acute stress on core executive functions: a meta-analysis and comparison with cortisol·
Neuroscience & Biobehavioral Reviews
Review
A meta-analysis of the impact of short-term sleep deprivation on cognitive variables·
Psychological Bulletin
Review
Moderators of working memory deficits in children with attention-deficit/hyperactivity disorder (ADHD): a meta-analytic review·
Clinical Psychology Review
Peer-reviewed study
Poverty impedes cognitive function·
Science
Peer-reviewed study
Poverty and economic decision-making: evidence from changes in financial resources at payday·
American Economic Review
Standard
Understanding WCAG 3.3.8: Accessible Authentication (Minimum)Web Content Accessibility Guidelines 2.2
Standard
Understanding WCAG 3.3.7: Redundant EntryWeb Content Accessibility Guidelines 2.2
Guidance
Memory recognition and recall in user interfaces