Short-Term Memory and Web Usability

by Jakob Nielsen on December 7, 2009

Summary: The human brain is not optimized for the abstract thinking and data memorization that websites often demand. Many usability guidelines are dictated by cognitive limitations.

People can't keep much information in their short-term memory. This is especially true when they're bombarded with multiple abstract or unusual pieces of data in rapid succession. Lest designers forget how easily users forget, let's review why our brains seem to be so weak.

Human beings are remarkably good at hunting the woolly mammoth. Our ancestors did fine work in exterminating most megafauna from Australia to North America armed with nothing better than flint weapons. (In today's more environmentally conscious world, we might deplore their slaughtering ways, but early humans were more interested in catching their dinner.)

Many of the skills needed to use computers aren't highly useful in slaying mammoths. Such skills include remembering obscure codes from one screen to the next and interpreting highly abbreviated form-field labels. It's no surprise that people are no good at these skills, since they weren't important for survival in the ancestral environment.

The human brain today is the same as the human brain 10,000 years ago. Indeed, I thought of using the title "Designing Websites for Cavemen" for our new course on how psychology explains usability guidelines and dictates effective website design. However, doing so would violate the writing guideline against using cute headlines that don't actually explain what a page (or, in this case, a seminar) is about.

Instead, we picked the title, "Usability and the Human Mind: How Your Customers Think."

If I'd gone with the first title, it would have primed your long-term memory to activate terms related to "cavemen" — probably including concepts such as man-eating dinosaurs lodged there by watching too many B-movies. It definitely wouldn't activate concepts related to improving your site's business performance. In contrast, the title we ultimately chose includes the word "customers," which primes the memory in a more appropriate way, attracts more clicks, and puts users in a business-oriented mindset.

Designing for Brainpower Limitations

When it comes to abstract thinking, humans have extremely limited brainpower. For example, short-term memory famously holds only about 7 chunks of information, and these fade from your brain in about 20 seconds.

It's a common misconception that limited short-term memory implies that menus should be similarly limited to 7 items. It's fine to have longer menus (if needed), because users don't have to memorize the full list of menu items. The entire idea of a menu is to rely on recognition rather than recall (one of the basic 10 heuristics for user interface design). There are many other usability issues in menu design, and shorter menus are certainly faster to scan. But if you make a menu too short, the choices become overly abstract and obscure.

Short-term memory limitations dictate a whole range of other Web design guidelines:

  • Response times must be fast enough that users don't forget what they're in the middle of doing while waiting for the next page to load.
  • Change the color of visited links so that users don't have to remember where they've already clicked.
  • Make it easy to compare products, highlighting the salient differences on both the initial category page and in special comparison views. If you require users to move back and forth between separate product pages to deduce differences, they'll get confused — particularly if the pages present the information in an inconsistent format.
  • Instead of using coupon codes, encode offers in special links embedded in your email newsletters and automatically transfer the coupon to the user's shopping cart. This has two benefits:
    • The computer carries the burden of remembering the obscure code and applying it at the correct time.
    • It eliminates the "enter coupon code" field, which scares away shoppers who don't have coupons (and who refuse to pay full price when the checkout flow blatantly signals that other users are getting a better deal).
  • Offer help and user assistance features in the context where users need them so they don't have to travel to a separate help section and memorize steps before returning to the problem at hand. (See our Application Usability course for more on help and user assistance.)

Individual Differences

Although the average human brain is better equipped for mammoth hunting than using websites, we're not all average. In fact, there are huge individual differences in user performance: the top 25% of users are 2.4 times better than the bottom 25%.

At the extreme, only about 4% of the population has enough brainpower to perform complex cognitive tasks such as making high-level inferences using specialized background knowledge. Most likely, you're in this elite group. And, worse yet, so are many other members of your Internet team. (And the rest are definitely in the top 25%, which is also much better than average users.)

That your own short-term memory may hold two more items than most users' might not seem like a lot. But if your website blocks off short-term memory slots by requiring users to remember extraneous information, a little extra STM capacity can make all the difference in usability. You still have enough spare slots to think about the product line, but if your customers exhaust their brain capacity, they'll find your site very frustrating indeed.

Even though it's a bad course title, it's a good overall mnemonic to design for cavemen and their literal-minded and limited-capacity brains. After all, your paying customers are only one step out of the cave.

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