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UX glossary

Cognitive Load

Cognitive load is the mental effort it takes to understand and use an interface. The less unnecessary thinking a design demands, the easier the actual task becomes.

Imagine you’re booking a train ticket online. Three ad banners are flashing, the form asks for things you don’t understand, and you have to remember the fares from page one because page two no longer shows them. By the end you feel drained, even though the task itself was simple.

That’s cognitive load in action: the website made you think harder than you needed to.

Explained simply

Cognitive load is the mental effort it takes to understand and use an interface. Most of that work happens in your working memory, the part of your memory that briefly holds and processes information. Its capacity is small. George Miller’s famous “seven plus or minus two” was meant as a rough estimate. More recent research, for example by Nelson Cowan, suggests you can hold roughly four chunks of information in mind at once.

Think of your working memory as a small kitchen counter. If it’s covered with flyers and dirty dishes, there’s hardly any room left to cook. Good design clears the counter.

The term comes from learning research. Australian psychologist John Sweller laid the groundwork for cognitive load theory in 1988 to explain why some learning materials get in the way of learning instead of supporting it. UX design later adopted the idea.

Necessary and unnecessary load

Not all effort is bad. For UX, two kinds matter most. Intrinsic load is built into the task itself: filing a tax return is more complex than checking a weather app, and good design can’t change that much. Extraneous load, on the other hand, comes from the way things are presented, such as unclear labels, busy layouts, or information you have to remember instead of being able to see. The theory also describes a third kind, germane load, which goes into building new knowledge.

So the goal isn’t to simplify everything. It’s to cut the unnecessary load, which leaves capacity for what really matters. If you want to know why short-term memory plays such a big role here, read Basics of Human Perception: Short-Term Memory.

An example

Here’s an example. An online store’s checkout is one long form with 18 fields, plus coupon notices and a newsletter box. Shipping costs only show up at the very end. Many people give up.

After the redesign, there are three short steps with clear headings. The shipping address is prefilled as the billing address, shipping costs are visible in the cart from the start, and everything unrelated to the purchase is gone. The task is the same, but it feels much lighter. You’ll find more rules like this in Forms Nobody Abandons: 12 Rules for Better Form UX.

In practice

  • Cut the noise. Remove elements that don’t help with the task, such as decorative images, duplicate links, or needless highlighting.
  • Use familiar patterns. What people already know from other websites, they don’t have to learn again. Almost everyone instantly understands a cart icon in the top right corner.
  • Take work off people’s plates. Show information again instead of asking for it, and set sensible defaults. Recognizing is easier than recalling.

Related terms

Hick’s Law, Progressive Disclosure, Gestalt Principles, Mental Model

Sources

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