Human memory is complex and a little mysterious. Unlike electronic data storage, human memory is not perfectly reliable and predictable. In this section, we’ll take a whirlwind tour of what we know about human memory, and then we’ll think about how we can apply this knowledge to user interface design.
A model of memory
There are a number of psychological models of human memory. Most distinguish between short-term and long-term memory as separate but interrelated structures or systems in the brain. While there is no consensus on the “correct” model, one model useful for us is as follows:
- Short-term memory or working memory is a temporary store that can hold a small amount of information, such as a handful of words, numbers, or symbols, related to your current train of thought. Working memory decays very rapidly; the information can be lost when your attention is drawn to something else, and so you often have to repeat the information to yourself to avoid having it disappear. The capacity of working memory is said to be about “seven, plus or minus two” items (Miller, 1956), and it’s for this reason that North American phone numbers were chosen to be seven digits long — it’s difficult to hold more than about seven digits in your mind if you’ve heard a phone number and you’re trying to write it down.
- Middle-term memory or contextual memory holds information required for you to be able to work on your current activity, but you won’t permanently remember most of this information. For example, during a conversation, you’ll have in mind the details of what has been discussed so far. Or if you’re working on your income tax return, you’ll know where on your desk you’ve put your different papers and receipts and you’ll remember some of the key numbers and details.
- Long-term memory is a more persistent store of knowledge and memories of experiences — facts, concepts, ideas, names, images, sounds, voices, places, emotional feeling states, and so on. Long-term memory also stores procedures and skills, for both cognitive and sensory-motor tasks. Long-term memory might alternatively be called “permanent memory“, but this is misleading as information is often subject to forgetting or “false recall”.
How does memorization happen?
Memorization, or committing something from short-term memory to long-term memory, most commonly involves repetition. The more often you encounter (see or hear) something, the more likely you are to remember it later. Studying involves actively intentionally re-reading, rehearsing, and practicing.
But we also tend to remember information and experiences that are surprising, novel, or unusual without any repetition.
The exact nature of how the brain forms memories remains unknown, but it is likely that information and memories stored in long-term memory are somehow stored symbolically. That is, if you hear a professor telling you information in a lecture, you may memorize much of the information in the lecture, but you will probably not store a perfect audio recording of the professor’s lecture. You may of course remember the professor’s voice, especially if it is particularly unique, but this is separate from the information content of the lecture, which you can make use of in practical contexts without “playing back” the “audio recording” of the professor’s voice.
There are some rare people who do have a perfect “photographic” memory, though, and most people can remember music precisely enough that they can distinguish if a later performance differs by only one note.
We tend to store information in logical groupings or chunks, and memorization is most effective when a chunk is associated with other existing chunks of information in memory. Associations are logical connections or relationships between pieces of information. If you meet and get to know a new person, for instance, you’ll associate the image of their face with their name and their other personal details, like their occupation and family members.
If you are trying to learn a complex concept or process, and you feel that your understanding is incomplete or insufficient because of unanswered questions, memorization and later recall will tend not to be as reliable as when you feel that you have a complete and logical understanding of the matter.
Recall and recognition
Recall of information from long-term memory is usually triggered by some cue. Seeing someone’s face, for instance, will typically trigger you to recall that person’s name.
Successful recall is never guaranteed. The more recently the information was memorized or accessed, though, the more likely you are to be able to recall it (the recency effect).
Successful recall of some piece of information is also more likely to occur when you’ve already recalled related information. It’s as if related information is stored in adjacent locations in the brain, and by accessing information in a particular region, “lighting up” that region, recalling other related information from that region becomes easier.
Sometimes you will struggle to recall something, and the information may or may not “come to you” at a later time. Sometimes recall is inaccurate; you recall incorrect information. You might misremember a formula when you’re taking a math test, for instance. Sometimes you may have doubt about whether the recalled information is correct, but just as frequently, you may not recognize the error.
Often you may not be able to recall something, but you can recognize it when you see it. The information was in your memory, but for some reason it was “shrouded” and didn’t lend itself to being accessed at that moment.
The less frequently a chunk of information is accessed from long-term memory, the more likely it is to be forgotten. This is natural — things that are relevant to your daily routines will be remembered, and additionally reinforced due to the recency effect. On the other hand, facts that you studied years ago but haven’t needed since, or the names of people whom you met years ago but haven’t kept in contact with since, will tend to fade away.
But there are also many cases where letting information or skills languish for long periods of time won’t necessarily guarantee that they will be forgotten. Highly-developed motor and cognitive skills that can be done unconsciously after much practice — like riding a bicycle or speaking a foreign language — can often still be performed with surprising levels of competence after years of neglect.
What all of this means for user interface design
On the basis of this understanding of memory, memorization, recall, and forgetting, here are some guidelines to keep in mind when designing software:
- Structure your interface to reduce or eliminate the need to memorize and recall things. Donald Norman introduced the notion of “knowledge in the world versus knowledge in the head“. For example, if you present a list of options in a menu, this knowledge is “in the world”: the user can view the menu, recognize the options, and make a selection without needing to memorize or recall anything. If you were to require the user to enter commands at a command-line interface, on the other hand, this would require the user to memorize the commands — thereby storing the “knowledge in the head” — and then the user must recall the names of the commands from memory.
- If a task has a defined sequence of steps, guide the user through the task workflow step-by-step using a “wizard” interface or something similar. Don’t force the user to remember a series of commands or how to navigate to various different screens to finish the task.
- While shortcut keystrokes and command-line interfaces are often appreciated as time-savers by advanced users, you shouldn’t make these the sole means of interaction as they require memorization and recall. If you must rely on shortcuts or commands, make it is easy to refer to a quick-reference chart or other help material.
- Make icons and names easily recognizable so that they can be found easily when scanning a list or menu. Icons can be clarifying if the image represents something concrete and recognizable, but if the user has to memorize and recall what an peculiar or abstract icon really means, then it defeats the purpose of using a graphical icon. Consider showing the image and text together if the icon is abstract or its meaning is unclear.
- If the user will have to work with ID numbers such as product or customer numbers, it can be advantageous to limit these to about 7 or fewer digits or characters in length, if possible, so that it’s easier to temporarily store the numbers in working memory.
- Arbitrary names are harder to remember and recall than names that accurately describe what they represent. When names don’t match what they actually represent, not only do they become problematic to learn, but the additional memorization and recall adds to the user’s cognitive burden. Commands in the Unix operating system shell are particularly bad at violating this prinicple. For example, most Unix systems offer a command called “less” for showing the contents of a text file. The name “less” is a play on words; “less” is an improvement of another command called “more”. (“more” is a filter command that lets you view a stream of data in a page-by-page fashion.) The name “less” doesn’t in any way communicate what that command does; it’s a dumb pun by somebody trying to be clever. “list” would be an example of a more appropriate, obvious, and memorable name.
- Offer a good online help system or other reference documentation so that, when the user has forgotten something, it can be looked up again quickly.
- In search and index systems, allow the user to use synonyms and variations in case they can’t recall the exact word or phrase (or the correct spelling of the word or phrase) needed to identify something.
- Try to use commonly accepted, well-known, standard names for things rather than inventing your own terminology. Avoid using abbreviations or acronyms if they are not immediately obvious.
- Be consistent; don’t make the user remember different ways of doing the same thing in different contexts. I’m familiar with one system where some drop-down lists had to be opened with a Ctrl+L keystroke combination, while other drop-down lists had to be opened with Alt+F11. (An absurd situation, given that in all other systems, drop-down boxes can be opened just by clicking on them.)
- Because first impressions are rarely forgotten, do everything you can to make sure your product gives a great first impression!