# Short-Term Memory (abbreviated STM, also known as "Working Memory")

Short-term memory is small. To emphasize STM's limited capacity to hold information, STM is often compared to other objects that have limited capacity: small buckets, small funnels, and small sponges. Because STM is so limited, STM is often referred to as "the bottle neck of the memory system."

Examples illustrating that STM is  small

#### How small is STM?

• Take one minute to play a guessing game that will help you understand that STM's limited capacity is usually about 7 items. Two important points:
1. By "about 7 items," we mean that not everybody would hold 7 items: Some can't hold that many; others can hold more. If you were to ask 10 people to repeat back random digits back to you, chances are pretty good that all of them could repeat back at least 5 items and that none could repeat back more than 9.  Consequently, psychologists say that most people can hold between 5-9 items in STM. To show off that psychologists can do some math, rather than say that people can hold 5-9 items, psychologists like to say that most people can hold  7 plus or minus 2 items. Perhaps because people, on average, can hold 7 items, 7 seems to be a "magical number" that everyone sees a lot: 7 days of the week, 7 numbers in a phone number, 7-point rating scales, 7 wonders of the world, 7 primary colors, 7 musical notes, and 7 deadly sins (originally, there were 8 deadly sins).
2. By usually, we mean that people can hold about 7 items if they treat each item as a unit; that is, if each item is a separate chunk. People can hold more than 7 items by chunking: grouping two or more individual items into one unit. We will discuss chunking soon, but for now, just realize that STM's capacity is not 7 plus or minus 2 items; instead, STM's capacity is 7 plus or minus 2 chunks.  If visuals help you, mouse over this text.

#### Implications of STM being so small

• Because STM--your conscious mind--is so limited, attention is limited.
Four reasons we have trouble paying attention to the right things
1. We can't pay attention to much (we have limited bandwidth; often, it is like we are a TV that can only tune in to one channel at a time).
2. We don't know when we are not paying attention (to know that we were not paying attention, we would have to be paying attention!)
3. We may think we are paying close enough attention, but we are just getting the general idea when we need specifics.
4. We may be paying attention, but not to the right things. So, strangely enough, the key to paying attention is often knowing what to ignore.
• Because STM is so small, if you are reading while distracted, very little of what you read will get into STM, and, therefore, very little of what you read will have any chance of getting into LTM. Furthermore, what little gets into STM will probably be quickly bumped out--and therefore also have little chance of getting into LTM. One way to focus your attention is to read in a distraction-free environment and to read with the purpose of answering questions. To have questions to answer, you could turn the chapter headings into questions before reading the chapter.
• Because STM is so small, when you are introduced to a complex concept,  you may not be able to absorb it all at first. As a result, you may have an oversimplified version of the real concept. Unfortunately, students sometimes think they know the concept when they really only know one or two of the concept's several key features.
• If you realize that (1) information has to get into STM before it can get into long-term memory and that, (2) because STM is limited, attention is limited, you can appreciate why Samuel Johnson said, "The true art of memory is the art of attention."

#### Short-term memory is short (it typically lasts about 20 seconds)

• If you need to remember certain information from lecture, you must transfer it to your notes or to your permanent memory within 20 seconds from the time you stopped rehearsing it. Otherwise, that information will be gone forever.
• One advantage of having a short STM is that you can quickly see if anything you read got beyond STM: If you try to summarize what you read 2 minutes ago, what you can recall is in permanent memory--whatever was only in STM left more than a minute ago.
• A fictional but humorous example of the problem of having an extremely short STM (from Monty Python)
The reason information stays in STM for such a limited time seems to be due to the limited size of our STM combined with our limited attention span. Some evidence:

• You can keep information in STM for longer than 20 seconds if you constantly pay attention to that information. For example, if you repeat a phone number for 5 minutes straight, you can keep that number in STM for 5 minutes. (Repeating information to yourself is called by three names: "Type 1 rehearsal," "Maintenance rehearsal," and "Rote rehearsal." As you will soon see, although repeating information to yourself is good for maintaining information in STM, repeating information is not very good for moving information to LTM.)
• You can't keep information in STM for even 20 seconds if your attention doesn't stay on that information. For example, if you try to remember 5408547 and then are also given 8416532--or are distracted by someone talking to you or by your own thoughts about something else--the original information will be pushed out (displaced) from STM because there isn't room for much in STM.  (Short demo: Experiencing extreme displacement)

#### Short term memory (also called working memory) is your conscious mind

• You are aware of everything in your STM. Without STM, you might do things, but not be aware that you were doing them. Right now, you often do many things without awareness, like breathing, balancing, and (sometimes) driving. Without STM, everything you did would be done without your being conscious of doing it. You would have no mental life, so you might act like a sleepwalking zombie robot, and you might feel nothing--as if you were always in a deep, dreamless sleep.

• Put another way, short term memory (STM) is not just a storage container for whatever you are aware of at the moment--It is your conscious mind. That is, STM is where you do your conscious thinking--where you silently speak to yourself.
• If you pay attention to something, it is in STM. However, paying attention to things is not easy.  Fortunately, however, there are easy things you can do to increase your ability to attend to lectures such as sitting up front and keeping your cell phone out of sight.
• Because short-term memory is the work space where you do much of your mental work, STM is often called "working memory." Because working memory is your conscious mind and because your conscious mind is complex, many psychologists break down STM into several parts (to learn about those parts, look at this diagram).

Although there are many aspects to STM, in this page, for simplicity's sake, we will focus on  two of STM's roles:
(1) holding information in consciousness and
(2) being the narrow, shaky bridge through which information goes in and out of  LTM.

Because working memory is limited (it holds, at most, 5-9 chunks [chunks are groups of items]), our thinking and our attention are limited. Specifically,

1. We can only pay attention to a few things at a time, so multi-tasking can't work.
2. Examples showing that we can only pay attention to a few things at a time: Analogies to help you understand that we can't multi-task:
• Suppose you can barely juggle 2 balls. In that case, this is what would happen when you tried to juggle more than 2 balls.  Similarly, juggling too many things in STM means something will be dropped.
• You start up your computer and have a single program running. Then, you open up another program. Soon, you have seven programs working at once. At that point, your computer slows down and  may even crash because there are limits to how well your computer can multitask. (To free up your computer's short-term memory so that your computer works normally, you will need to close the extra programs-- and you may even need to restart your computer.) The problem with this analogy is that you aren't nearly as good at multitasking as your computer is.
3. Teachers and presenters may overwhelm their audience's STM by going too fast or by presenting too much information on a PowerPoint slide.
4. The complexity of the world can't fit in STM, so we oversimplify the world, leading to not seeing differences between people, to stereotyping, and to seeing things in terms of absolutes (i.e., seeing things in terms of black and white rather than in terms of shades of gray).

#### What is chunking and how does it allow us to keep more information in STM?

The way to get around the limits short-term memory's limited size puts on us is to chunk: group several different individual bits into one unit.  For example, U.S. citizens could group the twelve numbers "177  614  922  02  4"  into three chunks:
1776     1492     2024.

Visual analogies illustrating that chunking makes it easier to keep more information in STM:

#### But why chunk information? (Why are big chunks better?)

Chunking, by allowing us to keep more information in STM, lets us think smarter.

To see the power of chunking, consider experts. Experts have formed large chunks of information related to their field. As a result, they can hold a large amount of that information in their head while still having room in their working memory to think about that information. So, when thinking about their field, they can think about many things at once (e.g., chess experts, physicians, and football coaches can quickly absorb much more information about their fields than the average person can when the experts can chunk that information). Note, however, that if experts are thinking about things outside of their field--where they can't chunk as well--their thinking is much more limited (one of many reasons why supposedly smart people do stupid things).

Some chunks that you may have learned that have made you more expert:

• Aspects of driving, like backing out of your driveway, no longer involve thinking through many separate steps. Instead, those steps have been connected and combined into one chunk.
• Reading is no longer a matter of sounding out each letter. Instead, you have learned to chunk letters into words and to chunk familiar words into phrases. As a result, you can read much faster and better than when you first learned to read. Under some conditions, you can even keep an entire paragraph in STM.
• You have learned key terms in a field (e.g., in psychology, "sensory memory"; in basketball, "zone defense") that contain a lot of information but take up only a single chunk in your STM. As a result, you can now think about these concepts in relationship to other concepts whereas, at first, just trying to know what the concept meant would overfill your STM. (You may have been in a class where some students were having no trouble keeping up with the pace of the professor's lecture whereas others were really struggling to keep up and were asking the professor to slow down and to repeat things. The students who were having an easier time keeping up may have been the ones who read the book before coming to class and so were able to process the professor's lecture in paragraph-sized chunks. In contrast, the students who couldn't keep up may have been processing the professor's lecture one word at a time.)
• When you are first told about a complex term or concept, you may think you have grasped the concept when, in fact, your short-term memory has only allowed you to grasp one or two elements of the concept. If you don't realize that your STM has limited you, you may only find out that you do not understand the concept when you are tested on it. If, however, you study the concept and understand that it has several aspects, you can form a chunk that captures those multiple aspects.

Since students who chunk information when studying get better grades in college (Gurung, 2005), you might wonder how to chunk information so that you could get better grades. One way is to study terms until each term's definition takes up only a single chunk in memory. In addition, you could turn the many terms you have to learn into a smaller number of groups of terms by

STM Myth STM  Fact
Short term memory lasts an hour or maybe even a couple of days. Short term memory lasts about 20 seconds.
Short term memory can hold 5 to 9 items. Short term memory can hold 5 to 9 chunks.
Short-term memory is big enough that people can multi-task effectively.  Because of STM's limitations, people are terrible at multi-tasking.
If information is in STM long enough, it will automatically move into permanent memory. Maintaining information in STM  for a long time does not necessarily move that information to permanent memory.

Review STM

Learn more about STM: To get a better understanding of what short-term memory is and how understanding short-term memory can help you think and learn better, read Scott Young's article on working memory (long, but useful!).

Reflect on STM's importance

Realize that STM, as the narrow bottle neck of the memory system, not only puts limits on how much information you can put into LTM at one time (so professors shouldn't speak to quickly or put too much information on a PowerPoint slide) but also limits how much information you can get out of LTM at one time (click to see visual analogy).  At one level, you know that STM limits how much information from LTM that you can bring up at once: You wouldn't ask your partner to name 20 things they love about you (unless you wanted to be depressed)--and you would certainly hope that a professor wouldn't call on you to name 10 important psychological discoveries. However, you may not have realized that, because all your relevant knowledge about a situation will sometimes be too big for STM to hold, all your relevant knowledge can't always come to mind when you  need it. As a result, you will make mistakes even though you knew--or at least your LTM knew--better.  Note that if you are distracted, preoccupied, emotional, sleep-deprived, or otherwise impaired, you will have less room in STM for information from LTM and thus will be even more likely to make mistakes due to not using what you know.

As you have seen, STM's limitations limit not only what you can keep in STM but also both what you can upload to LTM and what you can download from LTM. How can you get around these limits of STM? One way is to offload information from your STM to your phone, to a small notepad, or to a 3 X 5 index card. Another approach is to chunk information.

Without chunking, almost everyone can hold between 5 and 9 items in short-term memory. So, when President Trump was given a test in which he had to repeat five words, failing on that task would have been very bad. Succeeding on the task, however, was not terribly impressive. To judge the difficulty of that test, you can see it here.

President Trump implied that he did not use a strategy for remembering the 5 words: "Person, Woman, Man, Camera, TV." Instead, he attributed his ability to recall of those words to having a great memory. President Trump could have made it easier on himself  by chunking the 5 individual words into one or two chunks. If you had to remember "Person, Woman, Man, Camera, TV," how would you turn those 5 items into one or two chunks?

Most of the questions on the test that President Trump took involved memory. Some of the questions tested short-term memory; other questions (e.g., testing whether he could identify the animal in a picture as an elephant) tested long-term memory. As you can imagine, if someone did poorly on that test, their mind would be very limited. Indeed, such a test might be used to determine whether a person could live on their own. So, both short-term and long-term memory are important to living a full life. We have discussed short-term memory. We will now turn to long-term memory.