Resources

Basic Memory Resources and Diagrams

There are three stages in human memory: sensory memory, short-term memory, and long-term memory.

Sensory Memory. Sensory memory records what you see, hear, feel, taste and smell. In other words, things that you “sense.” Sensory memory is very limited. Your brain must transfer a sensation to short-term memory or it will disappear as soon as the experience is over.  Although this might seem inefficient, is is actually necessary for our survival.  Just a small portion of sensations we perceive are important to us, and the interface between sensory and short-term memory filters out most of them so we are not overwhelmed.

Short-term Memory. Short-term memory lasts as long as you pay attention to something. It might be a the telephone number that you have been repeating or the image of a flower you have noticed.  It will remain available in your memory as long as you actively think about it. However, if you stop paying attention to it, it will be erased.  In order to remember something after that, the brain has to transfer it to long-term memory.  The process of rehearsing a phone number is a way to get the number from short-term to long-term memory before it is lost.

The amount of information you can keep in short-term memory is also very limited.  The general rule is that only five to nine items of information can be in short-term memory at one time.  This is the reason that short-term memory is so “short.”  Each time you pay attention to a new piece of information that comes from sensory memory, you have to push out something that had your attention before.  For example, if something interrupts your concentration on the telephone number before you rehearse it into long-term memory, it will get bumped out and you will have to look it up again!

Long-term Memory. Generally, when we talk about memory, we have long-term memory in mind.  As far as we know, long-term memory can hold an unlimited amount of information.  Long-term memory contains perceptions and ideas that range from a few minutes old to the earliest weeks of life.  It is this memory that we use to develop ideas and interpret our experiences.  Although we believe that everything that has been stored in long-term memory is still there, we are painfully aware that we can’t always retrieve it.

The mechanisms of memory retrieval are not well understood. We do know that it helps to rehearse information and to relate it to other information. In addition to information received from sensory memory, short-term memory can retrieve then combine information from long-term memory. The results of that process can be resubmitted to long-term memory. As a result, our memories grow in complexity, meaningfulness and retrievability.  Here is a basic diagram that illustrates the three stages of memory.

Basic Stages of Memo

Almost miraculously, our brains generally accomplish all this without a hitch.   With that background, we will explore a question the occurs to most people from time to time:  What’s the difference between what you know and what you know how to do?

A More Detailed View of Long-term Memory. Humans have two kinds of long-term memory: Declarative and Procedural. “Declarative” memory is the memory of ideas or events.  “Procedural” memory is remembering how to do things.  The words themselves help us remember which is which; “declarative memory” makes it possible to express something, or “declare.”

“Procedural memory” helps us to do something - to “proceed.”  Procedural memory is not always easy to discuss, or explain.  However, even though we often can’t explain how we do something, we can use our memory of it without even consciously thinking about it.  Procedural learning and recall  are used in things like riding a bike, learning to touch type, learning to play a musical instrument or learning to swim.  We can drive a car from place to place all day long without being aware of the driving process most of the time, and be completely safe.  Once a “procedure” has been rehearsed mentally or practiced physically until it is firmly in long-term memory, it can be very long-lasting.  For example, people often observe that you can still ride a bike many years after the last time you did it!

Declarative memory comes in two flavors:  “semantic memory” and “episodic memory.” Semantic memory is theoretical, or abstract, memory.  It is independent of time and place.  It is an idea, or concept.  For example, knowing that an apple is called a “fruit” is a semantic memory.  Knowing that two plus two equals four is also semantic memory.  You can recall it, state it, you understand it, and you can use it to count things, but the formula doesn’t represent anything real or specific.

Episodic memory, on the other hand, is factual knowledge based on personal experience in a specific time and place.  It is something that happened or something you sensed.  For example, if you are thinking about looking over the Grand Canyon when you visited it as a child, you are experiencing an episodic memory.  Another example:  You can say, “When we were at the grocery store yesterday, John bought three oranges and Mary bought for oranges, so altogether we came home with seven oranges.”  You are using semantic memory to apply a formula to seven specific apples that you remember seeing, which is an episodic memory, or the memory of an “episode” in your life.  Here is an diagram of the way long-term memory is organized.

Types of long-term memory

These terms and concepts are important because the different types of memory are formed and stored by the brain in different ways and in different brain locations.  They are subject to improvement or damage in different ways, as well.   For example, not all kinds of memories are affected by aging in the same way.   Aging is an important topic in today’s world.  Research is beginning to indicate that more and more people will live to 100 years of age.  This can be good news or bad news, depending on the quality of life you expect and plan for during those later years.  As you continue to study and learn about memory, remember these basic ideas and diagrams to help you put your new knowledge and “memories” into context.