10.10 The Three Types of Memory Structure & Our Understanding of Knowledge
Path To Recall
Have you ever been trying to tell someone about an interesting fact and forgotten what you wanted to say? Did you think I knew this yesterday! My short term memory is so horrible!
How long do you think short-term memory lasts? A week? A day? A few hours? You might be surprised to learn that short-term memory, or working memory, really only lasts about a minute. It is simply a conduit for the information in the world to be processed into long term memory so that it can be recalled later.
There are three types of memory with varying lengths. They act as a conveyor belt (with holes) ferrying information from our environment to our information storage systems in our minds. Theoretically, there is no such thing as forgetting; as long as information reached long-term memory, it is there forever. It is a matter of properly conveying knowledge through the system to be processed into long-term memory that is the issue.
Types of Memory
Sensory memory comes first. It holds every environmental stimulus we experience. It is extremely short, lasting only about a second. Think about having a picture flashed in front of your eyes. For up to a second after the image is removed, you can successfully describe any requested corner of the image. Your sensory memory focuses on the requested information and sends it through to your working memory. The rest of the image is dumped (lost forever). Thus, sensory memory holds a great deal of information for a very short period of time and passes on only a tiny percentage to the next stage of information processing: short-term/working memory.
Many people think ”short-term” refers to days (or even weeks), but in reality, short-term refers to seconds leading up to a minute. This is the stage of the system in which information is intentionally processed and moved into long-term memory or lost forever. This is also the part of our memory which holds the information we are currently using, such as when doing calculations in our head. A typical adult can hold about 7 (plus or minus 2) items of information in working memory at once. You might notice that this number is identical to the number of digits in a local phone number! There is no coincidence in how phone numbers were developed to fit our working memory capabilities.
Finally, if information manages to survive both sensory memory and working memory, it is stored in long-term memory. Once information is successfully stored in long-term memory (through rehearsal or other intentional processing strategies), it is there forever. Sometimes recall of information can be challenging, but that is different from the concept of true forgetting (which implies that information that was previously successfully processed could be dumped from memory completely). Obviously, some medical situations can cause extreme lack of recall, but it is believed that the information is still stored in memory; it just cannot be accessed.
So, at each stage of information processing, information is being lost, but the information that gets through to the end will remain forever.
Knowledge Held in Long-Term Memory
We know that once information reaches long-term memory it stays forever, but what type of information are we talking about? Knowledge actually comes in multiple formats from that which we are aware of knowing (explicit knowledge) to that which we don’t even know we know (implicit knowledge).
How can you not know that you know something? Well, can you explain how to ride a bike in words? Most people who know how to ride a bike still can’t articulate the process because they ”just know” how to do it. Procedural memory is memory for things you do. These tend to be skills or tasks that you are very familiar with and no longer need to think about as you perform them. Some examples of procedural knowledge are writing, typing (if you are a touch typist), driving a car, or riding a bike. Some people think of this as muscle memory because it seems that our muscles remember what to do with our bodies without us needing to be consciously aware of what is going on.
Anything that we are consciously aware of is considered explicit memory found in the form of declarative knowledge. Declarative knowledge is knowledge of facts and/or events. All the facts you know (things you learned in school, history, names of friends, etc.) fall under the category of semantic knowledge. Everything else you know that you know (events and experiences in your own life) are referred to as episodic knowledge. It is easy to remember episodic knowledge because the root word is ”episode” which can remind you of an episode on television. You would need to remember what happened in the episode to tell a friend; likewise, you remember what happened when you recall episodic information.
The road to memory is actually much shorter than most people realize and most of what we are exposed to is lost in the process. Sensory memory holds everything for less than a second allowing only a small percentage of information to make it through to working memory which holds about 7 items of information at a time. Information can stay in working memory for up to a minute before it is either lost or processed into long term memory. If information makes it into long-term memory, it is theoretically never lost (or forgotten).
Knowledge held in long-term memory is categorized by awareness first: explicit memory is memory of knowledge we are aware of while implicit memory is that which is unconscious.
Implicit memories are procedural knowledge (unconscious knowledge of how to perform tasks) while explicit memories contain declarative knowledge (knowledge of facts and events). Declarative knowledge can be broken down into semantic knowledge (facts and concepts) and episodic knowledge (personal events).