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Three Systems of Memory
Psychologists have many theories to explain how we remember information. The most influential theory is that memory works as a kind of storage system, or storehouse, for information. According to this theory, there are three types of these storage systems with different functions that hold information for different amounts of time. These storage systems are sensory memory, short-term memory, and long-term memory.
Let’s start with the first storage system, sensory memory. It holds information for the shortest amount of time-- less than four seconds. An instant. Sensory memory is where stimuli, or things that stimulate our senses, are very briefly stored. We forget sensory memories almost instantly, unless they pass into another storage system. Examples of stimuli that usually go into sensory memory are things that we see and hear in the world such as a flash of lightning, or the sound of a door closing.
Now, let’s move on to the second storage system, short-term memory, which is also sometimes called "working memory". It holds information for about 15 to 25 seconds. This is not a very long time, but the information that passes into this system has more meaning for us than just sensory stimulation. It is not entirely clear how some sensory memories transfer into more meaningful short-term memories. However, it has been proven that memory going into this system is made up of "chunks," or groups, of meaningful information. It has been found that only around seven "chunks" of information can be stored in short-term memory. Therefore, there is not a lot of room for information in short-term memory, and it does not stay there for very long. Examples of the type of information that typically goes into short-term memory are telephone numbers, addresses, and names.
Finally, let’s look at the third story system, long-term memory, which holds information almost indefinitely, although retrieving it can sometimes be difficult. We can think of long-term memory as a very big library, or even a computer chip, with almost unlimited capacities for storage. Information gets filed, catalogued, and stored. Long-term memory has several different components, or modules, that correspond to separate memory systems in the brain. The main two categories of long-term memory are declarative memory and procedural memory. Declarative memory is where we store factual information, such as names, faces, and dates. Procedural memory is where we store memory of skills and habits, like how to ride a bike. Within declarative memory, there are two smaller categories of memory, namely, episodic memory and semantic memory. Episodic memory is where we place memories that relate to our personal lives, things we have done or experienced, such as having a car accident. Semantic memory is where we organize general knowledge or facts about the world, such as math formulas.
OK, to sum up, today we’ve taken a brief look at the three storage systems and their different functions of holding information for different amounts of time. Next time, we’ll look at some other aspects of psychology.