Types of memory
We talk about “memory” as if it is one thing, but actually memory is a combination of systems that sometimes work together. This lecture defines the different systems.
These notes are part of a series for the course.
|Short/long||Memory system||Also called||Definition||Example|
|Long-term||Episodic memory||Memory of specific events rather than generalized facts. When you think back to a point in time to remember something, and it's a bit like replaying part of a movie in your head, that's episodic memory. These memories are autobiographical: you see them from your point of view.||"Who was at the meeting, and what did they say?"
"What was it like the first time you ever went swimming?"
|Long-term||Semantic memory||When you remember a fact and you don't think of it within a context because you've been exposed to the fact for a long time. For example, when you first learned multiplication tables, perhaps remembering them involved episodic memory but now it's semantic memory.||"What's 6 x 6?"
"I before E except after C, and...?"
|Long-term||Procedural memory||Muscle memory||This is involved in physical activities. It is the memory of how to move muscles in a coordinated way, and in a particular order.||Riding a bike, dancing a waltz, driving a stick-shift car, pronouncing words in a particular language.|
|Short-term||Sensory memory||Iconic memory (from what you see); echoic memory (from what you hear); haptic memory (from what you touch)||Extremely short-term memory of something you detect with your senses. Sensory memories move into working memory.||Someone interrupts your train of thought, and after a few seconds you are able to recall what they said while you were thinking of something else.|
|Short-term||Working memory||Short-term memory||A temporary memory that you hold onto until it is stored as long-term memory, or a set of memories that you draw upon while solving problems with them.||Someone tells you a series of words and you repeat them over and over until you can write them down.|
Which is your least favorite?
The lecture ends with questions to consider. One asks which of the memory systems you would choose to lose if you had to: a (likely unintentionally) terrifying thing to consider. But if we’re meant to understand that the systems work together, then how can we imagine the loss of one without a knock-on effect on the others? I tried to think of a few examples, and only came up with more questions:
- The lecture briefly mentioned Kim Peek, who was the person upon which the Rain Man character was based. Dustin Hoffman’s character in the movie has autism, but Kim Peek didn’t; he had FG syndrome and as a result he didn’t have the nerves (called the corpus collosum) that connect the two hemispheres in his brain. I think Peek’s extraordinary memory wasn’t solely a result of FG syndrome, though, because that same bundle of nerves is sometimes severed in people with severe epilepsy, to stop their seizures, and those people do not wind up with the same effect to their memory. So which system can we say worked or didn’t work in Peek’s case?
- I think observing people with Alzheimer’s disease in some ways shows how these systems work together, and what happens when they no longer do so. For example, a person may be able to recall in great detail an event from their childhood (episodic), but can no longer recall facts from that same time (semantic). They may be unable to form new long-term memories from events happening in the present (working memory) and as the disease progresses, the person may even forget how to perform physical acts (procedural).
Hopefully I’ll have a more considered and reasonable response to the hypothetical question by the end of this lecture series!