Why do we have three stage memory?

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For some time I have wondered why humans have developed memory into a three-stage process; sensory memories, short-term memory, followed by long-term memory. Specifically, I am most fascinated by the difference in short-term and long-term memory.
Short-term memory is defined as the ability to hold 7 +/-2 pieces that only last about 15 seconds in our brains. Long-term memory seems to be essentially infinite in storage, and lasts seemingly forever. What is the evolutionary advantage to keeping these two processes separate? If the long-term memory has an infinite capacity, would it be harmful to us if we remembered everything that ever entered our short-term memory? I can think of all kinds of advantages this would have, but we can only hypothesize on what types of harm it would have.
If we remembered everything we ever moved from sensory memory to short term memory would no longer need address books, flash cards and studying, and no more embarrassing moments of forgetting a new persons name. However, there must be a reason that humans did not evolve this way. Perhaps the human memory works like an external hard drive. Right out of the box, a new hard drive can clock very impressive numbers on data transfer speeds, but as the drive gets used more and has more data placed on it, those data transfer speeds slow down. Its possible the human brain works like this. If this were true, this would be one possible explanation as to why the human brain has placed a limit on how much it cares to remember. Or another possibility may be that long-term memory is not nearly as expansive as it may appear. Perhaps it is much more limited than we believe.
Although we may never know the exact reason humans have not evolved to combining short term and long term memory, it is a fascinating topic to imagine what could be/could have been if everything we ever came across was easy to recall.

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This page contains a single entry by burke510 published on October 23, 2011 3:17 PM.

Is Discovery Learning Better Than Direct Instruction? was the previous entry in this blog.

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