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How short term memory works

Eugen G Tarnow  August 3 2011 10:35:11 AM
1.  It takes 0.5 to 3 seconds to put a word in your short term memory by looking at it or listening to it.  This "activation" time scale roughly corresponds to the time scale of synaptic exocytosis, i.e. the time it takes to have all the messenger molecules released from the "presynaptic" side of the synapse.  The activation time is longer for items that are complex than for items that are simple.

2.  The activation time is longer if the word is not presented to you at the time and there is no obvious path to the memory.  For example, free recall, in which a list of words are presented and then one tries to remember them uses up to 8 seconds to reactivate a word.

3.  It takes 3 seconds to 15 minutes to lose a short term memory.  It "decays" relatively slowly with time (logarithmically).  The time scale and functional behavior is roughly the same as for synaptic endocytosis, i.e. the time it takes for the presynaptic side of a synapse to heal back up and recreate the containers with the messenger molecules.

4.  Full activation in short term memory typically extends to three items at a time, this is referred to as "working memory".  You might think of these three reactivation paths as corresponding to the past, present and future - a minimal set that allows us to learn from the past and project into the future.

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