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PROFESSOR: What is memory?
Memory is the ability to store and retrieve
knowledge over time.
Knowledge can be our personal experiences,
like people we've been with and places we've gone to.
It can be factual knowledge.
2 plus 2 equals 4, or Paris is the capital of France.
Or it can be kinds of skills that we
acquire through practice.
Memory is thought to be composed of three successive stages.
First stage is encoding, the moment
of learning as we see or hear or think of something.
Information gets into our brain.
Second, storage-- the retention of that
encoded information over time.
And third, retrieval-- where we reach into storage
to bring to mind useful information that
has been encoded and stored.
The formation of memory is both powerful and selective.
Through memory, we know our own name, where we live,
who is in our family, all of our knowledge from school
and everyday life.
But we also forget a lot.
Think about your day exactly a year ago.
Unless it was a very specific day, like your birthday,
you probably have very few specific memories
from that day.
The study of memory tries to understand both
how we can remember things and why we forget so many things as
Memories have three kinds of storage
that have markedly different lifespans.
They vary by the amount of time over which a memory's retained.
Sensory memory holds sensory information
for a fraction of a second.
Short-term memory holds information for more than a
second but less than a minute.
Long-term memory holds information for hours, days,
weeks, or years.
To give yourself an intuitive sense of these three
kinds of memory, imagine you're walking down a busy street
to get an appointment on time.
As you walk along, you see people and objects,
and you glance at them briefly to make
sure you don't walk into them.
But you forget each person or object immediately.
That would be sensory memory.
Then, let's say you come to a corner,
and you look at traffic light to make sure it is safe to cross.
You see it's a red light, so you remember
that it's a red light as you start to cross the street
and make sure that the cars are stopping.
That would be short-term memory, because within a minute,
you will forget about that light.
But knowing that you have the appointment
and where and when you have to go
is long-term memory, because those memories must persist
over many minutes or hours.