We all know that our
memories aren't perfect. As frustrating as
it can be, we forget people's names, birthdays,
and other things we'd like to remember. One reason forgetting happens
is the very normal process of decay. When we don't encode
something well or when we don't retrieve
it for a long time, we become unable to
retrieve it later. One theory about
why this happens is that the pathway to
and from the memory, meaning the neural
connections between the cues and the memory, become weaker
over a period of disuse, so it becomes harder to
stimulate those neurons. This is sort of the classic
use it or lose it problem. If you learned something
once and don't ever revisit the memory, it's
likely to decay over time. One interesting
pattern of decay is that it seems pretty
consistent, even for different
types of materials. Your initial rate of
forgetting is very high, but it levels off
after a period of time. Back in the late 1800s, a German
philosopher and psychologist named Ebbinghaus
was the first person to really look at the
decay in human memory. He made himself learn a bunch
of three-letter nonsense syllables, and then
he tested himself to see how much he remembered
at different time intervals, from zero to 30 days. He found that his
rate of forgetting was very rapid at first. If he remembered those words
after a few days, however, then he generally remembered
them for all 30 days. Later on, people
replicated this pattern with different materials and
over different time intervals. And they found that
the more integrated the initial learning is,
the more stretched out the rate of forgetting
is, but it's still follows the same pattern. For example, if you study
a language for a few years, then it'll take you more
than a few days to forget it. Similar to Ebbinghaus's
original forgetting curve, though, most of
your forgetting will occur within the first
few years of disuse. After that point,
your forgetting will pretty much level off. The interesting thing
about decay and forgetting is that just because you
can't retrieve something doesn't mean it's
completely gone from your long-term memory. Other than outright
retrieval, one way we can tell if people
have learned something before is by how quickly they
re-learn that information or skill. So remember Ebbinghaus? In addition to forgetting,
he studied re-learning with those same three-letter
nonsense syllables. He found that even if
he couldn't produce all the syllables from his
list, it took him less time to learn the list
the second time around than the first
time, indicating that some foundation of
the memory still existed, even though he couldn't
produce it at the time. This foundation
is called savings, because it's what saved in your
memory, whether you realize it or not Re-learning works
with procedural skills, too. For example, imagine
that you learned how to play particular song
on the piano a few months ago, but you can't play
any of it today. Now I give you the
music to that song and ask you to learn it again. If the inability to
retrieve something meant that it was completely
gone from your long term memory, then it would take
you the same amount of time to learn the song the
second time around. However it probably
would take you less time to re-learn
it than it did for you to learn it originally. This faster rate of
re-learning tells us that you still have
some information about that song stored
in your long-term memory. Sometimes decay isn't
the problem, though. It's that something else seems
to be blocking our ability to get to the
information we want. This experience is
called interference, and there are two main types--
retroactive and proactive. Retroactive interference
is interference that goes backwards, that is,
some new piece of learning seems to reach back
and impair your ability to retrieve something
you used to know. For example, when you
move to a new place, you get used to writing
your new address on all the different forms
and documents and stuff. And after a while of
using this new address, you may find it difficult
to recall your old one. In this case, your
new address would be running some
retroactive interference on your old address Proactive interference,
on the other hand, is interference acting forward. Something you
learned in the past gets in the way of your ability
to learn and retrieve something correctly in the future. So I'll give you an
example of something that happened to me
a few months ago. I used one password for my
email for a really long time. But then I had to change it. Sometimes when I log in,
it's still hard for me to remember what
my new password is, because all I can come
up with is my old one. In this case, the prior
learning up my old password is impeding my ability
to remember the new one.