Memory: Priming facilitates information retrieval
"H.M.," as he's known in psychology textbooks, underwent an experimental
surgery in 1953 that involved removing the hippocampus and medial temporal
lobes of both hemispheres of the brain.
His surgery turned out to be the seminal event to show how memory is stored.
Even though they cannot remember facts about the world, including their
own personal histories, H.M. and other patients with organic amnesia can
remember how to do things.
For instance, in 1980, groups of such patients were taught the skill of
mirror reading. They took three days to become skillful at the task, about
the same number of days that other people take, and they retained a high
level of skill for the three months during which they were tested. Yet when
tested, many of the patients did not remember ever having worked at the
task before, and none of them could later remember the words that they had
read.
To some, this behavior suggests that H.M.'s amnesia might represent a problem
in retrieval from memory rather than a storage problem. But other researchers,
including Vanderbilt's Carolyn Cave, assistant professor of psychology,
think it is more likely that H.M., and others like him, just don't stockpile
all the information stored by normal people who learn to solve such problems.
They believe experiments, such as the one with mirror reading, suggest that
the brain processes different kinds of information in separate ways and
that each kind of information is stored differently.
Declarative or explicit memory is the type of memory best
known. It allows us to remember what happened at our 16th birthday or at
our college graduation. Procedural or implicit memory is the kind of memory
that allows a person to change his or her performance in some way without
knowledge of having learned anything.
Explicit memory requires processing in the temporal region and parts of
the thalamus. Impli-cit memory apparently doesn't. Rather, several brain
systems seem to be involved.
Cave became interested in implicit memory while doing post-doctoral work
with noted memory researcher Larry Squire. Now her research mostly involves
one of four specialized forms of implicit memory - priming. Priming is facilitating
performance on the basis of having a single prior exposure to stimuli that
can enhance it.
"Many of our experiments are based on a very simple paradigm in which
we expose people to stimuli, usually line drawings of common objects, and
then in a test session some time later, they will be exposed to some of
those same pictures along with new pictures in random order," Cave
explains.
When the subjects are asked to name all the pictures, they'll name the ones
they saw previously faster than the ones that are new. They get between
five and 10 percent faster based on a single prior exposure.
"So, independent of whether they knew which ones were old and new,
their behavior is facilitated, and not in a way that they can realize or
articulate," Cave says.
Cave completed a study (now under journal review) in late 1995 that explores
the duration of the priming phenomenon. Cave exposed the subjects to pictures
of common, everyday objects, such as a tree and a desk, for one second or
less. The subjects were tested up to 48 weeks after their initial exposure
to the pictures, and priming still occurred.
One of the questions that still remains and Cave hopes to answer in the
future is whether the environment in which the study and test situations
occur facilitates implicit memory.
"There's something potentially special about the conditions in which
subjects initially see those stimuli," Cave asserted. "There's
some kind of expectation set up about whether these are important for some
reason."
Cave believes environment is important in the priming process.
"Clearly people don't prime for everything they see. That's an assertion
on my part, but it is clear that if you primed for everything you wouldn't
be able to detect the phenomenon. You would be able to go as fast as you
could articulate and not get any faster.
"Priming is a byproduct. It's not a passive byproduct. Our studies
show that we can turn it on and off."
-Kelly C. Lockhart
-Photo by Billy Kingsley
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