Your ability to recall a word or event involves mechanisms
that enhance the item you want to remember and suppress competitors. It is like a bunch of 6-year-olds trying to
be picked for the kickball team. The
kids who jump the highest and shove the other kids hardest are the ones who are
selected.
Psychologists use the word inhibition to refer to the suppression of items in memory. The inhibitory mechanisms in the brain
involve circuits in the frontal lobes.
A fascinating observation over the past decade is that these
inhibitory mechanisms in the brain can cause subtle variability in people’s
heart rate through the vagus nerve. If
you measure someone’s resting heart rate and measure the amount of variability
in the time between beats, that variation may serve as a marker of the strength
of people’s ability to inhibit information in memory.
An interesting paper by Brandon Gillie, Michael Vasey, and
Julian Thayer in the February, 2014 issue of Psychological Science explored this possibility.
They used a memory test called the Think/No Think procedure
first developed by Michael Anderson and his colleagues. In this procedure, people learn a list of
associations between words. The list
might include items like “tape-radio.”
After practicing these associations 3 times, the Think/No
Think procedure begins. The first word
of a pair (tape) is presented in green or red (or is not presented at
all). If it is presented in green, then
people are instructed to think about the associated word for 4 seconds. If it is presented in red, then people are
instructed to avoid thinking about the associated word for those 4
seconds. This procedure is repeated 16
times, so that people get a lot of practice either thinking about the
association or not thinking about it.
There are two tests of recall. People see the first word of the pair and are
asked to recall the second. In a second
test, they see the first word of the pair and the first letter of the second
word and are asked to recall the second word.
Finally, all participants had their heart rate collected
using an electrocardiogram (ECG). The
ECG output was analyzed to determine the variability from beat-to-beat.
The standard finding with this procedure (which is also
obtained in this study) is that (on average) people recall about 10% more of
the associations when they see them in the Think condition than in the No Think
condition.
The group of participants was split into one group with
relatively high variability in heart rate and a second group with relatively low
variability in heart rate.
Having low heart rate variability is associated with having
low inhibitory control in memory. That group
showed very little difference between the Think and No Think conditions of the
study. They remembered the associated
words equally well regardless of whether they were instructed to think about
them or not to think about them.
Having high heart rate variability is associated with high
inhibitory control. That group showed a
big difference between the Think and No Think conditions. They remembered many more words when they
were encouraged to think about them than when they were encouraged not to think
about them.
The ability to inhibit unwanted items in memory is
valuable. Research suggests that this
ability degrades with age, which is one reason why older adults often have
trouble with memory. So, having a
physiological measurement that relates to this degree of inhibitory control is
useful.
As valuable as the ability to inhibit information can be, it
is important to recognize that the No Think condition does not eliminate
people’s ability to recall the associated words. Creativity requires being able to think about
information that does not seem obviously related to the current situation. Juxtaposing different information sources is
a great way to look for a novel solution to a problem. As a result, we want to have good inhibitory
mechanisms, but not ones that work too well.
