Wednesday, April 27, 2016

People Differ in Their Ability to Suppress Memories

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.