The Magical Number Seven, Plus 67,883
The extreme limits of memory retrieval and how to get there
Posted Nov 19, 2012
In his famous paper entitled "The Magical Number Seven, Plus or Minus Two: Some Limits on Our Capacity for Processing Information" cognitive psychologist George A. Miller of Princeton University argued that our working memory, our ability to hold information in our minds for a few seconds, is limited to 9 items. That's fewer items than the items of a regular out of town American phone number. In light of this you might wonder what to say about cases of people with extreme memory abilities. Chao Lu holds the Guinness world record in reciting Pi, a record dating back to 2005. Lu recalled 67,890 digits of Pi in 24 hours and 4 minutes with an error at the 67,891st digit, saying it was a 5, when it was actually a 0. How is it possible to retrieve this quantity of information accurately through working memory? Is it magic? After talking to several people working in memory sports, we found out that it's not.
Short-term memory falls into two categories: hippocampus-based memory and working memory. The hippocampus is an area in the brain's temporal lobe on the side of the head that keeps track of information that can be retrieved minutes, hours or days after storing it.
According to researchers reporting in the March 2010 issue of Neuron, the hippocampus unconsciously replays experiences in new ways. The researchers measured brain activity in mice traveling a maze and found that the least traveled paths and the untraveled paths were replayed most frequently during decision-making. For example, if a mouse had traveled from A to B and from B to C but never from A to C, then neurons representing the path from A to C would fire. This indicates that one function of hippocampus-based short-term memory is to create the alternatives available when making decisions.
Working memory is an area in the brain's prefrontal lobe that controls information for quick cognitive manipulation. You can consciously attend to information in your head only once it enters working memory. Explicit decision-making, reasoning and calculation make use of information in working memory. Working memory helps us make all the decisions we explicitly make—from choosing whether to buy soy milk or skim milk to deciding which grad schools to apply to.
People intentionally choose what information to feature in working memory depending on what they need it for. If you just looked up a phone number in the phone book and need to dial it, you can choose to keep that information active for long enough to dial the number. But you can also turn to the method of chunking. The method of chunking can assist in keeping information more easily retrievable. For example, to keep the 8-digit sequence "69911711" active, you can use the labels "U.S Route," "terrorism" and "convenience store." It's a variation on this method of chunking that is used by people competing in memory sports. People who can recite Pi to an extreme number of decimal points associate certain thoughts or images with particular strings of numbers.
Take the first 23 digits of Pi: 3.1415926535897932384626. Personally, I could divide it up as follows: 314-1592-6535-8979-3238-4626. The first is the area code for the city I live in. The next four digits is the year Galileo invented the thermometer. CG-6535 is the name of a coast guard aircraft that went lost in February 2012. 8979 Clanga is a main-belt asteroid. “LILLY 3238” is the imprint on 18 mg Strattera (atomoxetine), a drug frequently used to treat attention deficit hyperactivity disorder (ADHD). Form 4626 is a federal tax form for reporting alternative minimum tax for corporations.
Associating things or events with strings of digits of Pi does not suffice for remembering the 23 digits. I need to guarantee that I don't recall them in a different order. To accomplish this I venture on a journey through the universe that starts in St. Louis. Here I jump on a time machine back to 1592 and conduct an interview with Galileo. I then travel to Alabama in 2012 to observe the loss of the aircraft in Mobile Bay. After dawn I rent a plane from the coast guard and fly around looking for asteroid 8979 Clanga. As I start to get sleepy and it becomes difficult for me to focus, I land the plane in D.C. and steal a bottle of 18 mg Strattera pills with the imprint LILLY 3238 from a local pharmacy. The police are chasing me. But with the extra energy from the Strattera, I make it to a court case I have to attend concerning an issue on last year's federal tax form 4626.
As I practice this sequence of digits I visualize my route and my experiences during my journey. The visualization process triggers particular emotions, which will aid later memory retrieval. We remember emotional events better than boring ones. To ensure fast memory retrieval the most boring events on my journal must be dramatized. I don't simply pop an 18 mg Strattera with the imprint “LILLY 3238,” I steal the drug from a drug store and get chased by the police, and I don't simply hand in my federal tax form 4626, I have a major court case regarding last year's taxes.
Memorizing 23 digits of Pi takes less than 10 minutes. To memorize between 25,000 and 70,000 digits, which would be required to beat the European or World champions in reciting Pi, I'd need to practice a lot more. In his book Outliers journalist Malcolm Gladwell argues that prodigious abilities can be acquired through hard work: 10,000 hours of practice. That amounts to 417 days. Someone who is obsessed with an activity and practices two-third of her waking hours could accomplish prodigious abilities in less than two years. I'd better get started, if I want to beat Chao Lu's record by 2014.