Crunched for Space: Working-Memory Capacity

Mental Scarcity

This week, we're going to talk about something so fundamental to cognition that it is easy to overlook. To demonstrate the concept, let's play a simple game:

I'm going to give you a list of numbers, and your job is to repeat them back to me, in the order you saw them. Okay, maybe that's not so simple, but I know you can do it. Ready? Click "Play" to see the list:

Ok, quick, what was the list of numbers!? Did you get them all? If not, don't beat yourself up. I may have been a little unfair because I threw in twelve separate digits. According to this very famous paper [1], you should have only been able to repeat back 7 digits (give or take two) [2].

In other words, the amount of information that you can cram into working memory is severely limited, and we refer to that as your own personal Working-Memory Capacity. First, the bad news: the amount of information we can focus on and use at any one time is very small. Now, some good news: you can use various tricks to expand your working-memory capacity. 

One of the tricks is called Chunking. When I do this demonstration with large groups of people, there's always at least one person who can repeat back the entire list in order. How do they do it? Are they superhuman? Do they practice memorizing numbers all day long? Maybe. But the most likely explanation is that they don't see each digit as a single thing to be remembered. Instead, they focus on grouping the digits together into larger chunks of information. 

Here's the list again: 

1  4  9  2  1  7  7 6  1  9  4  2

Do you notice any patterns in the data? Let me give you a hint: Think about important dates in American history. How about now? Anything emerge? Instead of trying to remember 12 separate digits, now all you have to remember are three years: 1492, 1776, 1942. That's a lot easier, right?

A STEM Example

How does this play out in education? The most obvious example that I can think of is when a student is trying to learn a mathematical formula to calculate something complex, like the circumference of a circle. When a math teacher introduces the idea, there are a bunch of new concepts to learn along with the seemingly random association to their symbols: C is the circumference; pi is a constant; r is the radius. Not to mention that all of these symbols need to be written with operators between them (there's also a spatial configuration). Depending on how you count, that could be 5 (or seven) items to hold in working memory. 

Once you learn the circumference equation, it becomes a single chunk of information, which makes it easier to remember. However, it's easy to forget what it was like not to know something. It's important to keep that in mind when teaching this or any concept. The first time we encounter new information, it is going to appear much more complex because it contains several small chunks of information. As you become proficient in the domain, it becomes easier to take on additional complexity due to the process of chunking.


Share and Enjoy!

Dr. Bob

For More Information

[1] Here is a link to George Miller's very famous paper: The Magical Number Seven, Plus or Minus Two: Some Limits on Our Capacity for Processing Information. 

[2] Like the speed of light, the estimate of working-memory capacity is always changing. It depends on how you measure it! Some estimate that working memory is actually capped at a much lower rate -- around four separate items. One methodology for calculating working-memory capacity is the n-back task, which is notoriously difficult. Your job is to remember a digit (or whatever) that is n turns ago. For example, if n = 2, and I give you: 

3 5 7 8 x

When you see "x" you have to say "7" because it happened two turns ago. As if this isn't hard enough, there's also the murderously difficult dual n-back task. If you are feeling strong, try it yourself!