The Magical Number Seven, erm, Four

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At Barcamp Stuttgart last weekend, I gave one of my now-traditional sessions about better presentations. This time, I concentrated on the human brain and how we need to take some of its limitations into consideration for our presentations. Specifically, I talked about the prefrontal cortex and the short-term memory (and visuals).

You've probably heard this before: The human short-term memory can only keep track of a certain amount of things at the same time. Seven is the number usually given. You also hear "Seven plus or minus two" sometimes.

The Magical Number Seven

Where does this number come from? As it turns out, it all dates back to a speech that psychologist George A. Miller gave in 1956. The interesting thing is that Miller didn't provide any proof for that number. He was only, in the context of this speech, pointing out that the human short-term memory is limited and speculated that the limit would be somewhere around seven, plus or minus two items.

Only much later, when Alan Baddeley (in the 1990s) and Nelson Cowan (in the early 2000s) did any actual research did it become clear that the "magical" (as Miller had called it) number seven was wrong.

The Magical Number Four

Baddeley and Cowan found that the average human adult can only keep 4 items in short-term memory. And it's even worse - this only works for simple or familiar things. You cannot keep four complex ideas in short-term memory (unless you're already familiar with them); neither can you remember four words in a language that you don't speak or understand.

At this point, a word of clarification seems to be in order: The term "short-term memory" is ambiguous. Scientists prefer the term "working memory" for what we colloquially refer to as the short-term memory. This term better describes what this area of our memory is really used for and avoids confusion with another area that really only keeps one piece of information for a very short time (a few seconds). In the context of this article, I am using both terms synonymously.

Bullet Points

Now that this is out of the way: What does this fact have to do with presentations?

For one, it's part of the explanation why slides full of bullet points don't work. We simply cannot keep all the information presented in such a way (usually much more than 4 items) in working memory and therefore have trouble following the speaker's arguments. Plus, due to this "overflow", we have problems remembering - it's just too much information at once.

I've often argued against the (over-)use of bullet points on this site. The rule of thumb is: If you're going to talk about one of your points for more than a few seconds, it gets its own slide ("One idea per slide").

Lists and Chunking

Sometimes, however, you simply have a list of things that belong together. For example that your new mobile phone comes in configurations with 16, 32, and 64 GB of memory. You're probably not going to spend a lot of time explaining these differences and the intention is to give an overview over the available options. Then there's nothing wrong with putting them on one slide together. Even if you don't use any actual bullet points for these items, it's still a list - and there's nothing wrong with that.

However, you have to keep the number 4 in mind! So if you end up with a list of more than 4 items, you should break up that list into smaller pieces, i.e. shorter lists with a maximum of 4 items each. If you have a long list of things, chances are that you can group them and create a hierarchy. Repeat this step until you end up with a top-level list of not more than 4 items. The scientific term for this technique is "chunking".

This is also one of the techniques recommended by Dr. Medina in his book Brain Rules. Hierarchies help people remember things better. To get this effect, you start at the top. Obviously, if you were to start at the bottom, you would risk overwhelming your audience with lots of information (much more than four!) before you even get to the point where they can see the big picture.

Summary

If you have to use lists in your presentation, then:

  • avoid lists of more than four items
  • use chunking
  • start with the big picture, then go into details

This approach will make it easier for your audience to follow your talk and will also help them remember things better.

(Image Credits: "He who likes cherries soon learns to climb" by Kate Ter Haar, from Flickr)

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