Have you ever attended a presentation that felt like you had to drink from a fire hose? Even worse, have you delivered one?
Our minds contain a vast store of information accumulated over a lifetime of living and learning. But every new bit of information we have, first entered our minds through our working memory.
Think of working memory as a mental scratchpad. It’s not just the short term memory we might use to keep a telephone number in our heads for the few seconds it takes to find a phone and dial it, it’s the capacity to retain and manipulate that information, such as if we had to add the digits together before dialing the number. The problem with working memory is that we have a severely limited capacity which can easily be overwhelmed.
It’s easy to see how limited we are. For example, if I ask you to add 24 + 17 in your head, you probably won’t have too much trouble. But if I asked you to add 247 + 175, I might start overloading your working memory, because as you are adding the digits in your head you are also trying to remember the numbers I gave you. For years, it was thought that working memory was limited to about seven chunks of information at one time, but more recent research has shown that the more realistic estimate is three to four items. Remember that it’s an average, and some people can go higher while some can’t manage even that much.
What does this mean in terms of presentations? When your listeners receive information from you, they are not simply trying to remember the data as if it were a phone number. They are actively processing the information: contrasting it to what they already know, comparing it to other ideas, and considering its implications. Depending on the unfamiliarity or complexity of the new information, they may be stretching their working memory capacity to the limit.
We progress in our knowledge of a particular topic by “chunking” bits of information together, so that the new combination then becomes one piece of information to remember. For example, if I gave you directions to get to my house, I might have to give you a dozen or more instructions if you were from out of town. But if you live here, I could simply say, “Head east on 17th Street from Federal, turn right at the bridge, and left at the traffic circle.” That’s only three chunks. Fortunately for the human capacity to learn, the definition of chunk is very elastic. A chunk can be quite elaborate and contain a lot of information.
When you learn a topic, you gradually build the details into larger and larger chunks, which is the only way your mind can manipulate ever larger bodies of knowledge to make sense out of them. But the problem is that we forget how difficult it was for us to grasp the material at first, so we skip over the parts that now seem obvious. Psychologists call this the Curse of Knowledge. In one study, six programmers were asked to teach the steps they used in a debugging task. No one expert was able to describe more than 53% of the actual steps they used.
So all that learning can cause a communication problem when you’re feeding chunks to someone who is not yet familiar with them—they’re too large for them to swallow at once, and when you overload them they just shut down.
Because it’s not obvious to the listener, they start behind in the conversation and then have trouble catching up because while they are trying to make sense of what you have said, you’ve already moved on to the next phase.
Besides leaving out information that listeners need to make sense of our message, there are two other common ways of going too fast for them: speaking too fast and overloading slides with way too much information.
As it relates to personal credibility, a too-rapid rate of information transfer is double-edged. It can certainly give listeners the impression that you know what you’re talking about, but they may be turned off by your seeming lack of concern for their understanding.
How do you find the right rate?
Link to what they already know. You first have to know how familiar your audience is with your topic, to know where to start. Then figure out ways to relate the new material to what they already know, using analogies and comparisons.
Limit how much you try to say at one time. Sometimes you save time in the long run by doing short sessions or conversations, either in stages, or in deeper detail each time.
Organize your material into meaningful categories. If you have to provide a long list, for example, group the items into three or four main categories. Give the categories first and then fill in the detail.
Be clear on what they need to remember. A lot of material that you provide to people does not have to be memorized; they may just need to know where to find the details if they need them. For example, you can tell them the dates of the next six project milestones, or just tell them it’s in the handout.
Use the pull system. In lean production, manufacturers use the pull system to ensure that inventory is only produced when the downstream client needs it. The analogy for communication is to give them the bare minimum you think they need, and let them pull out additional information through questions if they need it. Or, supposing you have seven benefits to talk about, give them only the top three and only add others if necessary.
Don’t speak too fast, and pause to gauge whether they are getting it. Eye contact and “listening” to your audience is your best defense against working memory overload. Be especially alert to signs that someone is getting confused or tuning out, because they will be reluctant to speak up.
 Building Expertise, Ruth Colvin Clark, p. 78.