25. Expectations of Frequency Affect Attention

Farid Seif, a businessman from Houston, Texas, boarded a flight in Houston with a loaded handgun in his laptop case. He made it through security without a problem. Seif was not a terrorist. The gun was legal in Texas; he simply forgot to take it out of his laptop case before his trip.

Security at the Houston airport did not detect the gun. It should have been easily seen by security personnel looking at the x-ray scanner, but no one noticed it.

The US Department of Homeland Security routinely tests the ability to pass security screening with guns, bomb parts, and other forbidden items by sending them through with undercover agents. The US government won’t release the figures officially yet, but the estimate is that 70 percent of these tests fail, meaning most of the time the agents are able to get through security, like Farid Seif, with objects that are supposed to be spotted.

Why does this happen? Why do security personnel notice the bottle of lotion that is too large, but miss a loaded handgun?

A Mental Model of Frequency

Security personnel miss the loaded handguns and bomb parts at least in part because they don’t encounter them frequently. A security officer works for hours at a time, watching people and looking at the scanner screen. He develops an expectation about how frequently certain violations occur. For example, he probably encounters nail clippers or containers of hand lotion fairly often, and so he expects to see those and looks for them. On the other hand, he probably doesn’t encounter loaded handguns or bomb parts very often. He creates a mental model about how frequently any of these items will appear and then, unconsciously, starts paying attention accordingly.

Andrew Bellenkes (1997) conducted research on this expectation and found that if people expect something to happen with a particular frequency, they often miss it if it happens more or less than their expectations. They have a mental model of how often something will occur, and they have set their attention to that mental model.

People Habituate to Stimuli

Have you ever visited with someone who had a clock that chimed every hour? You’re lying in bed about to doze off, and there goes that darn clock again. “How can anyone get any sleep in this house?” you wonder. Yet everyone who lives in the house sleeps just fine. They have habituated to the sound of the clock chimes. Because they hear it every hour, they don’t pay attention to it anymore.

Your unconscious mind is constantly surveying your environment, making sure there is nothing in it that is dangerous. That’s why anything new or novel in the environment will get your attention. But if the same signal occurs again and again, eventually your unconscious mind decides it is not new anymore and therefore starts to ignore it.

Keeping Things Unpredictable

Because people habituate to stimuli, it helps to keep things at least a little bit unpredictable. If your presentation gets too predictable, people will lose attention. This goes against the adage “Tell them what you’re going to tell them, tell them, then tell them what you told them.” I give an alternative to that structure in the chapter “How to Craft Your Presentation.”

Although it is important to have an organized presentation, you need to build in some surprises. If you use the aforementioned mini-breaks, you will be making things a little bit unpredictable.