The Prevalence Error - Why We Look But Do Not See

By Rod Machado (rodmachado.com)

Recently, I was having a difficult time seeing things that were in plain view. I was even thinking about visiting the Our Lady of Fatima Optometry Center, where their motto is, “If we can’t correct your vision, at least you can have one.”

My problem began with placing a candy bar on the first shelf of the kitchen pantry (I hide my chocolate there because my wife, Princess Buttercup, goes cuckoo for cocoa). A few days later, I went in search of my candy bar. It had (mysteriously) migrated to a lower shelf (apparently, that’s where Buttercup hides her chocolate). I never saw it. I see, but eye not see. Despite looking at all three shelves, I simply couldn’t see what was clearly there to be seen on the middle shelf.

Fortunately, there’s nothing lethal about a candy bar that escapes notice. Calorically, I was better off to not-see and avoid. You can’t say the same if you fail to notice a crack in your propeller, nearby airborne traffic, or objects on the runway during landing. Now you understand my concern about the invisible candy bar.

It turned out that my earthly vision was just fine (reading glasses assumed, although I’m officially just two lenses away from being a fly). My inability to find sweet treats stemmed from another cause.

We occasionally fail to notice things that should be noticeable (especially if we kept searching). This happens when our expectations collide with our experience. Who wouldn’t expect to see their candy bar where they last placed it? It’s as if, failing to see what we expected to see, our mind stops the search prematurely. According Dr. Jeremy Wolf, a Harvard ophthalmology professor, that’s precisely what happens. He calls this the prevalence error.

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At Harvard’s Visual Attention Lab, Wolf and other researchers discovered that when we go in search of things without finding them (because they lack prevalence), we become less likely to find them during future searches when they’re actually present. There’s a good reason for this error, too. It turns out that you’re just plain lazy.

Don’t take it personally. This applies to all of us. Our brains are pretty good at minimizing our conscious workload when we fail to find what we’re looking for. If we don’t see it immediately, we tend to abandon our search quickly or at least don’t continue searching with the same intensity. That makes a certain kind of sense, since there’s little value in looking persistently for something when it’s most likely not there—as long as it isn’t a potentially-fatal hazard. Besides, looking is hard work, requiring intense concentration to say nothing of eyeball strain.

This explains why airport baggage screeners can miss important items when X-raying luggage. TSA agents scan for weapons but seldom find them, which makes it less likely that they’ll notice one when it’s actually there. The issue is especially pertinent now, given that TSA agents are also on the lookout for exploding underwear—otherwise known as Fruit of the Boom. Hotpants are back in fashion.

Do you see how the prevalence error can work against you as a pilot, especially when taking off or landing? Let’s say you glance down the runway, looking for aircraft, cars or animals. Because you’ve found few (if any) intruders in the past, the prevalence error suggests that you’re less likely to actually see an antelope interloper when it’s actually there. Sure, you might look, but you’re also likely to abandon your search a little too quickly.

What’s the antidote for the prevalence error? How about doing what police officers do when they’re in the roughest of neighborhoods? Treat everybody as a suspect. That’s right. The only thing you can do is to be sufficiently suspicious in those areas where the prevalence error might expose you to greater risk. That means treating critical things like your propeller, airborne traffic near airports or even the runway environment with suspicion.

Take the runway example, for instance. Is someone near it? On it? Approaching it? What the heck are they doing there? Call it runway profiling, because as far as you’re concerned all runways are assumed to be guilty until proven innocent. After all, they appear with white stripes on a black outfit, and each is identified with numbers. Treating with suspicion those items or events that require careful observation is how you force yourself to not abandon the search too quickly.

Clearly, the less often we see something, the less likely we are to see it when it’s actually there. We’re built to give up our searches early when experience suggests that the targets aren’t likely to be present. We simply have more important things to do with our brains.

Ultimately, we must force ourselves to spend more time looking where it counts and when it counts. It’s a strategy that applies to not only runways but other critical areas associated with flight, where a threat is not often present but can have serious consequences if it is there and not noticed. Now you understand why the TSA folks want to take a peek inside your shoes and shorts. That’s where the bombs are. So I’m happy to let them have a look. But only when I’m at the airport, of course.

Had I applied this high-risk/high-intensity strategy when searching for my candy bar, I might have found it quicker. Then again, I might just start buying candy bars with the letters “LOOK” on them. They have got to be easier to find. Sweet.