It’s surprising how much of the world we see and yet do not take in. Who better to teach us why we miss so much and what to do about it than Sherlock Holmes?

“The true art of memory is the art of attention,” wrote Samuel Johnson. Wise words, indeed, but what exactly is this art? Do we really know what it means when we say we are paying attention to something? One possible answer comes from another literary source that, while admittedly fictional, provides a great deal of insight into what it is that distinguishes actual attention from simple looking: Sherlock Holmes.

In A Scandal in Bohemia, Holmes asks his companion Dr Watson how many stairs lead up to their residence, 221B Baker Street. Watson draws a blank. “And yet I believe my eyes are as good as yours,” the doctor remarks. “Quite so,” Holmes is quick to respond. But the acuity of Watson’s vision is not the issue. He continues, “You see, but you do not observe. The distinction is clear.” And in that distinction lies the key to the meaning of attention. It’s not a matter of physically seeing; it’s a question instead of both seeing and observing.

Our vision is highly selective: the retina normally captures about ten billion bits per second of visual information, but only ten thousand bits actually make it to the first layer of the visual cortex. To top it off, only 10% of the area’s synapses are dedicated to incoming visual information at all. Or, to put it differently, our brains are bombarded by something like eleven million pieces of data at any given time, and of that, we are able to consciously process only about forty. What that basically means is that we “see” precious little of what’s around us. Instead, our sight is selectively filtered based on any number of factors: our state of mind, our mood, our thoughts, our motivation, our goals. So, we might think we’re paying attention, but what is it, exactly, that we’re paying attention to?

Consider the so-called cocktail party effect: you are at a party, surrounded by the din of conversation, when all of a sudden, your ears perk up after someone says your name. Now you begin to pay attention. What before was a meaningless wall of noise has in that single instant acquired meaning. As a study published last year in the journal Nature showed, when we pick up on one voice and ignore others, our brains somehow discard the information coming from superfluous sources.

This basic principle governs our attention all the time. We attend to things that are somehow important to us, and fail to note those that aren’t. It’s a common phenomenon. Pregnant women start noticing other pregnant women everywhere, whereas before, everyone seemed blissfully unattached. We tend to remember dreams that then seem to come true – and promptly forget those that don’t. After 9/11, people reported seeing the number eleven everywhere, as if it had suddenly materialized out of the blue. In none of these cases does the environment change. What changes is our perception of it, or, to put it in Holmes’s words, what changes is what we observe – and in the past, just passively saw without actively noting.

Gorilla tactics

Our attention is a finite resource. There is only so much of it to go around, and the choices we make about how we allocate it make a big difference in what we see versus what we both see and observe. As with most things, attention is about attaining a golden mean of sorts. Pay too much attention to one thing, and you fail to note anything else. Spread your attention between too many things, and you don’t really pay attention to any of them.

To illustrate this phenomenon, here’s a four-digit number: 5203. Take a metronome, or anything with a steady beat—there are free metronomes for your phone and your computer online—and set it to a beat per second (or you can always go down the old-fashioned route and use a clock that has audible ticks). Now, on every beat, you must add one to each of the numbers and say it out loud; in other words 5-2-0-3 becomes 6-3-1-4, and so on. When you reach the fourth digit, start again from the first – but remember, the number has now changed based on your addition from the round before, so the next four digits you say out loud are 7-4-2-5. It’s very important that you stay on rhythm. Try it for a minute or two. Ready? Go.

Done? You’ve just completed what psychologists call the classic add-one task. How did you do? I’m guessing fairly well – but not quite as well as you’d initially thought. The mandatory rhythm can make it tricky. If it was a piece of cake, try adding two, three, or even four (add-two, add-three, and add-four, respectively) to each of the numbers on each click. The more you add, the harder it gets. In fact, four seems to be about the limit of what even a practiced mind can do without straying from the beat.

Things get even harder when asked to do other tasks. For instance, if you had to stare at a dot on a computer screen at the same time, you would have probably missed any letters or other images that may have flashed on the screen while you were counting. Your eyes would have looked directly at them, yet your brain would have been so preoccupied by counting in a steady pattern that you failed to grasp them entirely. The way our intense focus on a specific thing makes us blind to practically all else is often termed “attentional blindness.” I myself like to call it attentive inattention.

Don’t believe me? Perhaps the most prominent example of this phenomenon is a famous study where a group of students was shown a video of a basketball game and told to count each pass. They did so, to great effect. The only rub? They missed a person in a giant gorilla suit who walked on to the court and deliberately made his way across it, pausing in the middle to thump his chest. They were so busy counting that they failed to see something that seems impossible to miss.

It’s a scary thought, but we are capable of wiping out entire chunks of our visual field without knowingly doing so. Holmes admonished Watson for seeing but not observing. He could have gone a step further: sometimes, we don’t even see.

And it’s far worse than the add-one or even an invisible gorilla would have you believe. We don’t even need to be actively engaged in a cognitively demanding task to let the world pass us by without so much as a realisation of what we’re missing. For instance, when we are in a foul mood, we quite literally see less than when we are happy. Our visual cortex actually takes in less information from the outside world. We could look at the exact same scene twice, once on day that has been going well and once on a day that hasn’t, and we would notice less – and our brains would take in less – on the gloomier of the two days.

Filter failure

The more research is conducted, the worse the picture gets. Up until recently, for example, psychologists generally accepted that our view of natural scenes is so automatic that is isn’t affected by inattentional blindness – in other words, we’re aware of natural scenes without needing to give them our full attention. Unfortunately, no such luck. As with the gorilla, if we are busy doing something else, we will remain largely unaware of the details and may even fail to realise we’ve seen something to begin with.

In a study published in 2011, researchers asked participants to keep their eyes focused on one of the following objects on a changing chessboard: a series of moving discs in study one; or a stream of letter and digits in study two. In the second case, they were instructed to count how many times a given digit appeared. In both experiments, a natural scene (including a beach, a building, animals and vehicles) would flash for a moment on the screen, and participants would then be asked to answer some basic questions about the scene.

What happened counteracted the results of prior experiments – which the researchers attributed to putting subjects through more demanding tasks. In the first study, 64% of participants experienced full inattentional blindness, while in the second – an easier task – fully 50% did so. To put that in perspective, when the task goals were reversed, so that observing the background was the key goal, 96% and 93%, respectively, could both see the scene and accurately identify its specific category.

So we can’t actually be aware unless we pay attention. No exceptions. Yes, awareness may require only minimal attention; but it does require some attention. Nothing happens quite automatically. We can’t be aware of something if we don’t attend to it.

Framing mindset

The add-one, the gorilla, the moving disc: these are, in essence, the flipside of the multitasking problem. When we multitask, we fail to pay attention because we try to divide finite resources too sparsely where we should be concentrating them; and when we try to count passes or add numbers, we fail to pay attention because we focus so much on a single aspect that we forget to note anything else. But the underlying problem remains the same: finite attentional resources and our limited task-switching ability. It’s the same problem, but triggered by being too engrossed in one task to realise there is another to switch to. In order to observe, we need to focus – and we need to focus just the right amount, not too little, and not too much. It’s a delicate balance.

Our brains aren’t stupid; our Watsonian attentional abilities are there for a reason. We don’t notice everything because noticing everything – each sound, each smell, each sight, each touch – would make us crazy. (In fact, a lack of filtering ability is the hallmark of many a psychiatric condition.) Do we really need to know how many steps lead up to 221B Baker Street? Maybe, maybe not. It all depends on what our end goal is going to be. But what we do need to know is that unless we make the active choice to pay attention, we won’t be able to count the number of proverbial steps even when they happen to be crucially important to us.

The problem lies in a lack of mindfulness, of the Holmes willingness to just take a moment to reflect, be still, and be present in whatever it is you are about to do. In the usual course of things, our brains pick and choose where to focus without much conscious forethought on our part – whatever seems intriguing or interesting (sparkly! tasty!) catches its interest, and away it goes. What we need to learn instead is how to tell our brains what and how to filter, instead of letting them be lazy and decide for us, based on what they think would make for the path of least resistance.

Holmes did this through mindset framing: he always considered beforehand what he wanted to get out of every situation. That way, he primed his mind to notice certain elements, and ignored others. Or as William James put it, “Whilst part of what we perceive comes through our senses from the objects around us, another part (and it may be the larger part) always comes out of our own head.”

This is an edited extract from Mastermind: How to Think Like Sherlock Holmes by Maria Konnikova. If you would like to comment on this story or anything else you have seen on Future, head over to our Facebook page or message us on Twitter.

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