Now you see it, now you don't

The retina, at the back of your eye, is an extension of your brain. We experience the sensory world as if the sights our brain creates from the light striking the retina is a faithful representation of what is going on out there in the real world. In actual fact this is mostly an illusion. A very convincing illusion admittedly, but an illusion all the same. All sorts of short cuts and ingenious neural strategies are used to fill in the gaps wherever the brain does not have enough information to do a decent job of capturing reality as it really is.

Of course, under normal circumstances, the brain is so good at “faking it” that we are all under the distinct impression that what we see is accurate. But it's not always the case. What we see is actively created by a large, dedicated part of the brain, your Occipital Lobe situated right at the very back of your skull (see left side of the brain tube map for the Occipital stretch of the Visual Lines).

Your permanent blind spot

Only the central part of the visual field is crystal clear. Everything else, believe it or not, is completely blurry. And, only the central part of the retina (Fovea) can see in colour, everything else is in black, white and shades of grey. If you hold both your hands out in front of you at arms length, with both your thumbnails in the centre of your field of view, that is roughly the area covered by your Fovea. Only the Fovea has light detectors that are colour-coded and only in your Fovea are they packed densely enough to give you high-res vision.

So why does it feel like you can see detail and colour in the periphery? It's because your eyes are constantly darting around to capture high-resolution, colour information with the central Fovea. This lingers in perception for a short while to enable your brain to piece together an impression of the overall scene. These eye movements are so tiny and happen so fast that you are completely unaware of them. We are so adept at shifting our gaze to allow our Fovea to harvest light from an interesting blur in the periphery and then back again that we don't even realize it is happening. Your brain fills in the gaps between snapshots taken by the Fovea with an image that fits in with the overall scene.

If you are unconvinced then try this. Cover your left eye and with your right eye look at the O below. Then, slowly, move the page towards you. At some point before your nose touches the page the X will disappear. That blind spot has been there your whole life. Usually your brain effortlessly fills in this gap in perception.

O X

Wiring up the senses

During the first six months to one year, a newborn's brain creates 990 trillion new connections between neurons – consequently its Prefrontal Cortex uses twice as much energy as that of an adult's.

A newborn baby is not born with the ability to see as we adults do. The vision of a newborn baby is 1/20 of the resolution of adult vision – that's extremely blurry. The part of the brain that does what we think of as seeing actually “learns” how to see as the interlocking networks of brain wires are honed according to experience through the early weeks of life outside the womb.

Hearing is a different matter. An unborn foetus starts responding to sounds from the outside world from the third trimester onwards. So the connections between brain wires in the Auditory Line in the Temporal Lobe that create what we hear from the sounds that reach our ears have had a three month head start over those in the Occipital Lobe. We know this because one observant mother noticed that her unborn child would always change its behaviour the minute the theme tune to a famous soap opera started playing on the television. It's a similar deal with taste. Mums who snack on aniseed flavoured food and drinks when pregnant find that once their baby is born it has a preference for this flavour.

A surprising amount of progress is made in the womb when it comes to wiring up our senses and this process only accelerates in the first few years of life. After a child's brain has made headway in developing its abilities to sense and start moving around to explore their environment, somewhere between the age of 12–20 months, it starts to develop a sense of self. Strange to think that we had no concept of “I” or “me” throughout our first year. No wonder we don't remember any of it.

Division of labour

Different areas along your brain's Visual Lines each have a complete map of visual space and each one extracts different aspects of any given scene. The brain stop known as V4 consists of a densely woven fabric of brain wires that actively extracts colour information from the light that hits the Fovea. We know that in rare cases where V4 is damaged in both halves of the brain, a person will lose the ability to see in colour. They see more or less the same patterns of both light and dark areas of objects, faces and landscapes, but it's all painted in shades of sludgy grey. This is because the job that area V4 evolved to perform is to compare the wavelengths of light in adjacent patches of retina and then “paint” the colour information into the visual scene created by all the other parts of the visual brain. Without V4 doing its job we simply cannot do colour. The fact is, outside your brain, there is no such thing as colour. Light in the outside physical world has no colour. What you see as colour is an interpretation made by your brain as it attributes colour to each wavelength of visible light. It is an illusion that helped us stay alive by making us better able to spot food and predators, but it is all in your mind!

At night our peripheral vision is better than vision at the centre. This is because the retina's high sensitivity light detectors (rod cells) are more concentrated around the edges than the middle of the Fovea.

Area V5 is located at the junction between the Occipital and Temporal Lobes and its job is to create the perception of motion when an object moves across your field of view. So, if area V5 is compromised in both sides of your brain, you won't be able to see moving objects. They remain invisible until they come to a standstill, at which point they will suddenly reappear as the intact areas of the visual brain kick in again.

Whenever you hear a particular song played on the radio the Auditory Line that runs through the upper part of the Temporal Lobe creates what you hear. There is strong evidence that a division of labour occurs in the sense of hearing as well. Some areas respond best to single tones (A1 stop), others prefer sound sweeps progressing from a low to high pitch or vice versa (PT stop).

A further division of labour was made evident when an advertising executive who had damaged a certain part of his brain selectively lost the ability to perceive music, yet his hearing of other sounds remained fine.

When you get a waft of a certain smell as you walk into a room the scent you perceive is generated in the inward facing part of the Temporal Lobe (Olfactory stop on your brain's tube map). Such sensory experiences are often associated with a certain person, place or time in life and can trigger an emotion and/or a specific memory which all come flooding back in an instant. Scents are particularly evocative in this way because the Olfactory Bulbs plug directly into the Limbic System unlike all the other senses, which go via the Thalamus.

Bottom-up and top-down pathways

Over 50 years of neuroscience research has taught us about how “bottom-up” pathways take information from the eyes, ears, mouth, nose and skin to “higher” brain areas that actively create our perceptions. They first convert physical disturbances caused by light, sound, pressure, heat, liquid or gaseous chemicals into electrical impulses that your brain can analyze to create your impressions of the world. Visual pathways deliver these electrical pulses to the back of your brain where the information is fed into different patches of cortex, each of which crunch the data in different ways to produce different aspects of your visual experience. Similarly, the inner ear converts pressure variations that hit the eardrum into electrical messages that the Auditory Cortex (A1, PT, STG and STS stops on the brain tube map) can divvy up into different patches. These patches are highly specialized to analyze and actively create different aspects of the sounds we ultimately end up hearing.

There are also “top-down” mechanisms involved in sensing the world around us. These bring certain assumptions about what types of sights and sounds are likely to occur in different environments into the mix. As we gain experience of different places we can start to anticipate the types of sensory experiences that are typical in any given place and this dramatically speeds up the process of crunching the data. For instance, imagine taking a stroll in a European park at dusk and you hear a creature scrabbling around in the bushes but when you direct your eyes towards the noise you cannot tell what animal it is due to leaves blocking your view. In these circumstances top-down brain mechanisms will narrow the possibilities. You'll identify the mystery creature fairly quickly as a dog, cat, fox, bird or rodent according to its characteristic shape and movements, having automatically excluded the possibilities of tiger, rhino, kangaroo or monkey. Your sensory experiences are shaped by what you've sensed in the past, which has the effect of speeding up perception by filling in the gaps when the available information is incomplete.

Sound the alarm!

Over the centuries, countless numbers of bleary-eyed sailors with the responsibility of keeping watch must have sounded the alarm only to discover that what they thought they had seen through their telescope wasn't in fact an enemy ship at all. With such a heavy burden of duty it's understandable why they would risk the wrath of the captain along with the entire ship's crew by getting it wrong, rather than risk the loss of everyone's lives; including their own. Naval technology may have advanced considerably but when it comes to making sense of weak sensory signals our brains are stuck with the same old kit.

During World War II, researchers found that radar operators performed completely differently in the context of training exercises as opposed to real-life combat situations. During actual combat there was a vastly increased incidence of false alarms, with operators concentrating so hard on the screens in front of them that they would often imagine blips on the screen that simply weren't there. These false alarms may have been a bit of an inconvenience but at least they rarely missed the approach of a genuine “incoming.”

Conversely, in training there was no problem with false alarms but a far greater incidence of real blips on the screen that weren't spotted!

Expectation has an enormous influence on how sensory information is evaluated. During training the operator knows that a blip isn't really the approach of an incoming enemy. The consequences of missing a blip in these practice scenarios are minimal with perhaps a reprimand from an instructor or, at worst, a low mark on that particular exercise. The “response threshold” to use the official term, is higher than in a real-life situation – the decision to sound the alarm will only be taken if they are absolutely sure they saw a blip. On the other side of the coin, when carrying out exactly the same task for real, the radar operator knows that any blip could well be a potential enemy strike. The consequences of missing one single blip are unthinkable and so the response criterion is lowered. The outcome being that even the dimmest looking, fleeting, half imagined blip on the screen was likely to send everyone scrambling to battle stations.

Do I know you?

Because of its immense importance, there is a specific piece of brain real estate that specializes in faces. The Fusiform Face Area's (see brain tube map) primary function is to process faces. As intensely sociable primates, faces are incredibly important to us humans. It is perhaps unsurprising to think that evolution has developed a dedicated patch for identifying and distinguishing different faces within just a split second, not to mention the expressions on them. Such information has proved invaluable to a creature like us. Over the centuries we have needed to be very quick at establishing whether an unexpectedly encountered face is friend or foe; it was often a matter of life or death. This ability was key to the survival of our ancestors.

However, when we come to associate certain faces with certain places, even this dedicated machinery can let us down. If a colleague we once worked with turns up on holiday then we can find ourselves completely unable to figure out why they look so familiar. The top-down mechanism that constrains which faces we usually encounter in which places, despite speeding recognition up under normal circumstances, actually slows us down when a face pops up out of context. We know they seem familiar but have no contextual cues to help resolve the conundrum of how exactly we know them. As we all know, this can be highly embarrassing, especially when they recognize you, start chatting and horror of horrors, start using your first name. You stand there, desperately trying to place them, not knowing whether to bluff it or come clean and ask them to remind you of their name. The crunch point usually comes when you suddenly find yourself in the truly awkward situation of having to introduce them to someone else and you're left with no choice but to confess!

Having a special area dedicated to processing faces can also lead to situations where we see a face when in reality no face is truly present. Seeing faces in the clouds for instance, or in the corner of the bedroom when we were six years old and scared of the dark. Low levels of illumination provide less information to the eye for the brain to use to define where one object ends and a separate object begins. In these circumstances such vague and incomplete information can result in the eerie sense of a ghost-like presence in a darkened bedroom. When our imagination gets the better of us (top-down), we can assemble the vague blurs formed by a variety of separate objects (bottom-up), and create the distinct impression of a monster's head staring at us (when in fact there is nothing really there but a dressing gown or perhaps an ornament on a bookshelf). Our brains are constantly looking for patterns in perceptual information and often find them even when they aren't really there!

Mind the gap

Certain strong perceptions can end up being paired with potent associations. These associations can lead to what we usually think of as assumptions. Even a single word can lead to a whole set of assumptions. A stand out example being that of a major online retailer that had a button on their website with the word “Register” on it. On replacing it with the word “Continue” they saw an increase in revenue that year to the tune of $300,000,000. The word “Register” for most of us conjures up the assumption that we'll have to waste time doing things like filling in forms and having to type in information, whereas the word “Continue” gives us a feeling of progress, of quickly moving on, of getting somewhere.

A deceptive encounter

As a result of assumptions that get associated with our perceptions we all develop preconceived ideas about people; ideas that often prove to be wrong. Many years ago, whilst driving down from London to Somerset, I stopped off at a busy roadside cafe. Shortly after I'd placed my order a man that I can only describe as the biggest, scariest looking human being that I'd ever seen came in and took a seat at a large round table next to me. When he turned around to talk to the waitress, the words HELLS ANGELS were clearly displayed on the back of his jacket. He placed his order but, before it arrived, he quickly got up and disappeared into the toilets. Whilst he was in there, a small group of five, distinguished, older looking men wearing bowls club blazers came in. The only place for them to sit together was at the large round table, upon which its absent occupant's breakfast had now arrived. Seeing this, the five bowlers asked the waitress if anyone was sitting there and she replied “Yes, there is a gentleman sat there but I'm sure he won't mind if you join him.” Obviously happy with this, they all took a seat. It may sound cruel, but I could not wait to see the reaction on the faces of these five old boys when what the waitress had described as a “gentleman” came back to his table. When he did eventually return, I was not disappointed! On seeing the colossal “being” that was now suddenly towering over them, they all, without communicating a single word, jumped up, kicked their chairs back and shot off to find another table – as far away as possible.

Having had his breakfast my Hells Angel neighbour suddenly pulled out a copy of The Times newspaper and started finishing off what looked like an almost completed crossword. Noticing that I was watching he smiled at me and in a very soft, extremely well-spoken voice he said “Crosswords are always a bit of a struggle on a Monday morning!” We got chatting and it turned out that having left Oxford University he'd gone travelling, eventually ending up in Rwanda where amongst other things he'd been working with landmine victims. He was one of the most intriguing people I have ever met, an unforgettable, fascinating character. He was the inspiration behind my Pineapple Person character – from a previous book – those who are spiky on the outside but very different on the inside. How wrong you can be!

– Adrian

Before we move on, a quick question for you. When you think of a wind farm, what picture springs to mind? Is it one of something that's clean, natural, positive and safe or is it one of something that's manmade, monstrous, noisy and damaging? Our associations with a concept such as wind farms can lead to a variety of assumptions that polarize our opinions – once formed they can leave us blind to the truth.

So, what has this all got to do with sorting your brain out? It's all about that gap between the bottom-up and the top-down mechanisms. This is where mistakes happen. But it is also where creativity is born. And the better you understand the quirks and shortcomings of this gap the less you'll misinterpret situations and the better you'll understand when those around you fail to “Mind the Gap.”

We now know that information from the outside world is actively extracted by a wide variety of different brain areas (please see brain tube map – page 8) to create what you see (Visual lines), hear (Auditory line), smell (Olfactory stop), touch (Somatosensory line) and taste (Gustatory Cortex). These separate but highly interconnected places all do a very good job of summarizing what's out there in the world and help us get along in it.

Consider the mind-boggling complexity of the challenges facing your Occipital Lobe when having to conjure up a convincing 3D visual world from the 2D array of light-detectors at the back of your eyeballs. You can only begin to imagine the technical difficulties involved in capturing the sound of an 80-piece orchestra from a bunch of pressure variations in the air, or the finely-tuned senses needed to detect delicate individual flavours in a meal, the ingredients of which could come from an almost infinite selection of food sources.

But it is not 100% reliable. Your senses can trick you. People who are overly confident about what their senses tell them can often end up, having misread situations, looking and probably feeling rather silly. On top of this, the brain constantly makes assumptions about what is and is not likely to exist in any given environment.

Impact of context and expectations on perception

Pleasant smells, foods and even music induce responses in the OFC brain stop – behind the middle of your forehead – which mirrors in real time the quality of your sensory experiences. We know this because neuroscientists scanned the brains of hungry subjects whilst they were fed bananas. Large responses in the OFC occurred during consumption of the first banana, reflecting the pleasure derived from satisfying their hunger. However, once they were stuffed silly and asked to eat yet more bananas, the additional bananas produced significantly lower responses, reflecting a decrease in enjoyment.

Other studies have indicated that the OFC does not respond to enjoyable perceptual experiences per se but rather how enjoyable you think they are going to be. OFC activations in response to a certain pungent odour were significantly increased when individuals were told that what they could smell was a high quality cheese. That is in comparison to when the exact same odour was squirted up their nose later on in the experiment, but this time participants were told it was a pair of sweaty socks. Your expectation can fundamentally influence your experience of certain sights, sounds, smells and tastes, positively or negatively via changes in the response of your OFC.

TV experiment

We took two bottles of wine, one an expensive bottle of grand cru, gold medal winning, limited addition Bordeaux and the other a very cheap looking bottle of mass-produced plonk. We poured the contents of both bottles down the nearest drain and, after rinsing them, refilled them both with exactly the same, average quality wine. Then we asked unsuspecting members of the public to taste the wines whilst wired up to portable EEG scanning electrodes to measure their brain's objective responses to these two “different” wines. Participants were also asked to describe the tastes and compare the two in terms of flavours, aromas and perceived quality.

Now what do you think happened? Did they cotton on to our little ruse? Did their sensory experience of exactly the same liquid tell them that they were being conned? Not a chance!

Their expectations, having been set up by the appearance of the bottle from which each glass was poured, along with an elaborate but completely fictional tale about each of these “two” individual wines unanimously tipped the balance in favour of the perceived “posh” wine.

Would your own taste buds be fooled by this simplistic charade? Or would you, completely uninfluenced by mere suggestion, quietly suggest that there has been some kind of mistake because both reds are in fact identical in every way?

It will come as no surprise that what they said about the flavours and aromas of each wine were totally different. The wine from the “posh” bottle was described in glowing terms and was deemed well worth the £40 price tag, whereas the wine from the “plonk” bottle was derided as being unimpressive, bitter and tasteless.

Our expectation of the amount of pleasure we might experience from a product can have a profound impact on how we actually experience it – so long as there are no powerful sensory signals that go against this expectation. If we had used the cheapest imaginable wine, alarm bells would have sounded and the experiment would not have worked. Equally had the wine from both bottles been a remarkable, exquisite wine with strong and distinctive character the experiment may also have failed as people would have found it difficult to believe that something so delectable could cost only £4. However, as there was no major disparity between the expectation and the sensory experience when the average wine was sipped twice – in the context of being poured from an expensive looking bottle and in the context of being poured from a cheap-looking bottle – their testimony regarding their perceptual experience of each followed their expectation precisely. Even more surprisingly, the objective measurements of activity in their OFC mirrored their subjective experience very closely. The more they said they liked it, the greater the response in the OFC as they sipped it!

– Jack

You have 12 million Olfactory receptors in your nose to detect different types of scent. Your average dog has at least 1 billion. Bloodhounds have 4 billion.

Below expectations

Another glowing example of context leading to massive assumptions was when one January morning, during rush hour, a man started playing a violin at a Metro subway Station in Washington DC. After 43 minutes only a tiny handful of people, out of the 1,097 that had passed by, paused to listen to him before moving on, the vast majority appearing to be deaf to the talent within their midst. The sum total of his efforts amounted to just over $32. This busker was Joshua Bell, one of the finest violinists in the world who three days earlier had sold out at Boston's Symphony Hall, the average ticket price being around $100.