5 things the Christmas Lectures taught us about the mind

Speech may have evolved by accident

We consider human speech to be one of the most complex and impressive abilities of our species, one that stands us apart from other animals. But that idea itself might be a load of hot air according to Professor Sophie Scott, a neuroscientist at University College London who gave the 2017 Christmas Lectures.

Instead we need only think of artists such as opera singers and beat boxers who can produce a magnificent range of sounds (Scott has even filmed a beat boxer inside an MRI machine to prove how intricate the vocal skills involved).

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Compared to these kinds of impressive vocal gymnastics human speech is pretty simple. We actually do the bare minimum when we talk to each other, Scott says, so it might be that we evolved impressive vocal abilities before we ever applied them to speech. Our ancestors may have used these complex sounds to impress mates or defend their territories, and the incredible human ability to talk evolved later on by accident.

“Once we’d evolved this absolutely extraordinary musical instrument of the human voice, maybe speech was almost an afterthought. An afterthought, of course, that has created the world we live in through the gift of language.”

You have a hole in your vision the size of a lemon

Hold out your fist at arms length. Now imagine you had a black spot in your field of vision the entire time. The truth is you do – we all do – but we never notice it thanks to a trick of the brain.

Physiologist Hamilton Hartridge was the first of many Christmas Lecturers to talk about the blind spot in his 1946 Lectures on colour vision. He explained how the retina at the back of the eye is lined with rods and cones, its job being to convert light waves hitting the eye into electrical signals that can be interpreted by the brain.

All of the nerve fibres carrying signals out of the back of the retina bundle together to form the optic nerve which relays all these signals to the brain. To make room for the bundle, there is one spot on the retina where there are no light receptors at all.

“In consequence, that particular eyeball is blind,” he said at the time.

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Professor Colin Blakemore revisited the subject in 1982, in an attempt to prove how our brain creates our experience of the world based on expectations, rather than what is really in front of our eyes.

In the case of the blind spot, it uses the imagery around the blind spot to invent what should be in it. “Your brain somehow fills in that missing gap in the information because it has the expectation that there really are no holes in the world,” he said.

By age 16 you will have lost half the connections in your brain

Humans spend much longer as dependent babies than any other animal, and for good reason. At birth, the human brain is the same size as that of a chimpanzee, measuring 350 cubic centimetres, but it continues to grow at a mind-boggling rate – as much as a quarter of a million neurons per minute, as Neuroscientist Professor Susan Greenfield explains in her Christmas Lectures, the first to be given by a woman, in 1994. In order for our brains to be fully formed at birth, pregnancy would last 21 months, she adds, and our heads would be so big we would never make it out of the birth canal.

A year after birth, our neurons have started to make firm connections and are covered in insulation, which helps them to orchestrate complex movements.

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By the time we approach adulthood, the brain has changed in dramatic and surprising ways. Rather than making new connections, “at 16 you’ve been losing connections since the age of two,” Greenfield says. You might think that’s bad news – after all, at this point you will have lost half of the connections in your brain, she adds. But this is actually a crucial process that sculpts the brain in response to our experiences.

After a flurry of connections are made during early childhood, the brain prunes away the connections and circuits we don’t use, while strengthening those we use the most. This is key to developing skills such as learning languages (and is why new languages are harder to pick up after childhood) or sports, as each of us is then left with the most useful and important combinations of circuits to suit our lives.

“Something as simple as a change in what you’re doing can actually change the connections in your brain,” Greenfield says.

You are blind for two hours of the waking day

“Most people think vision is like a camera,” says Professor Bruce Hood, a psychologist from the University of Bristol who gave the 2011 Royal Institution Christmas Lectures. But we know from studies that brain only processes the central part of our field of vision, an area about the size of your thumb if you were to hold it out horizontally at arm’s length. In theory then, the rest should be blurry, and yet we experience our vision as crystal clear. How so?

The answer is that our eyes are always on the move, darting about four or five times every second. Without trying, we are constantly sampling our surroundings, and storing the information to build a complete and complex picture of the world around us.

This explanation creates another mystery, however. If our eyes are constantly moving, this should make the world seem distorted. “It would make you seasick,” says Hood. So the brain does something dramatic to fix this. It simply cuts out the information it receives from the eyes each time we make one of these movements, called saccades. It’s as if we go blind for a fraction of a second. The brain then edits out all these tiny gaps to recreate our seamless sense of vision.

“Your brain is making you blind,” says Hood. And if you were to add up all that time, you would be blind for about two hours of the waking day. “Clearly the mind is full of tricks that keeps the world looking rich and full of detail.”

We taste with our eyes

We often consider our senses as discreet experiences. We might smell and hear a delicious meal being prepared before we even see it, savour the taste, and appreciate how beautiful it looks on the plate.

But there’s more to the adage that we ‘eat with our eyes first’, as Colin Blakemore demonstrates with the help of a special guest, renowned wine-master Michael Broadbent. First he is given a red wine to blind-taste, and manages to describe it with astonishing accuracy, getting the year and the grape right, and even getting close to pinpointing the location of the chateau.

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The next red wine has Broadbent stumped, however, until Professor Blakemore reveals the trick – it’s a white wine that has been carefully coloured a deep red. “We did this deliberately, I should say, because we wanted to try and show the importance of colour in determining the total judgement of taste,” Blakemore confesses.

That was in 1982, and today we now understand much more about how the brain combines information from many senses at once to give us our sensory experiences. Listening to high-pitched music can make food taste sharper, certain colours are associated with sweetness, and people rate the same food as tasting better and denser when eaten from a heavier bowl, to give just a few examples.

10 Voyages Through the Human Mind by Catherine de Lange is out now (£12.99, Michael O'Mara)