Time Warped (6 page)

He puts his survival down to his many years of experience skydiving. To him freefalling feels normal, so he didn’t panic. He’s not given up on the adventure sports either and is now building his own plane. Chuck believes that two
decades of skydiving have changed his perception of time, and not just when things are going wrong. To most of us five seconds seems like a short time, but he knows that it’s long enough to travel 1,000 feet when you’re falling. He now thinks that five seconds is a long time. His experience is a good illustration of the way we each create a sense of time in our minds. To understand how we do it, it is necessary to look at the way the brain counts time.

THE ALARM WENT
off at 5.00 a.m. It was the wet season in Costa Rica, and we had got used to downpours in which it seemed as though huge vats of water were being tipped from the sky. This morning though was calm and dry: ideal for a bird-watching expedition.

Ricky arrived exactly on time and spent some minutes carefully making a piratical skull cap out of his blue bandana. Once that was in place he topped it with a brown cap with the peak facing backwards. This headgear was decorated with an arrangement of twigs, leaves and bird feathers. Greying dreadlocks spilled out from under his hat and his weathered features were grizzled with a straggly, gorse-like beard. Our guide was a winning combination: Rastaman meets British naturalist David Bellamy.

Ricky, like many Costa Ricans, is a mixture of ethnicities. In his case part Afro-Caribbean and part Bribri, one of the indigenous groups of the country. As a boy he followed his friends in trapping birds and keeping them in cages. But unlike his friends he was never cruel. His grandmother
taught him to care for the birds – to admire them and then release them. As an adult he became a naturalist, and now he takes people from all over the world to see birds on Costa Rica’s Caribbean coast.

It was grey dawn and the sun couldn’t break through the cloud cover. This made the colours of the birds hard to see, but the Samasati valley was full of their sounds. Soon we heard the grating call of toucans and saw two flying overhead. When they landed at the top of a tall tree in the distance, one glimpse through the binoculars made it easy to see why so many tour agencies choose toucans for their logo. These were keel-billed toucans with green, red and yellow striped beaks with a streak of lime green across the top. In another tree we spotted a black-cheeked woodpecker that mimicked the exact movement of a toy I had on a spring on the end of my pencil at junior school.

And it wasn’t just birds that we saw. A bulky grey blob wedged in the fork of a tall, leafless tree turned out to be a female two-toed sloth. Sleeping, of course. Ricky told us that she would stay up there for days, venturing down only for her weekly defecation. Sloths are rather fastidious about their toilet, burying their deposits in the way cats do. This devotion to hygiene comes at a price, however, as many end up being killed by dogs while going about their ground-level business.

The morning was beginning to heat up and take on the familiar sticky humidity. We were tiring slightly. Then Ricky saw it. This was the bird we’d come to see, a bird with some most unusual skills – the rufous-tailed hummingbird. It was so small that it could almost have been a flying insect.
Weighing less than a large paperclip it hovered in mid-air, dipping its curved red beak into the flower heads, its wings whirring in a figure of eight too fast for the human eye to see. What we could see was its emerald green head and the famous rust-coloured tail.

Hummingbirds, or ‘hummers’ as their biggest fans like to call them, are the only birds in the world that can fly backwards. Quite a trick. But what is also fascinating about the hummingbird is its ability to judge the passage of time. Just as humans can guess when 20 minutes have passed, so can hummingbirds.

They visit a plant, hover there, wings ablur, while they dip their stick-thin bills and elongated tongues into the long flower tubes and suck out the nectar. Having had their fill, they move on. The rufous-tailed hummingbird protects its source of food by aggressively seeing off any other birds that enter its territory, but it has a second technique of ensuring it gets to the nectar before anything else does. This is known as trap-lining and allows the hummingbird to calculate exactly when 20 minutes have passed – the time it takes for the flower to replenish its nectar. By returning with such precise timing the hummingbird beats other birds to this life-giving substance.

So we know that hummingbirds can judge the passage of 20 minutes, but have they evolved to measure
only
this interval or could they somehow learn to judge shorter time intervals too? To find out, researchers at Edinburgh University created fake flowers with a nectar replenishment cycle of 10 minutes instead of 20. Could the hummingbirds in the lab learn to judge when 10 minutes had passed?
It turns out they could.
²⁰
And it isn’t just exotic birds that possess this remarkable skill. The everyday feral pigeon can be trained to judge time intervals with a fair degree of accuracy too.

As we saw in the last chapter, humans have this ability too. We can detect the millionths of seconds necessary to locate the direction of a noise, but we can also make a stab at guessing the year of every individual memory we hold. In this chapter, I will consider the competing explanations for how the brain copes with this range of time frames. It feels as though there must be a clock in the brain that ticks away the milliseconds, seconds, minutes and hours, allowing us to make judgements about time, but so far neither through dissection or ever-improving brain scanning techniques has a single clock structure been found. Just as Einstein’s theory of relativity tells us that there is no such thing as absolute time, neither is there an absolute mechanism for measuring time in the brain.

We do have a body clock, but this only controls our 24-hour circadian rhythms. It has no role in the judgement of seconds, minutes or hours. What neuroscientists in this field are all trying to establish is how the brain counts time when there is no organ to do so.

Just as Chuck Berry’s experience of time was dilated by terror during his long fall through the sky, and Mrs Hoagland’s by her fever, it is clear that however the brain counts time, it has a system that is very flexible. It takes account of all the factors I discussed in the last chapter – emotions, absorption, expectations, the demands of a task and even the temperature. The precise sense we are using
also makes a difference; an auditory event appears longer than a visual one. Yet somehow the experience of time created by the mind feels very real, so real that we feel we know what to expect from it, and are perpetually surprised whenever it confuses us by warping.

You can easily test your own skills at time estimation by starting the stopwatch on your phone, looking away and then trying to guess when a minute has passed without counting in any way. Most of us are fairly good at it, but there is individual variation and our skills decrease with age. We are also easily distracted; people can estimate the length of a song fairly accurately if that’s all they are concentrating on, but if you ask them to focus on the pitch of the song as well, they will overestimate its duration. Not surprisingly, people who are particularly prone to boredom tend to give an underestimate of that minute passing. Time has dragged so slowly that they might think the minute is over in just 30 or 40 seconds.

Discussion of any of these studies can be confusing because there are two ways of measuring time estimation: prospectively – where you ask sometime to estimate a minute starting from now – or retrospectively, where you give them a task and then afterwards you ask them to guess how much time has elapsed. If time is moving slowly a person will
under
estimate the passing of a minute at the time, but if they’re asked afterwards they will
over
estimate the duration. Both signify time passing slowly. Imagine you’re at a play that is particularly dull. If while you sat impatiently hoping for the interval, you were asked to say when an hour had passed, time would be dragging so much
that you might guess an hour had passed after only 40 minutes. When the interval finally does arrive you look back and insist the first half felt like two hours rather than an hour. So, glancing at the figures, one looks like an underestimate and one an overestimate, but they both indicate the perception that time is slow-moving.

Although no single clock of the brain has been discovered, several areas have been found to be implicated in time perception, each of which also reveal something about our experience of time. Let’s begin with the cerebellum. This area at the back of the brain, down towards the nape of the neck, accounts for just 10 per cent of the brain’s volume yet contains half of all our brain cells. The cerebellum, which means ‘little brain’, helps us to co-ordinate movement by processing huge quantities of information from the rest of the nervous system. It is thanks to this part of the brain that when we wake up in the morning we can immediately detect the position in which we are lying (a sense known as proprioception) because the cerebellum is constantly monitoring the position of each limb. Though this might sound inconsequential, having met Ian Waterman, who contracted a rare neurological illness at the age of 19 which severed the pathways sending messages from his body to his cerebellum, it is clear that this sense is vital. He has now learnt to learn to walk again and can drive a car, but in order to do so he must watch his own arms and legs continuously, consciously observing and thinking about every movement he makes. If he loses his focus for just a second, an action as simple as holding an egg results in the egg either smashed on the floor or crushed in his hand.

Ian’s difficulties are caused by the loss of all sensation below the neck, which means that his peripheral nerves are unable to provide feedback to the cerebellum. With its sheltered position at the back of the brain it is rare for the cerebellum itself to become injured, but if it does it’s not only the smooth co-ordination of movement that is disrupted, but the perception of the tiniest fractions of time.

If you puff a tiny amount of air onto someone’s eyeball they will blink in discomfort, but if a signal is given beforehand, then, just as Pavlov’s dogs began salivating at the sound of a bell, a person will blink at exactly the right moment in anticipation of the puff of air. Unlike Pavlov’s classically conditioned reflex to salivate, this blinking demands precision-timing and it is the cerebellum which makes the calculation. The finding that a person with a damaged cerebellum loses this ability is so robust that in 2009 a team working with patients in Cambridge and Buenos Aires found that this air-puff test could be used to predict which patients in a persistent vegetative state might one day recover consciousness. But the strongest evidence of all for the involvement of the cerebellum in time perception comes from a more dramatic technique.

ELECTRIFYING THE BRAIN

When I was shown into the consulting room, an old lady was sitting on a chair in the middle of the room. She looked anxious. The doctor approached her head holding what looked like a giant version of those bubble blowers
which children play with at birthday parties. It was attached by a long curly wire to a trolley packed with electrical equipment. I’m afraid when the doctor insisted, in a mittel-European accent, that ‘zis is perfectly armless’ I couldn’t help but think I was in a sci-fi film, with the mad professor intent, despite his assurances, on electrocuting his elderly patient.

‘Look at zis!’ he said, placing the coil against his own head and flicking a switch. Suddenly one side of his top lip was twitching up and down in a sneer. ‘And I can do zis.’ He moved the coil to a different part of his head, switched the machine on again and one of his arms shot up in the air, in a slightly limp version of a Nazi salute. ‘Do you want a go?’ he said, lunging towards me with the big coil. I was sure I didn’t.

The doctor was demonstrating equipment that induces convulsions through a gentler version of electro-convulsive therapy. The elderly lady was about to try an even milder variant. This weaker coil would simply stimulate a specific area of the brain through a process called Transcranial Magnetic Stimulation, or TMS. She was putting herself through the process because she was so depressed that she felt suicidal. Nothing else had so far made her feel better.

The doctor spent a long time examining her skull. When he was certain he had found exactly the right place he picked up the second coil, counted down from 10 and then applied a series of pulses to her brain. She moaned quietly, more in fear than in pain. But even so, she was hoping for some relief. In trials many people have found this treatment
reduces their depression. She would now wait to see whether it would work for her.

The ability of this equipment to target precise areas of the brain makes it useful not only therapeutically, but also for identifying the parts of the brain involved in time perception. The electric pulses can temporarily disable a specific brain region without lasting side-effects and this has provided the strongest evidence to date regarding the involvement of the cerebellum in time perception. When this part of the brain was dampened down using TMS, people found it harder to estimate time. More specifically, it reduces people’s ability to perform in tests where they have to judge milliseconds, but makes no difference when the time intervals are many seconds long. To assess those we need to use another area of the brain.