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Authors: Claudia Hammond

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Craig’s model of interoceptive salience can also make sense of Hoagland’s experiments with his wife’s raging temperature and the effect it had on her perception of time. The awareness that we are detecting warmth, itchiness, aches, thirst, hunger or pain comes through the anterior
insular cortex. Craig is proposing that this part of the brain gives us a reading of our emotional state from moment to moment across time – like a string of cut-out paper figures, each representing what he calls ‘an emotional moment’. It’s as though there is a line of ‘you’s going from the past, through the present and ahead into the future. The same system that indexes this succession of emotional moments could be used to count time. It could even explain the powerful emotional impact that music can have on a person. The same system that deals with emotions could count rhythm. The beauty of Craig’s idea is that it could also explain why fear slows time down. The succession of emotional moments needs to go faster in order to register the intensity of emotions in that terrifying moment. So the clock counts faster, making time feel slower.

It is becoming clear that there are more connections than were once realised between these different areas of the brain that deal with time. All four of the areas I’ve discussed seem to contribute, which might explain why deficits in time perception after a brain injury are rarely as bad as you might expect; damage to a single, tiny area can transform someone’s personality, ruin their memory or cause them to lose ability to speak or even comprehend other people’s speech, yet the problems with timing tend to be small and often apply only to one time-frame. This might be precisely because there is no single clock.

So neuroscientists know where the brain counts time, but the mystery remains as to
how
. Does information come in from the basal ganglia and the cerebellum and then somehow the frontal lobe counts up that information, giving
a sense of duration, or do we count up these emotional moments as Craig proposes? Either might be true. But there is one problem; with all the developments in neuroscience there is still no sign of this elusive clock to do the counting. There are several different theories about how the brain counts time and I’m going to look at some of the most influential. The chief area of debate concerns whether we measure time using memory, attention, a straightforward clock, a series of clocks or the everyday activity of the brain itself. Any theory needs to be able to explain why it is so easy to trick our sense of timing using the simple method below.

THE ODDBALL EFFECT

Imagine I were to play you a series of seven notes, all of which are identical except for the middle note – so three Cs, then a G, followed by three more Cs. Each note is of exactly the same length, but you would be convinced that the G lasted for longer. Likewise if I flashed up a sequence of pictures on a screen – giraffe, giraffe, giraffe, mango, giraffe, giraffe, giraffe – you would swear that the picture of a mango was on the screen for longer. It is as though time very briefly slowed down when you looked at the mango. This is known as the oddball effect. It is a basic error of timing which we make repeatedly and, simple as the test is, it can give us an insight into how a clock in the mind might work.

One solution that can account for the oddball effect is the minimalist clock model. The idea is that somewhere
inside the brain we have a pacemaker that ticks like a metronome, endlessly beating time. This is coupled with a counter that switches on at the start of a given time period and off at the end, counting up the number of beats which occurred. There are various theories about the precise mechanism, the most influential of which is called Scalar Expectancy Theory. The element of expectation comes in like this: if you are played two musical notes and asked to judge which was longer, your internal clock ticks away the milliseconds of the first note and counts them up. Then the second note is played to you. If it is the same length, you now have an idea of how long you would expect it to last. By comparing its actual duration with your expectation, you are able to judge whether it was longer or shorter. This theory can account for the oddball effect. The surprise of seeing a mango instead of yet another giraffe picture wakes you up emotionally which temporarily speeds up the ticking of the clock, leading the counter to count up more beats and giving you the impression that the mango was present for longer. The same happens with the first item in a sequence; its novelty emotionally arouses us very slightly, the clock ticks faster, more beats are counted and so it feels as though it lasted longer.

The problem with this theory is highlighted by studies where people are trained to discriminate between different time intervals. Musicians have the edge on the rest of us when it comes to estimating the passage of time. In Istanbul the Turkish psychologist Emre Sevinc conducted a cunning study where he measured the accuracy of time perception
in musicians using pairs of musical notes. People were asked to listen to pairs of notes and to say which pair had the smallest time interval between them.
24
We would expect a professional musician to find such a task easy, and they did, but what Sevinc wanted to know was whether such skills could generalise to other senses. So in the second part of the study the musicians were twice tapped on the hand. Again their task was to identify which pair of taps had the shortest interval of time between them. He was able to establish that skills in time-estimation can generalise to other senses. But, with the shortest time-scales of just 100 milliseconds, the non-musicians were equally skilled (or unskilled – it’s quite difficult), suggesting we might need different clocks for different time intervals. Similar studies with non-musicians have found that if you train people in this skill they improve quite quickly, and they can generalise their newfound skills in timing to other senses. But what they can’t do is to generalise to other time intervals. Even after the training if you play notes with longer time intervals between them, they are no better at making judgements than anyone else.

So if a single clock can’t do everything, does this mean that we have multiple clocks, each dealing with a different time span? If this is the case then somehow our brain manages to synthesise these different processes to give us a sense of time as one seamless stretch. Just as our brain takes the visual input from two eyes and adjusts it to give us a view that appears as one picture rather than two overlapping circles, so our brains make sense of the time cues we’re given from multiple processes. Some speculate that
we might have the equivalent of a bank of hourglasses in the brain, each pre-set to time a different interval. When you hear a starting tone in an experiment like the one above it sets off certain neural processes that do the equivalent of starting the sand falling through a set of hourglasses. At the next signal the sand stops, and depending on which hourglass has finished, you are given a duration. But then would every possible time interval require its own hour glass? There’s no sign of where this imaginary set of hourglasses might be, yet we can definitely give fairly good timings without a stopwatch and with practise we do get better. When you learn to drive you get used to how long a red light takes to change. Drive in a different country and a differing duration can take you by surprise. I know how long 40 seconds feels from making radio programmes where 40-second clips are so common, and therapists tell me the time-frame that they can best detect is 50 minutes, the standard length of a consultation. Even though they admit to finding therapy sessions with some clients more absorbing than others, they become adept at gauging when the time is almost up.

It is possible that the brain contains no specialised clocks, but instead possesses the ability to gauge size, whether in terms of length of time, number of sounds, distance, area or even volume. Even without rulers or measuring jugs, we are surprisingly good at judging magnitude. If people sustain damage to the area at the top of the head at the back, where the skull starts to curve downwards, they not only have difficulty judging distance, but the position and speed of objects too. This region, known as the parietal cortex, is
where we initiate an action which results in a movement. When a baby experiments to see what they can reach, push, lift, fit in their mouth or climb over, they are developing their parietal cortex.

Weber’s law states that errors of judgement rise in proportion to the magnitude of the property you’re judging. So if you are guessing a distance that’s a matter of several metres, any mistake you make will be smaller than if you guess a distance in miles. The Danish psychologist Steen Larsen proposes that since the same seems to happen with time, when we hold a particular duration in mind we somehow have an idea of a distance in time. As with geographical distance, small differences are less noticeable, the longer the time period we are considering. Weber’s law applies across species and regardless of the type of magnitude we’re estimating, so whether it’s babies being tested on their ability to compare the area of two pieces of coloured cardboard or pigeons being tested on the timing of beak-taps to get seed, the same thing happens. This suggests that judgements of size could hold the key to time perception.

So far the competing ideas I’ve covered for how we count time are these: the presence of a clock or series of clocks, a system based on emotional moments, or something simpler like an ability to gauge size. To work out which is the mostly likely explanation, the number three might help.

THE MAGIC OF THREE

The number three comes up a lot in research on time perception. Spoken language uses a three-second rhythmic
structure, with poets often writing three-second lines.
25
It is a time-frame that seems to appeal to us. You see it everywhere from the three-second stings used to break up radio programmes to those irritating start-up sounds on computers. The ethnologist Margret Schleidt worked with four different communities – Europeans, Kalahari Bushmen, Trobriand Islanders and Yanomami Indians – filming their daily lives and then timing everything from the movements of their heads to their feet.
26
She found that in all four cultures handshakes lasted – you’ve guessed it – three seconds. There seems to be an unspoken agreement on the appropriate time-frame for a handshake. If it is too long or too short you instantly become slightly wary.

It also comes up a lot in experiments on how long a ‘moment’ might last. In the eleventh book of his confessions, St Augustine declared that the past and the future are mental constructions that we can only see through ‘a window of presence’. A long line of researchers have tried to work out how long this ‘now’ or ‘moment’ might last. In 1864 the Russian biologist Karl Ernst von Baer proposed that different animals experience different lengths of moments. He defined these moments as the longest possible duration that could still be considered to be a single time-point. An hour is clearly too long, so is a minute, but many in the field feel a moment feels as though it lasts longer than a second, with the exception of the physicist Ernst Mach who wrote in 1865 that the maximum moment was a fraction of that at just 40 milliseconds.
27

More recent experiments suggest that a moment lasts between two or three seconds, which aligns not only with
what we see in poetry, but also in music, speech and movement. We seem to segment activities into a space of two or three seconds. Children with autism sometimes find time perception difficult, and if you play them a musical note and ask them to play it back to you for exactly the same length of time, whether it lasted one second or five, they will almost always play you a note of three seconds.

It is known from many classic studies on working memory that three seconds is the length of time we can keep something in mind without writing it down or devising a way of committing it to long-term memory. So if someone tells you a phone number you are able to dial it immediately as though you are reading it from your mind, but if you are distracted (and just pressing the correct buttons on a mobile to stop one call and start the next would be enough)
or
if you wait more than three seconds it is very difficult to do. It is as though every few seconds the brain asks what’s new.

One of the most important questions we’ve been discussing when it comes to how the brain measures time is how a mental clock or series of clocks can deal with different time-frames. Could the same fast pulse in the brain beat out five minutes as well as 100 milliseconds or would you need an entirely separate clock? If there are different clocks for different durations, where are the boundaries? This is where the three seconds come in. Experiments have demonstrated that the most definitive boundary in the way we judge different time-frames is between 3.2 and 4.6 seconds.
28

We saw at the beginning of this chapter that a surprising number of different parts of the brain are involved in time
perception. Maybe this is because we need to deal with so many different time-frames. We shouldn’t expect the sensation of two clicks on a Savart wheel to be measured in the same way as Michel’s freezing nights in his black ice cave. The German psychologist Ernst Pöppel suggests two different mechanisms – one for short durations and one for long. Others suggest that there might be a whole series of clocks for different durations, clocks which could sometimes overlap. I like to imagine it like a newsroom where each clock is set to a different time zone, but with a clock for every duration. Yet if this were the case then why can the same time-period feel longer if we are listening to a sound than looking at a picture? Would we need a whole new set of clocks for each of our senses?

It is possible that different areas of the brain measure different time-frames using distinct mechanisms. We know from research on the emotions that the brain is not designed like a neat, ceramic phrenological head divided into different sections for different emotions, but that each emotion uses a different combination of brain systems. Could the same be true of timing? Could the brain use different combinations of areas to assess durations of different lengths?

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