Paul Martin - Counting Sheep - The Science and Pleasures of Sleep and Dreams

Sleep-deprived people can often perform certain tasks reasonably well in short bursts, despite their fatigue. The real problems arise if they have to sustain their effort for any length of time. This lack of staying power was highlighted by experiments conducted in the 1950s at the Walter Reed Army Institute of Research in the USA. Sleep-deprived volunteers scored well in tests of reaction times when they were only required to react a few times over a period of one minute. But when they had to make lots of rapid responses spread irregularly over a period of 15 minutes, their performance fell apart. Sometimes they reacted quickly and sometimes they reacted very slowly or not at all. The more sleep-deprived they were, the more their responses varied. That experiment illustrates a general pattern that has emerged from studies of sleep deprivation – namely, that the performance of tired people becomes much more variable and inconsistent. Their accuracy and speed can fluctuate wildly over periods of a few minutes. In one study, for example, scientists monitored the performance of volunteers throughout an 88-hour period of total sleep deprivation. The subjects’ performance on a task requiring vigilance and coordination was much more variable (as well as just plain worse) than a comparison group, and the longer they went without sleep the more variable their performance became. These wild fluctuations in performance probably arose because their attention was repeatedly blotted out by microsleeps. As we saw earlier, someone who is very tired can lurch from wakefulness to sleep and back again in a matter of seconds without even noticing.

Much of the research on sleep deprivation has focused on how it impairs people’s ability to perform tasks requiring rapid but relatively simple decisions, involving very basic skills such as the ability to maintain attention under monotonous conditions. These skills are sensitive to sleep deprivation (which is partly why they have been so frequently measured) but they also have only a tenuous bearing on what happens in reality. The sorts of judgments and decisions we all have to make in real life usually demand far more than just the ability to stay awake and press buttons. Real decisions require us to assimilate and process complex, incomplete and often contradictory information, to keep track of our actions, assign priorities, ignore distractions and communicate with other people. The truly frightening aspect of sleep deprivation is the way it erodes all of these capacities.

Sleep-deprived people are bad at making complex decisions that require them to revise their plans in the light of unexpected news, to ignore irrelevant information and to communicate effectively. These are precisely the capabilities that we all need most when dealing with the vagaries of normal life – as do politicians, managers, doctors, military commanders and other key decision makers.

Even a single night without sleep will impair your ability to think flexibly and creatively. Sleep-deprived people perform badly on all aspects of creative thinking, including originality, flexibility, generating unusual ideas, being able to change strategy, word fluency and nonverbal planning. Tired people tend to persist with their current activity regardless of whether it is appropriate – a characteristic that psychologists call perseveration. In one cleverly revealing experiment, sleep-deprived volunteers played a realistic marketing game that required them to make complex decisions and then continually update those decisions in the light of new information. After 36 hours without sleep, the well-motivated subjects were still able to read and absorb written information. But their ability to make sound decisions based on that information deteriorated markedly. As they became more sleep-deprived they found it increasingly difficult to recognise when to change tactics in light of changed circumstances. Their thinking became rigid and they tended to persist with incorrect responses. Eventually, after 36 hours without sleep (the equivalent of losing just one night’s sleep) their ability to play the game collapsed.

Sleep-deprived people reveal their blunted creativity and mental inflexibility through alterations in their spoken language. After 36 hours of sustained wakefulness, people display a marked deterioration in verbal fluency and inventiveness. They are more reliant on routine responses and tend to become fixated with a particular category of words. They also start using inappropriate, monotonous or flattened intonation when reading out loud. Think about how people talk when they are drunk and you will get the picture. Tired people are bad at finding the right words. Their language becomes less spontaneous and expressive, and they are less willing to volunteer information that others might need to know. All in all, they are worse at communicating their thoughts, feelings, decisions and actions. Being a poor communicator is unhelpful, whether you are a head of state trying to deal with a crisis or simply someone who values their social life.

The supposedly robust adolescent is, if anything, even more vulnerable than older people. One study found that when youths aged 10–14 years were restricted to only five hours in bed for one night, their verbal creativity, verbal fluency and ability to learn new abstract concepts were all impaired. Less complex mental functions, such as rote learning, were unaffected by this modest degree of sleep restriction. So the sleep-deprived adolescent would still be able to go through the basic motions at school the next day, but would be unable to perform to anything like their true potential. And it is not entirely unknown for adolescents to go to school after getting less than a full night’s sleep.

As well as sapping our ability to perform, sleep deprivation also impairs our motivation. Tired people just can’t be bothered. In one experiment, researchers persuaded a group of male students to work continuously for 20 hours without sleep and then observed them in various social settings. Sleep deprivation diminished everyone’s performance, but the students who were working in groups performed even worse than those who were working individually. This was because working in a group gave them the opportunity to loaf – and they did.

Another alarming characteristic of sleep-deprived people, and something else they have in common with drunks, is their propensity to take risks. Experiments have shown that as people become more fatigued, they are more attracted by actions that might bring big rewards and less worried by the possible negative consequences of those actions. For instance, French scientists assessed the risk-taking propensities of military pilots who were involved in a maritime counter-terrorism exercise. This required them to make strenuous night flights, depriving them of sleep. The data showed that as the exercise progressed, the pilots became more impulsive. In effect, sleep-deprived people become more reckless and foolhardy. This is yet another characteristic that you would not wish to encounter in someone who is in charge of a hospital ward or a political crisis or a nuclear power station, or the family car for that matter.

It provokes the desire, but it takes away the performance.

William Shakespeare, Macbeth (1606)

Tired people resemble drunk people in several respects. Most obviously, tiredness and alcohol both hamper our ability to perform tasks that require judgment, attention, quick reactions and coordination – such as driving a car, for example. Missing a night’s sleep has an impact on driving skills comparable to drinking a substantial amount of alcohol. In both cases safe driving is no longer possible; in one case, however, it is both legal and socially acceptable.