“Uncertainty and mystery are energies of life. Don’t let them scare you unduly, for they keep boredom at bay and spark creativity.”
– R. I. Fitzhenry
Which do you think you would find more stressful – knowing that there is a small chance you may receive an electric shock, or knowing that the shock is inevitable?
You might think that knowing a shock is definitely coming would cause you more stress, but a new study found the opposite.
The study, published in Nature Communications, found that situations in which subjects had a 50% chance of receiving a shock were the most stressful while 0% and 100% chances were the least stressful. People whose stress levels tracked uncertainty more closely were better at guessing whether or not they would receive a shock, suggesting that stress may inform judgments of risk.
For the experiment, 45 volunteers played a computer game in which they turned over rocks that might have snakes under them. They had to guess whether or not there would be a snake, and when there was they received a mildly painful electric shock on the hand. Over time they learned which rocks were most likely to harbor snakes, but those odds changed throughout the experiment, generating fluctuating levels of uncertainty.
Participants’ uncertainty that any individual rock would have a snake under it was estimated from their guesses using a sophisticated computational model of learning. This uncertainty matched the stress levels reported by participants, which was also tracked using measurements of pupil dilation and perspiration.
Lead author Archy de Berker (UCL Institute of Neurology) explained the findings:
Using our model we could predict how stressed our subjects would be not just from whether they got shocks but how much uncertainty they had about those shocks.
Our experiment allows us to draw conclusions about the effect of uncertainty on stress.
It turns out that it’s much worse not knowing you are going to get a shock than knowing you definitely will or won’t.
We saw exactly the same effects in our physiological measures – people sweat more and their pupils get bigger when they are more uncertain.
This is the first time that the effect of uncertainty on stress has been quantified, but the concept is likely to be familiar to many people.
When applying for a job, you’ll probably feel more relaxed if you think it’s a long shot or if you’re confident that it’s in the bag.
The most stressful scenario is when you really don’t know. It’s the uncertainty that makes us anxious. The same is likely to apply in many familiar situations, whether it’s waiting for medical results or information on train delays.
Stress in the modern world is often seen as a negative and counterproductive response, but the study also found a potential benefit:
People whose stress responses spiked the most at periods of greatest uncertainty were better at judging whether or not individual rocks would have snakes under them.
Senior author Dr Sven Bestmann (UCL Institute of Neurology) explains:
From an evolutionary perspective, our finding that stress responses are tuned to environmental uncertainty suggests that it may have offered some survival benefit.
Appropriate stress responses might be useful for learning about uncertain, dangerous things in the environment.
Modern life comes with many potential sources of uncertainty and stress, but it has also introduced ways of addressing them. For example, taxi apps that show where a car is can offer peace of mind by reducing the uncertainty about when it will arrive.
Real-time information boards at bus stops and train platforms perform a similar role, although this can be undermined by unspecified delays which cause stress for passengers and staff alike.