Uncertainty can cause more stress than inevitable pain

Knowing that there is a small chance of getting a painful electric shock can lead to significantly more stress than knowing that you will definitely be shocked, finds a new UCL study funded by the Medical Research Council (MRC). The study 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 judgements of risk. The experiment involved 45 volunteers who 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 harbour 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.