Sadly, once we start full-time work not many of us get a chance for an afternoon nap. However, a study of 36 people by scientists at the University of California, Berkeley suggests that it can have an important effect on the way people perceive other people's emotions. In the study the participants were asked to rate four different categories of facial mood: fear, sadness, anger and happiness. They performed the task twice - once at midday and again at five in the afternoon. In between half the participants were allowed an afternoon nap of 60-90 minutes while the other half had to stay awake. Those people who had had a nap displayed an increased receptiveness to positive facial emotions while those who stayed awake were more receptive to faces depiciting anger and fear. The authors of the study pointed out that those people expected to make such judgements about these matters - for e.g. doctors, soldiers, new parents - are of often the ones who may be most at risk from sleep deprivation.