Just five cups a day could be enough to make your ears play tricks on you, according to researchers. In an experiment, volunteers who had consumed ‘high levels’ of caffeine thought they were listening to Bing Crosby singing White Christmas even though the song was not being played. In the tests, 92 volunteers were asked to listen to a constant fuzzy sound known as white noise. Professor Simon Crowe, of La Trobe University in Melbourne, said: ‘We also told them that within the white noise there may be parts of the song White Christmas and if you hear it, press a button. ‘We didn’t include White Christmas in the white noise but found that more people who were very stressed and had high levels of caffeine thought they heard the song. ‘The combination of caffeine and stress affect the likelihood of an individual experiencing a psychosis-like symptom.’ The team from the university’s School of Psychological Sciences found that five cups of coffee a day was enough to trigger this.