(CCN) - A new study suggests that people may hear things when they drink too much coffee.
Researchers from La Trobe University in Melbourne, Australia describe caffeine as the most commonly used psychoactive drug.
They studied a group of volunteers who were told to consume high levels of caffeine and listen to a white noise machine.
The test subjects were told the Bing Crosby song "White Christmas" would play in the background, and if they heard it, they should press a button.
The song never actually played, but several subjects actually thought they heard it.
Researchers say the combination of caffeine and stress can affect the likelihood of a person experiencing psychosis-like symptoms, and that as little as five cups of coffee a day is enough to trigger the effect.