The feeling of being watched makes people act more honestly, even if the eyes are not real, a study suggests.
A Newcastle University team monitored how much money people put in a canteen "honesty box" when buying a drink.
They found people put nearly three times as much in when a poster of a pair of eyes was put above the box than when the poster showed flowers.
The brain responds to images of eyes and faces and the poster may have given the feeling of being watched, they say.
Over the course of 10 weeks, an A5 poster listing hot drink prices was placed at eye-level above the honesty box.
Each week, the poster featured different images of either flowers or a pair of eyes looking directly at the observer.
At the end of every week, the team calculated the total amount of money collected and the amount of drink likely to have been consumed.
Processing faces
Dr Melissa Bateson, a behavioural biologist from Newcastle University and the lead author of the study, said: "We found that people paid 2.76 times as much money when we put a notice on the wall that featured a pair of eyes as opposed to when the image was of some flowers."
