When in doubt, the human brain is more likely to tell its owner that they're under the gaze of another person, researchers from the University of Sydney and The Vision Centre reveal in a recent article in Current Biology.
"Gaze perception - the ability to tell what a person is looking at - is a social cue that people often take for granted," says Professor Colin Clifford from the University's School of Psychology.
"Judging if others are looking at us may come naturally, but it's actually not that simple - our brains have to do a lot of work behind the scenes."
To tell if they're under someone's gaze, people look at the position of the other person's eyes and the direction of their heads, Professor Clifford explains. These visual cues are then sent to the brain where there are specific areas that compute this information.
However, the brain doesn't just passively receive information from the eyes. The study shows that when people have limited visual cues, such as in dark conditions or when the other person is wearing sunglasses, the brain takes over with what it 'knows'.
The researchers created images of faces and asked people to observe where the faces were looking.
"We made it difficult for the observers to see where the eyes were pointed so they would have to rely on their prior knowledge to judge the faces' direction of gaze," Professor Clifford explains. "It turns out that we're hard-wired to believe that others are staring at us, especially when we're uncertain.
So gaze perception doesn't only involve visual cues - our brains generate assumptions from our experiences and match them with what we see at a particular moment
There are several speculations to why humans have this bias, Professor Clifford says. "Direct gaze can signal dominance or a threat, and if you perceive something as a threat, you would not want to miss it. So assuming that the other person is looking at you may simply be a safer strategy.
"Also, direct gaze is often a social cue that the other person wants to communicate with us, so it's a signal for an upcoming interaction."
There is also evidence that babies have a preference for direct gaze, which suggests that this bias is innate.
"It's important that we find out whether it's innate or learned - and how this might affect people with certain mental conditions," Professor Clifford said.
"Research has shown, for example, that people who have autism are less able to tell whether someone is looking at them. People with social anxiety, on the other hand, have a higher tendency to think that they are under the stare of others.
"So if it is a learned behaviour, we could help them practice this task - one possibility is letting them observe a lot of faces with different eyes and head directions, and giving them feedback on whether their observations are accurate."