If you’ve ever felt like someone was watching you, you may have attributed that awareness to a sense of unease or a prickling on the back of your neck. But there’s nothing psychic about it; your brain was simply picking up on cues. In fact, your brain is wired to inform you that someone is looking at you — even when they’re not.

“Far from being ESP, the perception originates from a system in the brain that's devoted to detecting where others are looking,” writes social psychologist Ilan Shrira. This concept may sound confusing, but it actually makes a lot of sense when you think about it as a survival instinct.

Many mammals can tell when another animal is looking at them, but the human “gaze-detection system” is particularly good at doing this from a distance. We’re able to easily discern where someone is looking.

This system is especially sensitive when someone is looking at you directly, and studies have found that particular cells fire when this happens.

“Gaze perception — the ability to tell what someone is looking at — is a social cue people often take for granted,” Colin Clifford, a psychologist at the University of Sydney's Vision Center, told the Daily Mail. “Judging whether others are looking at us may come naturally, but it's actually not that simple as our brains have to do a lot of work behind the scenes.”

When you catch someone looking at you, what is it that clued you in? Often, it’s as simple as the position of the person's head or body.

If both the head and body are turned toward you, it’s clear where the person's attention is focused. It’s even more obvious when the person's body is pointed away from you but their head is facing you. When this happens, you immediately look to the person’s eyes to see where they're looking.

human eye and cat eyeThe whites of the eyes make it easy to determine a human's gaze, but that's not the case with all animals. (Photo: turlakova/Shutterstock)

Human eyes are different from those of other animals in this regard. Our pupils and irises are darker from the white part of the eyeball known as the sclera, and this contrast is why you can tell when someone's looking at you or simply looking past you.

Other species have less visible sclera, which is advantageous for predators that don’t want their prey to know where they’re looking. However, human survival is more dependent on communication, which is why we evolved to have larger, white sclera, which help us make eye contact.

But when head and body positions don’t provide much information, research shows that we can still detect another person’s gaze extraordinarily well because of our peripheral vision.

We evolved to be this sensitive to gaze to survive. Why? Because every look someone throws your way is a potential threat.

Clifford tested this by asking study participants to indicate where various faces were looking. He found that when people couldn’t determine the direction of a gaze — because of dark conditions or the faces were wearing sunglasses — people typically thought they were being watched.

He concluded that in situations where we’re not certain where a person is looking, our brain informs us that we’re being watched — just in case there's a potential interaction.

“A direct gaze can signal dominance or a threat, and if you perceive something as a threat, you would not want to miss it,” Clifford said. “So simply assuming another person is looking at you may be the safest strategy.”