How Do Our Brains Process Another Person's Gaze

How do we know when someone is looking at us' originally appeared on Quora - the knowledge sharing network where compelling questions are answered by people with unique insights. Answer by Paul King, Computational Neuroscientist, on Quora.There are several things going on when you see someone looking at you, all of which happen very quickly.This applies to actually seeing someone looking at you, not "sensing it" from behind or in the periphery.Primates (including humans) are unique in the degree to which the eyeball can move around in the eye socket. This allows visual attention to be shifted quickly without physically moving the head.Primates and certain other mammals can tell when another animal is looking at them, but humans are particularly good at doing this from a distance. In fact, humans have the added ability to be able to tell where someone is looking, even when it is not at them.It is easy to see why this skill confers an evolutionary advantage: By being able to do this, you can essentially "read out" the location of another animal's attention. If you are a social animal, and the one looking at you is a superior, you'd better behave. Or if it is an inferior, you are being challenged and need to respond so you don't lose your place in the status hierarchy. For humans, knowing where another human is looking allows you to read their mind regarding what they are thinking about. This is invaluable when trying to learn language, since it allows you to pair particular words with particular objects in the environment. Pointing is also effective for this.So, how do we do it'Detecting the direction of gaze has to do with noticing the relative location of the dark spot of the eye (the pupil and iris) in the context of the whites of the eye. The differential size and location of the white region shows where the eye is pointed. And if the pupil is exactly in the middle with equal white regions on each side, then the eyes are looking at you. We can see this from across the room. Head direction also provides a cue, which is primarily determined by where the region of the two eyes and the nose are relative to oval face region, with hair as another reference marker. When the head is turned, the brain has to do some geometry to determine gaze direction from both head angle and relative eye angle.
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