The ability to recognise faces is a useful skill that most humans possess, and which animals such as sheep also possess. It enables group members to recognise other members of the group, and to recognise when a non-member is approaching. However, this can lead to faces being seen even when no faces are in sight.

Pareidolia

Pareidolia is for 'alternative image'. It describes the phenomenon of interpreting random visual information as something recognisable. It can relate to seeing landscapes or animals in clouds or other abstract scenes, but also relates to seeing faces in everyday objects. Leonardo da Vinci described the phenomenon in one of his notebooks:

[W]hen you look at a wall spotted with stains, or with a mixture of stones, if you have to devise some scene, you may discover a resemblance to various landscapes, beautified with mountains, rivers, rocks, trees, plains, wide valleys and hills in varied arrangement; or again you may see battles and figures in action; or strange faces and costumes, and an endless variety of objects, which you can then reduce to complete and well drawn forms.
- translation taken from The Literary Works of Leonardo da Vinci, Jean Paul Richter, 1883.

There are various famous examples of pareidolia. The Shroud of Turin may be one. A cinnamon bun shaped like Mother Teresa that was found in 1996 is another. A face and a pyramid were even seen on Mars in photographs taken by the Viking Orbiter 1 space probe in 1976.

h2g2 Researchers have found examples of pareidolia, too. For example, they spotted a wooden locker with one or two faces on it, a dinosaur on a concrete floor and a face in a fragment of food.

The phenomenon can be exploited, especially in advertising. Face-like objects capture the attention more than objects without 'faces'. So for example, car headlights might be viewed as eyes, and the radiator grille as a mouth, or house windows might be eyes while a door is the mouth. Similarly, in advertising images, analogue clocks set to 10.08 are perceived as 'happy' as the hands make an upward V shape like a smiling mouth¹.

Facephenes

The term 'facephene', meaning 'illusory face', was coined in 2017 in a research paper² studying the effect of artificial stimulation of certain areas of the human brain.

Several areas of the human brain have been found to be involved with facial recognition - disruption or damage to those areas are causes of prosopagnosia (face-blindness). The Fusiform Face Area in the brain was first discovered in 1992 - during an MRI scan it can be seen to react when a person sees a face (and even reacts if a person touches a model of a face without seeing it). During the 2017 study, the Fusiform Face Area in the brain of a man with epilepsy was artificially stimulated using electrodes. The man reported seeing a face briefly appear when he looked at a box or a ball. When he looked at the experimenter's face while his Fusiform Face Area was being stimulated, the facial features became cartoon-like.

The Eyes Have It

Research in 2020³ found that faces seen through pareidolia also stimulated the Fusiform Face Area. So next time you see a house with eye-like windows and a mouth-like door, or a tree that appears to be staring at you through two knots in its trunk, you'll know there's a lot going on in your brain!