Pareidolia

It's not actually a face of any kind — just a yellow circle, two dark ellipses and some curved lines. Your brain does the rest, superimposing its "logic" on the world around it. Really think about that for a moment.

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“”You can’t just look at a cloud and say, ‘What an interesting lump of air molecules’. You have to say, ‘that looks a lot like a bear’. Or, especially, ‘a face’. We have face-recognition software built in.

—David McRaney

Pareidolia is the phenomenon of recognizing patterns, shapes, and familiar objects in a vague and sometimes random stimulus. It's the result of your brain trying to "make sense" of input that really has no sense to find in it. This is seen often in inkblot tests, where random splatters of ink suggest different images to different people (look, it's a conspiracy: they're all deliberately made to look like vaginas!) but also in cases of people seeing visions, ghosts, and other likenesses in what are actually just random patterns that happen to look like those things. It's part of the recurring discussion of representation in art (see The Treachery of Images) and is a fundamental component to understanding the philosophy behind modern art.

Psychology

Some people think that pareidolia is a side-effect of the human brain needing to very quickly recognise certain objects such as human faces or bodies — a form of Bayesian inference where we have more experience with actual objects than with random patterns that just look like those objects. For example, the shapes composing a face are more likely to correspond to a face than random patterns, so random patterns that are close to faces are interpreted actually as faces as the brain mistakes them for the real thing. Since humans are highly social and many of our interactions rely on very quickly gauging other people's moods by tiny hints in their facial expressions, most people are acutely receptive to such patterns. The emotions people can read from faces can also be exploited this way. Clock faces in clock-makers' shops will permanently show "ten past ten" because this is a happy face, and never "twenty past eight" - because this is a sad face. Meanwhile, designers have to be careful just in case what they've made accidentally resembles something else - such as when Nike had to withdraw a new design because people thought it looked too much like the word 'Allah' written in Arabic script — we know what shit that can cause.

Faces

Faaaaaaace! Oh, wait...

Faces are probably the most common form seen as an effect of pareidolia. Facial recognition occurs in a part of the brain known as the fusiform gyrus. Subjects shown unclear, fuzzy pictures and told beforehand that they will see a face show activation in the fusiform gyrus and report seeing a face even where there is none. Certain drugs and brain-injuries will completely rob you of this ability, and prosopagnosia, also known as "face blindness", is a neurological condition that prevents people from recognizing faces. Prosopagnosia also interferes with memory and has been a key condition when researching human-face recognition. Once thought to be extremely rare, this condition may occur in as much as 2% of the world's population.

Jiangang Liu et al. won the 2014 Ig Nobel Prize in Neuroscience for neural analysis of face pareidolia. They concluded:

“”Our findings suggest that human face processing has a strong top-down component whereby sensory input with even the slightest suggestion of a face can result in the interpretation of a face.

Examples

...and when you see it, you'll shit marble bricks.

Although pareidolia is most interesting when religious people see Jesus in a cheese toasty, there are numerous secular examples:

• The Rorschach test, or the famous "inkblot" test asks people what they see in otherwise random blobs of ink. The accepted standard answers for the first four are A) a bat, B) a bat, C) a bat, and D) my father killing my mother with a hypodermic needle.
• Volcano erupts into smiley face
• A cloud looks like a face and the Trump team says it's the Donald.
• The logo for the Ilfracombe Town Council met with criticism after people thought the stylised "i" looked a bit like a sperm.
• Charles Darwin in an eye scan
• David Beckham in some drying plaster.
• While Penn & Teller were testing pareidolia on people for their debunking show Bullshit! to see if people could see God, they found that someone managed to see the guitarist Slash in a piece of magnified salami. So yes, someone did see God.
• The infamous U.S. dollar bill folding tricks, giving 9/11 conspiracy theorists something to masturbate to.
• This house looks like Hitler (although, despite this being in the Daily Mail, they didn't comment on whether this moved the price up or down).
• This collection of "rock people" around the world.
• The London 2012 Olympic logo, famously, had at least three applied to it. A more light-hearted take on the jagged design suggested that it was Lisa Simpson performing fellatio while more seriously and (perhaps) more disturbingly, it was claimed in parts of the Islamic world that the logo was evidence of a Zionist conspiracy. In true conspiracy theorist fashion, this was because the numbers could be rearranged to spell ZION — although the fact that 2012 can be arranged into "ZION" in any font hardly crossed their minds, there was evidence that people were seriously running with this. In a twist of irony, other people complained that the logo looked like a swastika. Apparently it wasn't close enough for certain people.
• The things with faces meme — self explanatory, really.
• A devil's face spotted in a fresco by Giotto. The chief restorer Sergio Fusetti stated that it is probably intentional, reflecting a quarrel Giotto had with someone. Also, as art historian Chiara Frugoni points out, figures had been concealed in clouds in previous Renaissance paintings such as the knight in a painting of St Sebastian.
• Auditory pareidolia is familiar to radio operators who spend hours listening for faint CW signals in a noisy atmosphere. This form of pareidolia is heard as code symbols just below the threshold of intelligibility.
• Concerned parents groups also experienced audio pareidolia when searching for hidden messages in records played backwards. While a few records do have backwards messages recorded on them as a kind of Easter egg, most of the alleged backwards recordings of "worship satan!" in rock music aren't really there.
• The "Face on Mars", a part of the Cydonia region on the Red Planet, as imaged by the Viking 1 orbiter
• The "Mars rat" seen in a picture from the Curiosity rover.
• Eyes in Pyramids on maps.
• Towers underwater
• The Christian Cross in a Soiled Baby's Diaper and a potato
• This nebula. Some see a blue horse there, but looks far more like a blue dragon, complete with horns and smoke.

Ze math

$P(A|B)=\frac{P(B|A)\cdot P(A)}{P(B)}$
Bayes' Theorem

Consider the theorem named after Thomas Bayes in the mid 18th century. It allows us to successfully compute the likelihood that a particular hypothesis is true given certain amounts of evidence and a few other probabilities. It doesn't even require hard maths or precise numbers to calculate whether we will determine something to be of "high" or "low" probability. Firstly, the explanation of the terms (fuller explanations of the why and how can be found elsewhere) and what they mean in this case. As always, the piped probabilities like $P(A|B)$ are read as "probability of A, given B," or the probability that our hypothesis (A) is true given some evidence (B).

• $P(A|B)$ — The hypothesis we are testing — The probability that what we're seeing is a face (A) given that we see a face-like structure (B).
• $P(B|A)$ — The probability of seeing a face-like structure if we are looking at a face. The deformities required to make a human face not look like a face are extreme and beyond our normal experience. Indeed, even the most deformed of faces are recognised as faces — such is the power of our ability to recognise them. This probability is very high, if not near certain by definition.
• $P(A)$ — The prior probability of a face being around us. Given that we are social animals and interact with people on a near daily basis this probability can also be considered to be high.
• $P(B)$ The prior probability of encountering a face-like arrangement. Compared to the other two known values is relatively low.

So it can be seen that two high values in the numerator and a relatively small one in the denominator makes $P(A|B)$ quite high. Our brain does this calculation and thinks "this is a face-like arrangement of features, the odds of it being due to chance are low enough to discount so let's assume it really is a face." Pareidolia and psychological phenomena like it all hinge on $P(B)$, the probability of encountering a random arrangement of features to form a face. Or more specifically, because $P(B|A)$ is near certain, it is the ratio between $P(A)$ and $P(B)$ — how common a real face is to us (because of social interaction) compared to random noise forming a face — that dominates the result. We perceive $P(B)$ to be low compared to the others and conclude that we're seeing a face where there isn't one. Yes, the odds of a face randomly appearing in noise is very small, and we would be right to assume so. But the sheer amount of noise ensures that a face-like structure will appear at some point, and when it does we think it is an actual face and register it as such.

In a nutshell

Why do people supposedly see a woman in pictures sent from Mars by the Curiosity Rover and a very wide range of objects in pictures from Mars? For the same reason that people see Pepe the Frog in their toast, or Jesus in a tortilla. SciShow explains;

See also

• Apophenia
• Religious pareidolia
• Improbable things happen
• Face on Mars
• Mike Bara (who denied that pareidolia even exists, then showed around 100 examples of it)
• Electronic voice phenomenon
• Fun:Richard Dawkins' face found on tortilla
• Magical thinking
• Ideomotor effect

External links

• Entry in The Skeptic's Dictionary
• Things With Faces That Shouldn't Have
• Wiltshire Human Givens: Pattern Matching
• /r/pareidolia subreddit and imgur