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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.
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 is actually just random patterns that happen to look like those things.
It is thought 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 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 gauging other's moods by tiny hints in their facial expressions very quickly, most people are acutely receptive for such patterns. The emotions people can read from faces can also be exploited this way. Clock faces in shops will be permanently at "ten past ten" because this is a happy face, and never at "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 the case when Nike had to withdraw a new design because people thought it looked too much like the word 'Allah' - we know what shit that can cause.
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 the name for a neurological condition that prevents people from recognising faces. Prosopagnosia also interferes with memory and has been a key condition when researching human face recognition. Once thought to be extremely rare, the prevalence of this condition in the worlds' population may be as high as 2%.
- 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.
- The logo for the Ilfracombe Town Council met with criticism after people thought the stylised "i" looked a bit like a sperm.
- 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 don't comment on whether this moves the price up or down.)
- This collection of "rock people" around the world.
- The London 2012 Olympic logo has had at least three applied to it famously. A more light-hearted take on the jagged design suggest that it is Lisa Simpson performing fellatio while more seriously and (perhaps) more disturbingly, it has been claimed in parts of the Islamic world that the logo is evidence of a Zionist conspiracy. In true conspiracy theorist fashion, this is because the numbers can be rearranged to spell ZION - although the fact that 2012 can be arranged in to "ZION" in any font hardly crosses their mind, there is evidence that people are 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. Claimed by art historians to be intentional based on the fact that figures have been concealed in clouds in previous renaissance paintings.
- 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 "Mars rat" seen in a picture from the Curiosity rover.
- Eyes in Pyramids on maps.
- Towers underwater
 Ze math
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 are read as "probability of A, given B," or the probability that our hypothesis (A) is true given some evidence (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).
- - 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.
- - 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.
- - 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 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 , the probability of encountering a random arrangement of features to form a face. Or more specifically, because is near certain, it is the ratio between and - 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 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.
 See also
- Entry in The Skeptic's Dictionary
- Things With Faces That Shouldn't Have
- /r/pareidolia subreddit and imgur
- ↑ Nike to trash trainers that offended Islam, The Independent
- ↑ See the Wikipedia article on Fusiform gyrus.
- ↑ Summerfield et al. Mistaking a House for a Face: Neural Correlates of Misperception in Healthy Humans. Cerebral Cortex, Vol. 16, Issue4, pp. 500-508.
- ↑ What has been seen cannot be unseen... (How Guardian editors accepted that pun as a headline might be even worse.)
- ↑ Oh come on.
- ↑ 
- ↑ Continuous Wave, a carrier signal switched on and off in the patterns of Morse code
- ↑ http://www.space.com/21396-mars-rat-curiosity-rover-photo.html
- ↑ http://www.youtube.com/watch?v=jW1xQggvqhA,
- ↑ http://www.youtube.com/watch?v=eRUaxTF58js