
Pareidolia

Pareidolia (, ) is the tendency for perception to impose a meaningful interpretation on a nebulous visual stimulus (so that one sees an object, pattern or meaning where in fact there is none). 
Common examples are perceived images of animals, faces, or objects in cloud formations, or lunar pareidolia like the Man in the Moon or the Moon Rabbit. The concept of pareidolia may extend to include hidden messages in recorded music played in reverse or at higher- or lower-than-normal speeds, and hearing voices (mainly indistinct) or music, in random noise such as that produced by air conditioners or fans.
Pareidolia was at one time considered a symptom of psychosis, but it is now seen as a normal human tendency. Scientists have taught computers to use visual clues to "see" faces and other images.
Etymology.
The word derives from the Greek words "pará" (, "beside, alongside, instead [of]") and the noun "eídōlon" (, "image, form, shape").
The German word "Pareidolie" was used in articles by Karl Ludwig Kahlbaum — for example in his 1866 paper "Die Sinnesdelierien" ("On Delusion of the Senses"). When Kahlbaum's paper was reviewed the following year (1867) in "The Journal of Mental Science", Volume 13, "Pareidolie" was translated into English as "pareidolia", and noted to be synonymous with the terms "…changing hallucination, partial hallucination, [and] perception of secondary images."
Explanations.
Pareidolia can cause people to interpret random images, or patterns of light and shadow, as faces. A 2009 magnetoencephalography study found that objects perceived as faces evoke an early (165 ms) activation of the fusiform face area at a time and location similar to that evoked by faces, whereas other common objects do not evoke such activation. This activation is similar to a slightly faster time (130 ms) that is seen for images of real faces. The authors suggest that face perception evoked by face-like objects is a relatively early process, and not a late cognitive reinterpretation phenomenon. A functional magnetic resonance imaging (fMRI) study in 2011 similarly showed that repeated presentation of novel visual shapes that were interpreted as meaningful led to decreased fMRI responses for real objects. These results indicate that the interpretation of ambiguous stimuli depends upon processes similar to those elicited by known objects.
These studies help to explain why people generally identify a few lines and a circle as a "face" so quickly and without hesitation. (In autistic people, it was thought that fewer mirror neurons or mirror neurons not functioning properly may mean that everything is perceived as if it were an object. It does not now seem to be mirror neurons but clearly there are differences in perception in autistic people. People without an autism spectrum condition perceive the face quickly and without hesitation.) Cognitive processes are activated by the "face-like" object, at least in people who are not autistic, which alert the observer to both the emotional state and identity of the subject, even before the conscious mind begins to process or even receive the information. A "stick figure face", despite its simplicity, can convey mood information, and be drawn to indicate emotions such as happiness or anger. This robust and subtle capability is hypothesized to be the result of eons of natural selection favoring people most able to quickly identify the mental state, for example, of threatening people, thus providing the individual an opportunity to flee or attack pre-emptively. In other words, processing this information subcortically – therefore subconsciously – before it is passed on to the rest of the brain for detailed processing accelerates judgment and decision making when a fast reaction is needed. This ability, though highly specialized for the processing and recognition of "human" emotions, also functions to determine the demeanor of wildlife.
Mimetoliths.
A mimetolithic pattern is a pattern created by rocks that may come to mimic recognizable forms through the random processes of formation, weathering and erosion. A well-known example is the Face on Mars, a rock formation on Mars that resembled a human face in certain satellite photos. Most mimetoliths are much larger than the subjects they resemble, such as a cliff profile which looks like a human face.
Picture jaspers exhibit combinations of patterns such as banding from flow or depositional patterns (from water or wind), or dendritic or color variations, resulting in what appear to be miniature scenes on a cut section, which is then used for jewelry.
Chert nodules, concretions, or pebbles may in certain cases be mistakenly identified as skeletal remains, egg fossils, or other antiquities of organic origin by amateur enthusiasts.
In the late 1970s and early 1980s, Japanese researcher Chonosuke Okamura self-published a series of reports titled "Original Report of the Okamura Fossil Laboratory", in which he described tiny inclusions in polished limestone from the Silurian period (425 mya) as being preserved fossil remains of tiny humans, gorillas, dogs, dragons, dinosaurs and other organisms, all of them only millimeters long, leading him to claim, "There have been no changes in the bodies of mankind since the Silurian period... except for a growth in stature from 3.5 mm to 1,700 mm." Okamura's research earned him an Ig Nobel Prize (a parody of the Nobel Prizes) in biodiversity in 1996.
Some sources describe various mimetolithic features on Pluto, including a heart-shaped region.
Projective tests.
The Rorschach inkblot test uses pareidolia in an attempt to gain insight into a person's mental state. The Rorschach is a projective test that elicits thoughts or feelings of respondents that are "projected" onto the ambiguous inkblot images.
Literature and art.
Renaissance artists and authors have shown a particular interest in pareidolia. In William Shakespeare's play "Hamlet", for example, the character Hamlet points at the sky and "demonstrates" his supposed madness in this exchange with Polonius:
<poem>HAMLET
POLONIUS
HAMLET
POLONIUS
HAMLET
POLONIUS
Graphic artists have often used pareidolia in paintings and drawings: Andrea Mantegna, Leonardo Da Vinci, Giotto, Hans Holbein, Giuseppe Arcimboldo, and many more have shown images—often human faces—that due to pareidolia appear in objects or clouds.
In his notebooks, Leonardo da Vinci wrote of pareidolia as a device for painters, writing:
Architecture.
Two 13th-century edifices in Turkey display architectural use of shadows of stone carvings at the entrance. Outright pictures are avoided in Islam but tessellations and calligraphic pictures were allowed, so designed "accidental" silhouettes of carved stone tessellations became a creative escape. 
Religious.
There have been many instances of perceptions of religious imagery and themes, especially the faces of religious figures, in ordinary phenomena. Many involve images of Jesus, the Virgin Mary, the word Allah, or other religious phenomena: in September 2007 in Singapore, for example, a callus on a tree resembled a monkey, leading believers to pay homage to the "Monkey god" (either Sun Wukong or Hanuman) in the monkey tree phenomenon.
Publicity surrounding sightings of religious figures and other surprising images in ordinary objects has spawned a market for such items on online auctions like eBay. One famous instance was a grilled cheese sandwich with the face of the Virgin Mary.
During the September 11 attacks, television viewers supposedly saw the face of Satan in clouds of smoke billowing out of the World Trade Center after it was struck by the airplane. Another example of face recognition pareidolia originated in the fire at Notre Dame Cathedral, when a few observers claimed to see Jesus in the flames.
While attempting to validate that the imprint of a crucified man on the Shroud of Turin as Jesus Christ, a variety of objects have been described as being visible on the linen. These objects include a number of plant species native to Israel, a coin with roman numerals, and multiple insect species. In an experimental setting using a picture of plain linen cloth, participants told that there could possibly be visible words in the cloth collectively saw 2 religious words, those told that the cloth was of some religious importance saw 12 religious words, and those who were also told that it was of religious importance, but also given suggestions of possible religious words, saw 37 religious words. The researchers posit that the reason the Shroud has been said to have so many different symbols and objects is because it was already deemed to have the imprint of Jesus Christ prior to the search for symbols and other imprints in the cloth, and therefore it was simply pareidolia at work. 
Medical education, radiology images.
Medical educators sometimes teach medical students and resident physicians (doctors in training) to use the pareidolia and patternicity to learn to recognize human anatomy on radiology imaging studies. 
Examples include assessing radiographs (x-ray images) of the human vertebral spine. Patrick Foye, M.D., professor of physical medicine and rehabilitation at Rutgers University, New Jersey Medical School, has published that pareidolia is used to teach medical trainees to assess for spinal fractures and spinal malignancies (cancers). When viewing spinal radiographs, normal bony anatomic structures resemble the face of an owl. (The spinal pedicles resemble an owl's eyes and the spinous process resembles an owl's beak.) But when cancer erodes the bony spinal pedicle, the radiographic appearance changes such that now that eye of the owl seems missing or closed, which is called the "winking owl sign". Meanwhile, when viewing human spinal radiographs taken at a partially sideways angle (oblique view), there are parts of the bony that resemble the silhouette outline of a "Scotty dog". When there is a fracture of part of the spine called the pars interarticularis, it creates the appearance that the dog is now wearing a collar on its neck (the fracture line looks like a dog collar on the Scotty dog). This can help doctors to diagnosis this type of fracture. 
In 2021, Foye again published in the medical literature on this topic, in a medical journal article called "Baby Yoda: Pareidolia and Patternicity in Sacral MRI and CT Scans". Here, he introduced a novel way of visualizing the sacrum when viewing MRI magnetic resonance imaging and CT scans (computed tomography scans). He noted that in certain image slices the human sacral anatomy resembles the face of "Baby Yoda" (also called Grogu), a fictional character from the cable television show "The Mandalorian". Sacral openings for exiting nerves (sacral foramina) resemble Baby Yoda's eyes, while the sacral canal resembles Baby Yoda's mouth. These and other comparisons can help physicians to use the "Baby Yoda sign" to evaluate both normal and abnormal anatomic findings on the imaging studies.
Mars canals.
A notable example of pareidolia occurred in 1877, when observers using telescopes to view the surface of Mars thought that they saw faint straight lines, which were then interpreted by some as canals (see Martian canal). It was theorized that the canals were possibly created by sentient beings. This created a sensation. In the next few years better photographic techniques and stronger telescopes were developed and applied, which resulted in new images in which the faint lines disappeared, and the canal theory was debunked as an example of pareidolia.
Computer vision.
Pareidolia can occur in computer vision, specifically in image recognition programs, in which vague clues can spuriously detect images or features. In the case of an artificial neural network, higher-level features correspond to more recognizable features, and enhancing these features brings out what the computer sees. These examples of pareidolia reflect the training set of images that the network has "seen" previously.
Striking visuals can be produced in this way, notably in the DeepDream software, which falsely detects and then exaggerates features such as eyes and faces in any image.
Speech.
In 1971 Konstantīns Raudive wrote "Breakthrough", detailing what he believed was the discovery of electronic voice phenomena (EVP). EVP has been described as auditory pareidolia. Allegations of backmasking in popular music, in which a listener claims a message has been recorded backward onto a track meant to be played forward, have also been described as auditory pareidolia. In 1995, the psychologist Diana Deutsch invented an algorithm for producing phantom words and phrases with the sounds coming from two stereo loudspeakers, with one to the listener's left and the other to his right. Each loudspeaker produces a phrase consisting of two words or syllables. The same sequence is presented repeatedly through both loudspeakers; however, they are offset in time so that when the first sound (word or syllable) is coming from the speaker on the left, the second sound is coming from the speaker on the right, and vice versa. After listening for a while, phantom words and phrases suddenly emerge, and these often appear to reflect what is on the listener's mind, and they transform perceptually into different words and phrases as the sequence continues.
Related phenomena.
A shadow person (also known as a shadow figure, shadow being or black mass) is often attributed to pareidolia. It is the perception of a patch of shadow as a living, humanoid figure, particularly as interpreted by believers in the paranormal or supernatural as the presence of a spirit or other entity.
Pareidolia is also what some skeptics believe causes people to believe that they have seen ghosts.