Pareidolia is a psychological phenomenon in which the mind responds to a stimulus, usually an image or a sound, by perceiving a familiar pattern where none exists.
Common examples are perceived images of animals, faces, or objects in cloud formations, the Man in the Moon, the Moon rabbit, hidden messages within recorded music played in reverse or at higher- or lower-than-normal speeds, and hearing indistinct voices in random noise such as that produced by air conditioners or fans.
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Pareidolia can cause people to interpret random images, or patterns of light and shadow, as faces. A study found that objects perceived as faces evoke an early 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 that is seen for images of real faces.
Cognitive processes are activated by the "face-like" object, 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. 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.
Pareidolia can be considered a subcategory of Apophenia, unmotivated seeing of connections accompanied by a specific feeling of abnormal meaningfulness, Eearly stages of delusional thought, over-interpretations of actual sensory perceptions, as opposed to hallucinations. Apophenia has come to imply a universal human tendency to seek patterns in random information, such as gambling.
Rocks may come to mimic recognizable forms through the random processes of formation, weathering and erosion. Most often, the size scale of the rock is larger than the object it resembles, such as a cliff profile resembling a human face. Well-meaning people with a new interest in fossils can pick up chert nodules, concretions or pebbles resembling bones, skulls, turtle shells, dinosaur eggs, etc., in both size and shape.
The Rorschach inkblot test uses pareidolia in an attempt to gain insight into a person's mental state. The Rorschach is a projective test, as it intentionally elicits the thoughts or feelings of respondents that are "projected" onto the ambiguous inkblot images. Projection in this instance is a form of "directed pareidolia".
In his notebooks, Leonardo da Vinci wrote of pareidolia as a device for painters, writing, "If you look at any walls spotted with various stains or with a mixture of different kinds of stones, if you are about to invent some scene you will be able to see in it a resemblance to various different landscapes adorned with mountains, rivers, rocks, trees, plains, wide valleys, and various groups of hills. You will also be able to see divers combats and figures in quick movement, and strange expressions of faces, and outlandish costumes, and an infinite number of things which you can then reduce into separate and well conceived forms."
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.
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.
Pareidolia also arises in computer vision, specifically in image recognition programs, which can spuriously detect 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 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.
Electronic voice phenomena (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. A psychologist 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 one when the first sound 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.
Various European ancient divination practices involved the interpretation of shadows cast by objects. For example, in molybdomancy, a random shape produced by pouring molten tin into cold water is interpreted by the shadow it casts in candlelight.[citation needed]
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.
