Pattern perception is the way that the human mind seeks to filter, organize or group stimuli taken in by the senses. Much of the mind's information about the outside world is taken in via gestalt processing, in which objects or events are grouped together based on pattern perception. This perception is often very subjective, since the mind has a tendency to seek patterns even where they do not exist — a phenomenon known as illusory pattern perception. A person's pattern perception may vary depending on the actual stimuli presented, the patterns he or she expects to find, and his or her sense of control over a situation.
Much of the study of pattern perception has focused on visual patterns. Through gestalt processing a person's mind determines relationships among visual stimuli based on a number of criteria. All other factors being equal, objects that are close together are grouped together. For instance, if nine dots are arranged in a rectangle so that there is less horizontal distance than vertical distance between them, the mind will perceive them as three rows rather than three columns. On the other hand, if alternate columns are different colors, the mind will most likely perceive columns instead of rows regardless of proximity.
Other areas of pattern perception, however, are less dependent on the actual stimuli than on the relationship a person expects to find among data. One example would be a number of drawings containing optical illusions known as "ambiguous figures" that can be perceived as either a vase or as two faces looking at each other. If a person is told before seeing the picture that it is a vase he or she will most likely see a vase. The same person, however, will most likely see two faces if told before hand that he or she is going to see a picture of two faces.
A similar phenomenon occurs in people's perception of events. For instance, many people believe that the full moon causes people or animals to become hyperactive, moody or even aggressive. Scientific evidence indicates that this is not true. Those who hold this belief though are likely to remember strange incidents that occurred on the full moon. This type of selective memory leads to the perception of a pattern that reinforces a person's pre-existing beliefs.
While nearly all people experience illusory pattern perception to some degree, this tendency is increased by a person's sense that he or she has no control over the environment. Since a person's sense of well-being is often decreased by lack of control, he or she will compensate for it by perceiving patterns in random events. This form of self-deception, however, is not entirely negative since it can restore a person's sense of order and balance.
The tendency to find illusory patterns has other effects as well, such as increased creativity. This can be seen in the way the ancient Greeks created stories around constellations, which were based on their perception of the arrangement of stars. Children also often report seeing animals or other shapes in random cloud formations.