Principles of grouping

The Principles of grouping (or Gestalt laws of grouping) are a set of principles in psychology, first proposed by Gestalt psychologists to account for the observation that humans naturally perceive objects as organized patterns and objects. Gestalt psychologists argued that these principles exist because the mind has an innate disposition to perceive patterns in the stimulus based on certain rules. These principles are organized into six categories: Proximity, Similarity, Closure, Good Continuation, Common Fate, and Good Form.

Irvin Rock and Steve Palmer, who are acknowledged as having built upon the work of Max Wertheimer and others and to have identified additional grouping principles, note that Werheimer's laws have come to be called the "Gestalt laws of grouping" but state that "perhaps a more appropriate description" is "principles of grouping."

Proximity
The principle of proximity states that, all else being equal, perception tends to group stimuli that are close together as part of the same object, and stimuli that are far apart as two separate objects. This allows for the grouping together of elements into larger sets, and reduces the need to process a larger number of smaller stimuli. For this reason, people tend to see clusters of dots on a page instead of a large number of individual dots. The brain groups together the elements instead of processing a large number of smaller stimuli, allowing us to understand and conceptualize information more quickly.

Similarity
The principle of similarity states that, all else being equal, perception lends itself to seeing stimuli that physically resemble each other as part of the same object, and stimuli that are different as part of a different object. This allows for people to distinguish between adjacent and overlapping objects based on their visual texture and resemblance. Other stimuli that have different features are generally not perceived as part of the object. Our brain uses similarity to distinguish between objects who may lay adjacent to or overlap with each other based upon their visual texture. An example of this is a large area of land used by numerous independent farmers to grow crops. Each farmer may use a unique planting style which distinguishes his field from another. Another example is a field of flowers which differ only by color.

Closure
The principle of closure refers to the mind’s tendency to see complete figures or forms even if a picture is incomplete, partially hidden by other objects, or if part of the information needed to make a complete picture in our minds is missing. For example, if part of a shape’s border is missing people still tend to see the shape as completely enclosed by the border and ignore the gaps. This reaction stems from our mind’s natural tendency to recognize patterns that are familiar to us and thus fill in any information that may be missing.

Closure is also thought to have evolved from ancestral survival instincts in that if one was to partially see a predator their mind would automatically complete the picture and know that it was a time to react to potential danger even if not all the necessary information was readily available.

Good Continuation
When there is an intersection between two or more objects, people tend to perceive each object as a single uninterrupted object. This allows differentiation of stimuli even when they come in visual overlap. We have a tendency to group and organize lines or curves that follow an established direction over those defined by sharp and abrupt changes in direction...

Common Fate
When visual elements are seen moving in the same direction at the same rate, perception associates the movement as part of the same stimulus. For example, birds may be distinguished from their background as a single flock because they are moving in the same direction and at the same velocity, even when each bird is seen - from a distance - as little more than a dot. The moving 'dots' appear to be part of a unified whole.

Similarly, two flocks of birds can cross each other in a viewer's visual field, but they will nonetheless continue to be experienced as separate flocks because each bird has a direction common to its flock.

This allows people to make out moving objects even when other details (such as the objects color or outline) are obscured. This ability likely arose from the evolutionary need to distinguish a camouflaged predator from its background.

The law of common fate is used extensively in user-interface design, for example where the movement of a scrollbar is synchronised with the movement (i.e. cropping) of a window's content viewport; The movement of a physical mouse is synchronised with the movement of an on-screen arrow cursor, and so on.

Good Form
The principle of good form refers to the tendency to group together forms of similar shape, pattern, color, etc. Even in cases where two or more forms clearly overlap, the human brain interprets them in a way that allows people to differentiate different patterns and/or shapes. An example would be a pile of presents where a dozen packages of different size and shape are wrapped in just three or so patterns of wrapping paper.