When several objects are present in the visual field we tend to perceive them as organized into patterns or groupings. Gestalt Psychologists studied such organizations. Organization in perception partially explains our perception of complex patterns as unitary form, or objects. We see objects as objects only because grouping processes operate in perception.
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Perceptual experience is filled with groups and patterns of stimuli which are labelled as objects. The stimulation that people are constantly perceiving comes into their awareness as shapes and patterns.
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People do not ordinarily perceive the world around them as patches of colours, variations in brightness and loud or high pitched sounds.
Instead, they see tables, walls and buildings and hear vehicle horns, footsteps and words. Some of these perceptions of objects are due to learning but a major part is probably an unlearned property of our sense organs and nervous system.
These structures tend to organize sensory inputs into perception of simple patterns or objects.
As mentioned before Gestalt Psychologists have extensively studied the organizing tendencies in perception. They have pointed to the existence of such tendencies to strengthen their argument that the perceived world is not just the scene of simple sensory experiences. The principles of perception that helps to explain, how objects are organized and perceived include:
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1. Figure-grouping perception;
2. Grouping;
3. Contour; and
4. Closure.
1. Figure-Ground Perception:
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The most fundamental organizational tendency is the perception of figure and ground. The objects that fill our everyday experience are seen as standing out from the general background of our experience.
Pictures hang on walls, words are on a page. Here the picture and words are seen as figures, whereas the wall and the page are seen as ground. Geometrical patterns are always seen against a background and thus appear to be like objects with contours and boundaries. This primitive capacity to distinguish an object from its general sensory background is basic to all object perception.
Geometrical patterns are always seen against a background and thus appear to be like objects, with contours and boundaries. Figure-ground organization is basic to stimulus patterning. Patterns do not have to contain identifiable objects to be structured as figure and ground. Patterns of black and white and many wall paper designs are perceived as figure-ground relationships.
Very often figure and ground are reversable i.e. they show a reversable relation. What appears as figure at one moment is perceived as ground the next moment; what is perceived as ground at one moment, is perceived as figure the next moment.
Studies show that figure-ground organization is present even when other features of perception are missing. Blind adult persons who get cured of blindness and see for the first time have no difficulty in seeing something as a figure on a background although they are unable to identify familiar forms by sight. A figure-ground relationship is perceived through senses also other than vision.
2. Grouping:
Another kind of organizing tendency in perception is called grouping. Whenever several different stimuli are present, we tend to perceive them as grouped into some pattern. Even simple patterns of line and dots fall into ordered relationships when we look at them.
We tend to organize various stimulus patterns according to a few basic principles of perceptual grouping. Perception is an active process because it not only selects a few stimuli but also combines them into a meaningful whole.
The principles of perceptual grouping include: proximity (nearness), similarity, continuity and symmetry. These are also known as Gestalt Principles in Perceptual Grouping.
Proximity:
With all factors constant, subgroups tends to be formed from parts which are spatially close to each other i.e. stimulus elements that are close together tend to be perceived as belonging together. The following example illustrates the principle:
The above figure is seen as three pairs of parallel lines (ab, cd, ef), instead of six vertical lines. Items which are close together in space or time tend to be perceived as belonging together or constituting a group. It is practically impossible to perceive b and c, and d and e, as being members of the same perceptual pair. The principle of proximity is not limited to spatial factors; temporal contiguity can also lead to grouping. For example, in a series of irregularly occurring tabs, those which appear close together in time will also tend to be grouped.
Similarity:
The principle of nearness does not hold for all stimulus constellations. In some situations other factors operate to over-ride the influence. With other factors constant, the elements of a collection will be perceptually grouped according to their similarity:
In the figure, each black square is nearer to a circle than it is to another black square, yet the black squares are perceived as being grouped with other black squares instead of with the circles which are close to them.
This perceptual phenomenon illustrates the principle of similarity. The greater the similarity among stimuli, the more likely they will be perceived as part of a common group.
Symmetry:
Grouping according to similarity however, does not always occur. Symmetrical regions of a field are more likely to be seen as figural than asymmetrical ones. In general, the tendency to group is a tendency to form a balanced or symmetrical figure that includes all the parts.
Continuity:
A collection of elements may be so arranged that as a viewer scans the array, the elements seem to be properly located with respect to each other just as the successive notes of a melody seem to fit together.
When such “good continuation” prevails in spatially distributed visual elements, it is as though a pattern were generated by the smooth movement of a single element over each of the positions occupied by the separate figures that made up the actual pattern. In simple words there is a tendency to group together stimulus elements that are part of a continuous sequence.
Common fate:
This principle relates to grouping based upon common movement or change among a collection of elements in the field. Common fate finds wide application in the field of choreography. When several dancers are involved, the tendency to follow those who execute the same movements transforms potential chaos into a complex procession of figural elements on a dynamic ground.
These principles of grouping, partially explain our perception of complex patterns as units or objects. We see objects as objects, units as units, only because grouping processes operate in perception.
3. Contour:
Objects are separated from the general ground in our visual perception only because we can perceive contours. Contours are formed whenever a marked difference occurs in the brightness or colour of the background.
Contours give shape to the objects in our visual field because they mark off an object from other objects or from the general ground. However, contours are not shapes. Contours determine shape, but by themselves are shapeless.
4. Closure:
Our perception of objects is much more complete than the sensory stimulation we receive from them. Perceptual processes tend to organize the world by filling in gaps so that we may perceive a whole object, not disjointed parts.
This filling in is termed closure, or the tendency to complete in perception what is physically an incomplete pattern or object. The principle has been referred to as the “Pragnanz Theory” in perception, indicating fullness, wholeness and completeness.
Gestaltists, as mentioned earlier, have emphasized the factor in pointing to perceptual organization. The human mind has a tendency to complete whatever is incomplete, because a symmetrical form is more satisfying than a non-symmetrical one.