PERCEPTION

The science of perception delves into what many would deem to be optical illusions. Put simply, everything around us emits some sort of signal -- whether it is light, sound, or some other stimulation. Perception is how we utilize our minds to interpret these signals into a particular sound or a specific color. There is much debate as to whether perception is inborn or learned. It has been generally agreed on that while some aspects of the perceptual mind are accounted for at birth, much of our perception is determined by our experience. Through much research, psychologists have determined a number of tendencies in our perceptual views of the world.

One of the elementary aspects of perception deals with the issue of figure-ground reversal. This concerns a tendency of the eye to separate an object into the figure of focus and the background on which it is set. In the picture shown, some will see the dark region, a vase, as the figure while others view that as the background, making the two faces the primary feature. After a preliminary separation of the two areas, the eye will often reverse the two and view the picture in the opposite way. This results in the reversal.

[Figure-ground reversal]

Another important set of principles comes to us from the Gestalt philosophers, rules often referred to as Principles of Perceptual organization. These explain the brain’s tendencies when viewing a group of objects. One tendency is called proximity. In other words, the mind will group objects that are close together for matters of simplicity. Another method of organization is labeled similarity. By this, the mind groups similar objects together to form easily recognizable patterns. This may deal with the orientation or shape of the objects viewed. For example, if someone saw a group of X’s and O’s, they would tend to view the X’s as one group and the O’s as a second. Another phenomenon which Gestalt philosophers point out is called closure. In this, a common object which is drawn only partially may be seen as the complete object. For example, a circle with a slight gap in it would most likely be recognized as a circle, even though the visual stimuli is that of only a partial circle.

Yet another phenomenon of human perception involves real and illusionary motion. Ordinarily, if the stimulus is moving, the brain perceives motion. However, movement within the stimulus is not always necessary to create a perception of movement. This is demonstrated by the stroboscopic effect. This is the result of a repeatedly flashing light which creates the illusion of motion. The television is perhaps the most common example of this. The images seen on TV are nothing more than a series of still photos flashed in rapid succession. By virtue of the stroboscopic effect, this succession of pictures combine and appear to be in movement. In reality, the figures are not actually moving from within the television set, but we perceive motion even in its absence. Also apparent in this area is the phi phenomenon. This occurs when two lights are flashed rapidly in succession. The two lights are perceived as a single moving light, even though the individual lights are not moving.

The eye perceives movement in this image.

Now, we move on to constancies in our perceptual range. As is commonly known, objects which are farther away are perceived as being smaller. However, we have a sense of constancy when judging the size of a far away object. As an example, think of a basketball. Up close, you might see its diameter to be one foot. If the same ball was viewed from 30 feet away, the size may only appear to be an inch or so. However, if asked to estimate the size of the ball, one would probably guess its diameter within a fairly close range. This is because the mind accounts for the distance from which the object is being viewed and allows us to judge its size with high accuracy. Along the same line is shape constancy. If a plate were viewed from above, it would appear as a circle. If viewed from an angle, it would actually appear to have an oblong shape. The brain, once again, accounts for the change in angle and determines the shape to be round as well.

Next of importance is depth perception. How can we tell how far away an object is? The stimuli which makes this possible are called distance cues. There are two basic categories. The first, monocular cues, deals with those which require the use of only one eye to achieve. First is relative retinal size, meaning that farther away objects appear smaller. Also, farther objects seem to take on a bluish tint, though the full reason is not known. The third monocular cue is attributed to something called the texture gradient. As a general rule, objects that are very near appear to be sharper and more defined while further objects take on a coarse and rough texture, almost appearing fuzzy. By judging the texture, one can determine the distance. Another cue is the motion parallax. This is demonstrated by, for example, a person looking out of a car window. As the car drives by different objects, they seem to move at various speeds. Objects at further distances will always seem to be passing at a slower pace while nearby objects pass relatively quickly. The second category of distance cues involves the use of both eyes -- a binocular cue. Your two eyes, because of their slightly different orientations, receive slightly different views of visual stimuli. The brain analyzes both and comes up with a composite. The complex calculations of angles by which the object is viewed can be converted into a distance between the object and the viewer.