Perception

Perception studies have traditionally concerned with subjects like visual illusions, and depth or color recognition. At the present time, they are more concerned with the way people make use of their sensations, because the information that senses deliver must be grouped and categorized in order to be of any utility.

The classical perceptual theory--hold by Hermann Helmholtz (1821-1894) et al.--aimed at decomposing sensory experience into modalities: sight, touch, etc., and subdividing modalities into sensations. Perceptual experiences (or perceptions) were, under this theory, constructed from many sensations of different kinds. Sensations were essentially physiological phenomena in which neurons react to a particular type of energy. For example, a sensation was produced when the neurons of the retina were reached by light; the sense organ (the eye) would be responsible of the sensation of light and color. The relative brightness of an object, instead, was a perception that had to be learned by each individual.

Depth perception was explained similarly. The eyes would transmit to the brain the two-dimensional image of a landscape, and the brain would have to induce the third dimension from depth cues included in the image. Examples of depth cues are perspective and the hiding of one object by another. These cues, combined with sensations of muscular effort, would be stored in the brain and create in the subject the notion of distance. Thus, the perception of distance is also a learned one.

The preceding explanation, however, was shown to be faulty by experiments performed by E. L. Thorndike in 1899. These experiments made evident that at least some animals can respond adequately to visual depth cues of which they had no previous experience. Subsequent research has confirmed that depth perception can be innate rather than learned.

Perception issues

There are some issues related to visual perception that should be explained by any perception theory. One is the issue of constancy: how the mind realizes that a changing image corresponds always to the same object. A man that is approaching the observer has his image's size changed in the process. However, the perceived height of the man is always the same. Thus, the phenomenon of constancy helps us see the world better than what would be expected.

The issue of illusion refers to cases in which the image perceived by the senses does not accord with the characteristics of the object. For instance, the perceived size of line segments is affected if other lines are added to the drawing. It is difficult to explain what role does it play learning in making us perceive things that are not real.

The final issue is more complex and relates to the way in which the shape of figures is perceived in two-dimensional images. It has been observed that in certain cases a figure may be perceived as one object or another, but it cannot be perceived as both objects simultaneously. This is known as the organizational problem.

The Gestalt theory

'Gestalt' is a German word that means 'form.' It was also the name given to a German psychological school that opposed classical perceptual theory. Gestalt psychologists were intent on finding rules that governed perception. One such a rule was the 'law of good continuation,' which stated that people tend to give priority to the organization that breaks the fewer lines. They had various laws like this one, which tried to explain the issues previously exposed. Although lacking rigorous experimental confirmation, these laws did cover many strange aspects that occur in perception.

Gestalt's explanation of perceptual constancy was that the nervous system learns to identify a shape regardless of the background on which it is located. The psychological processes that Gestalt theory postulated in order to justify its laws, were later discredited. However, attempts have been made to substantiate them using other arguments. Nonetheless, the capital effect of Gestalt theory was to improve the classical theory of perception.

An attempt to explain constancies and illusions is the one that maintains that the person establishes visual associations related with the normal state of the world. For instance, perceived sizes are associated with distances, and so the visual system learns to take distances into account when estimating sizes. Of course, everything happens unconsciously, which makes hard to test this theory.

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