Perception

I

Introduction

Perception, process by which sensory stimulation is organized into usable experience. On a fairly simple level, perceptual psychology investigates such questions as how a frog distinguishes flies from the thousands of other objects in its world. On the more complex human level, perceptual psychology attempts to unravel such questions as how the brain translates stationary flashing lights into an illusion of motion, or how an artist responds to colours or shapes and translates them into painting.

II

Percepts

Perceptual psychologists recognize that most of the raw, unorganized sensory stimuli that come from seeing, hearing, and the other senses are almost instantaneously and subconsciously “corrected” into percepts, or usable experience. For example, a car moving along a road is seen as full-sized no matter how small or large the image it actually makes on the retinas of an observer's eyes. Similarly, a musical theme can be followed through a maze of individual notes and rhythms no matter how many times the composer has changed the key. Perception is not a simple matter of organizing direct sensory stimuli into percepts. Percepts themselves, gained from past experience, also become organized, thus greatly advancing the accuracy and speed of the individual's present perception.

The study and theory of percepts reach beyond academic psychology to possible practical applications in learning, education, and clinical psychology. To “underperceptualize”—to fail to organize sensory stimuli—often means to experience the world as chaos. To “overperceptualize”—to organize sensory stimuli to the extent that stimuli not fitting into that organization are shut off or stimuli are perceived when none exist—means to experience the world in a state of depression or hallucination.

Despite the fundamental role that perception plays in the lives of humans and all but the most simple animals, its processes remain largely obscure, for two main reasons: because researchers have had only limited success in breaking down perception into analysable units—and because empirical and scientifically verifiable findings are difficult to obtain or repeat, as the study of perception depends mostly on subjective and introspective reports.

III

Classical Theory

One phenomenon that researchers have attempted to explain is the principle of perceptual constancy. Once an object has been perceived as an identifiable entity, it tends to be seen as a stable object having permanent characteristics, despite variations in its illumination, the position from which it is viewed, or the distance at which it appears. Therefore, although a given object produces a much smaller retinal image at 100 m than at 20 m, it tends to be perceived as having an intrinsic size.

According to the classical theory of perception advanced by the German physiologist and physicist Hermann Ludwig Ferdinand von Helmholtz in the mid-19th century, constancy—as well as depth perception and most other percepts—is a result of an individual's ability continually to synthesize past experience and current sensory cues. As a newborn animal or a human infant explores its world, it soon learns to organize what it sees into a three-dimensional pattern, taking as its guides largely those discovered by Leonardo da Vinci: linear perspective, occlusion of a far object by a near one, and increasing haze as objects become more distant.

Using tactile and audio cues as well, the growing infant quickly learns a host of specific associations that correspond to the properties of objects in the physical world. Such associations, or percepts, are made automatically and with such speed that even a trained adult cannot decipher, with any degree of accuracy, the visual cues from which they are derived.

Proponents of the classical theory of perception believed that most percepts are derived from what they called “unconscious inference from nonnoticed sensations”. Only when one is experiencing an illusion or misreading visual cues, as when cars and houses appear like toys from the altitude of an aircraft, does one become aware of such sensations and gain some insight into their role in the organization of percepts. Much experimental research in perception consists of testing subjects with illusory material in an attempt to separate individual perceptual units from the process as a whole.

IV

Gestalt Theory

According to Gestalt psychology, which gained popularity after World War I, perception is to be understood not by analysing isolated units such as single sensations, but by taking into account total configurations (German, Gestalten) of mental processes. In this view, the real perceptual unit is the form: a mental structure that takes its attributes from a corresponding structure of brain processes. Experiments by proponents of the Gestalt theory showed that perception of form does not depend on perception of individual elements making up the form. Thus, “squareness” can be perceived in a figure made up of four red lines as well as in one of four black dots. Similarly, the mind experiences music not as a compounding of individual notes from various instruments and voices, but according to laws of organization by which the individual perceives a single, organized unit from beginning to end.

Although the Gestalt movement made important contributions to learning and the creative process, the introspective reports that it depended on to explain perception remained too subjective to be of much scientific value. Furthermore, the “innate physiological processes” to which the Gestaltists attributed their laws of organization have been largely discredited.