Perception 2 Essay, Research Paper

Psychology: Experiments on Perception

by Peter Lafferty

The great cookie-cutter experiment

One of the basic questions examined by psychology is: ‘How do humans perceive things?’ Perception is the process of forming a coherent picture of the world. But how does perception work?

Until the 1960s, a rather simplistic view was taken of perception. The organs of perception the eyes and ears, for example were considered as passive receptors of data from the surroundings. It was thought that the act of perception simply consisted of constructing a world-picture from the external data. However, there were some early indications that this could not be the whole story.

Stimulus … and no response

Early experiments on perception maintained a person in as passive a condition as possible, so that he or she became a simple receptor. The person was then subjected to stimuli of various sorts sounds, flashing lights, and so on to see how the stimuli were perceived. These experiments produced alarming results: a person held in a completely passive condition did not perceive the world as made up of things and, furthermore, after a short time did not perceive anything at all! These experiments should have warned psychologists that something was wrong with their theories of perception. But psychologists are very conservative, and in the middle of the 20th century the experimental study of perception continued along lines established in the 19th century.

Another very simple experiment demonstrates that perception cannot be regarded as a completely passive process. When the head is moved, the images produced on the retina of the eye move; yet the world is perceived as stationary. Presumably, when a moving object passes in front of a stationary eye, the images on the retina move in much the same way. In this case, however, we perceive that it is the object which is moving. In other words, the same retinal stimulus can produce different perceptions.

Mr and Mrs Gibson’s work

The mechanism of perception was clarified by the work of US psychologist James Gibson in the early 1960s. Gibson was born in McConnelsville, Ohio, in 1904. He was educated at Princeton University. In 1932 he married his wife Eleanor, also a psychologist, and much of his later work was done in collaboration with her. Most of his work was done at Cornell University. He is credited with a discovery that revolutionized the teaching of pilots to land. He found that, as an aircraft descends, only one point appears not to change in relation to its surroundings; this is the point at which the aircraft will touch down. This discovery perhaps revealed to Gibson the importance of those things which appear unchanging in our environment. He put forward a new theory that perception was based on an active exploration of the world. According to Gibson, our world-picture is built up from observation of invariants or unchanging quantities.

Active exploration

To prove his ideas correct, Gibson undertook a series of experiments using cookie cutters, perhaps from his own kitchen. The cutters were of different shapes some square, some star-shaped, and so on. In the first part of the experiment, the cutters were pressed onto the upturned palm of a hand with a standard pressure. The subject was held still, and he could not see the cutter. This corresponded to the passive condition so well loved by earlier experimenters. It was found that only 29% of the subjects could correctly identify the shape of the cutter. Next, the subject was allowed to use his fingers to feel the cutter, to turn it, and actively explore the shape. Now 95% of the subjects identified the shape correctly. Another experiment was done in which the cutters were pressed to the palm of the hand, and then rotated gently. In this case, 72% of the subjects correctly identified the shape.

The best explanation of the results is that accurate perception of shape requires changing stimuli. The unchanging stimulus when the cutter is pressed onto the palm is least helpful in perceiving shape. The most accurate perception occurs when the fingers are used to actively explore a cutter; in this case, the subject receives changing stimuli not only from the hand but also from the arm and hand muscles. When the cutter is rotated on the palm, stimuli are received from the hand but not the arm an intermediate case. From among the changing stimuli, the brain extracts the unchanging information and constructs a picture of the cutter from this.

In this simple experiment, Gibson demonstrated that perception is a process of active exploration, not a passive reception of information. The reason why we know whether an object is moving, or whether our head is moving, is now clear. We receive information from our head muscles and neck joints when the head moves. Put another way, we use information which does not arise from external stimuli when we perceive the world

sense organ

Any organ that an animal uses to gain information about its surroundings. All sense organs have specialized receptors (such as light receptors in the eye) and some means of translating their response into a nerve impulse that travels to the brain. The main human sense organs are the eye, which detects light and colour (different wavelengths of light); the ear, which detects sound (vibrations of the air) and gravity; the nose, which detects some of the chemical molecules in the air; and the tongue, which detects some of the chemicals in food, giving a sense of taste. There are also many small sense organs in the skin, including pain, temperature, and pressure sensors, contributing to our sense of touch.

Animal senses

Research suggests that our noses may also be sensitive to magnetic forces, giving us an innate sense of direction. This sense is well developed in other animals, as are a variety of senses that we do not share. Some animals can detect small electrical discharges, underwater vibrations, minute vibrations of the ground, or sounds that are below (infrasound) or above (ultrasound) our range of hearing. Sensitivity to light varies greatly. Most mammals cannot distinguish different colours, whereas some birds can detect the polarization of light. Many insects can see light in the ultraviolet range, which is beyond our spectrum, while snakes can form images of infrared radiation (radiant heat). In many animals, light is also detected by another organ, the pineal body, which ’sees’ light filtering through the skull, and measures the length of the day to keep track of the seasons.