Perception is the process by which human beings and other organisms sense, know, and understand their environment. The world around us consists of various kinds and levels of physical energy. Our knowledge of the world comes through our sense organs, which react to these energies. For example, certain wavelengths of electromagnetic energy stimulate our eyes. Our eyes have the ability to translate these waves of electromagnetic energy into the experience of light. Our noses and tongues are sensitive to certain kinds of chemical stimuli—that is, changes in our surroundings that produce a response. These chemical stimuli are perceived as smell and taste. Sense organs in our skin respond to pressure, temperature changes, and other stimuli related to pain. Different organs in our joints, tendons, and muscles are sensitive to body movement and position.
Sense organs convert various environmental energies into nerve impulses. These impulses are transmitted through the nervous system to the brain, which organizes and interprets the signals. Through the physical process of perception, the patterns of energies become known, or perceived, as objects, events, people, and other aspects of the world.
Part of what we perceive comes through our senses from the object or event before us, but another part is produced by our brain. We see light and color, but there is no light or color in the electromagnetic waves that stimulate the eyes. In the same way, there is no music or noise in the vibrations that stimulate the ear. The brain organizes and interprets nerve impulses from the eyes as light and color, and impulses from the ears as sound. The sense organs and the brain transform physical energy from environmental stimuli into information about the objects and events around us.
The process of translating the physical world into our experience is incredibly complex. Yet the human brain accomplishes this task so well that we rarely think about it. For example, tall buildings appear smaller when they are far away. However, our brain is aware that the small objects we see are sometimes large objects viewed from a distance. Thus, we do not perceive the far away buildings as small objects.
Factors affecting perception
Various factors influence what and how we perceive. The ways our bodies are structured to receive and process stimuli from the environment influences our perceptions. Our emotions, needs, expectations, and learning also affect our perceptions.
Receptors.
Each sensory system, such as vision or touch, has its own specialized receptors in the body. These receptors convert energy from the environment into nerve impulses. The human eye, for example, has two major kinds of receptors in the retina (the light-sensitive part of the eye). These receptors are called rods and cones. The rods respond to light but not to color—that is, different frequencies of light. The cones, on the other hand, do respond to different frequencies of light. The rods allow us to see in dim light, and the cones enable us to see colors and sharp detail in bright light.
At night, people tend to rely more on rods than cones for vision. This can be demonstrated by a simple experiment. After standing in a well-lit room, turn off the lights. You will likely find that it takes some time before you are able to see objects in the dark. This occurs because the rods are starting to activate as the cones become less active. The particular ways that receptors function helps determine the perceptual effects related to them.
The brain.
The human brain is organized into different areas that specialize in translating sensory information. The brain has distinct regions where it processes touch, taste, smell, vision, and hearing. The brain blends the sensory impulses from the senses together to create our experiences. For example, when you watch a motion picture, various elements of the movie represent different kinds of stimuli. The music, dialogue, costumes, scenery, and other effects are all separate stimuli transmitted through various senses. Your brain processes these stimuli separately and blends them together to create the experience of the movie. Scientists do not fully understand how the brain manages the vast amounts of sensory information to create our experiences.
Learning, emotion, and motivation.
Early experiences, learning, emotion, and motivation are all important in determining what and how people perceive. Scientists learn about how these factors affect perception by studying and comparing how people in different cultures perceive things. The perception of such things as form, color, pain, and touch may differ from culture to culture. The differences may be due to different environments, habits, customs, and training of children.
People may lose sensitivity to stimuli as the body adjusts to different environments. For example, jumping into a pool of cold water is often shocking. However, after a short time in the water, most people get used to the temperature and feel comfortable.
Emotions and motivation can also have an important effect on perception. At times, severe emotional disturbance can prevent perception completely, as when an emotional shock causes individuals to lose their hearing temporarily. We are also more likely to perceive those aspects of our environment that are related to our motives. For example, hungry people may perceive food as larger or more colorful than usual.
Understanding perception
Types of perception.
Perception has three levels of complexity: (1) detection, (2) recognition, and (3) discrimination. Detection refers to whether people can sense that they are being stimulated by some form of energy. Recognition means being able to identify as well as detect a particular pattern of stimulation. Discrimination means being able to perceive patterns of stimulation as different. For example, a person may hear slight differences between two similar musical tones.
Principles of perception.
There are a number of general principles that help us understand the process of perception. Manipulating objects in certain ways can cause inappropriate interpretations of images, called illusions, that help illustrate these principles.
One of the most important principles of perception is closure. This principle points out that people have a tendency to perceive things as complete and unified. People tend to “fill in” parts that are missing, or parts that conform to an overall impression. Read the phrases inside the two triangles at the top of the illustration with this article. Did you see the duplicate words? Most people do not. In learning to read, we learn not to perceive each letter and word separately. As our skills improve, we become increasingly able to scan the overall pattern and “fill in” the rest. Therefore, an experienced reader has a greater chance of overlooking the duplicated word in each phrase than does a beginning reader.
The principle of constancy states that despite changes that occur in stimulation, we tend to perceive objects as constant in size, shape, color, and other qualities. For example, an orange will be perceived with its characteristic color under different kinds of light.
Another important principle relates to perceptual context. The perception of an object or event depends in part on the context (surrounding conditions). For example, background intensity and color may affect the color and intensity of elements upon it. Look at the two rectangles containing the words World Book in the illustration. Do they look the same? To most people, the letters surrounded by black seem brighter and larger than the letters surrounded by gray. However, the words are printed with the same ink and are the same size. The effect is opposite with the two gray triangles with black and white detail. In this case, the gray with black detail appears darker rather than brighter.
