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Perception is the process by which we receive and
interpret information from the world around us. 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. Certain
wavelengths of electromagnetic radiation stimulate our eyes. Our ears sense
certain kinds of mechanical vibrations in the air. Our noses and tongues are
sensitive to certain chemical stimuli. Sense organs in our skin respond to
pressure, temperature changes, and various stimuli related to pain. Sense
organs in our joints, tendons, and muscles are sensitive to body movement and
position.
The sense organs change the various environmental
energies into nervous impulses, which go to the brain. Through the
psychological process of perception, the patterns of energies become known as
objects, events, people, and other aspects of the world.
The
process of perception does not reveal objects and events of the world. We see
light and colour, but there is no light or colour 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 nervous
impulses from the eyes as light and colour, and impulses from the ears as
sound. Together, the sense organs and the brain transform physical energy from
environmental stimuli into information about the events around
us.
When looking at the illustration on this page, you may first
see only a complicated pattern of dark and light areas. As you study the
pattern, your first perception may change, particularly if you are told that a
bearded man is in the picture. After you have seen the man, it will be almost
impossible not to see him when you look at the picture
again.
This picture emphasizes two important points about
perception. First, stimulation of the sense organs alone does not determine
the nature of what is perceived. Second, perception is a dynamic process of
"working on" sensory data to produce perceptual objects and events. The "work"
involves many physical, physiological, and psychological
factors.
Factors affecting
perception
Various factors influence what and how we
perceive. Our perceptions are influenced by the ways our bodies are structured
to receive and process stimuli from the environment. Our perceptions also
reflect our emotions, needs, expectations, and
learning.
Receptors. Each sensory system, such as vision,
hearing, or touch, has its own specialized body parts. These parts are called
receptors, and they change energies from the environment into nervous
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 the intensity of light, but not to different
frequencies of light (different colours). The cones do respond to different
frequencies of light, and are called colour receptors. The rods allow us to
see in dim light, and the cones enable us to see colours and sharp detail in
bright light. Thus, the particular ways that receptors are structured and
function help determine the perceptual effects related to
them.
The brain. Certain physical and functional features
of the brain also determine some aspects of perception. The part of the brain
that serves vision has different kinds of cells that respond only under
certain conditions of stimulation. Some of these cells respond only when a
light goes off. Others respond when a light comes on, but they stop responding
if the light stays on. Such cells also are arranged in special ways in the
brain, and this fact is related to how we perceive. For example, some cells
are arranged in columns or in clusters. Such arrangements are related to how
we perceive edges and forms. Experiments suggest that some cells in the brain
allow us to perceive movement. Thus, the structure of the brain is an
important element in perception.
Learning, emotion, and
motivation.
Much evidence points to the conclusion that early
experience, learning, emotion, and motivation are important in defining what
and how we perceive. Part of this accumulating evidence comes from experiments
that compare how people in different cultures perceive things. The perception
of such things as form, colour, pain, and touch may differ from culture to
culture, depending on habits and customs, and training of
children.
A simple example of how learning can affect perception
is provided by reading the phrases inside the two triangles in the
illustration on the next page. Did you fail to see the duplicate word in each
phrase? Most people do, and some continue to do so even with many repeated
readings. In learning to perceive words and sentences, we learn not to
perceive each letter and word separately. Instead, we become able to scan the
overall pattern and "fill in" the remainder. A poor reader is more likely than
a good reader to see the duplicate word in each phrase.
Some
illusions are related to learning and past experience. An illusion is not a
false perception, as many people believe, but one that is inconsistent with
another perception. Since perception does not literally reveal the
environment, no sensory system is closer to some absolute truth than any
other. We tend to check visual illusions against touch, but touch can involve
illusory effects, too. Look at the two triangular patches of grey containing
black and white detail in the illustration on this page. If you see the
patches as being different shades of grey, you are experiencing an illusion.
The patches are the same shade of grey.
Emotions and motivation
can have an important effect on perception. Sometimes a severe emotional
disturbance can prevent perception completely, as when emotional shock causes
individuals to lose their hearing temporarily. We are more likely to perceive
those aspects of our environment that are related to our motives. For example,
motivation can affect the perceived characteristics of objects. To hungry
people, food may appear larger or more colourful 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. For example, a light may be so dim they can barely detect its
presence. Recognition means being able to identify as well as detect a
particular pattern of stimulation. Discrimination means being able to perceive
one pattern of stimulation as different from another. For example, a person
may hear slight differences between two similar musical
tones.
The field of study that deals with levels of perception is
called psychophysics. Experimental psychologists investigate the relationships
between the physical properties of stimulus patterns and the perceived effects
of the stimuli. For example, they may study the relationship between sound
frequency and the perceived pitch of sound.
Principles of
perception.
There are a number of general principles that help us
understand the process of perception. One of the most important is the
principle of closure. It tells us that we have the general tendency to
perceive things as complete and unified. We tend to "fill in" parts that are
missing, or parts that conform to an overall impression.
The
principle of constancy states that despite changes that occur in stimulation,
we have a strong tendency to perceive objects as constant in size, shape,
colour, and other qualities. For example, an orange will be perceived with its
characteristic colour under different kinds of light.
The
opposite of the principle of constancy is also important. Sometimes an object
or pattern of stimulation will remain constant, but the perceived effect will
vary. Look at the grey and black cubes in the illustration on this page. At
one moment you will see three complete cubes, and at another you may see
five.
Another important principle relates to perceptual context.
The perception of an object or event depends in part on the context
(surrounding conditions). Look at the two rectangles containing the words
World Book in the illustration on this page. The words are printed with the
same ink. Do they look the same? Background intensity and colour may affect
the colour and intensity of elements upon it. To most people, grey surrounded
by black appears brighter and somewhat larger. This effect is called visual
induction. Notice, too, that the effect is opposite to that observed with the
two grey triangles with black and white detail. In this case, the grey with
black detail appears darker rather than brighter.
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