SENSATION AND PERCEPTION
The
Senses
Sensation is
the process by which physical energy from objects in the world or in the body
stimulates the sense organs. The brain interprets and organizes this sensory
information in a process called perception. Psychophysics is
the study of how the physical properties of stimuli relate to people’s
experience of stimuli. Research in psychophysics has revealed much information
about the acuity of the senses.
Measuring
the Senses
Psychologists assess the
acuity of the senses in three ways:
1. Measuring
the absolute threshold
2. Measuring
the difference threshold
3. Applying
signal detection theory
The absolute
threshold is the minimum amount of stimulation required for a person
to detect the stimulus 50 percent of the time. The difference threshold is
the smallest difference in stimulation that can be detected 50 percent of the
time. The difference threshold is sometimes called the just noticeable
difference (jnd), and it depends on the strength of the
stimulus.
Example: If
someone were comparing two weak stimuli, such as two very slightly sweet
liquids, he’d be able to detect quite a small difference in the amount of
sweetness. However, if he were comparing two intense stimuli, such as two
extremely sweet liquids, he could detect only a much bigger difference in the
amount of sweetness.
Weber’s Law
Nineteenth-century
psychologist Ernst Weber proposed a principle demonstrating the fact that we
can’t detect the difference between two stimuli unless they differ by a certain
proportion and that this proportion is constant. In other words, the just
noticeable difference for a stimulus is in a fixed proportion to the magnitude
of a stimulus. Weber’s Law holds true except in the most extreme kinds of
stimulation.
Researchers use signal
detection theory to predict when a weak signal will be detected. This
theory considers the fact that the ability to detect a signal depends not only
on the strength of the signal but also on the perceiver’s experience,
motivation, expectation, and degree of alertness. Different people respond
differently to the same signal, and the same person may detect a particular
signal at one time but not another. Furthermore, people can often detect one
type of signal in a sensory modality such as hearing or vision but be oblivious
to other types of signals in the same sensory modality.
Sensory
Adaptation
When people walk into a
restaurant, they probably notice food smells right away. However, as they sit
in the restaurant, the smells gradually become less noticeable. This phenomenon
occurs because of sensory adaptation. Sensory adaptation is
the decrease in sensitivity to an unchanging stimulus. The smells don’t
disappear—the people just become less sensitive to them.
Development
of the Senses
Babies have all the basic
sensory abilities and many perceptual skills, but these abilities develop and
grow more sensitive over time. Babies can recognize the difference between a
human voice and other sounds, and they can locate a sound’s origin. They can
recognize the difference between smells and, very early on, can recognize their
mother’s particular smell. As for taste, they can differentiate between sweet
and salty. Babies also have fairly adept visual abilities. Soon after birth,
they can distinguish objects of different colors and sizes. When they are just
a few weeks old, they begin to differentiate among contrasts, shadows, and
patterns, and they can perceive depth after just a few months.
Sensitive
Periods
Even innate perceptual
skills need the right environment to develop properly. A lack of certain
experiences during sensitive periods of development will impair a person’s
ability to perceive the world.
Example: People
who were born blind but regain their vision in adulthood usually find the
visual world confusing. Since these adults were blind in infancy, they missed
the sensory experiences necessary for their visual system to develop fully.
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