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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:
- Measuring the absolute threshold
- Measuring the difference threshold
- 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.
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.
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