CHAPTER 5 (SUMMARY): SENSATION
Sensation is concerned with how the outside world gets represented inside our heads, and we
are exquisitely sensitive to some of the stimuli around us. Research reveals that we process
some information from subliminal stimuli, but only under certain restricted conditions.
The task of each sense is to receive stimulus energy, transduce it into neural signals, and
send those neural messages to the brain. In vision, light waves are converted into neural
impulses by the retina; after being coded, these impulses travel up the optic nerve to the brain’s
cortex, where they are interpreted. The Young-Helmholtz and opponent-process theories
together help explain color vision.
In hearing, sound waves are transmitted to the fluid-filled cochlea, where they are converted
to neural messages and sent to the brain. Together, the place and frequency theories explain
how we hear both high-pitched and low-pitched sounds.
The sense of touch is actually four senses—pressure, warmth, cold, and pain—that combine
to produce other sensations such as “hot.” Taste, a chemical sense, is a composite of sweet,
sour, salty, bitter, and umami sensations, and of the aromas that interact with information from
the taste buds. Smell, also a chemical sense, does not have basic sensations as there are for
touch and taste. Our effective functioning also requires a kinesthetic sense and a vestibular
sense, which together enable us to detect body position and movement.
Sensing the World: Some Basic Principles
Sensation versus perception.
Sensation is the process by which we detect physical energy from our environment and encode it
as neural signals; it involves what psychologists call bottom-up processing. Perception is the
process of selecting, organizing, and interpreting sensory information, enabling us to recognize
meaningful objects and events; it involves top-down processing.
Absolute versus difference thresholds; research findings on subliminal stimulation.
In studying the relationship between physical energy and psychological experience, researchers
in psychophysics identified an absolute threshold as the minimum stimulation needed to detect a
particular stimulus 50 percent of the time. Signal detection theory predicts when and how we
detect the presence of a faint stimulus, assuming that our individual absolute thresholds vary
with our psychological state.
Recent research reveals that we can process some information from stimuli too weak to
recognize. But the restricted conditions under which this occurs would not enable advertisers to
exploit us with subliminal messages.
A difference threshold is the minimum difference between two stimuli that a person can detect 50