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Smell? Taste?
10. What sense would become more acute if the sense of touch was lost? Again, people can
sometimes compensate for the loss of a sense in a variety of ways, but there is no
compensatory increase in physical ability in the remaining senses.
SUPPLEMENTAL LECTURE MATERIAL
Sensation and Perception
Why do we study sensation and perception? Primarily because it is through the sensory systems
that we make and maintain our contact with the environment. What are some of the reasons that
figure into this contact with the environment? There are many reasons, but some of the more
pertinent follow.
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1. For purposes of communication to and from the brain, between our internal and external
environments.
2. For organizational and functional principles that are applicable across the various sensory
and perceptual systems.
3. For comprehension of anatomical structure at a physiological level.
4. For assistance with deficits in the various systems, such as abnormalities, deficiencies,
prosthetics, and so on. This is especially important in vision and audition, in that
“normal” individuals get 80 percent of their sensory input through vision and 15—18
percent through audition. The remaining 2—5 percent is distributed across the other
various systems.
5. Finally, for philosophical reasons, to what extent is our world experience predicated on
sensation and perception? On what else could it be predicated?
Other principles and properties that are characteristic of all sensory systems include the following:
1. Limited Receptivity. Human senses are structurally designed to respond to a certain type of
energy, and, within that type of energy, to a limited range of output. All senses respond to
some form of energy. Human vision responds to electromagnetic radiation (light), from just
above the ultraviolet to just below the infrared portions of the spectrum. This is known as
the visible range of light. Audition responds to pressure, from about 50 Hz to about 15,000
Hz in humans. The range for dogs is much higher, up to about 100,000 Hz. The individual
ranges for all types of receptivity are species-specific.
2. Specific Irritability. Within a given system, there are subsystems with specialized functions.
In the visual system, rods are more sensitive to shorter wavelengths of light; cones are more
sensitive to longer wavelengths. Gustation, the sense of taste, relies on chemical energy.
The tongue has four basic types of taste receptors: sweet, salty, bitter, sour. Each of these
subsystems is sensitive to different chemicals.
3. Adaptation. Sensory systems are designed such that they will not respond to steady,
repetitive, nonchanging stimuli, which carry no further information. This permits our
senses to respond over a wide range of energy potential, such as from dark to bright light.
Adaptation permits resetting of the system threshold, over a vast range of energy and
intensity, as needed.
4. Contrast. Sensory systems are designed to respond to change relative to a mean level.
5. Threshold, Saturation, and Dynamic Range. The threshold is the minimum amount of energy
required for the system to respond. Once above a threshold level, as intensity increases, so
does the subjective sensation of that intensity, across the specific range to which the system
responds. Beyond a certain level, further increase in physical intensity no longer produces
a subjective change in intensity, because the system is saturated.
6. Response Latency. Every system is a transducer, in that it converts energy from one medium
to another so that it can be processed. This transduction process takes about 20—30
milliseconds, and about 200—500 milliseconds following the stimulus, you become aware
of the sensation. Thus, we live 200 milliseconds in the past.
The Sensory System
In learning about sensation, it is important for your class to be aware that we have three different
types of sensory systems, each of which performs different functions.
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1. Exteroceptors. These sensory receptors take data from the external world. Types of
exteroceptors include distal and proximal receptors. Distal receptors include those
associated with vision. Objects rarely make direct contact with the eye, rather they are
discerned at a distance, with no need for contact in order to experience the sensation.
Proximal receptors are associated with touch, taste, and possibly olfaction. Thermal
radiation does not always require proximity; you can tell that the sun is warm via your
distal receptors–you do not have to touch it. In most instances, proximal systems require
direct contact with the stimulus.
2. Interoceptors. These are internal system monitors; they work to keep you aware of the
internal working of your body, such as letting you know when you are hungry, thirsty, in
pain, nauseated, fatigued, and so on.
3. Proprioceptors. These receptors monitor the position of the body or limbs relative to some
reference point. They let you know where you are physically located in space.
Proprioceptors are found in the vestibular system, where they permit maintenance of your
physical position, in the pressure receptors of the skin, in the muscle stretch receptors of
your muscles, and in the joint movement receptors of your limbs.
Auditory Localization
We use our ears to point our eyes in the direction of sound-producing events. For this to happen,
the auditory system must be able to perceive the direction from which a sound is originating, and
the system’s perception of space must be integrated with the visual system’s perception of space.
Unlike the eye, the ear has no direct coding of spatial direction. Information about the sound’s
direction is perceived by comparing the stimulation in one ear with that in the other. In this respect,
sound localization is much like the visual-depth cue of binocular disparity.
There are two basic sources of information about sound coming from the left or right; the sound
entering one ear differs from that entering the other in both intensity and time. When a sound comes
from directly in front of your head, its intensity is equal at your two ears. In the case of high-
frequency sounds coming from the side, your head creates a sound shadow, making the sound less
intense at the ear farthest away from the sound than at the ear closest to the sound. It is only for
high frequencies that there is information about how far to one side or another a sound is located.
The other major source of information about the horizontal direction of a sound is the time at which
it arrives at your two ears. When a sound comes from directly in front of your head, the arrival times
are the same because your two ears are the same distance away from the sound. However, when the
sound comes from the side, the sound wave must travel farther to reach the ear on the far side. Even
though this extra distance takes only a little extra time—less than one-thousandth of a second—it is
enough to tell us which side sound is coming from.
The direction of sounds from left to right, or right to left, is probably the most important part of
spatial hearing, but it is not the only part. You can also tell whether a sound is coming from above
or below—the sound of a jet streaking overhead or of an object dropped at your feet. You are not
able to perceive vertical direction from simple arrival times or intensities, however. It is the shape of
the external ear that allows you to perceive the vertical dimension of space. Notice that your ear is
asymmetrical. There are many complex, sound-reflecting folds in the pinna above the ear canal, and
few below it. These differences in the shape of the external ear make subtle changes in the sound
wave that enters your ears, depending on the vertical direction of the sound source. Somewhere in
the auditory centers of the brain, these differences are detected and decoded, allowing you to
perceive upward and downward directions of environmental sounds.
We are left with the problem of perceiving the third dimension of depth—how far away the source
of a sound is from us. A sound that is near is louder than one that is far away, so you might think
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that intensity would provide all the information you need about the distance (or depth) of the
source of a sound. Unfortunately, it is not that easy. A low-intensity sound at the ear might have
come from either a loud sound far away or a soft one nearby. This situation is analogous to the
relations among retinal size, object distance, and object size in visual perception. If the sound is one
whose usual intensity you know, such as someone speaking in a normal voice or the sound of an
average car engine, you can perceive its approximate distance by sound using intensity
information. If the sound is one whose usual intensity you do not know, you cannot tell how far
away it is by hearing it; you have to look. Because you can locate the direction that the sound is
coming from using your ears, you can use them to point your eyes in the correct direction, which
can then do the job of judging distance.
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BIOGRAPHICAL PROFILES
Hermann von Helmholtz (1821–1894)
Hermann Von Helmholtz obtained his M.D. in Berlin and served subsequently as an Army surgeon
for seven years. Following his military service, he studied math and physics and held academic
appointments over the next 30 years at Bonn, Heidelberg, and Berlin, initially as a physiologist,
later as a physicist. Helmholtz, whose versatility and intellectual brilliance manifested itself in
various disciplines, is considered one of the true giants in the history of science.
Helmholtz’s prominence in physiology came chiefly from his discovery of the rate of neural
conduction, a finding that surprised many of his contemporaries who had assumed that nerve
impulses must travel at or near the speed of light. In addition, he invented the opthalmoscope while
researching vision, and was involved in the development of theories of color vision and pitch
perception that remain influential today. His published works include the three-volume series
Physiological Optics (1856—1866).
Ernst Heinrich Weber (1795—1879)
Ernst Weber taught anatomy and physiology at the University of Leipzig, Germany, from 1820 until
the end of his career. He is remembered in psychology for his studies of psychophysical relations,
especially for the sensations of temperature and touch. Weber was the first to investigate the two-
point threshold for touch, observing that sensitivity to touch varied across different parts of the
body and demonstrating that regions of the body are differentially sensitive to tactile stimulation.
Weber’s analysis of difference thresholds led to the finding that the size of the difference threshold
remains a constant fraction of the stimulus intensity, an orderly relationship referred to as Weber’s
Law.
Ronald Melzack (b. 1929)
Ronald Melzack was raised and educated in Montreal, Canada, obtaining his Ph.D. from McGill
University in 1958. He conducted research in pain sensation at the University of Oregon Medical
School from 1954 to 1957. Following this, he was a visiting lecturer at University College, London,
and spent a year conducting physiological research in Italy at the University of Pisa. He was
appointed to the faculty of the Massachusetts Institute of Technology (MIT) in 1959, but returned to
McGill University in 1963.
Melzack’s doctoral research on pain in experimental animals resulted in his collaboration with
Patrick Wall. Out of this effort emerged the gate-control theory of pain, which remains today the
most widely accepted theory of pain sensation and regulation. Its implications have influenced not
only basic research on pain but also the clinical practice of pain management. Melzack continues to
refine and modify this successful theory.
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TIMELINE
Year Event
1838 Johannes Müller formulated his doctrine of specific nerve energies, which states that
sensory experience depends not on the stimulus, but on the part of the nervous system
that is activated.
1839 M. E. Chevreul published On the Law of simultaneous Contrast of Colors.
1843 S.ren Kierkegaard published Either/Or.
1846 Ernst Weber postulated that the difference threshold is a constant proportion of the initial
stimulus intensity, a notion later formalized as Weber’s Law.
1855 Walt Whitman published Leaves of Grass.
1857 Based on the earlier work of Thomas Young, Hermann von Helmholtz proposed that color
vision is due to three different types of color receptors (cones), each of which is sensitive to
a specific range of wavelengths of light.
1860 Gustav Fechner published Elemente der Psychophysik, marking the founding of
psychophysics, the study of the relationship between subjective experience and physical
stimulation.
1898 The Spanish-American War was fought.
1929 The Great Depression began with the stock market crash.
1938 H. Keffer Hartline discovered that optic nerve fibers respond to stimulation from different
receptive fields.
19501953
The Korean War was fought.
1954 Tanner and Swets proposed the application of signal detection theory to the study of
thresholds.
1954 The first hydrogen bomb was exploded.
1957 S. S. Stevens demonstrated that changes in one’s subjective impression of stimulus
magnitude are a power function of the actual stimulus magnitude.
1957 Leo Hurvich and Dorothea Jameson, building on the work of Ewald Hering, postulated
the theory that color vision is based on opposing neural processes, the opponent-process
theory of color vision.
1959 David Hubel and Torsten Wiesel discovered that cells in the visual cortex of cats (and, in
1968, of monkeys) respond differentially to form and movement.
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SUGGESTIONS FOR FURTHER READINGS
Kosslyn, S. M. (1995). Visual Cognition: An Invitation To Cognitive Science, Vol. 2 (2nd ed.). Cambridge:
MIT Press. Explores the mental aspects of visual processing. Discusses the important research,
discoveries, and insights in various areas of research on visual cognition and attempts to
integrate work from related fields.
Kosslyn, S., & Koenig, O. (1992). Wet Mind: The New Cognitive Neuroscience. New York: Free Press. A
comprehensive, integrated, and accessible overview of recent insights into how the brain gives
rise to mental activity. Examines a large number of syndromes that occur following brain
damage, and accounts for them according to an analysis of the operation of a normal brain. The
authors also present an interesting theory of consciousness.
Link, S. (1994). Rediscovering the Past: Gustav Fechner and Signal Detection Theory. Psychological
Science, 5(6), 335-340. Suggests that the origins of experimental psychology are found in the
theoretical works of Gustav Fechner and that Fechner is not given the credit that he is due for
his contributions. Argues that his works spawned many new ideas and theories, including the
response bias found in signal detection theory.
Matlin, M. W., & Foley, H. J. (1992). Sensation and Perception. (3rd edition). Boston: Allyn and Bacon.
A well-written introduction to the fields of sensation and perception.
Sekuler, R. (1995). Motion Perception as a Partnership: Exogenous and Endogenous Contributions. Current
Directions in Psychological Science, 4(2), 43–47. Describes the process of motion detection as a
result of the interaction of exogenous and endogenous influences.
DISCOVERING PSYCHOLOGY
PROGRAM 7: SENSATION AND PERCEPTION
Overview
Explores how we make contact with the world outside our brain and body. See how biological,
cognitive, social, and environmental influences shape our personal sense of reality, and gain an
understanding of how psychologists use perceptual errors to study how the constructive process of
perception works.
Key Issues
Visual illusions, the biology of perception, the visual pathway, how the brain processes information
during perception, sensory feedback in visual perception, and perceptual constancy.
Demonstrations
Sensory feedback in visual perception. A Stanford student demonstrates the problems that football
quarterbacks face in the adjustment to special kinesthetic cues with distortion goggles that displace
feedback from the perceived visual field.
Perceptual constancy. Philip Zimbardo demonstrates visual misperception in the Ames distorted room
in the Exploratorium in San Francisco.
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Interviews
Nobel Prize winner David Hubel (Harvard University) explains the mapping of the reaction of receptor
cells along the visual pathway of primates. Hubel’s award-winning experiment of the response of
neurons to electrical activity in the visual cortex of a cat illustrates his point.
Misha Pavel uses computer graphics to demonstrate how the visual system of the brain breaks down
and recombines visual stimulation into recognizable, coherent images.
FILMS AND VIDEOS
A Touch of Sensitivity (1981). BBC, 50 minutes
This NOVA presentation discusses the importance of touch and the effects of touch deprivation.
This film examines the importance of touch for development at various ages. Many interesting areas
of research are cited.
The Mind: Pain and Healing (1988). HARR, 24 minutes
Reviews the influence of the mind on people’s ability to control pain, and on their ability to promote
physical healing. An excellent film. Traces the progress of a woman through a three-week clinic
program to reduce chronic pain. The changes in her movement and affect are dramatic.
Demonstrates the placebo effect, and shows how cues, such as a doctor’s white coat, can trigger the
release of endorphins to reduce pain. In the final segment, a cancer patient discusses how the
interaction of cognitive therapy and physical therapy increased her life expectancy and quality.
The Senses: Eyes and Ears (1985). FFHS, 26 minutes
Visual and auditory distance receptors are discussed. Demonstrations of how each processes
information are also shown.
The Senses: Skin Deep (1985). FFHS, 26 minutes
The sense receptors that depend on immediate contact with the world–taste buds, olfactory cells,
and touch sensors–are examined.
CASE STUDY LECTURE LAUNCHER
Five months before her second birthday, Helen Keller was stricken with a mysterious illness that
deprived her of both sight and hearing. Helen’s other senses became highly developed—a
phenomenon experienced by many people who suffer long-term sensory deprivation—and her
sensory experiences were eloquently documented: “I cannot recall what happened during the first
months after my illness. I only know that I sat in my mother’s lap or clung to her dress as she went
about her household duties. My hands felt every object and observed every motion, and in this way,
I learned to know many things. . . . Sometimes I stood between two persons who were conversing
and touched their lips. I could not understand, and was vexed” (Keller, 1902, pp. 26—27).
In her seventh year, Helen Keller became the pupil of Annie Sullivan, a young woman whose vision
was partially impaired. In letters to a matron at the Perkins School in Boston where Annie had been
educated, she wrote of the pleasure Helen derived from her remaining senses: “On entering a
greenhouse her countenance becomes radiant, and she will tell the names of the flowers with which
she is familiar, by the sense of smell alone. . . . She enjoys in anticipation the scent of a rose or a
violet; and if she is promised a bouquet of these flowers, a peculiarly happy expression lights her
face” (Sullivan, 1954, p. 294).
Helen herself wrote about the way that her sense of smell gave her advance warning of storms. “I
notice first a throb of expectancy, a slight quiver, a concentration in my nostrils. As the storm draws
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near my nostrils dilate, the better to receive the flood of earth odors, which seem to multiply and
extend, until I feel the splash of rain against my cheek. As the tempest departs, receding farther and
farther, the odors fade, become fainter and fainter and die away beyond the bar of space.” (Keller,
Ackerman, 1990, p. 44).
Annie Sullivan reported that Helen’s “whole body is so finely organized that she seems to use it as
a medium for bringing herself into closer relations with her fellow creatures.” Annie was puzzled
at first by Helen’s “inexplicable mental faculty” for picking up emotions and physical sensations.
She soon realized, though, that Helen had developed an exquisite sensitivity to the muscular
variations of those around her. “One day, while she was out walking with her mother, . . . a boy
threw a torpedo, which startled Mrs. Keller. Helen felt the change in her mother’s movements
instantly, and asked, ‘What are we afraid of?”