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b） Different sensory experiences； such as sight and smell； do not
produce different types of nerve activity。 Rather they produce the
same type of nerve activity； but in different regions of the brain。
c） All sensory systems share the same basic flow of information。
Environmental events are detected by specialized sensory receptor
neurons； called stimulus detector units； which convert the
physical energy received from the environment into neural signals
that can be processed by the central nervous system。
II。 The Visual System
A。 The Importance of Vision
1。 The most plex； highly developed； and important sense for humans
and most other mobile creatures
2。 Provides a tremendous evolutionary advantage
B。 The Human Eye
1。 Light enters the eye through the cornea； a transparent bulge on the front
of the eye
2。 Light then passes through the anterior chamber； which is filled with a
clear liquid called aqueous humor
3。 Then through the pupil； an opening in the opaque iris
4。 Then through the lens； which focuses the ining light
5。 Then through the vitreous humor； another clear liquid
6。 And then finally strikes the retina； a thin sheet of neuron that lines the
rear wall of the eyeball
C。 The Pupil and the Lens
1。 The iris makes the pupil dilate to control the amount of light entering the
eye。 The lens focuses the light on the retina； reversing and inverting the
light as it does so。 The lens is responsible for focusing to account for the
distance to the object。
2。 Acmodation is the change in the thickness of the lens。 Problems with
acmodation are responsible for many vision problems； such as near…
and far…sightedness。
D。 The Retina
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CHAPTER 4： SENSATION
1。 The retina is posed of specialized photoreceptor cells called rods and
cones that convert light energy into nerve energy
a） Rods function best in low light
b） Cones function best in bright light
2。 Dark adaptation is the gradual improvement of the eyes’ sensitivity after
a shift in illumination from light to near darkness
3。 The area of sharpest vision is called the fovea； a small area near the
center of the retina that contains only densely packed cones
4。 Bipolar cells are nerve cells that bine information from many receptor
cells and send the results to ganglion cells
5。 Ganglion cells then integrate the information from bipolar cells into a
single firing rate
6。 The axons of the ganglion cells prise the optic nerve； which carries
visual information to the brain
7。 Horizontal and Amacrine cells do not send information to the brain but
rather integrate information across the retina
a） Horizontal cells connect receptors to each other
b） Amacrine cells connect bipolar cells to bipolar cells and ganglion
cells to ganglion cells
8。 The optic disk or blind spot is the area where the optic nerve exits the
retina。 It contains no receptor cells。 Blindness is not experienced at this
spot because the blind spots for each eye are different areas of the visual
field and because the brain automatically fills in the blind spot。
E。 Pathways to the Brain
1。 After processing by other brain regions； the ultimate destination of much
visual information is the part of the occipital lobe known as the visual
cortex
2。 The axons of the millions of ganglion cells that form the optic nerve
e together at the optic chiasma； where they are divided into two
bundles called optic tracts
3。 Half of the nerve fibers from each retina stay on the side from which they
originated。 The other half cross over to the other side of the brain。
4。 Much visual information then flows to the primary visual cortex； where
roughly 30 anatomical subdivisions of the primary visual cortex process
information concerning form； color； position； and depth
F。 Seeing Color
1。 Visible light （wave length of 400–700 manometers） is just a small portion
of the electromagnetic spectrum； which includes X rays； microwaves； and
radio waves
55
PSYCHOLOGY AND LIFE
2。 Wavelength refers to the distance between crests of two consecutive
waves。 Wavelength determines the color perceived。
3。 All experiences of color can be described in terms of hue； saturation； and
brightness
a） Hue captures the qualitative experience of color of the light
stimulus
b） Saturation captures the purity and vividness of color sensations
c） Brightness captures the intensity of the light
4。 Humans can discriminate about 7 million different colors
5。 The bination of all wavelengths of light yields white light
6。 Wavelengths of light that appear directly across from each other on the
color wheel are called plementary； and create the sensation of white
light when mixed
7。 Color Blindness is the inability to distinguish colors。 More males than
females are color blind； and most color blindness involves the inability
to distinguish red from green。
8。 There are two primary theories of color vision： The Young…Helmholtz
Trichromatic Theory and the Opponent…Process Theory
a） The Trichromatic Theory of color perception； proposed by Sir
Thomas Young and Hermann von Helmholtz； suggests that all
colors perceived are produced by just three types of color receptors
in the eye： red； green； and blue。 All other colors are binations
of these。 This theory adequately explains color blindness and
people’s color sensations； but did not explain afterimages and
certain types of color blindness。
b） The Opponent…Process Theory of color perception； proposed by
Ewald Hering； suggests that color results from three systems； each
of which includes two opponent elements： red versus green； blue
versus yellow； or black versus white。 Hering argued that
afterimages were produced when one element of a system became
fatigued； due to over stimulation； and thus led to the over
contribution of its opponent element。 This theory also better
explained why color blindness is usually found in pairs。
9。 After debating the relative merits of these two theories； scientists came to
agree that they are not in conflict； but rather describe different stages in
color perception
10。 A modern version of the Opponent…Process Theory； proposed by
Hurvich and Jameson； suggests that the two members of each color pair
work in opposition by means of neural inhibition。 Some ganglion cells
are excited by light that appears red and inhibited by light that appears
green。 Other cells are excited by green light and inhibited by red light。
G。 plex Visual Analysis
1。 David Hubel and Torsten Wiesel won a Nobel Prize for their work on
receptive fields in the visual cortex in 1981
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CHAPTER 4： SENSATION
2。 Hubel and Wiesel found there are several types of receptive cells
a） Simple cells respond most strongly to bars of light in their
“favorite” orientation
b） plex cells respond most strongly to moving bars of light in
their “favorite” orientation
c） Hyperplex cells respond most strongly to moving bars of light of
a particular length or angle
III。 Hearing
A。 Hearing is the Principle Sensory Modality for Human munication
B。 The Physics of Sound
1。 Sound travels as a vibrational sine wave through a medium； usually air；
at a rate of about 1100 feet per second
2。 Sine waves have two basic properties： frequency and amplitude
a） Frequency measures the number of cycles the wave pletes in a
given amount of time and is usually measured in Hertz （Hz）； or
cycles per second
b） Amplitude measures strength of the wave in peak to valley height
C。 Psychological Dimensions of Sound
1。 Pitch is the highness or lowness of a sound as determined by a wave’s
frequency。 High frequencies produce high pitch； while low frequencies
produce low pitch。
2。 Loudness is the physical intensity of a sound as determined by a wave’s
amplitude。 Small amplitude waves are experienced as quiet sound and
large amplitude waves are experienced as loud sound。
3。 Timbre reflects the plex ponents of a sound wave。 A pure tone
has only one frequency and one amplitude。 Most sounds； however； are
not pure tones； which is reflected in timbre。
D。 The Physiolog