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
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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 Physiology of Hearing
1。 In order for hearing to occur； four basic energy transformations must
take place
a） First； airborne sound waves must be translated into fluid waves
within the cochlea of the ear。 Sound waves travel into the ear until
they reach the end of the canal。 There they encounter the tympanic
membrane or eardrum。 The sound waves move the eardrum； and
the eardrum transmits the vibrations from the outer ear to the
middle ear； which contains the hammer； the anvil； and the stirrup。
These tiny bones transmit the vibrations from the eardrum to the
primary organ of hearing； the cochlea in the inner ear。
b） Second； the fluid waves must stimulate mechanical vibrations of
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the basilar membrane。 Vibration of fluid in the cochlea causes a
coiled tube membrane in the cochlea； the basilar membrane； to
move in a wavelike fashion。
c） Third； these vibrations must be converted into electrical impulses。
The wavelike motion of the basilar membrane bends tiny hair cells
connected to the membrane。 As the hair cells bend； they stimulate
nerve endings； transforming the wave motion into neural activity。
d） Fourth； the impulses must travel to the auditory cortex from the
cochlea via the auditory nerve。 Information from one ear goes to
both sides of the brain。
2。 There are two types of hearing impairment； each caused by a defect in
one or more ponents of the auditory system： conduction deafness
and nerve deafness
a） Conduction deafness is the less serious of the two and involves a…
problem in the conduction of air vibrations to the cochlea。 It can
often be corrected by the insertion of artificial anvils or stirrups。
b） Nerve deafness is more serious and involves a defect in the neural
mechanisms that create nerve impulses or that relay them to the
auditory cortex
E。 Theories of Pitch Perception
1。 Two major theories have been posited to explain sensations of pitch：
place theory and frequency theory
a） Place theory； proposed first by Helmholtz and later modified by
Bekesy； suggests that different portions of the basilar membrane
move depending on the frequency of the sound wave。 High…
frequency tones produce greatest motion at the base of the cochlea；
while low…frequency tones produce the greatest motion at the
opposite end。
b） Frequency theory suggests that the rate of vibration of the tone is
reflected in the rate of vibration of the basilar membrane。 If a tone
vibrates at 100 Hz； the basilar membrane will also vibrate at 100
Hz and will cause neurons to fire at 100 Hz。 For high…pitched
sounds； however； this is impossible； because they cannot fire more
than 1；000 times per second。 The volley principle may overe
this limitation。
2。 The Volley Principle suggests that several neurons could work together
and could fire in a volley to match higher cycles per second
3。 Frequency and Place Theories are not mutually exclusive。 Place theory
accounts well for pitch perception of frequencies above 1；000 Hz； while
frequency theory accounts well for pitch perception of frequencies below
5；000 Hz。
F。 Sound Localization
1。 Some animals； such as bats； use echolocation instead of vision to
determine distances； locations； sizes； textures； and movements of objects。
Humans lack this ability； but do use sound to determine location
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through two primary mechanisms； assessment of relative timing and
relative intensity。
2。 Relative timing involves the parison of the relative times at which
ining sound reaches the ear。 For example； a sound to your right
reaches your right ear before it reaches your left ear。
3。 Relative intensity involves the parison of the relative intensity at
which ining sound reaches the ear。 The head casts a sound shadow
over the ear farthest from the sound that weakens the sound。
IV。 Your Other Senses
A。 Smell
1。 Odors first interact with receptor proteins on the membranes of tiny
hairs （olfactory cilia） in your nose
2。 As few as eight molecules of a substance can initiate a nerve impulse；
but at least 40 nerve endings must be stimulated before a substance can
be smelled。
3。 Once initiated； nerve impul