Download 8.2 The Senses

Sensation and Perception
8.2 The Senses
I. Introduction
A.  You probably think that you have just five
senses: vision, hearing, taste, smell, and
touch. In addition, people have two more
internal senses: vestibular and kinesthetic.
B.  Each sense organ receives some sort of
external stimulus, such as light, sound
waves, or pressure. It then changes the
sensation into a chemical-electrical
message that the brain can understand.
I. Introduction (con’t)
II. Vision
A.  The vision process begins when light
enters the eye through the pupil and
reaches the lenses. The lens changes
shape to focus light on the retina.
B.  The retina is a coating at the back of the
eye. It contains two types of lightsensitive cells called rods and cones.
These cells change light impulses that the
neurons carry over the optic nerve to the
brain.
II. Vision (con’t)
C.  Cones require more light than rods, they work
best in daylight. Rods work in lower light and
are more useful at night. There are many more
rods than cones, but cones are sensitive to
color.
D.  Colors we see are actually different
wavelengths of light. We see color only after
light waves hit objects and bounce back to us.
We sense texture and solidity of objects by the
speed at which the waves bounce back.
II. Vision (con’t)
E. When cones are not working well, a person
cannot see color well. This condition is
called color deficiency.
F. Our vision system receives two images
because we have two eyes. Instead of
seeing double we see a combination of the
images, this is called binocular fusion.
II. Vision (con’t)
G. Each eye projects a slightly different image
on the retina. This difference is called
retinal disparity.
Example: Bring an object such as an eraser close to your
eyes. Without moving it, look at the eraser first with one
eye and then with the other. You will see the difference in
the two images because of the different viewpoint each eye
has. When you open both eyes, you will see no difference.
II. Vision (con’t)
H. Retinal disparity is important to your sense
of depth. Your brain knows that a large
difference between objects each eye brings
in (retinal disparity) means the object is
near. A small difference means the object is
far away.
II. Vision (con’t)
III. Hearing
A. Hearing depends on sound waves, or
vibrations in the air. Sound waves pass
through several bones and fluids until the
reach the inner ear. The inner ear contains
tiny hairs that move back and forth changing
vibrations into signals that neurons carry to
the brain along the auditory nerve.
III. Hearing (con’t)
B. The amplitude, or height of sound waves,
determines the loudness. Loudness is
measured in decibels.
C. The sound’s pitch depends on the waves
frequency, or rate of vibration. Low
frequencies produce deep bass sounds, high
frequencies produce squeaks.
III. Hearing (con’t)
D. Your ears work together to determine
where a sound is coming from. Typically
noise will be received louder in one ear than
another telling the brain where the sound
comes from.
E. The outer ear directs sound waves down a
short tube called the auditory canal.
III. Hearing (con’t)
F.  The middle ear is made up of three small
bones (the hammer, anvil, and stirrup) and
filled with air. These bones are connected
to the cochlea.
G.  The cochlea is the inner ear. The cochlea
turns sounds into vibrations that create
impulses that are carried to the brain.
III. Hearing (con’t)
IV. Balance
A. Your body’s sense of balance comes from
the vestibular system located in the inner
ear. This system has three semicircular
canals filled with fluid. When you move
this fluid also moves sending stimuli to your
brain to indicate spinning, falling, of tilting
movements.
V. Smell and Taste
A.  Smell and taste are chemical senses.
Inside your nose are smell receivers that
send stimuli to the brain through the
olfactory nerve.
B.  To taste something, molecules must
stimulate taste buds on your tongue. The
taste buds relay information to the brain
regarding taste, temperature, and texture
of the item being eaten.
V. Smell and Taste (con’t)
C. Four sensory experiences
make up taste: sour, salty,
bitter, and sweet. Much
of what you taste is
actually a result of your
sense of smell.
D. Sensations of warmth,
cold, and pressure also
affect taste.
VI. The Skin Senses
A.  Your skin provides at least four kinds of
information to your brain: pressure,
warmth, cold, and pain.
B.  The gate control theory of pain states
that people can reduce their pain by
shifting their attention away from it, or
may send other signals to compete with
the pain signals.
VII. The Body Senses
A.  Kinesthesis is the sense of movement and
body position. It works with the
vestibular system to control posture and
balance.
B.  Receivers for kinesthesis are located near
the muscles, tendons, and joints.
C.  Kinesthetic sensations help keep body
movement coordinated.