Download Receptor Cells

The Visual System
The Awareness Test
Just for fun, let’s test your
awareness of your surroundings…
How do we see?
No light? No sight!

light enters the eye as waves
of electromagnetic energy

length of the wave determines
a light’s color

the height of the wave
(amplitude) determines
brightness
Structure of the
Visual System
Optic Nerve (1)
 nerve
that carries visual information from
the eye to the occipital lobes of the brain
Blind Spot (2)
where the optic nerve exits the eye
 no rods and cones at this point, so there is a
small blind spot in vision (pg. 166)

Retina (3)

has cells that
convert light
energy to nerve
impulses

made up of three
layers of cells:
 Receptor cells
 Bipolar cells
 Ganglion cells
Receptor Cells
 sight
- change light into neural impulses
the brain can understand
 visual
system has two types of receptor
cells – rods and cones
Rods

only detect black,
white, and shades of
gray
Cones

detect sharp images
and color

cluster at the fovea
Bipolar Cells

middle layer
of retina

gather
information
from rods &
cones and pass
it on to the
ganglion cells
Ganglion Cells

axons of
ganglion cells
form the optic
nerve

blind spot is
created where
optic nerve
exits the eye
(page 166)
Cornea (4)

outside layer on
the front of the
eyeball

two tasks:
focuses light by
bending it
toward a central
focal point
 protects the eye

Pupil (5)

opening in center
of eye

controls amount
of light entering
the eye
(surrounded by
the iris)
Iris (6)

colored portion of
the eye

regulates the size
of the pupil by
changing its size allowing more or
less light to enter
the eye
Lens (7)

focuses the image
on the back of the
eye (retina)

muscles that change
the thickness of the
lens change how the
light is bent thereby
focusing the image
Fovea
 central
focal point of the retina
 spot where vision is best (most detailed)
Color Vision Theories
Trichromatic (three-color) Theory

cones are “tuned” to be
sensitive to red, green
& blue wavelengths of
light

all the colors we see
are a combination of
these three colors
Color Deficient Vision

people who lack one
of the three types of
cones

usually the red or
green receptors are
missing

inherited & found
more in males
Opponent-Process Theory of Color
 color-processing
neurons oppose one
another:
 red – green
 yellow – blue
 black – white
 light
that stimulated one half of the pair
inhibits the other half
Hearing
Sound

sound comes in
waves that are
produced by
vibration
The Structure of the
Auditory System
Auditory Canal (6)

opening where
sound waves enter
the ear for
processing
Tympanic Membrane/Eardrum (7)

transfers sound
vibration from
the air to the
ossicles
Tympanic Membrane (w/ tear)
Ossicles

three tiny bones
that transfer
sound waves
from the eardrum
to the cochlea
hammer (5)
 anvil (4)
 stirrup (3)

Ossicles – Hammer, Anvil, Stirrup
Oval Window

receives sound
vibration from
the ossicles

vibrates the fluid
in the cochlea
Cochlea (2)

where sound
waves are
changed into
neural impulses

filled with fluid
Cochlea
Hair Cells

receptor cells in the cochlea that change sound
vibrations into neural impulses
Hair Cells
Semicircular Canals

used in sensing
body orientation
and balance
(vestibular sense)

relies on fluid in
the canals
Auditory Nerve (1)

formed by fibers
at the base of
each hair cell

nerve that carries
sound from the
ears to the
temporal lobes
How can we tell the difference
between different sounds?

3 Theories:
place theory
 volley theory
 frequency theory

Place Theory of Hearing

different types of sound waves vibrate
different locations/places on the cochlea

high sounds vibrate one area, low sounds
another

problem: very low sounds cause entire
cochlea to vibrate
Frequency Theory of Hearing

frequency with which the cochlea is
vibrated tells us what sound we hear

problem: cannot explain how we tell the
difference between high-pitched sounds
(neurons can only fire so fast)
Volley Theory of Hearing

sensory neurons in the cochlea (the hair
cells) fire in groups, as volleys

pattern of firing allows us to tell the
difference between sounds
Sensation
Sensation
 awareness
of the
world
 process
where our
sensory systems &
nervous system
receive stimuli from
the environment
Perception
 interpretation
of
sensory information
 process
of
organizing &
interpreting sensory
information
Two ways we process information:
1.
2.
bottom-up processing
 analyze the raw material entering through
the eyes, ears, etc.
top-down processing

focus on expectations & experiences in
interpreting sensory information
Sensation v. Perception Example
(don’t write this )

Identify an unknown object based
on elements of sensation:
red sphere
 cool, hard surface
 fits comfortably in your hand
 pleasant aroma
 satisfying crunch when bitten
 tastes both sweet and tart


Analysis of this data leads to the
perception that the unknown
object is an _________________.
Top-down or Bottom-up? Example
(don’t write this either)

Would the descriptions below be
processed top-down or bottomup? Explain.







red sphere
cool, hard surface
fits comfortably in your hand
pleasant aroma
satisfying crunch when bitten
tastes both sweet and tart
What types of sensations would
you experience when eating the
food pictured to the right?
Module 10: Perception
Illusions
Illusions
 misinterpreting
 help
sensory stimuli
researchers understand how sensation
and perception normally works
Müller-Lyer Illusion
Müller-Lyer Illusion
Most people think segment AB equals BC.
In reality AB is much longer than BC.
Theory: we have learned to interpret
arrowheads at the ends of a line as an
indication of distance
Müller-Lyer Illusion
Müller-Lyer Illusion
Müller-Lyer Illusion
Ames Room Photos

explain the photos at the top of page 200

video Segment: “Ames Room Illusion
Explained”
Ames Room Illusion: Secret
Revealed