Transcript Vision - APPsychBCA

Vision
EYE
see
you!
Transduction
 Transduction:
Technically speaking,
transduction is the process of
converting one form of energy into
another.
 As it relates to psychology,
transduction refers to changing
physical energy into electrical signals
(neural impulses) that can make their
way to the brain.
Vision: Transduction and Light Energy


Transduction: Our
eyes have the ability
to convert one form
of energy – in this
case LIGHT – into
messages that our
brain can interpret as
a visual experience
We can only see a
small part of the
electromagnetic
spectrum
The Physical Properties of
Waves
These properties apply to audition (hearing), too:
• The higher the frequency, the higher the pitch and vice versa
• The greater the amplitude the louder the sound and vice versa
The Structure of the Eye
The Structure of the
The Structure of the Eye
Cornea = outer covering of the eye.
The Structure of the Eye
Pupil = the adjustable opening in the center of the eye through which
light enters.
The Structure of the Eye
Iris = a ring of muscle tissue that forms the colored portion of the eye
around the pupil and controls the size of the pupil opening.
• The iris dilates/constricts in response to changing light intensity
The Structure of the Eye
Lens = the transparent structure behind the pupil that changes shape to
help focus images on the retina.
The Structure of the Eye
Retina = the light-sensitive inner surface of the eye, containing the
receptor rods and cones plus layers of neurons that begin the processing
of visual information.
The Visual System

Cornea


Pupil



Focuses light onto the retina
Changes shape through
accommodation to help focus
image on retina
Retina


Colored part of the eye
Lens


Small opening in the iris through
which light enters the eye
Iris


Transparent protective coating
over the front of the eye
Lining of the eye containing
receptor cells that are sensitive
to light
Fovea

Center of the visual field
Properties of Color and Light
Energy

Hue



Colors we see such as
red and green
Determined by
wavelength
Shorter wavelength
results in blue-violet;
longer results in red

Brightness



“loudness” or intensity
of a color
Determined by
amplitude
Saturation

Vividness of a hue
The Eye
The Retina
Rods
Cones
and Cones
Rods
Receptor Cells
 Cells
in the retina that are
sensitive to light
 Visual receptors are called rods
and cones
 Rods




About 120 million rods
Respond to light and dark
Very sensitive to light
Provide our night vision
 Cones
 About 8 million cones
 Respond to color as well as light and
dark
 Work best in bright light
 Found mainly in the fovea
 Marker Demonstration?
 Stars in the sky?
Rods & Cones
 One
to try at home: In a dark room (or
outside) focus on an image or object.
Notice how detailed the object appears.
Then focus your foveal vision just to the
side of the image or object you were
looking at. You should notice that the
image becomes more detailed
The Eye
The Retina
Optic
nerve
Blind spot
Fovea
The Structure of the Eye
Blind Spot = the point at which the optic nerve leaves the eye, creating a
“blind” spot because no receptor cells are located there.
The Structure of the Eye
Fovea = the central focal point in the retina, around which the eye’s
cones cluster.
The Structure of the Eye
Optic Nerve = the nerve that carries neural impulses from the eye to the
brain.
Pathways from the eyes to the
visual cortex
From Eye to Brain

Optic nerve



Optic chiasm


Made up of axons
of ganglion cells
carries neural
messages from
each eye to brain
Point where part of
each optic nerve
crosses to the
other side of the
brain
Thalamus relays
sensory info to
visual cortex in
occipital lobes
Visual information processing
Visual information processing
Feature Detection
 Feature
detectors are neurons in the brain that
respond to specific aspects of a stimulus: edges,
lines, movements, angles


Feature detectors in the visual cortex send signals to
other areas of the cortex for higher-level processing
These areas – called supercell clusters – work in teams to
determine familiar patterns – such as faces (processed in
the right-side of temporal lobe)
 Parallel


processing
Our brains process multiple features of visual experience
at once and integrate these features to create our
experience of vision
If parts of this integration are disrupted through damage
or electromagnetic pulses, we may lose our ability to
processes certain aspects of vision such as movement or
lines (blindsight)
Stuff you should know
 How
the eye works with the thalamus and
the occipital lobes (review)
 Feature detector cells
 The significant difference in number and
function of rods and cones
 How parallel processing works with vision
(color, motion, form and depth)
 What if you could not perceive motion?
Hermann Grid (why?)
Theories of Color Vision
 Additive



color mixing
Mixing of lights of different hues
Lights, T.V., computer monitors (RGB)
Lights add wavelengths
 Subtractive


color mixing
Mixing pigments, e.g., paints
Pigments absorb or subtract wavelengths
Color Theory
 Young-Helmholtz
Trichromatic theory
 Herring’s opponent-process theory
 Afterimages
Color Vision
Young-Helmholtz
trichromatic (three color)
theory
– Green - Blue
Monochromatic
vision
Dichromatic
vision
Red
Theories of Color Vision
 Trichromatic
Helmholtz)

Three different types of cones





theory (Young-
Red
Green
Blue
Experience of color is the result of mixing
of the signals from these receptors
Can account for some types of
colorblindness



Approximately 10% of men and 1% of
women have some form of
“colorblindness” (sex linked trait)
Dichromats: Two colors only
Monochromats: One color only
Ishihara Test
Color Vision
Opponent-process
Three
sets of colors
Red-green
Blue-yellow
Black-white
Afterimage
theory
After image- evidence for the opponent
process theory of color vision
.
Stare at the dot in the image
below
What do you see (Blink a bit)
Theories of Color Vision
 Trichromatic
color vision



theory cannot explain all aspects of
People with normal vision cannot see “reddish-green”
or “yellowish-blue”
Red-Green colorblind people can see yellow, which
Helmholtz argues is a result of red and green cones firing
– if Helmholtz is correct, how could this be?
Color afterimages?
 Opponent-process

Three pairs of color receptors





theory (Ewald Hering)
Yellow-blue
Red-green
Black-white
Members of each pair work in opposition
Can explain color afterimages
 Both
theories of color vision are valid
Adaptation
 Dark

Increased sensitivity of rods and cones in
darkness
 Light

adaptation
adaptation
Decreased sensitivity of rods and cones in
bright light
 Afterimage

Sensory experience that occurs after a
visual stimulus has been removed in
response to overstimulation of receptors
Color Vision in Other Species

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Other species see colors differently
than humans
Most other mammals are dichromats
Rodents tend to be monochromats, as
are owls who have only rods
Bees can see ultraviolet light
Stomatopods have the most complex
color hyperspectral vision in the animal
kingdom, allowing them to differentiate
between colors that may appear the
same to other human and non-human
animals.
The Mantis Shrimp is a stomatopod with
hyperspectral vision. Hyperspectral
capabilities enable the mantis shrimp to
recognize different types of coral, prey, or
predators.
A question for the ages:
 How
do I know if I am seeing the same
color as someone else?
 Answer: The wavelength determines
color, so in a properly functioning eye, it
will be the same, although color shades
can vary significantly and people may
name them differently.