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Chapter 4: Vision
About the Visual Stimulus…
1.
What do we see?
2.
Wavelengths of about 380 nanometers
(purple) to about 720 nm ( red)
3.
Different characteristics of light waves give
us different color characteristics:
 Hues
 Amplitude
Electromagnetic Energy
Basic Eye Anatomy

Your eye from the outside in:
1.
2.
3.
4.
5.
Cornea
Iris
Pupil
Lens
Retina
The Eye
Retinal Details

The retina contains two kinds of visual
sensory receptor cells



Rods
Cones
Three other kinds of cells in the retina that
also play key parts:


Bipolar cells  Ganglion cells (axons = optic
nerve) Brain
Amacrine cells  ‘instant messaging’ system of
the eye
The Retina
More Specifics about the Retina


Fovea
 Less impediment from other cells & blood
vessels
 One to one communication with bipolar cells
& ganglion cells
You really do have a blind spot
From your Eye to your Brain
1.
Information actually flows away from the
brain first
2.
First stop in the brain= sensory ‘toll booth’ –
who can tell me?
3.
Then on to what lobe of the cortex?
Trichromatic Theory of Color Vision

Also known as the Young-Helmholtz theory
of color vision, and was ‘thunk’ up in the
mid-1800’s

This theory says:


We have three different kinds of cones – red,
green, and blue
We see other colors by various combinations of
activity of these three cones
Opponent-Process Theory of Color
Vision
1.
We perceive color in pairs of opposites:



2.
Red vs. green
Blue vs. yellow
Black vs. white
This is how we see negative color
afterimages – Let’s try one
Retinex Color Vision Theory
1.
This theory deals with color constancy
2.
We use context (i.e. other objects) to make
‘decisions’ about color brightness
3.
Then the cortex compares information from
different parts of the retina to make color
and brightness determinations
Problems with Color Vision
1.
Color vision deficiency (color blindness) is
the inability to see some colors
2.
This is a sex-linked, genetic condition,
effecting men more often than women
3.
Red-Green (long-wavelength) deficiency is
the most common –

Either lack of the cones or photopigment is
missing
How our System Processes Visual Info
1.
Visual and Receptive fields
2.
Lateral inhibition – this is how our
system is able to see edges and
borders
Initial Processing in the Cortex
1.
2.
Primary visual cortex
The next stop is the secondary visual cortex
 Information about what an object is goes
to the temporal lobe
 Information about where an object is goes
to the parietal lobe
Vision in the Cerebral Cortex:
Color
1.
Blob cells
2.
Parietal cortex
Vision in the Cerebral Cortex: Motion
and Depth
1.
The benefits of two eyes
2.
The temporal lobe is important for our
ability to detect motion.
Problems with Vision in the Cortex
(i.e. Not the Eye itself!)
We can have brain damage in the visual
system at any level of the cortex
1.
2.
Motion blindness
inability to perceive depth
3.
problems with visual attention
1.
2.
Visual agnosia – inability to recognize
objects
1. prosopagnosia
Development in the Visual
System
Infants
1.
Infants are born with poor vision
2.
But they can see!
Deprivation in Humans
1.
People who have been born blind
2.
Visual development in the cortex seems to
have a critical window
3.
Sometimes deprivation is purposefully
applied
Lack of Movement in our Experience
1.
We get movement information in two ways:



Outside of ourselves
From the movements of our eyes, neck, and head
Both kinds of movement are important for us to
learn depth perception
1.
2.
Effects of total Blindness on the
Brain
What would you guess?
 Atrophied cortex?
Other sensory systems ‘invade’ the
visual cortex