1. Visual System: Sight

2. The Stimulus Input: Light Energy
Electromagnetic spectrum--Energy that includes radio waves, X-rays, microwaves, and visible light
Visible spectrum--Energy in the form of light visible to the human eye
Light can be described as a particle and a wave that varies in hue (color) and intensity (amplitude)
Humans can detect about
5 million different hues.
Shorter Wavelengths
Longer
Wavelengths

3. The Stimulus Input: Light Energy
Hue is the color of light as determined by the wavelength of the light energy
Remember ROY G. BIV --> red, orange, yellow, green, blue, indigo and violet
The eye can detect 7 million separate hues
The brightness of light as determined by the height (or amplitude) of the wave
The taller the wave, the brighter the color

4. Afterimage Stare at the red dot in the green square and count
to forty. Then stare at the white square and tell
me what you see. You should see a greenish/blue
dot in a reddish/purple background. That is called
an “afterimage”.

5. The Visual Pathway Cool = Cornea People = Pupil Like = Lens
Fish = Fovea (Rods &
Cones)
Because = Bipolar Cells
Gangsters = Ganglion Cells
Never = Optic Nerve
Cheat = Optic Chiasm
The = Thalamus
Officers = Occipital Lobe

6. Primary Visual Pathway: Thalamus processes info about form, color, brightness & depth
Secondary Visual Pathway: Midbrain processes info about the location of an object

7. Visual Information Processing
Vision is the most complex, best developed and most important sense for humans and other highly mobile creatures.
Think of the eye as the brain’s camera. It gathers light, focuses it, converts it to a neural signal, and sends these signals on for further processing.
The eye transduces the characteristics of light into neural signals that the brain can process. This transduction happens in the retina, the light sensitive layer of cells at the back of the eye.
In the visual cortex, the brain begins working by transforming neural impulses into visual sensations of color, motion, form, and depth.
This process is called parallel processing -- the simultaneous processing of several aspects of a problem

8. Visual Information Processing
Different parts of the visual cortex are used to identify different images
Afterimages – Sensations that linger after the stimulus is removed
Transduction -- The purpose of the visual system is transforming light energy into an electro-chemical neural response (i.e. action potential and synaptic transmission) represented in the characteristics of objects in our environment.

9. Color Vision
Despite the way the world appears, color does not exist outside the brain, because color is a perception the brain creates based on the wavelength of light striking our eyes.
Color is created when the wavelength in a beam of light is recorded by the photoreceptors in the form of neural impulses. It is then sent to specific regions of the brain for processing.
Color brightness depends on the intensity of the light waves. Color blindness is a visual disorder that prevents an individual from discriminating certain colors.
Opponent-process theory
--Sensory receptors come in pairs (red-green/
blue-yellow/black-white)
--If one color is stimulated, the other color is
inhibited
--Explains afterimages
Young-Helmholtz trichromatic (three color) theory
-- There are three cones (red, green, blue) that
form millions of combinations of colors
-- Monochromatic and dichromatic vision

10. Ishihara Test (Color Blindness)
People who suffer red-green blindness have trouble perceiving the number within the design
They lack functioning red- or green- sensitive cones, or sometimes both

11. Sensory Deprivation And Restored Vision
Critical period for normal sensory and perceptual development
Subjects blind from birth whose sight is later restored have trouble making perceptions
Facial recognition, perceptual constancy is lacking

12. Visual Problems
Farsightedness--misshapen eye focuses light rays from near objects past the retina. See far!
Nearsightedness--misshapen eye focuses light rays from a distant object in front of the retina. See near!
Misshapen eye focuses light rays from a distant object in front of the retina. Can see near but not far.
Presbyopia--form of farsightedness caused when lens becomes brittle and inflexible
Astigmatism--uneven curvature of the cornea causes multiple focus points/images on the retina, resulting in blurry vision

13. How Do We Correct Vision?
Glasses, contact lenses, or LASIK surgery reshape
the cornea (which is also involved in bending light
to provide focus).

14. Parts Of The Eye

15. Parts Of The Eye
Pupil --> adjustable opening in the center of the eye that controls amount of light
(bright conditions, iris expands, pupil smaller; dark conditions, iris contracts, pupil larger)
Iris --> ring of muscle that forms the colored portion of the eye around the pupil and controls the size
of the pupil opening
Cornea --> near the center of the retina that begins to focus the light by bending it; protects the eye
Lens --> transparent structure behind pupil that changes shape through accommodation to focus
images on the retina
Retina --> light-sensitive inner surface of the eye, containing receptor rods and cones plus layers of
neurons that begin the processing of visual information
Optic Nerve --> carries neural impulses from the eye to the brain
Blind Spot --> point at which the optic nerve leaves the eye, creating a “blind spot” because there are
no receptor cells located there
Fovea --> central point in the retina; highest concentration of rods and cones; area of sharpest
vision (visual acuity)

16. Retina’s Reaction To Light
Rods are visual receptors that detect black and white and
respond to less light.
Cones are visual receptors that detect sharp images and color
and respond to more light.
Ganglion cells are neurons that pass information from the
bipolar cells; their axons form the optic nerve.

17. Retina’s Reaction To Light
Photoreceptors are light-sensitive cells (neurons) in the retina
that convert light energy into neural energy. That is, light
energy strikes the rods and cones to produce chemical changes
that general neural signals.
Optic Nerve: The bundle of neurons that carries the visual information from the retina to the thalamus to the occipital lobe of the brain.
--Where the stimulus, once
changed into a neural
impulse, gets passed onto
the brain.
Blind Spot: The point where the optic nerve exits the eye and where there are no photo-receptors.
--Any stimulus that falls on
this area cannot be seen.
--We do not notice it because
each eye compensates for
the other and your brain
“fills in” for the missing
information. (top-down
process & Gestalt)

18. Retina’s Reaction To Light
Cover your right eye and stare at the can as you move closer to the screen. Notice the spider disappear in your peripheral vision?

19. The Cosmic Flower
Does this picture seem to pulsate? Because the lens of your eye is not perfectly round some parts of what you look at are blurry. Your eyes make micro movements to try to put this entire picture into focus, which creates the pulsation.

20. The Hermann Grid
Are there gray dots between the squares? Rods in the periphery are responsible. When you look at an area directly there is no dot because you are using your cones but the periphery has dots because the rods are trying to do two things, show you there is a dark area and a light area.