1. Vision- How do we see what we see?

2. Vision Purpose of the visual system
transform light energy into an electro-chemical neural response
Represent characteristics of objects such as-
size, color, shape, and location

3. Step One: Gathering Light
Light is reflected off objects & gathered by eyes
2)Light Waves :
Vary in: perceptions:
Amplitude (height) Brightness
Wavelength Color (hue)
Fill is opject cahracteritics= discuss paralell process

4. Wavelength in nanometers (billionths of a meter)
Wavelength to longest to shortest red ,orange yellow, green blue, indigo , violet
Gamma
rays
X-rays
Ultra-
violet
Infrared
Radar
Broadcast
bands AC
circuits
Visible light
Prism
White
light
400
500
600
700 10 -5 -3 -1 1 3 5 7 9 11 13 15 17
Wavelength in nanometers (billionths of a meter)

5. Step Two: In the Eye

6. Cont…

7. STEP THREE: IN THE BRAIN
Retina
Optic
tract
chiasm
nerve
Visual area
of the thalamus
Visual
cortex

8. How do I remember it all? Cool People in line rarely cut,
real blonde girls flirt
Cornea…Pupil…Iris…Lens…Retina…Cones…Rods…. Bipolar cells
Ganglion Cells….Feature Detectors

9. Additive Color Mixture
Combining lights of different wavelengths =the perception of new colors
Examples:
red + green = yellow
red + blue = purple

10. Trichromatic Theory of Color Vision
Mixing three primary lights= experience of all possible colors
(Young and Helmholtz)

11. Complementary Afterimages http://www. psychologie. tu-dresden
After staring at this image for about 3 minutes a red white and blue afterimage should be seen. To do this the students must be led to stare at the fixation point in the green flag for 3 minutes without moving their eyes. This is difficult to do but critical to the demo which is based upon the green flag falling on the same retinal location until fatigue of the cone pigments occurs.
After the adaptation period have the students refixate on the white screen. They should see a red white & blue flag.
Ask them how this can be explained from the viewpoint of trichromatic theory.
It cannot and requires an opponent process theory. Yet trichromaticity is an accepted theory of the retina. Therefore this kind of afterimage must reflect properties of post-retinalstructures, and in fact the opponent processes illustrated by this demo arise in the ganglion cells that form the head of the ooptic nerve.

13. Opponent-Process Theory ( an antagonistic process)
Herring proposed that we have two types of color opponent cells
red-green opponent cells
blue-yellow opponent cells

14. Video Clip- Blue man

15. Overview of Visual System
The eye is like a camera, but instead of using film to catch the light we have rods and cones
Cones allow us to see fine spatial detail and color, but can not function well in dim light
Rods enable us to see in dim light, but at the loss of color and fine spatial detail
Our color vision is based on the presence of 3 types of cones, each maximally sensitive to a different range of wavelengths

16. Visual information is processed by ganglion cells ________ it is processed by rods and cones and ________ it is processed by bipolar cells.
a. before; after
b. after; before
c. before; before
d. after; after

17. The opponent-process theory is most useful for explaining one of the characteristics of:
a. phantom limb sensations.
b. prosopagnosia.
c. Weber's law.
d. accommodation.
e. afterimages

18. Demo: Additive Color Mixing

19. Color Mixing Two basic types of color mixing subtractive color mixture
example: combining different color paints