1. The Eye contains visual sensory receptors focuses light on the retina
contains most of the eye’s cones
hole that allows light to enter eye
muscle that controls (pupil) how much light enters eye
OBJECTIVE 13-2| Describe the major structure of the eye, and explain how they guide the incoming ray of light toward the eye’s receptor cells.
transparent outer covering of eye
Where optic nerve leaves eye…no receptors here

2. Hue (color): dimension of color determined by wavelength of light.
Wavelength (Hue)
Hue (color): dimension of color determined by wavelength of light.
Wavelength the distance from the peak of one wave to the peak of the next.

3. Different wavelengths of light result
Wavelength (Hue)
Violet
Indigo
Blue
Green
Yellow
Orange
Red
400 nm
700 nm
Long wavelengths
Short wavelengths
Different wavelengths of light result
in different colors.

4. Intensity (Brightness)
Intensity Amount of energy in a wave determined by amplitude; related to perceived brightness.

5. Intensity (Brightness)
Blue color with varying levels of intensity.
As intensity increases or decreases, blue color
looks more “washed out” or “darkened.”

6. The Lens
Nearsightedness: A condition in which nearby objects are seen more clearly than distant objects b/c eye elongated & image focus before it hits the retina
Farsightedness: A condition in which faraway objects are seen more clearly than near objects b/c eye shortened & image would focus after it hit the retina

7. Retina
The light-sensitive inner surface of the eye, containing receptor rods and cones plus layers of other neurons (bipolar, ganglion cells) that process visual information.
OBJECTIVE 13-3| Contrast the two types of receptor cells in the retina, and describe the retina’s reaction to light.

8. Fovea
Central point in the retina, around which the eye’s cones cluster…because of this there is little color vision in the farthest periphery of our vision
Let’s test this fact…

9. Shares one with other rods
Photoreceptors
CONES
RODS
RODS
CONES
Number
6 million
120 million
Location
Center (fovea)
Periphery
Color sensitive?
Yes No
Sensitivity in dim light?
Low
High
Ability to detect detail?
High
Low
Number of bipolar cells?
Each has own
Shares one with other rods
E.R. Lewis, Y.Y. Zeevi, F.S Werblin, 1969

10. Bipolar & Ganglion Cells
Bipolar cells receive messages from photoreceptors and transmit them to ganglion cells, which form the optic nerve (axons).
Remember…
Cones each have their own bipolar cell.
Multiple rods share one bipolar cell.

11. Test your Blind Spot
Blind spot – no visual receptors here because of all the information leaving the eye
To find your blind spot, close your right eye and look at the cookie monster at eye level. Maintain your focus on the cookie monster and slowly move your paper from your eyes until the cookie disappears.
Under normal circumstances, you are unaware of your blind spot because one eye sees what the other does not. WHY DO YOU SEE WHITE WHERE THE COOKIE SHOULD BE? Even with one eye closed, you're not aware of the gap because your brain "fills in" the missing information by making an assumption about what belongs in the void.

12. Feature Detection
Nerve cells in the visual cortex that respond to specific features, like edges, angle, length and movement.
There are even some feature detectors that are specifically sensitive to the human face!

13. Visual Information Processing
Processing of several aspects of the stimulus simultaneously is called parallel processing. The brain divides a visual scene into subdivisions such as color, depth, form and movement etc.
OBJECTIVE 13-5| Discuss parallel processing and discuss its role in visual processing.
Movement Aftereffects:
*To show you that we have detectors for movement we are going to isolate that detector (and show you how our senses adapt).

14. from visual cortex to assoc. areas
from assoc. areas to memory
info sent
to visual cortex
Tim Bieber/ The Image Bank

15. Theories of Color Vision
Trichromatic theory: Based on behavioral experiments, Helmholtz suggested that retina contains three receptors sensitive to red, blue and green colors.
Standard stimulus
OBJECTIVE 13-6| Explain how the Young-Helmholtz and opponent-process theories help us understand color vision.
Comparison stimulus
Max
Medium
Low
Blue
Green
Red

16. Photoreceptors
Blue
Cones
Green
Cones
Red
Cones
MacNichol, Wald and Brown (1967) measured directly the absorption spectra of visual pigments of single cones obtained from the retinas of humans.
Short
wave
Medium
wave
Long
wave

17. Color Deficiency(blindness)
Genetic disorder which prevents individuals from discriminating between certain colors due to a weakness in or lack of one of the cones
Most common form of color “blindness” is difficulty distinguishing between red and green
Complete color deficiency does exist but is very rare…it would be like watching a black and white movie.

18. Ishihara (color blindness)Test25 6 42 5 56 8

19. Normal vision red/green deficiency
Photos from:

20. Above represent the art in “normal vision”…below what it would look like to a person with red/green deficiency

21. Opponent Process Theory
Hering, proposed that we process four primary colors opposed in pairs of red-green, blue-yellow, and black-white.
Cones
Retinal
Ganglion
Cells

22. Afterimages… Gaze at the middle of the flag for about 30
seconds, when it disappears, stare at the dot and report
if you see America’s flag.

23. Gaze at the middle of the light bulb for about 30
Afterimages…
Gaze at the middle of the light bulb for about 30
seconds, when it disappears, stare at the white space and report what you see.

24. Spanish castle afterimage….
Afterimages…
Spanish castle afterimage….

25. Color Constancy
the color of an object will remain roughly constant even if the lighting and wavelengths change
OBJECTIVE 13-7| Explain the importance of color constancy.