1. Psychological dimensions:
COLOR VISION
Psychological dimensions:
Hue = basic color; determined by dominant wavelength in mixture
Saturation = purity of color; determined by a combination of light intensity and how much it is distributed across the spectrum of different wavelengths. The purest color is achieved by using just one wavelength at a high intensity.
Brightness = psychological dimension of color which most closely relates to physical intensity

2. Psychological Components of Color Vision
chapter 6
Psychological Components of Color Vision
Hue
Visual experience specified by color names and related to the wavelength of light
Brightness
Visual experience related to the amount of light emitted from or reflected by an object
Saturation
Visual experience related to the complexity of light waves

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

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

5. Intensity (Brightness)
Intensity: Amount of energy in a wave determined by the amplitude. It is related to perceived brightness.

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

7. Saturation
- the ratio of the dominant wavelength to other wavelengths in the color

8. chapter 6
What we see

9. chapter 6
Trichromatic theory
Young (1802) and von Helmholtz (1852) both proposed that the eye detects 3 primary colors
Red, blue, and green
All other colors derived by combination

10. Color Vision
Trichromatic theory: Young and von Helmholtz suggested that the eye must contain three receptors that are sensitive to red, blue and green colors.
Standard stimulus
Preview Question 7: What theories help us understand color vision?
Comparison stimulus
Max
Medium
Low
Blue
Green
Red

11. Theories of Color Vision
Trichromatic theory (Young-Helmholtz)
3 different kinds of cones in retina (short wavelength/blue, medium/green, long/red)
cones contain different opsins (light sensitive chemicals)
each opsin is most sensitive to different wavelengths.
wavelengths are absorbed by opsins most sensitive to them
absorbed wavelengths = the color we see
does not explain gray or afterimages

12. Opponent-process theory
chapter 6
Opponent-process theory
A competing theory of color vision, which assumes that the visual system treats pairs of colors as opposing or antagonistic
Opponent-process cells are inhibited by a color, and have a burst of activity when it is removed.

13. Color Blindness
Genetic disorder in which people are blind to green or red colors. This supports the Trichromatic theory.
Ishihara Test

14. Colorblindness
Far more common in males than females
Different levels of severity
Genetic
Most = dichromatic (have 2 kinds of cones) = red/green or yellow/blue
- protanopia & deuteranopia
Rare = monochromatic (only rods or only 1 kind of functioning cone)

15. Opponent Process Theory (Hering)
visual elements sensitive to color = 3 pairs
pairs (red-green, blue-yellow, black-white) oppose/inhibit each other
object reflects light of certain wavelength, stimulates firing of cells sensitive to that color & inhibits firing of cells sensitive to opposite color
afterimages = use cells for one color; when stop stimulation, one used is fatigued; opposite is activated; afterimage occurs until balance is restored
Both theories apply:
Trichromatic explains how cones in retina transform lightwaves into color
(photoreceptors)
Opponent Process explains how color coding occurs in brain (ganglion cells)

16. Opponent Colors Gaze at the middle of the flag for about 30
Seconds. When it disappears, stare at the dot and report
whether or not you see Britain's flag.

18. Opponent Process: Color Aftereffects

19. Opponent Process: Motion Aftereffects
(Two Eyes/One Eye – difference? Why?)