Exam next week

• Covers everything about all sensory modalities except hearing

• This includes:visionbalance/touch/taste/smell/

proprioception/theroception

Binocular Disparity

• points nearer than horopter have crossed disparity

• points farther than horopter have uncrossed disparity

The Horopter

AutostereogramsAny repeating objects that have a spacing different from the background will have either crossed or uncrossed disparity when the convergence angle of the

eyes is set to a point in front of or behind the screen

What would you see?

“Magic Eye” Stereograms• Usually viewed with uncrossed convergence • Imagine gazing farther than the surface (let your eyes

“relax”)• Now try to notice objects or forms in the blurriness• As you become aware of shapes, try to focus

(accommodate) the plane of the image without converging your eyes

Autostereograms

Autostereograms

Autostereograms

• What color is this box?

Wavelength and Color• Recall that light is electromagnetic radiation

Wavelength and Color• Recall that light is electromagnetic

radiation• Light waves have a

frequency/wavelength

Wavelength and Color• Recall that light is electromagnetic

radiation• Light waves have a

frequency/wavelength• Frequency/wavelength is the physical

property that corresponds (loosely) to the perception called color

Color Vision• Different wavelengths correspond

roughly to the “colors” of the spectrum

Wavelength and Color

Color Vision• White light is a mixture of wavelengths

– prisms decompose white light into assorted wavelengths

Wavelength and Color

Color Vision• Primary colors

Perceiving Color

What are the primary colors?

Color Vision• Primary colors

Perceiving Color

Red Green Blue

Color Vision• Primary colors

Perceiving Color

What makes them primary?

Color Vision• Primary colors

• Every color (hue) can be created by blending light of the three primary colors in differing proportions

Perceiving Color

Color Vision• Primary colors

• Every color (hue) can be created by blending light of the three primary colors in differing proportions

• Led to prediction that there must be three (and only three) distinct color receptor types

Perceiving Color

Color VisionPerceiving Color• Four absorption peaks in retina: 3 cone types plus

rods

Abs

orpt

ion/

Con

e re

spon

se

Color VisionTrichromatic Theory of Color Vision

“Blue”

“Green”

“Red”

Blue

Wavelength Input Cone Signal to Brain

Color VisionTrichromatic Theory of Color Vision

“Blue”

“Green”

“Red”

Green

Wavelength Input Cone Signal to Brain

Color VisionTrichromatic Theory of Color Vision

“Blue”

“Green”

“Red” Red

Wavelength Input Cone Signal to Brain

Color VisionTrichromatic Theory of Color Vision

“Blue”

“Green”

“Red”

Yellow

Equal Parts Red and Green =

Wavelength Input Cone Signal to Brain

Color VisionTrichromatic Theory of Color Vision

“Blue”

“Green”

“Red”

Yellow

Equal Parts Red and Green =

Wavelength Input Cone Signal to Brain

Color VisionTrichromatic Theory of Color Vision

“Blue”

“Green”

“Red”

Yellow

Equal Parts Red and Green =

Wavelength Input Cone Signal to Brain

Color Vision• Trichromatic theory of color vision:

– brain interprets the relative amounts of signaling from each of these cone types

Theories of Color Vision: Trichromatic Theory

Color Vision• Trichromatic theory of color vision:

– brain interprets the relative amounts of signaling from each of these cone types

• This means that some colors can be matched by a pair of wavelengths– metamers: colors that have no definite single

wavelength (e.g. yellow)

Theories of Color Vision: Trichromatic Theory

Color Vision• Trichromatic theory of color vision:

– brain interprets the relative amounts of signaling from each of these cone types

• This means that some colors can be matched by a pair of wavelengths– metamers: colors that have no definite single

wavelength (e.g. yellow)• This also means that any color can be

matched by mixing (not more than) three different wavelengths

Theories of Color Vision: Trichromatic Theory

• What color can only exist as a metamer (an additive mixture of wavelengths)? In other words, what color cannot be made with a single wavelength?

• What color can only exist as a metamer (an additive mixture of wavelengths)? In other words, what color cannot be made with a single wavelength?

MagentaThink about why!

• Both yellow and blue pigments reflect a bit of green

wavelength

Am

ount

of r

efle

ctio

n

blue green yellow red

• Subtractive mixing is commonly used in color printers

• Problem with Trichromatic Theory:

Theories of Color Vision: Trichromatic Theory

• Problem with Trichromatic Theory:

YELLOW

Theories of Color Vision: Trichromatic Theory

• Problem with Trichromatic Theory:– most people categorize colors into four

primaries: red, yellow, green, and blue

– some colors simply cannot be perceived as gradations of each other• redish green !?• blueish yellow !?

– It is as if these colors are opposites

Theories of Color Vision: Trichromatic Theory

• Opponent-Process Theory– color is determined by outputs of two

different continuously variable channels:• red - green opponent channel• blue - yellow opponent channel

Theories of Color Vision: Opponent-Process Theory

• Opponent-Process Theory– Red opposes Green– (Red + Green) opposes Blue

• Opponent-Process Theory explains color afterimages

Theories of Color Vision: Opponent-Process Theory

• Everything you’ve learned so far is wrong.

• Everything you’ve learned so far is wrong.

• Well, not really wrong, just far from complete.