read land’s article about color vision for tuesday next week

• Read Land’s article about color vision for Tuesday next week.

Midterm 2

November 2nd and 3rd

Covers everything about vision

RIGHT EYE LEFT EYE

If you uncross convergence, your right eye gets these faces shifted slightly to left, left eye gets them shifted to right = CROSSED DISPARITY

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

What would you see?

RIGHT EYE LEFT EYE

If you uncross convergence, right eye gets these faces shifted slightly to right, left eye gets them shifted to left = UNCROSSED DISPARITY

AutostereogramsAny repeating objects that have a spacing difference from the background will have either crossed or uncrossed disparity

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

The Correspondence Problem

• What is the Correspondence Problem?

The Correspondence Problem

• What is the Correspondence Problem?

– How does the brain know what contours to match up…what images correspond?

The Correspondence Problem

• Maybe shape analysis is done first to make it easier to match up corresponding parts

How did Bela Julesz prove this model wrong?

The Correspondence Problem

• Bela Julesz tested this with random-dot stereograms

• No contours or form available in monocular image!

• Surface in depth still visible

Left Eye Right Eye

The Correspondence Problem

• A different model must be adopted:

The Correspondence Problem

• A different model must be adopted:Visual system can extract form by matching up individual elements (dots) in an image, computing disparity between them, and finding the most likely surfaces.

Might this involve top-down mechanisms? How could you test that hypothesis?

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

• White light is a mixture of wavelengths– prisms decompose white light into assorted

wavelengths– likewise, adding all wavelengths together

recovers white light

What happens if you mix several different paints together?

Wavelength and Color

Color Vision

• Objects have different colors because they reflect some but not all wavelengths of light

– the surfaces of objects are like filters that selectively absorb certain 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 VisionTheories of Color Vision

“Blue”

“Green”

“Red”

Blue

Wavelength Input Cone Signal to Brain

Color VisionTheories of Color Vision

“Blue”

“Green”

“Red”

Green

Wavelength Input Cone Signal to Brain

Color VisionTheories of Color Vision

“Blue”

“Green”

“Red” Red

Wavelength Input Cone Signal to Brain

Color VisionTheories of Color Vision

“Blue”

“Green”

“Red”

Yellow

Equal Parts Red and Green =

Wavelength Input Cone Signal to Brain

Color VisionTheories of Color Vision

“Blue”

“Green”

“Red”

Yellow

Equal Parts Red and Green =

Wavelength Input Cone Signal to Brain

Color VisionTheories of Color Vision

“Blue”

“Green”

“Red”

Yellow

Equal Parts Red and Green =

Wavelength Input Cone Signal to Brain