## Presentation on theme: "Read Land’s article about color vision for Tuesday next week."— Presentation transcript:

Midterm 2 November 2nd and 3rd Covers everything about vision

RIGHT EYELEFT EYE If you uncross convergence, your right eye gets these faces shifted slightly to left, left eye gets them shifted to right = CROSSED DISPARITY Autostereograms Any repeating objects that have a spacing different from the background will have either crossed or uncrossed disparity What would you see?

RIGHT EYELEFT EYE If you uncross convergence, right eye gets these faces shifted slightly to right, left eye gets them shifted to left = UNCROSSED DISPARITY Autostereograms Any 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

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 Vision Perceiving Color Four absorption peaks in retina: 3 cone types plus rods Absorption/Cone response

Color Vision Theories of Color Vision “Blue” “Green” “Red” Blue Wavelength InputCone Signal to Brain

Color Vision Theories of Color Vision “Blue” “Green” “Red” Green Wavelength InputCone Signal to Brain

Color Vision Theories of Color Vision “Blue” “Green” “Red” Red Wavelength InputCone Signal to Brain

Color Vision Theories of Color Vision “Blue” “Green” “Red” Yellow Equal Parts Red and Green = Wavelength InputCone Signal to Brain

Color Vision Theories of Color Vision “Blue” “Green” “Red” Yellow Equal Parts Red and Green = Wavelength InputCone Signal to Brain

Color Vision Theories of Color Vision “Blue” “Green” “Red” Yellow Equal Parts Red and Green = Wavelength InputCone Signal to Brain