Eye is the window to our soul

English physicist Sir Isaac Newton, in an experiment, observed that a ray of sunlight, or white light, was broken up into the brilliant colors of the spectrum when it passed through a glass prism. He then noticed that the ray recombined into white light when it was beamed back through another prism.

It occurred to Newton that since light rays are not colored, color must not be an actual physical quality in the world

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He concluded that color must exist only in the mind and not in nature.

If color does not actually exist in the world around us, then where do colors come from? To answer this question, we will need to understand how our visual sensory system translates different wavelengths of light into neural impulses so that our brain can interpret the information it receives as the sensation of color.

 How does the eye work 

Phototransduction:

conversion of light energy turns into neural messages http://www.youtube.com/watch?v=JadaWSDxBYk

Visible Spectrum

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Wavelength (hue/color) Intensity (brightness) Saturation (purity)

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The distance from the peak of one light wave to the peak of the next.

•The distance determines the

hue

(color) of the light we perceive.

The amount of energy in a light wave.

Determined by the height of the wave.

The higher the wave the more intense the light is.

Intensity Amount of energy in a wave determined by the amplitude. It is related to perceived brightness.

Saturated Saturated Monochromatic light added to green and red makes them less saturated.

https://www.youtube.com/watch?v=l8_fZPHasdo

Two Major Theories

Three types of cones:      Red Blue Green These three types of cones can make millions of combinations of colors.

Does not explain afterimages or color blindness well.

Opponent-Process Theory- opposing retinal processes enable color vision “ON” “OFF” red green red green blue yellow black white white black yellow blue

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

The sensory receptors come in pairs.

  Red / Green

Yellow

/ Blue   Black/white If one color is stimulated, the other is inhibited.

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Opponent Processing Theory

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Does this make your eyes all weird out??

Opponent Process- Afterimage Effect They are caused by fatigued cells in the retina responding to light.

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After image: Stare at this picture for around 30 seconds. If you look away from the computer monitor and stare at the wall, do you see an after image on the wall?

Psychology, 4/e by Saul Kassin ©2004 Prentice Hall

Opponent processing theory: we see in pairs

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Rods

concentrated in periphery  approx. 120 million  detect black, white and gray  twilight or low light

Cones

 Concentrated near center of eye (fovea)  fine detail and

color

vision  daylight or well-lit conditions 

approx. 6 million Blind Spot region with NO rods or cones http://dragon.uml.edu/psych/bspot.html

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Cornea: Transparent tissue where light enters the eye. (COVERS get it Cornea) Iris: Muscle that expands and contracts to change the size of the opening (pupil) for light.

Lens: Focuses the light rays on the retina.

Retina: Contains sensory receptors that process visual information and sends it to the brain.

Lens: Transparent structure behind the pupil that changes shape to focus images on the retina.

Accommodation: The process by which the eye’s lens changes shape to help focus near or far objects on the retina.

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Bipolar cells

in the first layer translate the information from rods and cones back out to the ganglion cells.

Ganglion cells

then transfer the information down toward the optic nerve. The point where the optic nerve exits the eye is a blind spot. You cannot see anything because there are no photo-receptors at the point at which those cells exit the retina.

 The information is carried down the optic nerve, where it undergoes additional processing. Color information is added at the thalamus. At the end of the optic nerve is the occipital lobe, the structure most responsible for visual processing.

Optic nerve: Carries neural impulses from the eye to the brain. Blind Spot: Point where the optic nerve leaves the eye because there are no receptor cells located there. This creates a blind spot. Fovea: Central point in the retina around which the eye’s cones cluster.

http://www.bergen.org

lab Use your textbook (p. 207). Close your left eye, and fixate your right eye on the black dot. Move the page towards your eye and away from your eye. At some point the car on the right will disappear due to a blind spot.

   We need both of our eyes to use these cues.

Retinal Disparity (as an object comes closer to us, the differences in images between our eyes becomes greater.

Convergence (as an object comes closer our eyes have to come together to keep focused on the object).

Optic nerves connect to the thalamus in the middle of the brain, and the thalamus connects to the visual cortex.

Nerve cells in the visual cortex respond to specific features, such as edges, angles, and movement.

Hubel and Wiesel received a Nobel Prize for their work on Feature Detectors. These specialized nerons in the occipital lobe’s visual cortex receive information from individual ganglion cells in the retina.

https://www.youtube.com/watch?v=y_l4kQ5wjiw

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.

 The dragon is anything but red.

 The dragon rejects the long wavelengths of light that to us are red- so red is reflected of and we see it.

 Also, light has no real color.

 It is our mind that perceives the color.

Genetic disorder in which people are blind to green or red colors. This supports the Trichromatic theory.

Ishihara Test

 Check out these sites to see what a color blind person sees (normal, red blind, blue blind, monochromatic)   http://www.colblindor.com/coblis-color blindness-simulator/ l http://www.webexhibits.org/causesofcolor/2.htm

Color of an object remains the same under different illuminations. However, when context changes the color of an object may look different.