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. 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: Phototransduction: conversion of light energy turns into neural messages

http://www.youtube.com/watch?v=JadaWSDxBYk

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1. Wavelength (hue/color)

2. Intensity (brightness)

3. Saturation (purity)

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.

Monochromatic light added to green and redmakes them less saturated.

Saturated

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 greengreen red blue yellow yellow blue black whitewhite black

Hering proposed that we process four primary colors combined in pairs of red-

green, blue-yellow, and black-white.

Cones

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Cells

The sensory receptors come in pairs.

Red/Green Yellow/Blue Black/white If one color is

stimulated, the other is inhibited.

Opponent Processing

TheoryDoes this make your

eyes all weird out??

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

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?

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

Opponent processing theory: we see in pairs

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- Blind Spot- region with NO rods or coneshttp://dragon.uml.edu/psych/bspot.html

1. Cornea: Transparent tissue where light enters the eye. (COVERS get it Cornea)

2. Iris: Muscle that expands and contracts to change the size of the opening (pupil) for light.

3. Lens: Focuses the light rays on the retina.4. 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.

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.

http://www.bergen.org

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.

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.

lab

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.

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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/

http://www.webexhibits.org/causesofcolor/2.html

Color of an object remains the same under different illuminations. However, when context

changes the color of an object may look different.

R. B

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