Do Now• Try to label the

diagram of the eye

• Use your textbook and the terms on the right to help you

• Optic nerve• Pupil• Lens• Retina• Vitreous• Iris• Cornea

Vision

• The Visual System• Color Vision and Theories

Vision Test!!!

• First stare continuously at the center of the upper square for about 20 seconds, then look at the dot in the lower square.

• Within a moment, a gray-and-white afterimage should appear inside the lower square

The Visual SystemStructures and Functions

• Cornea – Clear protective coating that covers the front of the eye– Where light enters the eye

• Pupil– Opening in the center of the eye to let light pass through

Pupil

Cornea

Iris

• Iris – Colored part of the

eye– Contract in bright

light (protects eye)– Expand in dim light

(let in extra light)

The Visual SystemStructures and Functions

• Lens – Transparent, inside pupil– Focuses light on retina– Changes shape to see near vs. far

• Retina – Inner surface in back of eyeball– Contains receptor cells– Very center is called the fovea

RetinaVitreous

Optic Nerve

Lens Pupil

Cornea

Iris

Find Your Blind Spot

Place on the retina where

the optic nerve enters

the retina and where

there are no receptor

cells

The Visual SystemReceptor Cells

• Location = retina• Sensitive to electromagnetic energy,

primarily light• Rods

– Respond to intensities of light/dark– Night vision - sensitive to light– About 120 million

• Cones– Responsible for seeing colors– Found in fovea – About 8 million

• Bipolar cells – Specialized neurons connected to

receptors

Do Now

• Fill out Receptor Cell info on packet page #1

The Visual SystemAdaptation

• Dark adaptation– Process by which rods and cones

become more sensitive to darkness– Not enough light to activate cones

• CANNOT SEE COLOR

• Light adaptation– Process by which sensitivity of rods and

cones decreases in bright light

This is called afterimage

Sense experience that occurs after a visual stimulus has been

removed

Pop Quiz!!!

What do you see with?

YOUR BRAIN

Color VisionProperties of Color

• Hues– Aspects of color that correspond to general

color names like red, green, and blue• Saturation

– Vividness or richness of a hue– Forrest green, olive green, pale green, neon

green, etc.• Brightness

– Based on the nearness of a color to white as opposed to black

– Is the color more white or black?

Color VisionTheories

• Primary colors for light mixtures: red, green, blue• Additive color mixing

– Mixing light of different wavelengths to create new hue• Subtractive color mixing

– Mixing pigments– Concerned with what colors are absorbed and reflected

• Trichromatic theory– Perception of all colors is based on three color receptors (red,

green, blue) in the retina• Opponent-process theory

– Color receptors come in pairs (yellow-blue, red-green, black-white)

• Trichromatic = normal vision• Color blindness…dichromat and monochromat

Color VisionFun Facts!!!

• Color is in the eye of the beholder

• Humans and most primates are trichromats

• Rodents and owls (nocturnal animals) are monochromats

• Bees can see ultraviolet light