VisionBy: Bethany, Iqra, Clint, Cameron,

Nick

The Process

• Light enters eye through the cornea • Then, it goes through the pupil which is

surrounded by the iris– Fun Fact: When you’re around someone you

like, your pupils dilate– Dark adaptation: pupils get bigger or smaller

depending on surrounding

• Behind pupil is the lens which focuses the light rays into an image on the retina– Lens first reverses the image

The Process Cont.

Accommodation: lens will change its curvature to focus what you see

Nearsightedness: when the lens focuses objects in front of retina

Farsightedness: when the lens focuses objects behind the retina

How It Works

• Retina: where transduction happens. – Thin, light sensitive layer of cells at the back

of the eye

• Eye gathers light, focuses it, converts it to neural signals, sends to brain

• Transduction: eye converts light into neural signals the brain can process

Photoreceptors• These cells are called

photoreceptors– Convert light energy into

neural impulses

• Two types:– rods: especially sensitive to

dim light but not to colors.– cones: especially sensitive to

colors but not to dim light

• Cones are concentrated in the fovea where our vision is sharpest

Other Important Cells in Eyes

• Bipolar cells: take impulses from rods & cones and takes it to ganglion cells

• Ganglion cells: collects visual information– Axons make up the optic nerve which

transports this information to brain• Blind spot: small area of retina where

there are no photoreceptors– where the optic nerve leaves the eye– DEMO: Find YOUR Blind Spot!

Optic Chiasm

Optic chiasm: where optic nerves from each eye meet

The Brain• Thalamus: sends the

information to the visual cortex

• Visual cortex: gets all information from optic nerve– Transforms neural impulses

into visuals with color, form, movement

– Makes 2D patterns 3D– Part of the occipital lobe

which puts together the entire picture

• Forebrain: makes connections, analyzes what you sees, spatial relationships

The Brain cont.

• Parallel processing: brain divides each visual scene into subdimensions like color, movement, form and depth and works on each one at the same time

• Brain creates color vision from wavelengths of light

Light

Radiant light: visible energy released by an object (sun, lightbulb)

Reflected light: visible energy reflected by object

(grass, flowers)

Color Vision• Amplitude: intensity,

brightness• Photoreceptors pick up

wavelengths of light and change into neural impulses

• Hue: color of object, created in visual cortex– Not a property of things– Psychological sensation

created in the brain from the wavelengths of visible light

– Saturation: how much color an object has

• Acuity: how clear your vision is

How We Sense Color

• Young-Helmhotlz trichromatic theory: colors are sensed by 3 different types of cones that see red, blue, and green wavelengths. Earliest stage of color vision

• Opponent-process theory: cells in visual system process colors in complementary pairs (red or green and blue or yellow)

-Afterimages: sensations that linger afterstimulus is removed because of retinafatigue. Usually are negative reversed)

Vision Disorders

• Monochromats– complete color blindness. can’t distinguish

any colors

Vision Disorders

• Dichromats– Kind of color blindness where one of the three

colors is missing