Vision Chapter

Evolution of Vision color

to make it easier to find safe food and avoid poisionious food

Hue

essential color of light

processed by the wavelengths of light

Wavelengths of light

ROY G BIV

Short wavelength → blueish

Long wavelength → redish

Brightness

describes how intense the light is

processed by the height of the wavelength

Saturation

How pure the light is

undiluted colors

Pastels are less saturated because you add white

Primary colors

Red, Green, and Blue → When mixed together, you get white

Humans can tell the difference between 7 million colors, but most can only identify roughly 200

The human eye

Cornea

Iris

Lens

Vitreous Humour

Retina

Fovea

Optic Nerve

Inside the Retina

Rods

Cones

Bipolar cell

Cornea

the outer part of the eye

transparent membrane that protects the eye

refracts light, to go through the pupil

This is 80% of a person’s ability to focus (Lasik surgery)

Iris

colored area of the eye

Controls the pupil

Pupil

black dot in the center of the eye

Smaller in bright light

Larger in low light

Larger on drugs/alcohol

Emotions play a role in pupil control

Head Trauma

one pupil is often larger than the other when this has occurred

Lens

Where they originally thought focusing took place

The shape changes based on the distance of the object

When the object is close this is thicker when the object is farther this is thinner

20% of a person’s focus is in the lens

Vitreous Humor

Empty white space behind the lens that is a gel like clear liquid that allows people to see images and images that pass through → projected onto retina

This also gives the eyeball its shape

It can also hydrate you (ex: eating fish eyes if stranded at sea)

Retina

light-sensitive layer of cells

This is actually red in color (digital camera red eyes)

Red means the retina is healthy

Fovea

pit-shaped → peach/avocado

Where you focus what you are looking at

objects outside of this are blurry

this is a part of the retina

filled with cones to help focus the image

Optic nerve

Nerves→ Mylein sheath→ white apperance

Goes to the back of the brain

Creates a blind spot

cicadic eye movement to cover the blind spot

Order of Vision (steps)

Cornea → Pupil → Lens → the image inverts in the vitreous humor → Fovea/Retina → optic nerve

Rods

way more rods than cones in the retina

plays a role in processing black and white

low-level light

connected to a bipolar cell (middle man)

multiple rods connect to one bipolar cell → which leads to spatial summation

Spatial summation (++)

action potential

Bipolar cell

10 units to fire, 5 rods connect, only 2 units from each rod means this is easily activated

Cones

detail vision

processes color

1 bipolar cell to 1 cone = harder to activate

Dark adaptation

takes 10 minutes for full adaptation

close one eye and the dark adaptation comes back much quicker

pirates used eye patches for quick transition from light to dark

Ganglion cells

axons from these make up the optic nerve

receptive fields

Center on / Surrond-off

Center - Off/ surround on

recognizes light changes

Types of Ganglion cells

parvocellular (p-cells)

Magnocellular (M-cells)

Kaniocellular (K-cells)

Parvocellular

responds to motionless or sustained stimuli

detects color, depth, fine texture, and stitching (our ability to see grains of sand), patterns

Objects that are not moving

Magnocellular

moving objects

depth

brightness differences

Kaniocellular

grating → color changes (light versus dark colors)

(hues and ques game)

Optic Chiasm

where it crosses (axons of ganglion)