Vision

By Michelle, Kim, Kayla, and Sean

• Discuss sensory process including the specific nature of energy transduction, relevant anatomical structures and specialized pathways in the brain for vision• Explain common sensory disorders

related to vision• Identify the major components of the

visual system and the function of each

Key Objectives

•How does sensory information impact human behavior?• To what extend are our perceptions of the environment accurate?

Keep in Mind

• Detects targets• Detect threats• Detect environmental changes and

stimuli

Importance of Vision

• Creates neural signals from light waves

• Light waves the only form of electromagnetic energy we can see called visible light

• Transduction happens in the retina

• Transduction is the transformation of one form of energy into another

• For vision this would be transferring light waves into neural signals

Basics of Vision

Visible Light

• Wavelength – this is the distance between peaks of the wave• Affects perceived color• Amplitude – this is the height of the wave• Affects perception of brightness• Saturation – the amount of whiteness in a color; the less

white, the more saturated • Hue – this is color, a sensation the brain produces from the

wavelengths of visible light • Radiant Light – light that is emitted • The sun, lights, fireflies• Reflected Light – light that is reflected• The color of your shift is reflected light

Properties of Light

• Light enters the transparent window of eye called the cornea

• Then through the lens• Forms an upside down imagine on the retina behind it• The brain is in charge of flipping the image back:

accommodation

How Vision Works

• The retina is…• Retina is the farthest light gets in the visual system before it

is converted• Where transduction takes place, light waves converted to

neural signals• The retina is like a the spinal cord but for vision and can

process images• The retina has a variety of cells including photoreceptors,

rods, cones, • Photoreceptors are the light sensitive neurons in the eye• There are two types: rods and cones

The Retina

The Eye

• Rod-shaped• Sensitive to dim light• NOT sensitive to colors• For night vision and peripheral

vision • Outnumber cones in the

peripheral area of the retina• Highest concentration of rods is

just outside the fovea and gradually decreases

Rods

• Cone-shaped photoreceptors• Sensitive to colors• For day vision and color vision• NOT sensitive to dim light• They sense waves in red, blue, and green wave lengths• Cones concentrate in area of retina called the fovea• This is where you have the sharpest vision

Cones

• The process is which the eyes become more sensitive to light in low illumination.

• This when you go from really bright light to low light and your eyes adjust

• Like when you walk from outside in the middle of summer into a dark room

• Light adaption is the opposite

Dark Adaptation

• Starts as light enters the eye • Stimulates rods and cones at

the back of the retina• They convert the light waves

into neural impulses• The impulses are collected by

bipolar cells• Then sent off to ganglion cells• The axons of the ganglion are

bundled together to form the optic nerve

• Impulses travel through the optic nerve (out of the optic disk) to the brain

Light stimulus to Neural Impulse

• The axons that go from your eye to your brain meet at the optic disk, which is a whole in the retina where optic nerve fibers leave the eye

• Since there is a whole in the retina there is a blind spot in your vision

• Most people are not aware that they have a blind spot because your other eye fills in your brain with the information you are missing

• On a piece of paper:• draw a cross and a dot• Close left eye, stare at cross• Start 8 inches from face• Move paper back• Dot will disappear

Blind Spots

• Optic Chasm – the point at which the optic nerves from the inside half of each eye cross over and then project to the opposite half of the brain

• From there they go the thalamus – the brain’s major relay station

• Then they are sent to different parts of the visual cortex which is located in the occipital lobe

• All of this takes place in the forebrain• You “look with your eyes but see with your brain”• Brain is in charge of processing info from eyes• Parallel Processing: simultaneously extracting

different kinds of information from the same input• Retinal Disparity - is the difference between the

visual images formed by the different angles of the eye

• The brain connects the over lapping image and creates one without seems

• Retinal disparity is important for depth perception

Vision in the Brain

Visual cortex• Where all visual images are processForebrain• The Diencephalon is an area of this region of the brain that

also helps process visual images, but from a more cognitive side.

Thalamus• Before being able to travel to the Cortex, visual image fibers

must travel through the lateral geniculate nucleus, which is a part of the Thalamus. The fibers synapse into the LGN at this point.

Occipital Lobe• Area of the cerebral cortex that contains the visual cortex.

Brain Summary

• Color depends on three properties• Wavelength makes the hue• Amplitude makes the

brightness• Purity or Saturation • Brightness – caused by

the intensity of the light waves; also a sensation

• Acuity: the sharpness, acuteness of vision

Vision Properties

• Binocular Cues are depth cues that require both eyes, usually required for judging how far away close objects are. • Example: hold two pens in

front of you and touch tips together, try again with only one eye open….its harder

• Monocular Cues are depth cues that (interposition and linear perspective) that are available to both eyes• Trying to tell how far a car

straight ahead a far distance is

Monocular Cues vs. Binocular Cues

• Trichromatic theory: The idea that colors are sensed by three different types of cones sensitive to light in the red, blue, and green wavelengths. Explains the earliest stage of color sensation

• Opponent Process theory: The idea that cells in the visual system process colors in complementary pairs

• Young-Helmholtz Theory: (Thomas Young and Hermann von Helmholtz) is a theory of trichromatic color vision - the manner in which the photoreceptor cells in the eyes of humans and other primates work to enable color vision.

• Color Afterimage: A color a person will continue to see after looking at an object

Theories of Color Sensation

• Nearsightedness – you can see close objects clearly while distant ones are blurry

• Farsightedness – you can see distant objects clearly but close ones are blurry

• Diplopia – or “double vision” when you see two images instead of one

• Color Deficiencies

Vision Disorders

• This means that you cannot see all of the colors• Monochromat: A person who are completely color blind• Dichromat: one affected with dichromatism (a defect of

vision in which the retina responds to only two of the three primary colors)

Color deficiencies