Presented By: Jenna, Jeff, and Olivia Vision Presented By: Jenna, Jeff, and Olivia

My head is spinning just from reading these! Essential Questions What parts of the visual system create and process images? What are some theories related to color vision and what do they state? Name some common visual disorders and what causes them. My head is spinning just from reading these!

Structure of the Eye

Structure Iris: Colored part of the eye; contracts and expands retina in response to light and protects it Pupil: Hole in the center of the iris where light passes through Cornea: Clear, dome-shaped surface that covers eye; first (and most powerful) lens Lens: keeps images in focus (adjustable for close work/distance); inverts images and sends to brain

Retina: film over the eye; converts light into electrical signals to send to the brain Blind Spot: location where the optic nerve exits the eye; anything that falls in this area is not seen Bipolar cells: cells in the retina that connect receptors to ganglion cells Ganglion cells: axons of these cells form the optic nerve; located in the retina Fovea: area of the retina that controls central vision

Structures that help with vision, but aren’t totally located in the eye Optic Chiasm: where the optic nerve fibers from each eye meet Optic Nerve: group of neurons that transfer visual information from the retina to the brain Visual Cortex: area in the brain that processes vision, and combines it in order to create an image Forebrain: receives and processes visual information (contains the visual cortex) Occipital Lobe: located in the forebrain; contains the visual cortex Thalamus: processes visions; information from the optic nerves is relayed here, and then to the cerebral cortex

Photoreceptors Light sensitive cells (neurons) in the retina that convert light energy to neural impulses Furthest that light travels in the visual system Two types: Rods: most sensitive to light, but not to color; 120 million Cones: provide eye’s color sensitivity; 6-7 million Visual Phototransduction: process through which photoreceptors convert light into electrical signals in the rods and cones of the retina

Visual Processing Images enter through lens and are inverted info on viewer’s left is taken in on right side of the eye Eye sends info to optic chiasmus info on left side sent to be right cerebral hemisphere, processed by right occipital lobe Neurons of cerebral cortex pass their separate analyses of the image into parietal lobe and temporal lobe assembled and integrated w/ emotions, memories into meaningfulness

Eye Disorders Nearsighted: inability to see objects that are far away; eyes have difficulty refracting light Farsighted: inability to see objects that are nearby; eye ball is either too short or lens cannot become round Blindness: inability to see Cataracts: clouding of the lens Glaucoma: increased pressure within the eye

Some Functions of the Eye Accommodation: when eye muscles change to focus on something close or far away Normally in lens, pupil size, and movement of eyes in opposite directions to keep binocular vision Dark Adaptation: chemical and physical changes undergone in eye to make it possible to see in relative darkness Includes dilating pupil, and increasing activity in rods

More Functions of the Eye Parallel Processing: ability of brain to simultaneously process incoming messages of different quality (multitasking for your eyes) Important for vision because brain first divides vision into color, motion, shape, depth then synthesizes it Acuity: clearness of vision Usually depends on focused retina, and how well brain interprets images

What is color? Color/ Hue: sensation created in the brain from wavelengths of light and visual information gathered from the eyes Color is a sensation, so it does not exist outside of the brain Only exists in the individual mind Created when light waves are translated by photoreceptors into neural impulses, and are transferred to specialized areas of the brain to be processed

Electromagnetic Spectrum The range of electromagnetic energy Includes: Radio waves Microwaves Infrared Visible Light Ultraviolet X-Rays Gamma Rays

More information about the Electromagnetic Spectrum Classifications in the electromagnetic spectrum depend on the wavelength of a wave as well as its amplitude Wavelength: length of a light wave Amplitude: strength/ intensity of something (usually a stimulus) Peak/ Crest: Top of the wave Trough: bottom of the wave Frequency: Speed of the wave The only section of the electromagnetic spectrum that is visible to us is the small, and properly named, section called “Visible Light”

Visible Spectrum Small section of the Electromagnetic Spectrum that our eyes are sensitive to Light waves with different wavelengths within the Visible Spectrum, create different colors Waves come from Radiant and/or Reflected Light Radiant light: visible energy emitted by something Reflected light: energy reflected by objects The eye extracts information from the wavelength of a light ray in order for the brain to process color

Visible Spectrum Visual experiences of color, form, position, and depth, are all based on processing one stream of sensory information in multiple parts of the visual cortex Since color only exists within the brain, perception of a color can vary in saturation and brightness Saturation: purity of a color Brightness: psychological sensation that is based on a light wave’s intensity

Theories on viewing colors Trichromatic theory: idea that colors are sensed by three different types of cones sensitive to light in red, blue, and green wavelengths explains earliest stages of color sensation also called Young-Helmholtz theory

Another theory Opponent-process theory: idea that cells in visual system process colors in complementary pairs, such as red and green or yellow and blue explains color sensation from bipolar cells onward in visual system

Afterimages Sensations that linger after stimulus is removed negative afterimages appear in reversed colors

Monocular Cues Depth perceived in each individual eye Types: relative size, interposition, relative clarity, texture gradient, relative height, relative motion, light, shadow

Binocular Cues Depth perceived using both eyes Types: Retinal disparity, Convergence Retinal disparity: the difference between the visual images that each eye perceives because of the different angles viewed Convergence: coordinated movement of eyes inward to focus on objects close to us

Optical Illusions (Fun ways to mess with your eyes!)

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