Transcript Vision
Vision By Michelle, Kim, Kayla, and Sean Key Objectives • 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 Keep in Mind • How does sensory information impact human behavior? • To what extend are our perceptions of the environment accurate? Importance of Vision • Detects targets • Detect threats • Detect environmental changes and stimuli Basics 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 Visible Light Properties of 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 How Vision Works • 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 The Retina • 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 Eye Rods • 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 Cones • 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 Dark Adaptation • 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 Light stimulus to Neural Impulse • 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 Blind Spots • 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 Vision in the Brain • 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 Brain Summary Visual cortex • Where all visual images are process Forebrain • 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. Vision Properties • 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 Monocular Cues vs. Binocular Cues • 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 Theories of Color Sensation • 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 Vision Disorders • 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 Color deficiencies • 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)