3.2 Vision

1. 3.2 Vision • 70% of your receptor cells are in your eyes • taste and touch need direct contact where as sight and smell don’t • Sight can be experienced from farthest distance

3. Vision Draw the diagram of the eye above and label each part (hint: use color to distinguish different parts of the eye)

4. The Visual System • Cornea • Transparent protective coating over the front of the eye • Pupil • Small opening in the iris through which light enters the eye • Iris • Colored part of the eye

5. The Visual System • Lens • Focuses light onto the retina, is transparent and changes shape to focus on things at different distances • Retina • Lining of the eye containing receptor cells that are sensitive to light • Fovea • Center of the visual field, images are in sharpest focus here

6. Diagram • Create a diagram showing the path of light from a subject through the different parts of the eye, ending at the optic nerve.

7. Receptor Cells in the eye • Cells in the retina that are sensitive to light • Light- small segment of electromagnetic spectrum to which our eyes are sensitive. • Visual receptors are called rods and cones

8. Receptor Cells • Rods • About 120 million rods • Respond to light and dark • Very sensitive to light • Provide our night vision • Dominant outside of fovea • Cones • About 8 million cones • Respond to color as well as light and dark • Work best in bright light • Found mainly in the fovea Both get sparse as you move away from the fovea at the back of the eye.

9. Receptor Cells • Bipolar cells • Receive input from receptor cells(rods/cones) • Only have one axon and dendrite • In fovea, cones usually only connect to ONE bipolar cell • Elsewhere, several rods/cones share a single cell

12. Receptor Cells • Ganglion cells • Receive input from bipolar cells • Axons of these join to form optic nerve that carries messages to the brain • Cells summarize and organize information for the brain

13. Receptor Cells • Blind spot • Area where axons of ganglion cells leave the eye • No receptor cells • Even when light from a small object is focused directly on the blind spot, the object will not be seen • Pg. 101 test

14. Receptor Cells • Visual acuity- ability to distinguish fine details visually • Pg. 101 x test

15. From Eye to Brain • Optic nerve • Made up of axons of ganglion cells • carries neural messages from each eye to brain • Optic chiasm • Point where part of each optic nerve crosses to the other side of the brain

16. Adaptation • Dark adaptation • Increased sensitivity of rods and cones in darkness • Usually only see in grey scale, little color • Reason for many accidents at night • Light adaptation • Decreased sensitivity of rods and cones in bright light • Squint to reduce amount of light striking your retina • Within a minute you usually fully adapt • Afterimage • Sense experience that occurs after a visual stimulus has been removed • Light experiment

17. Feature detectors • Feature detectors- specialized brain cells that only respond to particular elements in the visual field such as movement or lines of specific orientation. • Cortical blindness- severe damage to visual cortex • Blightsight-they behave as if they can see forms, colors, and motion– even though they cannot see • Ex. Patient might duck if an object is thrown at her, even though she reports not having seen it; she might turn her head toward a bright flashing light although she can’t see it.

18. Properties of color Hue – refers to colors such as red and green Most people can identify about 150 hues Saturation – refers to the vividness of a hue Brightness – the nearness of a color to white Color Vision

19. Theories of Color Vision • Additive color mixing • Mixing of lights of different hues to create new hues • Each light adds additional wavelengths to the over all mix • Lights, T.V., computer monitors (RGB) • Subtractive color mixing • Mixing pigments, e.g., paints, each of which absorbs some wavelengths of light and reflects others

20. Theories of Color Vision • Trichromatic theory • Three different types of cones • Red • Green • Blue-violet • Experience of color is the result of mixing of the signals from these receptors • Can account for some types of colorblindness

21. Forms of Colorblindness • Approximately 10% of men and 1% of women have some form of colorblindness • Dichromats • People who are blind to either red-green or blue-yellow • Monochromats • People who see no color at all, only shades of light and dark • Tests • http://www.youtube.com/watch?v=yEIM4jmK1F0

22. Theories of Color Vision • Trichromatic theory cannot explain all aspects of color vision • People with normal vision cannot see “reddish-green” or “yellowish-blue” • Color afterimages

25. Theories of Color Vision • Opponent-process theory • Three pairs of color receptors • Yellow-blue • Red-green • Black-white • Members of each pair work in opposition • Can explain color afterimages • Both theories of color vision are valid

26. Color Vision in Other Species • Other species see colors differently than humans • Most other mammals are dichromats • Rodents tend to be monochromats, as are owls who have only rods • Bees can see ultraviolet light