1. VisionVisionVisionVision Our most dominating sense.

2. Transduction Transduction: Conversion of one form of energy to another. How is this important when studying sensation? Stimulus energies are converted to neural impulses.

3. Light Energy What strikes our eyes is not color but pulses of electromagnetic energy that our visual system perceives as color

4. We only use light energy to see. The visible spectrum for humans is only a slim portion of the total range of wavelengths. Other animals have different capabilities. For example, many insects can see shorter wavelengths than humans can see. These wavelengths are in the ultraviolet spectrum. Many fish and reptiles can see longer wavelengths than humans can see. These wavelengths are in the infrared spectrum.

5. Wavelength = Hue (color) Wavelength: The distance from the peak of one light wave to the peak of the next. The distance determines the hue (color) of the light we perceive (ex: red vs. blue).

6. Phase One: Gathering Light The length of the wave gives us its hue (color). ROY G BIV The longer the wavelength, the more red the hue. The shorter the wavelength, the more violet the hue.

7. Amplitude = Intensity (Brightness) Intensity: amount of energy in a light wave Determined by the height (amplitude) of the wave. The higher the wave, the more intense the light is.

8. Structure of the Eye

9. Sclera The white part of the eyeball is called the sclera (say: sklair-uh). –The sclera is made of a tough material and has the important job of covering most of the eyeball. –Look very closely at the white of the eye, and you'll see lines that look like tiny pink threads. These are blood vessels, the tiny tubes that deliver blood, to the sclera.

10. Cornea The cornea, a transparent dome, sits in front of the colored part of the eye. –The cornea helps the eye focus as light makes its way through. –It is a very important part of the eye, but you can hardly see it because it's made of clear tissue. Like clear glass, the cornea gives your eye a clear window to view the world through.

11. Iris and Pupil Behind the cornea are the iris and the pupil. Iris: is the colorful part of the eye. –Iris has muscles attached to it that change its shape. –This allows the iris to control how much light goes through the pupil. –LINK LINK

12. Iris and Pupil Pupil:is the black circle in the center of the iris --Which is really an opening in the iris, and it lets light enter the eye. –What happens when someone flashes a bright light in your eyes?

13. Lens & Retina After light enters the pupil, it hits the lens. Lens: sits behind the iris and is clear and colorless. The lens' job is to focus light rays on the back of the eyeball — a part called the retina. –The lens works much like the lens of a movie projector at the movies. –Next time you sit in the dark theater, look behind you at the stream of light coming from the projection booth. –This light goes through a powerful lens, which is focusing the images onto the screen, so you can see the movie clearly. In the eye's case, however, the film screen is your retina.

14. Lens & Retina Retina: is in the very back of the eye. It holds millions of cells that are sensitive to light. The retina takes the light the eye receives and changes it into nerve signals so the brain can understand what the eye is seeing

15. Ciliary Muscle The lens is suspended in the eye by a bunch of fibers. These fibers are attached to a muscle called the ciliary muscle. Ciliary muscle: has the amazing job of changing the shape of the lens Try looking away from your computer and focusing on something way across the room. Even though you didn't feel a thing, the shape of your lenses changed. When you look at things up close, the lens becomes thicker to focus the correct image onto the retina. When you look at things far away, the lens becomes thinner.

16. Fovea The tiny area of sharpest vision in the retina Cones cluster in and around the fovea

17. What happens in the retina The retina is a piece of neural tissue that lines the back of the eye…it absorbs light, processes images, and sends information to the brain. The visual receptor cells are the rods (for black and white and low light vision) and the cones (for color and daylight vision). Adaptation, or becoming more or less sensitive to light as needed, occurs in part due to chemical changes in the rods and cones. Adaptation, or becoming more or less sensitive to light as needed, occurs in part due to chemical changes in the rods and cones.

18. More on Rods and Cones The retina uses special cells called rods and cones to process light. How many rods and cones does your retina have? About 120 million rods and 7 million cones — in each eye! Rods: see in black, white, and shades of gray and tell us the form or shape that something has. –Rods can't tell the difference between colors, but they are super-sensitive, allowing us to see when it's very dark.

19. More on Rods and Cones Cones: sense color and they need more light than rods to work well. Cones are most helpful in normal or bright light. –The retina has three types of cones. –Each cone type is sensitive to one of three different colors — red, green, or blue — to help you see different ranges of color. –Together, these cones can sense combinations of light waves that enable our eyes to see millions of colors.

20. Colored scanning electron micrograph (SEM) of rods (yellow) and cones (green) in the retina of the eye. The outer nuclear layer is purple. Magnification x1800 when printed at 10 centimeters wide.

21. Rods and Cones - Demo Remember that cones cluster in and around the fovea (the retina’s area of central focus). Because there are low concentrations of cones (color and fine detail) and higher concentrations of rods (black, white, gray, and twilight vision) in the periphery of the retina, color vision and visual acuity are poor in the periphery of the visual field –For example -experiment –128)

22. Transduction of Light in the Retina –Optic nerve – transports visual information from the eye to the brain –http://www.youtube.com/watch? v=RE1MvRmWg7I -- X http://www.youtube.com/watch? v=RE1MvRmWg7Ihttp://www.youtube.com/watch? v=RE1MvRmWg7I –http://www.youtube.com/watch? v=gvozcv8pS3c -- X http://www.youtube.com/watch? v=gvozcv8pS3chttp://www.youtube.com/watch? v=gvozcv8pS3c

23. Conversion Light Impulses Instructor’s Notes Copyright © Houghton Mifflin Company. All rights reserved. PowerPoint® 2000 or better with Flash® plug-in required to view animations. Right-click on animation for playback controls.

24. The Blind Spot Axons from the retina to the brain converge at the optic disk, a hole in the retina where the optic nerve leaves the eye. If an image falls on this hole, it can’t be seen…the blind spot. Why don’t we notice this blind spot all the time? –The brain makes an educated guess based on what it knows of the surrounding area – it fills it in for you.

25. Where is your blind spot? Close your right eye. With your left eye, look at the +. You should see the red dot in your peripheral vision. Keep looking at the + with your left eye. The red dot will move from the left to the right and disappear and reappear as the dot moves into and out of your blind spot.

26. Transduction Continued Once information reaches the optic nerve, the optic nerve sends the information on to the thalamus Then sent to primary visual cortex.

27. In the Brain The Visual Cortex is located in the Occipital Lobe of the Cerebral Cortex. Feature Detectors - specific nerve cells in the brain that respond to specific features of the stimulus, such as shape, angle, or movement. Parallel Processing – the processing of many aspects of a problem simultaneously; the brain’s natural mode of information processing for many functions. We have specific cells that respond to specific features of this turkey – to particular edges, lines, angles, and movements. These cells are called feature detectors. Color Depth Form Motion

28. Trichromatic Theory – Young and Helmholtz Young and Helmholtz, in the mid 1800’s, came up with the first theory of color vision… Trichromatic Theory. They realized that any color can be created by combining the light waves of three primary colors: So they guessed that we have 3 different types of receptor cells (cones) in our eyes. These 3 types of cones have differing sensitivities to different light wavelengths…one for Red, one for Green, and one for Blue. All colors can be seen, according to this theory, because of color mixing. http://www.youtube.co m/watch?v=Jzl9VPnA 3OY

29. Problems with the Thrichromatic Theory Most color-deficient people are not actually “colorblind” - they simply lack cone receptor cells for one or more of these primary colors. –Their vision is monochromatic (one color) or dichromatic (two color) instead of trichromatic. http://colorvisiontesting.com/ishihara.htm#plate %20with%2057%20answer http://colorvisiontesting.com/ishihara.htm#plate %20with%2057%20answer So how is it that those blind to red and green can often still see yellow? –This is where the trichromatic theory might become problematic.

30. Opponent-Process Theory Edward Hering, in 1878, proposed Opponent Process Theory, which says that sensory receptors come in pairs of colors: –Red/Green –Yellow/Blue –Black/White If one color is stimulated, the other is inhibited. When receptors for a color become fatigued, a sort of rebound in the receptors produces the opponent color. –This explains the concept of afterimages.

31. Opponent-Process Theory: Flag 2 Instructor’s Notes Copyright © Houghton Mifflin Company. All rights reserved. PowerPoint® 2000 or better with Flash® plug-in required to view animations. Right-click on animation for playback controls.

32. Castle Afterimage Illusion Castle Optical Afterimage Illusion http://www. youtube.co m/watch?v =w6ccBwn c5KU

33. Afterimages

34. So which theory of color vision is right? While researchers argued about which was right for almost a century, most psychologists now agree that it takes both theories to explain color vision. Taken together, the two theories explain color vision: the trichromatic theory explains color processing in the cones, while the opponent- process theory explains what happens in cells and beyond.