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Vision Chapter 6, Lecture 2

Vision Chapter 6, Lecture 2. “Color, like all aspects of vision, resides not in the object but in the theater of our brains, as evidenced by our dreaming in color.” - David Myers. “…as you read this page, the printed squiggles are transmitted by reflected light rays onto your

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Vision Chapter 6, Lecture 2

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  1. VisionChapter 6, Lecture 2 “Color, like all aspects of vision, resides not in the object but in the theater of our brains, as evidenced by our dreaming in color.” - David Myers

  2. “…as you read this page, the printed squiggles are transmitted by reflected light rays onto your retina, which triggers a process that sends formless nerve impulses to several areas of your brain, which integrates the information and decodes meaning, thus completing the transfer of information across time and space from my mind to your mind…That all of this happens instantly, effortlessly, and continuously is indeed awesome.” - David Myers

  3. Transduction In sensation, the transformation of stimulus energy (sights, sounds, smells) into neural impulses.

  4. The Stimulus Input: Light Energy Both Photos: Thomas Eisner Visible Spectrum

  5. Physical Characteristics of Light • Wavelength (hue/color) • Intensity (brightness)

  6. Wavelength (Hue) Hue (color)is the dimension of color determined by the wavelength of the light. Wavelengthisthe distance from the peak of one wave to the peak of the next.

  7. Wavelength (Hue) Violet Green Orange Red Indigo Blue Yellow 400 nm 700 nm Long wavelengths Short wavelengths Different wavelengths of light result in different colors.

  8. Intensity (Brightness) Intensity:Amount of energy in a wave determined by the amplitude. It is related to perceived brightness.

  9. Intensity (Brightness) Blue color with varying levels of intensity. As intensity increases or decreases, blue color looks more “washed out” or “darkened.”

  10. The Eye

  11. Parts of the eye • Cornea:Transparent tissue where light enters the eye. • Iris:Muscle that expands and contracts to change the size of the opening (pupil) for light. • Lens:Focuses the light rays on the retina. • Retina:Contains sensory receptors that process visual information and sends it to the brain.

  12. The Lens Lens:Transparent structure behind the pupil that changes shape to focus images on the retina. Accommodation:The process by which the eye’s lens changes shape to help focus near or far objects on the retina.

  13. Retina Retina:The light-sensitive inner surface of the eye, containing receptor rods and cones in addition to layers of other neurons (bipolar, ganglion cells) that process visual information.

  14. Optic Nerve, Blind Spot & Fovea Optic nerve:Carries neural impulses from the eye to the brain. Blind Spot:Point where the optic nerve leaves the eye because there are no receptor cells located there. Fovea:Central point in the retina around which the eye’s cones cluster. http://www.bergen.org

  15. Test your Blind Spot Use your textbook. Close your left eye, and fixate your right eye on the black dot. Move the page towards your eye and away from your eye. At some point the car on the right will disappear due to a blind spot.

  16. Photoreceptors E.R. Lewis, Y.Y. Zeevi, F.S Werblin, 1969

  17. Bipolar & Ganglion Cells Bipolar cells receive messages from photoreceptors and transmit them to ganglion cells, which converge to form the optic nerve.

  18. The Hermann Grid Works through lateral inhibition

  19. Visual Information Processing Optic nerves connect to the thalamus in the middle of the brain, and the thalamus connects to the visual cortex.

  20. Feature Detection Nerve cells in the visual cortex respond to specific features, such as edges, angles, and movement. Ross Kinnaird/ Allsport/ Getty Images

  21. Shape Detection Specific combinations of temporal lobe activity occur as people look at shoes, faces, chairs and houses. Ishai, Ungerleider, Martin and Haxby/ NIMH

  22. Visual Information Processing Processing of several aspects of the stimulus simultaneously is called parallel processing. The brain divides a visual scene into subdivisions such as color, depth, form, movement, etc.

  23. From Sensation to Recognition p.243

  24. Color Vision Trichromatic theory: Young and von Helmholtz suggested that the eye must contain three receptors that are sensitive to red, blue and green colors. Standard stimulus Comparison stimulus Max Low Medium Blue Red Green

  25. Color Blindness Genetic disorder in which people are blind to green or red colors. This supports the Trichromatic theory. Ishihara Test

  26. Opponent Colors Gaze at the middle of the flag for about 30 Seconds. When it disappears, stare at the dot and report whether or not you see Britain's flag.

  27. Opponent Colors The three sets of opponent colors: red-green, yellow-blue, white-black Neurons that respond according to this opponent process are located in the retina and the thalamus (before the signal reaches the primary visual cortex).

  28. Blindsight A localized area of blindness in part of a person’s field of vision. Look at this handout and video clip on this intriguing phenomenon…

  29. Homework Read p.245-252

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